diff --git a/configure.ac b/configure.ac
index 64fa12fc7..c0e989d85 100644
--- a/configure.ac
+++ b/configure.ac
@@ -177,7 +177,7 @@ fi
 PKG_CHECK_MODULES([OPENSSL], [libcrypto], [CXXFLAGS="$OPENSSL_CFLAGS $CXXFLAGS"])
 
 
-# Checks for libarchive
+# Look for libarchive.
 PKG_CHECK_MODULES([LIBARCHIVE], [libarchive >= 3.1.2], [CXXFLAGS="$LIBARCHIVE_CFLAGS $CXXFLAGS"])
 # Workaround until https://github.com/libarchive/libarchive/issues/1446 is fixed
 if test "$shared" != yes; then
diff --git a/doc/manual/src/command-ref/env-common.md b/doc/manual/src/command-ref/env-common.md
index 3f3eb6915..5845bdc43 100644
--- a/doc/manual/src/command-ref/env-common.md
+++ b/doc/manual/src/command-ref/env-common.md
@@ -7,42 +7,11 @@ Most Nix commands interpret the following environment variables:
     `nix-shell`. It can have the values `pure` or `impure`.
 
   - [`NIX_PATH`]{#env-NIX_PATH}\
-    A colon-separated list of directories used to look up Nix
-    expressions enclosed in angle brackets (i.e., `<path>`). For
-    instance, the value
-
-        /home/eelco/Dev:/etc/nixos
-
-    will cause Nix to look for paths relative to `/home/eelco/Dev` and
-    `/etc/nixos`, in this order. It is also possible to match paths
-    against a prefix. For example, the value
-
-        nixpkgs=/home/eelco/Dev/nixpkgs-branch:/etc/nixos
-
-    will cause Nix to search for `<nixpkgs/path>` in
-    `/home/eelco/Dev/nixpkgs-branch/path` and `/etc/nixos/nixpkgs/path`.
-
-    If a path in the Nix search path starts with `http://` or
-    `https://`, it is interpreted as the URL of a tarball that will be
-    downloaded and unpacked to a temporary location. The tarball must
-    consist of a single top-level directory. For example, setting
-    `NIX_PATH` to
-
-        nixpkgs=https://github.com/NixOS/nixpkgs/archive/master.tar.gz
-
-    tells Nix to download and use the current contents of the
-    `master` branch in the `nixpkgs` repository.
-
-    The URLs of the tarballs from the official nixos.org channels (see
-    [the manual for `nix-channel`](nix-channel.md)) can be abbreviated
-    as `channel:<channel-name>`.  For instance, the following two
-    values of `NIX_PATH` are equivalent:
-
-        nixpkgs=channel:nixos-21.05
-        nixpkgs=https://nixos.org/channels/nixos-21.05/nixexprs.tar.xz
-
-    The Nix search path can also be extended using the `-I` option to
-    many Nix commands, which takes precedence over `NIX_PATH`.
+    A colon-separated list of directories used to look up the location of Nix
+    expressions using [paths](../language/values.md#type-path)
+    enclosed in angle brackets (i.e., `<path>`),
+    e.g. `/home/eelco/Dev:/etc/nixos`. It can be extended using the
+    [`-I` option](./opt-common#opt-I).
 
   - [`NIX_IGNORE_SYMLINK_STORE`]{#env-NIX_IGNORE_SYMLINK_STORE}\
     Normally, the Nix store directory (typically `/nix/store`) is not
diff --git a/src/libcmd/common-eval-args.cc b/src/libcmd/common-eval-args.cc
index 140ed3b88..dc0de4b9f 100644
--- a/src/libcmd/common-eval-args.cc
+++ b/src/libcmd/common-eval-args.cc
@@ -32,7 +32,60 @@ MixEvalArgs::MixEvalArgs()
     addFlag({
         .longName = "include",
         .shortName = 'I',
-        .description = "Add *path* to the list of locations used to look up `<...>` file names.",
+        .description = R"(
+  Add *path* to the Nix search path. The Nix search path is
+  initialized from the colon-separated [`NIX_PATH`](./env-common.md#env-NIX_PATH) environment
+  variable, and is used to look up the location of Nix expressions using [paths](../language/values.md#type-path) enclosed in angle
+  brackets (i.e., `<nixpkgs>`).
+
+  For instance, passing
+
+  ```
+  -I /home/eelco/Dev
+  -I /etc/nixos
+  ```
+
+  will cause Nix to look for paths relative to `/home/eelco/Dev` and
+  `/etc/nixos`, in that order. This is equivalent to setting the
+  `NIX_PATH` environment variable to
+
+  ```
+  /home/eelco/Dev:/etc/nixos
+  ```
+
+  It is also possible to match paths against a prefix. For example,
+  passing
+
+  ```
+  -I nixpkgs=/home/eelco/Dev/nixpkgs-branch
+  -I /etc/nixos
+  ```
+
+  will cause Nix to search for `<nixpkgs/path>` in
+  `/home/eelco/Dev/nixpkgs-branch/path` and `/etc/nixos/nixpkgs/path`.
+
+  If a path in the Nix search path starts with `http://` or `https://`,
+  it is interpreted as the URL of a tarball that will be downloaded and
+  unpacked to a temporary location. The tarball must consist of a single
+  top-level directory. For example, passing
+
+  ```
+  -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/master.tar.gz
+  ```
+
+  tells Nix to download and use the current contents of the `master`
+  branch in the `nixpkgs` repository.
+
+  The URLs of the tarballs from the official `nixos.org` channels
+  (see [the manual page for `nix-channel`](nix-channel.md)) can be
+  abbreviated as `channel:<channel-name>`.  For instance, the
+  following two flags are equivalent:
+
+  ```
+  -I nixpkgs=channel:nixos-21.05
+  -I nixpkgs=https://nixos.org/channels/nixos-21.05/nixexprs.tar.xz
+  ```
+  )",
         .category = category,
         .labels = {"path"},
         .handler = {[&](std::string s) { searchPath.push_back(s); }}
diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index 301e7bf4b..5cdd3e12c 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -793,7 +793,8 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
         if (file == "-") {
             auto e = state->parseStdin();
             state->eval(e, *vFile);
-        } else if (file)
+        }
+        else if (file)
             state->evalFile(lookupFileArg(*state, *file), *vFile);
         else {
             auto e = state->parseExprFromString(*expr, absPath("."));
diff --git a/src/libcmd/repl.cc b/src/libcmd/repl.cc
index 557952277..c704fcfb1 100644
--- a/src/libcmd/repl.cc
+++ b/src/libcmd/repl.cc
@@ -787,7 +787,7 @@ void NixRepl::loadFlake(const std::string & flakeRefS)
             flake::LockFlags {
                 .updateLockFile = false,
                 .useRegistries = !evalSettings.pureEval,
-                .allowMutable  = !evalSettings.pureEval,
+                .allowUnlocked = !evalSettings.pureEval,
             }),
         v);
     addAttrsToScope(v);
diff --git a/src/libexpr/eval-cache.cc b/src/libexpr/eval-cache.cc
index b259eec63..3e2a8665e 100644
--- a/src/libexpr/eval-cache.cc
+++ b/src/libexpr/eval-cache.cc
@@ -645,17 +645,17 @@ NixInt AttrCursor::getInt()
             cachedValue = root->db->getAttr(getKey());
         if (cachedValue && !std::get_if<placeholder_t>(&cachedValue->second)) {
             if (auto i = std::get_if<int_t>(&cachedValue->second)) {
-                debug("using cached Integer attribute '%s'", getAttrPathStr());
+                debug("using cached integer attribute '%s'", getAttrPathStr());
                 return i->x;
             } else
-                throw TypeError("'%s' is not an Integer", getAttrPathStr());
+                throw TypeError("'%s' is not an integer", getAttrPathStr());
         }
     }
 
     auto & v = forceValue();
 
     if (v.type() != nInt)
-        throw TypeError("'%s' is not an Integer", getAttrPathStr());
+        throw TypeError("'%s' is not an integer", getAttrPathStr());
 
     return v.integer;
 }
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 76a10b9f8..b67ed853e 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1806,7 +1806,7 @@ void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res)
 Nix attempted to evaluate a function as a top level expression; in
 this case it must have its arguments supplied either by default
 values, or passed explicitly with '--arg' or '--argstr'. See
-https://nixos.org/manual/nix/stable/expressions/language-constructs.html#functions.)", symbols[i.name],                 
+https://nixos.org/manual/nix/stable/language/constructs.html#functions.)", symbols[i.name],
                 *fun.lambda.env, *fun.lambda.fun);
             }
         }
diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index 119c556ac..6b5d6f6b3 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -353,7 +353,7 @@ LockedFlake lockFlake(
 
         std::function<void(
             const FlakeInputs & flakeInputs,
-            std::shared_ptr<Node> node,
+            ref<Node> node,
             const InputPath & inputPathPrefix,
             std::shared_ptr<const Node> oldNode,
             const InputPath & lockRootPath,
@@ -362,9 +362,15 @@ LockedFlake lockFlake(
             computeLocks;
 
         computeLocks = [&](
+            /* The inputs of this node, either from flake.nix or
+               flake.lock. */
             const FlakeInputs & flakeInputs,
-            std::shared_ptr<Node> node,
+            /* The node whose locks are to be updated.*/
+            ref<Node> node,
+            /* The path to this node in the lock file graph. */
             const InputPath & inputPathPrefix,
+            /* The old node, if any, from which locks can be
+               copied. */
             std::shared_ptr<const Node> oldNode,
             const InputPath & lockRootPath,
             const Path & parentPath,
@@ -452,7 +458,7 @@ LockedFlake lockFlake(
                         /* Copy the input from the old lock since its flakeref
                            didn't change and there is no override from a
                            higher level flake. */
-                        auto childNode = std::make_shared<LockedNode>(
+                        auto childNode = make_ref<LockedNode>(
                             oldLock->lockedRef, oldLock->originalRef, oldLock->isFlake);
 
                         node->inputs.insert_or_assign(id, childNode);
@@ -481,7 +487,7 @@ LockedFlake lockFlake(
                                         .isFlake = (*lockedNode)->isFlake,
                                     });
                                 } else if (auto follows = std::get_if<1>(&i.second)) {
-                                    if (! trustLock) {
+                                    if (!trustLock) {
                                         // It is possible that the flake has changed,
                                         // so we must confirm all the follows that are in the lock file are also in the flake.
                                         auto overridePath(inputPath);
@@ -521,8 +527,8 @@ LockedFlake lockFlake(
                            this input. */
                         debug("creating new input '%s'", inputPathS);
 
-                        if (!lockFlags.allowMutable && !input.ref->input.isLocked())
-                            throw Error("cannot update flake input '%s' in pure mode", inputPathS);
+                        if (!lockFlags.allowUnlocked && !input.ref->input.isLocked())
+                            throw Error("cannot update unlocked flake input '%s' in pure mode", inputPathS);
 
                         /* Note: in case of an --override-input, we use
                             the *original* ref (input2.ref) for the
@@ -544,7 +550,7 @@ LockedFlake lockFlake(
 
                             auto inputFlake = getFlake(state, localRef, useRegistries, flakeCache, inputPath);
 
-                            auto childNode = std::make_shared<LockedNode>(inputFlake.lockedRef, ref);
+                            auto childNode = make_ref<LockedNode>(inputFlake.lockedRef, ref);
 
                             node->inputs.insert_or_assign(id, childNode);
 
@@ -564,15 +570,19 @@ LockedFlake lockFlake(
                                 oldLock
                                 ? std::dynamic_pointer_cast<const Node>(oldLock)
                                 : LockFile::read(
-                                    inputFlake.sourceInfo->actualPath + "/" + inputFlake.lockedRef.subdir + "/flake.lock").root,
-                                oldLock ? lockRootPath : inputPath, localPath, false);
+                                    inputFlake.sourceInfo->actualPath + "/" + inputFlake.lockedRef.subdir + "/flake.lock").root.get_ptr(),
+                                oldLock ? lockRootPath : inputPath,
+                                localPath,
+                                false);
                         }
 
                         else {
                             auto [sourceInfo, resolvedRef, lockedRef] = fetchOrSubstituteTree(
                                 state, *input.ref, useRegistries, flakeCache);
-                            node->inputs.insert_or_assign(id,
-                                std::make_shared<LockedNode>(lockedRef, ref, false));
+
+                            auto childNode = make_ref<LockedNode>(lockedRef, ref, false);
+
+                            node->inputs.insert_or_assign(id, childNode);
                         }
                     }
 
@@ -587,8 +597,13 @@ LockedFlake lockFlake(
         auto parentPath = canonPath(flake.sourceInfo->actualPath + "/" + flake.lockedRef.subdir, true);
 
         computeLocks(
-            flake.inputs, newLockFile.root, {},
-            lockFlags.recreateLockFile ? nullptr : oldLockFile.root, {}, parentPath, false);
+            flake.inputs,
+            newLockFile.root,
+            {},
+            lockFlags.recreateLockFile ? nullptr : oldLockFile.root.get_ptr(),
+            {},
+            parentPath,
+            false);
 
         for (auto & i : lockFlags.inputOverrides)
             if (!overridesUsed.count(i.first))
@@ -611,9 +626,9 @@ LockedFlake lockFlake(
 
             if (lockFlags.writeLockFile) {
                 if (auto sourcePath = topRef.input.getSourcePath()) {
-                    if (!newLockFile.isImmutable()) {
+                    if (auto unlockedInput = newLockFile.isUnlocked()) {
                         if (fetchSettings.warnDirty)
-                            warn("will not write lock file of flake '%s' because it has a mutable input", topRef);
+                            warn("will not write lock file of flake '%s' because it has an unlocked input ('%s')", topRef, *unlockedInput);
                     } else {
                         if (!lockFlags.updateLockFile)
                             throw Error("flake '%s' requires lock file changes but they're not allowed due to '--no-update-lock-file'", topRef);
@@ -737,7 +752,7 @@ static void prim_getFlake(EvalState & state, const PosIdx pos, Value * * args, V
                 .updateLockFile = false,
                 .writeLockFile = false,
                 .useRegistries = !evalSettings.pureEval && fetchSettings.useRegistries,
-                .allowMutable  = !evalSettings.pureEval,
+                .allowUnlocked = !evalSettings.pureEval,
             }),
         v);
 }
diff --git a/src/libexpr/flake/flake.hh b/src/libexpr/flake/flake.hh
index 524b18af1..10301d8aa 100644
--- a/src/libexpr/flake/flake.hh
+++ b/src/libexpr/flake/flake.hh
@@ -108,11 +108,11 @@ struct LockFlags
 
     bool applyNixConfig = false;
 
-    /* Whether mutable flake references (i.e. those without a Git
+    /* Whether unlocked flake references (i.e. those without a Git
        revision or similar) without a corresponding lock are
-       allowed. Mutable flake references with a lock are always
+       allowed. Unlocked flake references with a lock are always
        allowed. */
-    bool allowMutable = true;
+    bool allowUnlocked = true;
 
     /* Whether to commit changes to flake.lock. */
     bool commitLockFile = false;
diff --git a/src/libexpr/flake/flakeref.hh b/src/libexpr/flake/flakeref.hh
index fe4f67193..a36d852a8 100644
--- a/src/libexpr/flake/flakeref.hh
+++ b/src/libexpr/flake/flakeref.hh
@@ -35,7 +35,7 @@ typedef std::string FlakeId;
 
 struct FlakeRef
 {
-    /* fetcher-specific representation of the input, sufficient to
+    /* Fetcher-specific representation of the input, sufficient to
        perform the fetch operation. */
     fetchers::Input input;
 
diff --git a/src/libexpr/flake/lockfile.cc b/src/libexpr/flake/lockfile.cc
index 629d2e669..a3ed90e1f 100644
--- a/src/libexpr/flake/lockfile.cc
+++ b/src/libexpr/flake/lockfile.cc
@@ -31,7 +31,7 @@ FlakeRef getFlakeRef(
 }
 
 LockedNode::LockedNode(const nlohmann::json & json)
-    : lockedRef(getFlakeRef(json, "locked", "info"))
+    : lockedRef(getFlakeRef(json, "locked", "info")) // FIXME: remove "info"
     , originalRef(getFlakeRef(json, "original", nullptr))
     , isFlake(json.find("flake") != json.end() ? (bool) json["flake"] : true)
 {
@@ -49,15 +49,15 @@ std::shared_ptr<Node> LockFile::findInput(const InputPath & path)
 {
     auto pos = root;
 
-    if (!pos) return {};
-
     for (auto & elem : path) {
         if (auto i = get(pos->inputs, elem)) {
             if (auto node = std::get_if<0>(&*i))
                 pos = *node;
             else if (auto follows = std::get_if<1>(&*i)) {
-                pos = findInput(*follows);
-                if (!pos) return {};
+                if (auto p = findInput(*follows))
+                    pos = ref(p);
+                else
+                    return {};
             }
         } else
             return {};
@@ -72,7 +72,7 @@ LockFile::LockFile(const nlohmann::json & json, const Path & path)
     if (version < 5 || version > 7)
         throw Error("lock file '%s' has unsupported version %d", path, version);
 
-    std::unordered_map<std::string, std::shared_ptr<Node>> nodeMap;
+    std::map<std::string, ref<Node>> nodeMap;
 
     std::function<void(Node & node, const nlohmann::json & jsonNode)> getInputs;
 
@@ -93,12 +93,12 @@ LockFile::LockFile(const nlohmann::json & json, const Path & path)
                     auto jsonNode2 = nodes.find(inputKey);
                     if (jsonNode2 == nodes.end())
                         throw Error("lock file references missing node '%s'", inputKey);
-                    auto input = std::make_shared<LockedNode>(*jsonNode2);
+                    auto input = make_ref<LockedNode>(*jsonNode2);
                     k = nodeMap.insert_or_assign(inputKey, input).first;
                     getInputs(*input, *jsonNode2);
                 }
-                if (auto child = std::dynamic_pointer_cast<LockedNode>(k->second))
-                    node.inputs.insert_or_assign(i.key(), child);
+                if (auto child = k->second.dynamic_pointer_cast<LockedNode>())
+                    node.inputs.insert_or_assign(i.key(), ref(child));
                 else
                     // FIXME: replace by follows node
                     throw Error("lock file contains cycle to root node");
@@ -122,9 +122,9 @@ nlohmann::json LockFile::toJSON() const
     std::unordered_map<std::shared_ptr<const Node>, std::string> nodeKeys;
     std::unordered_set<std::string> keys;
 
-    std::function<std::string(const std::string & key, std::shared_ptr<const Node> node)> dumpNode;
+    std::function<std::string(const std::string & key, ref<const Node> node)> dumpNode;
 
-    dumpNode = [&](std::string key, std::shared_ptr<const Node> node) -> std::string
+    dumpNode = [&](std::string key, ref<const Node> node) -> std::string
     {
         auto k = nodeKeys.find(node);
         if (k != nodeKeys.end())
@@ -159,10 +159,11 @@ nlohmann::json LockFile::toJSON() const
             n["inputs"] = std::move(inputs);
         }
 
-        if (auto lockedNode = std::dynamic_pointer_cast<const LockedNode>(node)) {
+        if (auto lockedNode = node.dynamic_pointer_cast<const LockedNode>()) {
             n["original"] = fetchers::attrsToJSON(lockedNode->originalRef.toAttrs());
             n["locked"] = fetchers::attrsToJSON(lockedNode->lockedRef.toAttrs());
-            if (!lockedNode->isFlake) n["flake"] = false;
+            if (!lockedNode->isFlake)
+                n["flake"] = false;
         }
 
         nodes[key] = std::move(n);
@@ -201,13 +202,13 @@ void LockFile::write(const Path & path) const
     writeFile(path, fmt("%s\n", *this));
 }
 
-bool LockFile::isImmutable() const
+std::optional<FlakeRef> LockFile::isUnlocked() const
 {
-    std::unordered_set<std::shared_ptr<const Node>> nodes;
+    std::set<ref<const Node>> nodes;
 
-    std::function<void(std::shared_ptr<const Node> node)> visit;
+    std::function<void(ref<const Node> node)> visit;
 
-    visit = [&](std::shared_ptr<const Node> node)
+    visit = [&](ref<const Node> node)
     {
         if (!nodes.insert(node).second) return;
         for (auto & i : node->inputs)
@@ -219,11 +220,12 @@ bool LockFile::isImmutable() const
 
     for (auto & i : nodes) {
         if (i == root) continue;
-        auto lockedNode = std::dynamic_pointer_cast<const LockedNode>(i);
-        if (lockedNode && !lockedNode->lockedRef.input.isLocked()) return false;
+        auto node = i.dynamic_pointer_cast<const LockedNode>();
+        if (node && !node->lockedRef.input.isLocked())
+            return node->lockedRef;
     }
 
-    return true;
+    return {};
 }
 
 bool LockFile::operator ==(const LockFile & other) const
@@ -247,12 +249,12 @@ InputPath parseInputPath(std::string_view s)
 
 std::map<InputPath, Node::Edge> LockFile::getAllInputs() const
 {
-    std::unordered_set<std::shared_ptr<Node>> done;
+    std::set<ref<Node>> done;
     std::map<InputPath, Node::Edge> res;
 
-    std::function<void(const InputPath & prefix, std::shared_ptr<Node> node)> recurse;
+    std::function<void(const InputPath & prefix, ref<Node> node)> recurse;
 
-    recurse = [&](const InputPath & prefix, std::shared_ptr<Node> node)
+    recurse = [&](const InputPath & prefix, ref<Node> node)
     {
         if (!done.insert(node).second) return;
 
diff --git a/src/libexpr/flake/lockfile.hh b/src/libexpr/flake/lockfile.hh
index 96f1edc76..02e9bdfbc 100644
--- a/src/libexpr/flake/lockfile.hh
+++ b/src/libexpr/flake/lockfile.hh
@@ -20,7 +20,7 @@ struct LockedNode;
    type LockedNode. */
 struct Node : std::enable_shared_from_this<Node>
 {
-    typedef std::variant<std::shared_ptr<LockedNode>, InputPath> Edge;
+    typedef std::variant<ref<LockedNode>, InputPath> Edge;
 
     std::map<FlakeId, Edge> inputs;
 
@@ -47,11 +47,13 @@ struct LockedNode : Node
 
 struct LockFile
 {
-    std::shared_ptr<Node> root = std::make_shared<Node>();
+    ref<Node> root = make_ref<Node>();
 
     LockFile() {};
     LockFile(const nlohmann::json & json, const Path & path);
 
+    typedef std::map<ref<const Node>, std::string> KeyMap;
+
     nlohmann::json toJSON() const;
 
     std::string to_string() const;
@@ -60,7 +62,8 @@ struct LockFile
 
     void write(const Path & path) const;
 
-    bool isImmutable() const;
+    /* Check whether this lock file has any unlocked inputs. */
+    std::optional<FlakeRef> isUnlocked() const;
 
     bool operator ==(const LockFile & other) const;
 
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index 346741dd5..5ad5d1fd4 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -150,7 +150,7 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool withPaths, bool onlyOutputsToInstall
         /* Check for `meta.outputsToInstall` and return `outputs` reduced to that. */
         const Value * outTI = queryMeta("outputsToInstall");
         if (!outTI) return outputs;
-        const auto errMsg = Error("this derivation has bad 'meta.outputsToInstall'");
+        auto errMsg = Error("this derivation has bad 'meta.outputsToInstall'");
             /* ^ this shows during `nix-env -i` right under the bad derivation */
         if (!outTI->isList()) throw errMsg;
         Outputs result;
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 7c623a07d..2be560d76 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -289,7 +289,6 @@ std::string showAttrPath(const SymbolTable & symbols, const AttrPath & attrPath)
 }
 
 
-
 /* Computing levels/displacements for variables. */
 
 void Expr::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 8a4c19f7c..283d2746b 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1461,10 +1461,10 @@ static RegisterPrimOp primop_storePath({
 static void prim_pathExists(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     /* We don’t check the path right now, because we don’t want to
-      throw if the path isn’t allowed, but just return false (and we
-      can’t just catch the exception here because we still want to
-      throw if something in the evaluation of `*args[0]` tries to
-      access an unauthorized path). */
+       throw if the path isn’t allowed, but just return false (and we
+       can’t just catch the exception here because we still want to
+       throw if something in the evaluation of `*args[0]` tries to
+       access an unauthorized path). */
     auto path = realisePath(state, pos, *args[0], { .checkForPureEval = false });
 
     try {
diff --git a/src/libfetchers/fetchers.cc b/src/libfetchers/fetchers.cc
index 6957d2da4..c767e72e5 100644
--- a/src/libfetchers/fetchers.cc
+++ b/src/libfetchers/fetchers.cc
@@ -266,7 +266,7 @@ std::optional<time_t> Input::getLastModified() const
     return {};
 }
 
-ParsedURL InputScheme::toURL(const Input & input)
+ParsedURL InputScheme::toURL(const Input & input) const
 {
     throw Error("don't know how to convert input '%s' to a URL", attrsToJSON(input.attrs));
 }
@@ -274,7 +274,7 @@ ParsedURL InputScheme::toURL(const Input & input)
 Input InputScheme::applyOverrides(
     const Input & input,
     std::optional<std::string> ref,
-    std::optional<Hash> rev)
+    std::optional<Hash> rev) const
 {
     if (ref)
         throw Error("don't know how to set branch/tag name of input '%s' to '%s'", input.to_string(), *ref);
@@ -293,7 +293,7 @@ void InputScheme::markChangedFile(const Input & input, std::string_view file, st
     assert(false);
 }
 
-void InputScheme::clone(const Input & input, const Path & destDir)
+void InputScheme::clone(const Input & input, const Path & destDir) const
 {
     throw Error("do not know how to clone input '%s'", input.to_string());
 }
diff --git a/src/libfetchers/fetchers.hh b/src/libfetchers/fetchers.hh
index bc9a76b0b..17da37f47 100644
--- a/src/libfetchers/fetchers.hh
+++ b/src/libfetchers/fetchers.hh
@@ -107,26 +107,25 @@ public:
  * recognized.  The Input object contains the information the fetcher
  * needs to actually perform the "fetch()" when called.
  */
-
 struct InputScheme
 {
     virtual ~InputScheme()
     { }
 
-    virtual std::optional<Input> inputFromURL(const ParsedURL & url) = 0;
+    virtual std::optional<Input> inputFromURL(const ParsedURL & url) const = 0;
 
-    virtual std::optional<Input> inputFromAttrs(const Attrs & attrs) = 0;
+    virtual std::optional<Input> inputFromAttrs(const Attrs & attrs) const = 0;
 
-    virtual ParsedURL toURL(const Input & input);
+    virtual ParsedURL toURL(const Input & input) const;
 
-    virtual bool hasAllInfo(const Input & input) = 0;
+    virtual bool hasAllInfo(const Input & input) const = 0;
 
     virtual Input applyOverrides(
         const Input & input,
         std::optional<std::string> ref,
-        std::optional<Hash> rev);
+        std::optional<Hash> rev) const;
 
-    virtual void clone(const Input & input, const Path & destDir);
+    virtual void clone(const Input & input, const Path & destDir) const;
 
     virtual std::optional<Path> getSourcePath(const Input & input);
 
diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index 7b7a1be35..1f7d7c07d 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -18,6 +18,7 @@
 using namespace std::string_literals;
 
 namespace nix::fetchers {
+
 namespace {
 
 // Explicit initial branch of our bare repo to suppress warnings from new version of git.
@@ -26,23 +27,23 @@ namespace {
 // old version of git, which will ignore unrecognized `-c` options.
 const std::string gitInitialBranch = "__nix_dummy_branch";
 
-bool isCacheFileWithinTtl(const time_t now, const struct stat & st)
+bool isCacheFileWithinTtl(time_t now, const struct stat & st)
 {
     return st.st_mtime + settings.tarballTtl > now;
 }
 
-bool touchCacheFile(const Path& path, const time_t& touch_time)
+bool touchCacheFile(const Path & path, time_t touch_time)
 {
-  struct timeval times[2];
-  times[0].tv_sec = touch_time;
-  times[0].tv_usec = 0;
-  times[1].tv_sec = touch_time;
-  times[1].tv_usec = 0;
+    struct timeval times[2];
+    times[0].tv_sec = touch_time;
+    times[0].tv_usec = 0;
+    times[1].tv_sec = touch_time;
+    times[1].tv_usec = 0;
 
-  return lutimes(path.c_str(), times) == 0;
+    return lutimes(path.c_str(), times) == 0;
 }
 
-Path getCachePath(std::string key)
+Path getCachePath(std::string_view key)
 {
     return getCacheDir() + "/nix/gitv3/" +
         hashString(htSHA256, key).to_string(Base32, false);
@@ -57,13 +58,12 @@ Path getCachePath(std::string key)
 //   ...
 std::optional<std::string> readHead(const Path & path)
 {
-    auto [exit_code, output] = runProgram(RunOptions {
+    auto [status, output] = runProgram(RunOptions {
         .program = "git",
+        // FIXME: use 'HEAD' to avoid returning all refs
         .args = {"ls-remote", "--symref", path},
     });
-    if (exit_code != 0) {
-        return std::nullopt;
-    }
+    if (status != 0) return std::nullopt;
 
     std::string_view line = output;
     line = line.substr(0, line.find("\n"));
@@ -82,12 +82,11 @@ std::optional<std::string> readHead(const Path & path)
 }
 
 // Persist the HEAD ref from the remote repo in the local cached repo.
-bool storeCachedHead(const std::string& actualUrl, const std::string& headRef)
+bool storeCachedHead(const std::string & actualUrl, const std::string & headRef)
 {
     Path cacheDir = getCachePath(actualUrl);
-    auto gitDir = ".";
     try {
-        runProgram("git", true, { "-C", cacheDir, "--git-dir", gitDir, "symbolic-ref", "--", "HEAD", headRef });
+        runProgram("git", true, { "-C", cacheDir, "--git-dir", ".", "symbolic-ref", "--", "HEAD", headRef });
     } catch (ExecError &e) {
         if (!WIFEXITED(e.status)) throw;
         return false;
@@ -96,7 +95,7 @@ bool storeCachedHead(const std::string& actualUrl, const std::string& headRef)
     return true;
 }
 
-std::optional<std::string> readHeadCached(const std::string& actualUrl)
+std::optional<std::string> readHeadCached(const std::string & actualUrl)
 {
     // Create a cache path to store the branch of the HEAD ref. Append something
     // in front of the URL to prevent collision with the repository itself.
@@ -110,16 +109,15 @@ std::optional<std::string> readHeadCached(const std::string& actualUrl)
         cachedRef = readHead(cacheDir);
         if (cachedRef != std::nullopt &&
             *cachedRef != gitInitialBranch &&
-            isCacheFileWithinTtl(now, st)) {
+            isCacheFileWithinTtl(now, st))
+        {
             debug("using cached HEAD ref '%s' for repo '%s'", *cachedRef, actualUrl);
             return cachedRef;
         }
     }
 
     auto ref = readHead(actualUrl);
-    if (ref) {
-        return ref;
-    }
+    if (ref) return ref;
 
     if (cachedRef) {
         // If the cached git ref is expired in fetch() below, and the 'git fetch'
@@ -250,7 +248,7 @@ std::pair<StorePath, Input> fetchFromWorkdir(ref<Store> store, Input & input, co
 
 struct GitInputScheme : InputScheme
 {
-    std::optional<Input> inputFromURL(const ParsedURL & url) override
+    std::optional<Input> inputFromURL(const ParsedURL & url) const override
     {
         if (url.scheme != "git" &&
             url.scheme != "git+http" &&
@@ -265,7 +263,7 @@ struct GitInputScheme : InputScheme
         Attrs attrs;
         attrs.emplace("type", "git");
 
-        for (auto &[name, value] : url.query) {
+        for (auto & [name, value] : url.query) {
             if (name == "rev" || name == "ref")
                 attrs.emplace(name, value);
             else if (name == "shallow" || name == "submodules")
@@ -279,7 +277,7 @@ struct GitInputScheme : InputScheme
         return inputFromAttrs(attrs);
     }
 
-    std::optional<Input> inputFromAttrs(const Attrs & attrs) override
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
     {
         if (maybeGetStrAttr(attrs, "type") != "git") return {};
 
@@ -302,7 +300,7 @@ struct GitInputScheme : InputScheme
         return input;
     }
 
-    ParsedURL toURL(const Input & input) override
+    ParsedURL toURL(const Input & input) const override
     {
         auto url = parseURL(getStrAttr(input.attrs, "url"));
         if (url.scheme != "git") url.scheme = "git+" + url.scheme;
@@ -313,7 +311,7 @@ struct GitInputScheme : InputScheme
         return url;
     }
 
-    bool hasAllInfo(const Input & input) override
+    bool hasAllInfo(const Input & input) const override
     {
         bool maybeDirty = !input.getRef();
         bool shallow = maybeGetBoolAttr(input.attrs, "shallow").value_or(false);
@@ -325,7 +323,7 @@ struct GitInputScheme : InputScheme
     Input applyOverrides(
         const Input & input,
         std::optional<std::string> ref,
-        std::optional<Hash> rev) override
+        std::optional<Hash> rev) const override
     {
         auto res(input);
         if (rev) res.attrs.insert_or_assign("rev", rev->gitRev());
@@ -335,7 +333,7 @@ struct GitInputScheme : InputScheme
         return res;
     }
 
-    void clone(const Input & input, const Path & destDir) override
+    void clone(const Input & input, const Path & destDir) const override
     {
         auto [isLocal, actualUrl] = getActualUrl(input);
 
@@ -603,9 +601,9 @@ struct GitInputScheme : InputScheme
         {
             throw Error(
                 "Cannot find Git revision '%s' in ref '%s' of repository '%s'! "
-                    "Please make sure that the " ANSI_BOLD "rev" ANSI_NORMAL " exists on the "
-                    ANSI_BOLD "ref" ANSI_NORMAL " you've specified or add " ANSI_BOLD
-                    "allRefs = true;" ANSI_NORMAL " to " ANSI_BOLD "fetchGit" ANSI_NORMAL ".",
+                "Please make sure that the " ANSI_BOLD "rev" ANSI_NORMAL " exists on the "
+                ANSI_BOLD "ref" ANSI_NORMAL " you've specified or add " ANSI_BOLD
+                "allRefs = true;" ANSI_NORMAL " to " ANSI_BOLD "fetchGit" ANSI_NORMAL ".",
                 input.getRev()->gitRev(),
                 *input.getRef(),
                 actualUrl
diff --git a/src/libfetchers/github.cc b/src/libfetchers/github.cc
index 2115ce2f5..1ed09d30d 100644
--- a/src/libfetchers/github.cc
+++ b/src/libfetchers/github.cc
@@ -26,11 +26,11 @@ std::regex hostRegex(hostRegexS, std::regex::ECMAScript);
 
 struct GitArchiveInputScheme : InputScheme
 {
-    virtual std::string type() = 0;
+    virtual std::string type() const = 0;
 
     virtual std::optional<std::pair<std::string, std::string>> accessHeaderFromToken(const std::string & token) const = 0;
 
-    std::optional<Input> inputFromURL(const ParsedURL & url) override
+    std::optional<Input> inputFromURL(const ParsedURL & url) const override
     {
         if (url.scheme != type()) return {};
 
@@ -100,7 +100,7 @@ struct GitArchiveInputScheme : InputScheme
         return input;
     }
 
-    std::optional<Input> inputFromAttrs(const Attrs & attrs) override
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
     {
         if (maybeGetStrAttr(attrs, "type") != type()) return {};
 
@@ -116,7 +116,7 @@ struct GitArchiveInputScheme : InputScheme
         return input;
     }
 
-    ParsedURL toURL(const Input & input) override
+    ParsedURL toURL(const Input & input) const override
     {
         auto owner = getStrAttr(input.attrs, "owner");
         auto repo = getStrAttr(input.attrs, "repo");
@@ -132,7 +132,7 @@ struct GitArchiveInputScheme : InputScheme
         };
     }
 
-    bool hasAllInfo(const Input & input) override
+    bool hasAllInfo(const Input & input) const override
     {
         return input.getRev() && maybeGetIntAttr(input.attrs, "lastModified");
     }
@@ -140,7 +140,7 @@ struct GitArchiveInputScheme : InputScheme
     Input applyOverrides(
         const Input & _input,
         std::optional<std::string> ref,
-        std::optional<Hash> rev) override
+        std::optional<Hash> rev) const override
     {
         auto input(_input);
         if (rev && ref)
@@ -227,7 +227,7 @@ struct GitArchiveInputScheme : InputScheme
 
 struct GitHubInputScheme : GitArchiveInputScheme
 {
-    std::string type() override { return "github"; }
+    std::string type() const override { return "github"; }
 
     std::optional<std::pair<std::string, std::string>> accessHeaderFromToken(const std::string & token) const override
     {
@@ -240,14 +240,29 @@ struct GitHubInputScheme : GitArchiveInputScheme
         return std::pair<std::string, std::string>("Authorization", fmt("token %s", token));
     }
 
+    std::string getHost(const Input & input) const
+    {
+        return maybeGetStrAttr(input.attrs, "host").value_or("github.com");
+    }
+
+    std::string getOwner(const Input & input) const
+    {
+        return getStrAttr(input.attrs, "owner");
+    }
+
+    std::string getRepo(const Input & input) const
+    {
+        return getStrAttr(input.attrs, "repo");
+    }
+
     Hash getRevFromRef(nix::ref<Store> store, const Input & input) const override
     {
-        auto host = maybeGetStrAttr(input.attrs, "host").value_or("github.com");
+        auto host = getHost(input);
         auto url = fmt(
             host == "github.com"
             ? "https://api.%s/repos/%s/%s/commits/%s"
             : "https://%s/api/v3/repos/%s/%s/commits/%s",
-            host, getStrAttr(input.attrs, "owner"), getStrAttr(input.attrs, "repo"), *input.getRef());
+            host, getOwner(input), getRepo(input), *input.getRef());
 
         Headers headers = makeHeadersWithAuthTokens(host);
 
@@ -262,8 +277,10 @@ struct GitHubInputScheme : GitArchiveInputScheme
 
     DownloadUrl getDownloadUrl(const Input & input) const override
     {
-        auto host = maybeGetStrAttr(input.attrs, "host").value_or("github.com");
+        auto host = getHost(input);
+
         Headers headers = makeHeadersWithAuthTokens(host);
+
         // If we have no auth headers then we default to the public archive
         // urls so we do not run into rate limits.
         const auto urlFmt =
@@ -273,17 +290,17 @@ struct GitHubInputScheme : GitArchiveInputScheme
             ? "https://%s/%s/%s/archive/%s.tar.gz"
             : "https://api.%s/repos/%s/%s/tarball/%s";
 
-        const auto url = fmt(urlFmt, host, getStrAttr(input.attrs, "owner"), getStrAttr(input.attrs, "repo"),
+        const auto url = fmt(urlFmt, host, getOwner(input), getRepo(input),
             input.getRev()->to_string(Base16, false));
 
         return DownloadUrl { url, headers };
     }
 
-    void clone(const Input & input, const Path & destDir) override
+    void clone(const Input & input, const Path & destDir) const override
     {
-        auto host = maybeGetStrAttr(input.attrs, "host").value_or("github.com");
+        auto host = getHost(input);
         Input::fromURL(fmt("git+https://%s/%s/%s.git",
-                host, getStrAttr(input.attrs, "owner"), getStrAttr(input.attrs, "repo")))
+                host, getOwner(input), getRepo(input)))
             .applyOverrides(input.getRef(), input.getRev())
             .clone(destDir);
     }
@@ -291,7 +308,7 @@ struct GitHubInputScheme : GitArchiveInputScheme
 
 struct GitLabInputScheme : GitArchiveInputScheme
 {
-    std::string type() override { return "gitlab"; }
+    std::string type() const override { return "gitlab"; }
 
     std::optional<std::pair<std::string, std::string>> accessHeaderFromToken(const std::string & token) const override
     {
@@ -346,7 +363,7 @@ struct GitLabInputScheme : GitArchiveInputScheme
         return DownloadUrl { url, headers };
     }
 
-    void clone(const Input & input, const Path & destDir) override
+    void clone(const Input & input, const Path & destDir) const override
     {
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("gitlab.com");
         // FIXME: get username somewhere
@@ -359,7 +376,7 @@ struct GitLabInputScheme : GitArchiveInputScheme
 
 struct SourceHutInputScheme : GitArchiveInputScheme
 {
-    std::string type() override { return "sourcehut"; }
+    std::string type() const override { return "sourcehut"; }
 
     std::optional<std::pair<std::string, std::string>> accessHeaderFromToken(const std::string & token) const override
     {
@@ -433,7 +450,7 @@ struct SourceHutInputScheme : GitArchiveInputScheme
         return DownloadUrl { url, headers };
     }
 
-    void clone(const Input & input, const Path & destDir) override
+    void clone(const Input & input, const Path & destDir) const override
     {
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("git.sr.ht");
         Input::fromURL(fmt("git+https://%s/%s/%s",
diff --git a/src/libfetchers/indirect.cc b/src/libfetchers/indirect.cc
index 9288fc6cf..b99504a16 100644
--- a/src/libfetchers/indirect.cc
+++ b/src/libfetchers/indirect.cc
@@ -7,7 +7,7 @@ std::regex flakeRegex("[a-zA-Z][a-zA-Z0-9_-]*", std::regex::ECMAScript);
 
 struct IndirectInputScheme : InputScheme
 {
-    std::optional<Input> inputFromURL(const ParsedURL & url) override
+    std::optional<Input> inputFromURL(const ParsedURL & url) const override
     {
         if (url.scheme != "flake") return {};
 
@@ -50,7 +50,7 @@ struct IndirectInputScheme : InputScheme
         return input;
     }
 
-    std::optional<Input> inputFromAttrs(const Attrs & attrs) override
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
     {
         if (maybeGetStrAttr(attrs, "type") != "indirect") return {};
 
@@ -68,7 +68,7 @@ struct IndirectInputScheme : InputScheme
         return input;
     }
 
-    ParsedURL toURL(const Input & input) override
+    ParsedURL toURL(const Input & input) const override
     {
         ParsedURL url;
         url.scheme = "flake";
@@ -78,7 +78,7 @@ struct IndirectInputScheme : InputScheme
         return url;
     }
 
-    bool hasAllInfo(const Input & input) override
+    bool hasAllInfo(const Input & input) const override
     {
         return false;
     }
@@ -86,7 +86,7 @@ struct IndirectInputScheme : InputScheme
     Input applyOverrides(
         const Input & _input,
         std::optional<std::string> ref,
-        std::optional<Hash> rev) override
+        std::optional<Hash> rev) const override
     {
         auto input(_input);
         if (rev) input.attrs.insert_or_assign("rev", rev->gitRev());
diff --git a/src/libfetchers/mercurial.cc b/src/libfetchers/mercurial.cc
index 5c5671681..86e8f81f4 100644
--- a/src/libfetchers/mercurial.cc
+++ b/src/libfetchers/mercurial.cc
@@ -43,7 +43,7 @@ static std::string runHg(const Strings & args, const std::optional<std::string>
 
 struct MercurialInputScheme : InputScheme
 {
-    std::optional<Input> inputFromURL(const ParsedURL & url) override
+    std::optional<Input> inputFromURL(const ParsedURL & url) const override
     {
         if (url.scheme != "hg+http" &&
             url.scheme != "hg+https" &&
@@ -69,7 +69,7 @@ struct MercurialInputScheme : InputScheme
         return inputFromAttrs(attrs);
     }
 
-    std::optional<Input> inputFromAttrs(const Attrs & attrs) override
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
     {
         if (maybeGetStrAttr(attrs, "type") != "hg") return {};
 
@@ -89,7 +89,7 @@ struct MercurialInputScheme : InputScheme
         return input;
     }
 
-    ParsedURL toURL(const Input & input) override
+    ParsedURL toURL(const Input & input) const override
     {
         auto url = parseURL(getStrAttr(input.attrs, "url"));
         url.scheme = "hg+" + url.scheme;
@@ -98,7 +98,7 @@ struct MercurialInputScheme : InputScheme
         return url;
     }
 
-    bool hasAllInfo(const Input & input) override
+    bool hasAllInfo(const Input & input) const override
     {
         // FIXME: ugly, need to distinguish between dirty and clean
         // default trees.
@@ -108,7 +108,7 @@ struct MercurialInputScheme : InputScheme
     Input applyOverrides(
         const Input & input,
         std::optional<std::string> ref,
-        std::optional<Hash> rev) override
+        std::optional<Hash> rev) const override
     {
         auto res(input);
         if (rev) res.attrs.insert_or_assign("rev", rev->gitRev());
diff --git a/src/libfetchers/path.cc b/src/libfetchers/path.cc
index f0ef97da5..61541e69d 100644
--- a/src/libfetchers/path.cc
+++ b/src/libfetchers/path.cc
@@ -6,7 +6,7 @@ namespace nix::fetchers {
 
 struct PathInputScheme : InputScheme
 {
-    std::optional<Input> inputFromURL(const ParsedURL & url) override
+    std::optional<Input> inputFromURL(const ParsedURL & url) const override
     {
         if (url.scheme != "path") return {};
 
@@ -32,7 +32,7 @@ struct PathInputScheme : InputScheme
         return input;
     }
 
-    std::optional<Input> inputFromAttrs(const Attrs & attrs) override
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
     {
         if (maybeGetStrAttr(attrs, "type") != "path") return {};
 
@@ -54,7 +54,7 @@ struct PathInputScheme : InputScheme
         return input;
     }
 
-    ParsedURL toURL(const Input & input) override
+    ParsedURL toURL(const Input & input) const override
     {
         auto query = attrsToQuery(input.attrs);
         query.erase("path");
@@ -66,7 +66,7 @@ struct PathInputScheme : InputScheme
         };
     }
 
-    bool hasAllInfo(const Input & input) override
+    bool hasAllInfo(const Input & input) const override
     {
         return true;
     }
diff --git a/src/libfetchers/tarball.cc b/src/libfetchers/tarball.cc
index 6c551bd93..e9686262a 100644
--- a/src/libfetchers/tarball.cc
+++ b/src/libfetchers/tarball.cc
@@ -185,7 +185,7 @@ struct CurlInputScheme : InputScheme
 
     virtual bool isValidURL(const ParsedURL & url) const = 0;
 
-    std::optional<Input> inputFromURL(const ParsedURL & url) override
+    std::optional<Input> inputFromURL(const ParsedURL & url) const override
     {
         if (!isValidURL(url))
             return std::nullopt;
@@ -203,7 +203,7 @@ struct CurlInputScheme : InputScheme
         return input;
     }
 
-    std::optional<Input> inputFromAttrs(const Attrs & attrs) override
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
     {
         auto type = maybeGetStrAttr(attrs, "type");
         if (type != inputType()) return {};
@@ -220,16 +220,17 @@ struct CurlInputScheme : InputScheme
         return input;
     }
 
-    ParsedURL toURL(const Input & input) override
+    ParsedURL toURL(const Input & input) const override
     {
         auto url = parseURL(getStrAttr(input.attrs, "url"));
-        // NAR hashes are preferred over file hashes since tar/zip files        // don't have a canonical representation.
+        // NAR hashes are preferred over file hashes since tar/zip
+        // files don't have a canonical representation.
         if (auto narHash = input.getNarHash())
             url.query.insert_or_assign("narHash", narHash->to_string(SRI, true));
         return url;
     }
 
-    bool hasAllInfo(const Input & input) override
+    bool hasAllInfo(const Input & input) const override
     {
         return true;
     }
diff --git a/src/libmain/progress-bar.cc b/src/libmain/progress-bar.cc
index d160a83e9..e9205a5e5 100644
--- a/src/libmain/progress-bar.cc
+++ b/src/libmain/progress-bar.cc
@@ -132,7 +132,7 @@ public:
         log(*state, lvl, fs.s);
     }
 
-    void logEI(const ErrorInfo &ei) override
+    void logEI(const ErrorInfo & ei) override
     {
         auto state(state_.lock());
 
diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 12d0c32fb..149d414d3 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -346,7 +346,7 @@ void BinaryCacheStore::narFromPath(const StorePath & storePath, Sink & sink)
     try {
         getFile(info->url, *decompressor);
     } catch (NoSuchBinaryCacheFile & e) {
-        throw SubstituteGone(e.info());
+        throw SubstituteGone(std::move(e.info()));
     }
 
     decompressor->finish();
diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index 87ec081cb..d3b995a4f 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -134,7 +134,7 @@ void DerivationGoal::killChild()
 void DerivationGoal::timedOut(Error && ex)
 {
     killChild();
-    done(BuildResult::TimedOut, {}, ex);
+    done(BuildResult::TimedOut, {}, std::move(ex));
 }
 
 
@@ -971,7 +971,7 @@ void DerivationGoal::buildDone()
                 BuildResult::PermanentFailure;
         }
 
-        done(st, {}, e);
+        done(st, {}, std::move(e));
         return;
     }
 }
@@ -1434,7 +1434,7 @@ void DerivationGoal::done(
         fs << worker.store.printStorePath(drvPath) << "\t" << buildResult.toString() << std::endl;
     }
 
-    amDone(buildResult.success() ? ecSuccess : ecFailed, ex);
+    amDone(buildResult.success() ? ecSuccess : ecFailed, std::move(ex));
 }
 
 
diff --git a/src/libstore/build/entry-points.cc b/src/libstore/build/entry-points.cc
index bea7363db..e1b80165e 100644
--- a/src/libstore/build/entry-points.cc
+++ b/src/libstore/build/entry-points.cc
@@ -30,7 +30,7 @@ void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMod
             if (ex)
                 logError(i->ex->info());
             else
-                ex = i->ex;
+                ex = std::move(i->ex);
         }
         if (i->exitCode != Goal::ecSuccess) {
             if (auto i2 = dynamic_cast<DerivationGoal *>(i.get())) failed.insert(i2->drvPath);
@@ -40,7 +40,7 @@ void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMod
 
     if (failed.size() == 1 && ex) {
         ex->status = worker.exitStatus();
-        throw *ex;
+        throw std::move(*ex);
     } else if (!failed.empty()) {
         if (ex) logError(ex->info());
         throw Error(worker.exitStatus(), "build of %s failed", showPaths(failed));
@@ -109,7 +109,7 @@ void Store::ensurePath(const StorePath & path)
     if (goal->exitCode != Goal::ecSuccess) {
         if (goal->ex) {
             goal->ex->status = worker.exitStatus();
-            throw *goal->ex;
+            throw std::move(*goal->ex);
         } else
             throw Error(worker.exitStatus(), "path '%s' does not exist and cannot be created", printStorePath(path));
     }
diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 6fe3bc49c..dccd096ec 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -230,7 +230,7 @@ void LocalDerivationGoal::tryLocalBuild() {
         outputLocks.unlock();
         buildUser.reset();
         worker.permanentFailure = true;
-        done(BuildResult::InputRejected, {}, e);
+        done(BuildResult::InputRejected, {}, std::move(e));
         return;
     }
 
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index fe99c3c5e..42a53912e 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -448,7 +448,7 @@ std::string Derivation::unparse(const Store & store, bool maskOutputs,
 
 
 // FIXME: remove
-bool isDerivation(const std::string & fileName)
+bool isDerivation(std::string_view fileName)
 {
     return hasSuffix(fileName, drvExtension);
 }
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
index af198a767..f3cd87fb1 100644
--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -224,7 +224,7 @@ StorePath writeDerivation(Store & store,
 Derivation parseDerivation(const Store & store, std::string && s, std::string_view name);
 
 // FIXME: remove
-bool isDerivation(const std::string & fileName);
+bool isDerivation(std::string_view fileName);
 
 /* Calculate the name that will be used for the store path for this
    output.
diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index 5746c32a3..2ff411e18 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -142,9 +142,9 @@ struct curlFileTransfer : public FileTransfer
         }
 
         template<class T>
-        void fail(const T & e)
+        void fail(T && e)
         {
-            failEx(std::make_exception_ptr(e));
+            failEx(std::make_exception_ptr(std::move(e)));
         }
 
         LambdaSink finalSink;
@@ -472,7 +472,7 @@ struct curlFileTransfer : public FileTransfer
                     fileTransfer.enqueueItem(shared_from_this());
                 }
                 else
-                    fail(exc);
+                    fail(std::move(exc));
             }
         }
     };
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 96a29155c..48cf731a8 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -447,7 +447,7 @@ void RemoteStore::queryPathInfoUncached(const StorePath & path,
             } catch (Error & e) {
                 // Ugly backwards compatibility hack.
                 if (e.msg().find("is not valid") != std::string::npos)
-                    throw InvalidPath(e.info());
+                    throw InvalidPath(std::move(e.info()));
                 throw;
             }
             if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 17) {
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 8811ab578..80b60ca1b 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -19,21 +19,21 @@ using json = nlohmann::json;
 namespace nix {
 
 
-bool Store::isInStore(const Path & path) const
+bool Store::isInStore(PathView path) const
 {
     return isInDir(path, storeDir);
 }
 
 
-std::pair<StorePath, Path> Store::toStorePath(const Path & path) const
+std::pair<StorePath, Path> Store::toStorePath(PathView path) const
 {
     if (!isInStore(path))
         throw Error("path '%1%' is not in the Nix store", path);
-    Path::size_type slash = path.find('/', storeDir.size() + 1);
+    auto slash = path.find('/', storeDir.size() + 1);
     if (slash == Path::npos)
         return {parseStorePath(path), ""};
     else
-        return {parseStorePath(std::string_view(path).substr(0, slash)), path.substr(slash)};
+        return {parseStorePath(path.substr(0, slash)), (Path) path.substr(slash)};
 }
 
 
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 151ec10d6..4a88d7216 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -179,7 +179,7 @@ public:
 
     /* Return true if ‘path’ is in the Nix store (but not the Nix
        store itself). */
-    bool isInStore(const Path & path) const;
+    bool isInStore(PathView path) const;
 
     /* Return true if ‘path’ is a store path, i.e. a direct child of
        the Nix store. */
@@ -187,7 +187,7 @@ public:
 
     /* Split a path like /nix/store/<hash>-<name>/<bla> into
        /nix/store/<hash>-<name> and /<bla>. */
-    std::pair<StorePath, Path> toStorePath(const Path & path) const;
+    std::pair<StorePath, Path> toStorePath(PathView path) const;
 
     /* Follow symlinks until we end up with a path in the Nix store. */
     Path followLinksToStore(std::string_view path) const;
diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
index 4b0636129..0e2b9d12c 100644
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -35,10 +35,6 @@ static ArchiveSettings archiveSettings;
 
 static GlobalConfig::Register rArchiveSettings(&archiveSettings);
 
-const std::string narVersionMagic1 = "nix-archive-1";
-
-static std::string caseHackSuffix = "~nix~case~hack~";
-
 PathFilter defaultPathFilter = [](const Path &) { return true; };
 
 
diff --git a/src/libutil/archive.hh b/src/libutil/archive.hh
index ac4183bf5..e42dea540 100644
--- a/src/libutil/archive.hh
+++ b/src/libutil/archive.hh
@@ -103,7 +103,9 @@ void copyNAR(Source & source, Sink & sink);
 void copyPath(const Path & from, const Path & to);
 
 
-extern const std::string narVersionMagic1;
+inline constexpr std::string_view narVersionMagic1 = "nix-archive-1";
+
+inline constexpr std::string_view caseHackSuffix = "~nix~case~hack~";
 
 
 }
diff --git a/src/libutil/fmt.hh b/src/libutil/fmt.hh
index 7664e5c04..e879fd3b8 100644
--- a/src/libutil/fmt.hh
+++ b/src/libutil/fmt.hh
@@ -148,7 +148,7 @@ inline hintformat hintfmt(const std::string & fs, const Args & ... args)
     return f;
 }
 
-inline hintformat hintfmt(std::string plain_string)
+inline hintformat hintfmt(const std::string & plain_string)
 {
     // we won't be receiving any args in this case, so just print the original string
     return hintfmt("%s", normaltxt(plain_string));
diff --git a/src/libutil/logging.cc b/src/libutil/logging.cc
index cb2b15b41..ac86d8ac2 100644
--- a/src/libutil/logging.cc
+++ b/src/libutil/logging.cc
@@ -105,14 +105,6 @@ public:
 
 Verbosity verbosity = lvlInfo;
 
-void warnOnce(bool & haveWarned, const FormatOrString & fs)
-{
-    if (!haveWarned) {
-        warn(fs.s);
-        haveWarned = true;
-    }
-}
-
 void writeToStderr(std::string_view s)
 {
     try {
@@ -130,11 +122,11 @@ Logger * makeSimpleLogger(bool printBuildLogs)
     return new SimpleLogger(printBuildLogs);
 }
 
-std::atomic<uint64_t> nextId{(uint64_t) getpid() << 32};
+std::atomic<uint64_t> nextId{0};
 
 Activity::Activity(Logger & logger, Verbosity lvl, ActivityType type,
     const std::string & s, const Logger::Fields & fields, ActivityId parent)
-    : logger(logger), id(nextId++)
+    : logger(logger), id(nextId++ + (((uint64_t) getpid()) << 32))
 {
     logger.startActivity(id, lvl, type, s, fields, parent);
 }
diff --git a/src/libutil/logging.hh b/src/libutil/logging.hh
index d0817b4a9..4642c49f7 100644
--- a/src/libutil/logging.hh
+++ b/src/libutil/logging.hh
@@ -82,7 +82,7 @@ public:
         log(lvlInfo, fs);
     }
 
-    virtual void logEI(const ErrorInfo &ei) = 0;
+    virtual void logEI(const ErrorInfo & ei) = 0;
 
     void logEI(Verbosity lvl, ErrorInfo ei)
     {
@@ -225,7 +225,11 @@ inline void warn(const std::string & fs, const Args & ... args)
     logger->warn(f.str());
 }
 
-void warnOnce(bool & haveWarned, const FormatOrString & fs);
+#define warnOnce(haveWarned, args...) \
+    if (!haveWarned) {                \
+        haveWarned = true;            \
+        warn(args);                   \
+    }
 
 void writeToStderr(std::string_view s);
 
diff --git a/src/libutil/ref.hh b/src/libutil/ref.hh
index bf26321db..7d38b059c 100644
--- a/src/libutil/ref.hh
+++ b/src/libutil/ref.hh
@@ -83,6 +83,11 @@ public:
         return p != other.p;
     }
 
+    bool operator < (const ref<T> & other) const
+    {
+        return p < other.p;
+    }
+
 private:
 
     template<typename T2, typename... Args>
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index 2c3597775..c653db9d0 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -338,7 +338,7 @@ Sink & operator << (Sink & sink, const StringSet & s)
 
 Sink & operator << (Sink & sink, const Error & ex)
 {
-    auto info = ex.info();
+    auto & info = ex.info();
     sink
         << "Error"
         << info.level
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
index 84847835a..7da5b07fd 100644
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -331,17 +331,9 @@ T readNum(Source & source)
     unsigned char buf[8];
     source((char *) buf, sizeof(buf));
 
-    uint64_t n =
-        ((uint64_t) buf[0]) |
-        ((uint64_t) buf[1] << 8) |
-        ((uint64_t) buf[2] << 16) |
-        ((uint64_t) buf[3] << 24) |
-        ((uint64_t) buf[4] << 32) |
-        ((uint64_t) buf[5] << 40) |
-        ((uint64_t) buf[6] << 48) |
-        ((uint64_t) buf[7] << 56);
+    auto n = readLittleEndian<uint64_t>(buf);
 
-    if (n > (uint64_t)std::numeric_limits<T>::max())
+    if (n > (uint64_t) std::numeric_limits<T>::max())
         throw SerialisationError("serialised integer %d is too large for type '%s'", n, typeid(T).name());
 
     return (T) n;
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 4f2caaa40..993dc1cb6 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -1594,6 +1594,21 @@ std::string stripIndentation(std::string_view s)
 }
 
 
+std::pair<std::string_view, std::string_view> getLine(std::string_view s)
+{
+    auto newline = s.find('\n');
+
+    if (newline == s.npos) {
+        return {s, ""};
+    } else {
+        auto line = s.substr(0, newline);
+        if (!line.empty() && line[line.size() - 1] == '\r')
+            line = line.substr(0, line.size() - 1);
+        return {line, s.substr(newline + 1)};
+    }
+}
+
+
 //////////////////////////////////////////////////////////////////////
 
 static Sync<std::pair<unsigned short, unsigned short>> windowSize{{0, 0}};
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 94d8cc555..9b149de80 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -510,6 +510,18 @@ std::optional<N> string2Float(const std::string_view s)
 }
 
 
+/* Convert a little-endian integer to host order. */
+template<typename T>
+T readLittleEndian(unsigned char * p)
+{
+    T x = 0;
+    for (size_t i = 0; i < sizeof(x); ++i, ++p) {
+        x |= ((T) *p) << (i * 8);
+    }
+    return x;
+}
+
+
 /* Return true iff `s' starts with `prefix'. */
 bool hasPrefix(std::string_view s, std::string_view prefix);
 
@@ -563,6 +575,12 @@ std::string base64Decode(std::string_view s);
 std::string stripIndentation(std::string_view s);
 
 
+/* Get the prefix of 's' up to and excluding the next line break (LF
+   optionally preceded by CR), and the remainder following the line
+   break. */
+std::pair<std::string_view, std::string_view> getLine(std::string_view s);
+
+
 /* Get a value for the specified key from an associate container. */
 template <class T>
 const typename T::mapped_type * get(const T & map, const typename T::key_type & key)
@@ -737,4 +755,13 @@ inline std::string operator + (std::string && s, std::string_view s2)
     return std::move(s);
 }
 
+inline std::string operator + (std::string_view s1, const char * s2)
+{
+    std::string s;
+    s.reserve(s1.size() + strlen(s2));
+    s.append(s1);
+    s.append(s2);
+    return s;
+}
+
 }
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index 85f142c39..96e265f9e 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -932,7 +932,6 @@ static void opServe(Strings opFlags, Strings opArgs)
                     worker_proto::write(*store, out, status.builtOutputs);
                 }
 
-
                 break;
             }
 
diff --git a/src/nix/daemon.cc b/src/nix/daemon.cc
index 940923d3b..c527fdb0a 100644
--- a/src/nix/daemon.cc
+++ b/src/nix/daemon.cc
@@ -257,7 +257,7 @@ static void daemonLoop()
         } catch (Interrupted & e) {
             return;
         } catch (Error & error) {
-            ErrorInfo ei = error.info();
+            auto ei = error.info();
             // FIXME: add to trace?
             ei.msg = hintfmt("error processing connection: %1%", ei.msg.str());
             logError(ei);
diff --git a/src/nix/flake-update.md b/src/nix/flake-update.md
index 2ee8a707d..8c6042d94 100644
--- a/src/nix/flake-update.md
+++ b/src/nix/flake-update.md
@@ -16,7 +16,7 @@ R""(
 # Description
 
 This command recreates the lock file of a flake (`flake.lock`), thus
-updating the lock for every mutable input (like `nixpkgs`) to its
+updating the lock for every unlocked input (like `nixpkgs`) to its
 current version. This is equivalent to passing `--recreate-lock-file`
 to any command that operates on a flake. That is,
 
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 336f6723a..96f035117 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -215,7 +215,7 @@ struct CmdFlakeMetadata : FlakeCommand, MixJSON
             if (!lockedFlake.lockFile.root->inputs.empty())
                 logger->cout(ANSI_BOLD "Inputs:" ANSI_NORMAL);
 
-            std::unordered_set<std::shared_ptr<Node>> visited;
+            std::set<ref<Node>> visited;
 
             std::function<void(const Node & node, const std::string & prefix)> recurse;
 
@@ -227,7 +227,7 @@ struct CmdFlakeMetadata : FlakeCommand, MixJSON
                     if (auto lockedNode = std::get_if<0>(&input.second)) {
                         logger->cout("%s" ANSI_BOLD "%s" ANSI_NORMAL ": %s",
                             prefix + (last ? treeLast : treeConn), input.first,
-                            *lockedNode ? (*lockedNode)->lockedRef : flake.lockedRef);
+                            (*lockedNode)->lockedRef);
 
                         bool firstVisit = visited.insert(*lockedNode).second;
 
diff --git a/src/nix/profile-list.md b/src/nix/profile-list.md
index bdab9a208..fa786162f 100644
--- a/src/nix/profile-list.md
+++ b/src/nix/profile-list.md
@@ -20,11 +20,11 @@ following fields:
 * An integer that can be used to unambiguously identify the package in
   invocations of `nix profile remove` and `nix profile upgrade`.
 
-* The original ("mutable") flake reference and output attribute path
+* The original ("unlocked") flake reference and output attribute path
   used at installation time.
 
-* The immutable flake reference to which the mutable flake reference
-  was resolved.
+* The locked flake reference to which the unlocked flake reference was
+  resolved.
 
 * The store path(s) of the package.
 
diff --git a/src/nix/profile-upgrade.md b/src/nix/profile-upgrade.md
index e06e74abe..39cca428b 100644
--- a/src/nix/profile-upgrade.md
+++ b/src/nix/profile-upgrade.md
@@ -2,7 +2,7 @@ R""(
 
 # Examples
 
-* Upgrade all packages that were installed using a mutable flake
+* Upgrade all packages that were installed using an unlocked flake
   reference:
 
   ```console
@@ -32,9 +32,9 @@ the package was installed.
 
 > **Warning**
 >
-> This only works if you used a *mutable* flake reference at
+> This only works if you used an *unlocked* flake reference at
 > installation time, e.g. `nixpkgs#hello`. It does not work if you
-> used an *immutable* flake reference
+> used a *locked* flake reference
 > (e.g. `github:NixOS/nixpkgs/13d0c311e3ae923a00f734b43fd1d35b47d8943a#hello`),
 > since in that case the "latest version" is always the same.
 
diff --git a/src/nix/profile.md b/src/nix/profile.md
index be3c5ba1a..273e02280 100644
--- a/src/nix/profile.md
+++ b/src/nix/profile.md
@@ -88,8 +88,7 @@ has the following fields:
   the user at the time of installation (e.g. `nixpkgs`). This is also
   the flake reference that will be used by `nix profile upgrade`.
 
-* `uri`: The immutable flake reference to which `originalUrl`
-  resolved.
+* `uri`: The locked flake reference to which `originalUrl` resolved.
 
 * `attrPath`: The flake output attribute that provided this
   package. Note that this is not necessarily the attribute that the
diff --git a/src/nix/registry.cc b/src/nix/registry.cc
index c496f94f8..b5bdfba95 100644
--- a/src/nix/registry.cc
+++ b/src/nix/registry.cc
@@ -183,14 +183,12 @@ struct CmdRegistryPin : RegistryCommand, EvalCommand
 
     void run(nix::ref<nix::Store> store) override
     {
-        if (locked.empty()) {
-            locked = url;
-        }
+        if (locked.empty()) locked = url;
         auto registry = getRegistry();
         auto ref = parseFlakeRef(url);
-        auto locked_ref = parseFlakeRef(locked);
+        auto lockedRef = parseFlakeRef(locked);
         registry->remove(ref.input);
-        auto [tree, resolved] = locked_ref.resolve(store).input.fetch(store);
+        auto [tree, resolved] = lockedRef.resolve(store).input.fetch(store);
         fetchers::Attrs extraAttrs;
         if (ref.subdir != "") extraAttrs["dir"] = ref.subdir;
         registry->add(ref.input, resolved, extraAttrs);
diff --git a/tests/eval.sh b/tests/eval.sh
index d74976019..ffae08a6a 100644
--- a/tests/eval.sh
+++ b/tests/eval.sh
@@ -29,3 +29,7 @@ nix-instantiate --eval -E 'assert 1 + 2 == 3; true'
 [[ $(nix-instantiate -A attr --eval "./eval.nix") == '{ foo = "bar"; }' ]]
 [[ $(nix-instantiate -A attr --eval --json "./eval.nix") == '{"foo":"bar"}' ]]
 [[ $(nix-instantiate -A int --eval - < "./eval.nix") == 123 ]]
+
+# Check that symlink cycles don't cause a hang.
+ln -sfn cycle.nix $TEST_ROOT/cycle.nix
+(! nix eval --file $TEST_ROOT/cycle.nix)
diff --git a/tests/fetchGit.sh b/tests/fetchGit.sh
index 4ceba0293..da09c3f37 100644
--- a/tests/fetchGit.sh
+++ b/tests/fetchGit.sh
@@ -122,6 +122,7 @@ git -C $repo commit -m 'Bla3' -a
 path4=$(nix eval --impure --refresh --raw --expr "(builtins.fetchGit file://$repo).outPath")
 [[ $path2 = $path4 ]]
 
+status=0
 nix eval --impure --raw --expr "(builtins.fetchGit { url = $repo; rev = \"$rev2\"; narHash = \"sha256-B5yIPHhEm0eysJKEsO7nqxprh9vcblFxpJG11gXJus1=\"; }).outPath" || status=$?
 [[ "$status" = "102" ]]
 
diff --git a/tests/flakes/absolute-paths.sh b/tests/flakes/absolute-paths.sh
new file mode 100644
index 000000000..e7bfba12d
--- /dev/null
+++ b/tests/flakes/absolute-paths.sh
@@ -0,0 +1,17 @@
+source ./common.sh
+
+requireGit
+
+flake1Dir=$TEST_ROOT/flake1
+flake2Dir=$TEST_ROOT/flake2
+
+createGitRepo $flake1Dir
+cat > $flake1Dir/flake.nix <<EOF
+{
+    outputs = { self }: { x = builtins.readFile $(pwd)/absolute-paths.sh; };
+}
+EOF
+git -C $flake1Dir add flake.nix
+git -C $flake1Dir commit -m Initial
+
+nix eval --impure --json $flake1Dir#x
diff --git a/tests/flakes/flakes.sh b/tests/flakes/flakes.sh
index 267e2cd6f..8cdc320fb 100644
--- a/tests/flakes/flakes.sh
+++ b/tests/flakes/flakes.sh
@@ -53,7 +53,11 @@ cat > $flake3Dir/flake.nix <<EOF
 }
 EOF
 
-git -C $flake3Dir add flake.nix
+cat > $flake3Dir/default.nix <<EOF
+{ x = 123; }
+EOF
+
+git -C $flake3Dir add flake.nix default.nix
 git -C $flake3Dir commit -m 'Initial'
 
 cat > $nonFlakeDir/README.md <<EOF
@@ -109,11 +113,12 @@ nix build -o $TEST_ROOT/result git+file://$flake1Dir
 nix build -o $flake1Dir/result git+file://$flake1Dir
 nix path-info $flake1Dir/result
 
-# 'getFlake' on a mutable flakeref should fail in pure mode, but succeed in impure mode.
+# 'getFlake' on an unlocked flakeref should fail in pure mode, but
+# succeed in impure mode.
 (! nix build -o $TEST_ROOT/result --expr "(builtins.getFlake \"$flake1Dir\").packages.$system.default")
 nix build -o $TEST_ROOT/result --expr "(builtins.getFlake \"$flake1Dir\").packages.$system.default" --impure
 
-# 'getFlake' on an immutable flakeref should succeed even in pure mode.
+# 'getFlake' on a locked flakeref should succeed even in pure mode.
 nix build -o $TEST_ROOT/result --expr "(builtins.getFlake \"git+file://$flake1Dir?rev=$hash2\").packages.$system.default"
 
 # Building a flake with an unlocked dependency should fail in pure mode.
@@ -460,7 +465,7 @@ nix flake lock $flake3Dir --update-input flake2/flake1
 # Test 'nix flake metadata --json'.
 nix flake metadata $flake3Dir --json | jq .
 
-# Test flake in store does not evaluate
+# Test flake in store does not evaluate.
 rm -rf $badFlakeDir
 mkdir $badFlakeDir
 echo INVALID > $badFlakeDir/flake.nix
diff --git a/tests/flakes/unlocked-override.sh b/tests/flakes/unlocked-override.sh
new file mode 100644
index 000000000..8abc8b7d3
--- /dev/null
+++ b/tests/flakes/unlocked-override.sh
@@ -0,0 +1,30 @@
+source ./common.sh
+
+requireGit
+
+flake1Dir=$TEST_ROOT/flake1
+flake2Dir=$TEST_ROOT/flake2
+
+createGitRepo $flake1Dir
+cat > $flake1Dir/flake.nix <<EOF
+{
+    outputs = { self }: { x = import ./x.nix; };
+}
+EOF
+echo 123 > $flake1Dir/x.nix
+git -C $flake1Dir add flake.nix x.nix
+git -C $flake1Dir commit -m Initial
+
+createGitRepo $flake2Dir
+cat > $flake2Dir/flake.nix <<EOF
+{
+    outputs = { self, flake1 }: { x = flake1.x; };
+}
+EOF
+git -C $flake2Dir add flake.nix
+
+[[ $(nix eval --json $flake2Dir#x --override-input flake1 $TEST_ROOT/flake1) = 123 ]]
+
+echo 456 > $flake1Dir/x.nix
+
+[[ $(nix eval --json $flake2Dir#x --override-input flake1 $TEST_ROOT/flake1) = 456 ]]
diff --git a/tests/function-trace.sh b/tests/function-trace.sh
index 0b7f49d82..d68e10df5 100755
--- a/tests/function-trace.sh
+++ b/tests/function-trace.sh
@@ -11,7 +11,7 @@ expect_trace() {
             --expr "$expr" 2>&1 \
             | grep "function-trace" \
             | sed -e 's/ [0-9]*$//'
-    );
+    )
 
     echo -n "Tracing expression '$expr'"
     set +e
diff --git a/tests/local.mk b/tests/local.mk
index 340817ec3..2f7f76261 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -7,6 +7,8 @@ nix_tests = \
   flakes/follow-paths.sh \
   flakes/bundle.sh \
   flakes/check.sh \
+  flakes/unlocked-override.sh \
+  flakes/absolute-paths.sh \
   ca/gc.sh \
   gc.sh \
   remote-store.sh \
@@ -110,7 +112,8 @@ nix_tests = \
   fetchClosure.sh \
   completions.sh \
   impure-derivations.sh \
-  path-from-hash-part.sh
+  path-from-hash-part.sh \
+  toString-path.sh
 
 ifeq ($(HAVE_LIBCPUID), 1)
 	nix_tests += compute-levels.sh
diff --git a/tests/nix_path.sh b/tests/nix_path.sh
index d3657abf0..2b222b4a1 100644
--- a/tests/nix_path.sh
+++ b/tests/nix_path.sh
@@ -9,3 +9,6 @@ nix-instantiate --eval -E '<by-relative-path/simple.nix>' --restrict-eval
 
 # Should ideally also test this, but there’s no pure way to do it, so just trust me that it works
 # nix-instantiate --eval -E '<nixpkgs>' -I nixpkgs=channel:nixos-unstable --restrict-eval
+
+[[ $(nix-instantiate --find-file by-absolute-path/simple.nix) = $PWD/simple.nix ]]
+[[ $(nix-instantiate --find-file by-relative-path/simple.nix) = $PWD/simple.nix ]]
diff --git a/tests/restricted.sh b/tests/restricted.sh
index 242b901dd..9bd16cf51 100644
--- a/tests/restricted.sh
+++ b/tests/restricted.sh
@@ -3,7 +3,7 @@ source common.sh
 clearStore
 
 nix-instantiate --restrict-eval --eval -E '1 + 2'
-(! nix-instantiate --restrict-eval ./restricted.nix)
+(! nix-instantiate --eval --restrict-eval ./restricted.nix)
 (! nix-instantiate --eval --restrict-eval <(echo '1 + 2'))
 nix-instantiate --restrict-eval ./simple.nix -I src=.
 nix-instantiate --restrict-eval ./simple.nix -I src1=simple.nix -I src2=config.nix -I src3=./simple.builder.sh
diff --git a/tests/toString-path.sh b/tests/toString-path.sh
new file mode 100644
index 000000000..07eb87465
--- /dev/null
+++ b/tests/toString-path.sh
@@ -0,0 +1,8 @@
+source common.sh
+
+mkdir -p $TEST_ROOT/foo
+echo bla > $TEST_ROOT/foo/bar
+
+[[ $(nix eval --raw --impure --expr "builtins.readFile (builtins.toString (builtins.fetchTree { type = \"path\"; path = \"$TEST_ROOT/foo\"; } + \"/bar\"))") = bla ]]
+
+[[ $(nix eval --json --impure --expr "builtins.readDir (builtins.toString (builtins.fetchTree { type = \"path\"; path = \"$TEST_ROOT/foo\"; }))") = '{"bar":"regular"}' ]]