Improve path:// handling

In particular, doing 'nix build /path/to/dir' now works if
/path/to/dir is not a Git tree (it only has to contain a flake.nix
file).

Also, 'nix flake init' no longer requires a Git tree (but it will do a
'git add flake.nix' if it's a Git tree)

src/libexpr/flake/flake.cc

@@ -176,7 +176,7 @@ static FlakeInput parseFlakeInput(EvalState & state,
         if (!attrs.empty())
             throw Error("unexpected flake input attribute '%s', at %s", attrs.begin()->first, pos);
         if (url)
-            input.ref = parseFlakeRef(*url);
+            input.ref = parseFlakeRef(*url, {}, true);
     }
 
     return input;
@@ -630,7 +630,7 @@ void callFlake(EvalState & state,
 static void prim_getFlake(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     auto flakeRefS = state.forceStringNoCtx(*args[0], pos);
-    auto flakeRef = parseFlakeRef(flakeRefS);
+    auto flakeRef = parseFlakeRef(flakeRefS, {}, true);
     if (evalSettings.pureEval && !flakeRef.input->isImmutable())
         throw Error("cannot call 'getFlake' on mutable flake reference '%s', at %s (use --impure to override)", flakeRefS, pos);
 

src/libexpr/flake/flakeref.cc

@@ -47,9 +47,9 @@ FlakeRef FlakeRef::resolve(ref<Store> store) const
 }
 
 FlakeRef parseFlakeRef(
-    const std::string & url, const std::optional<Path> & baseDir)
+    const std::string & url, const std::optional<Path> & baseDir, bool allowMissing)
 {
-    auto [flakeRef, fragment] = parseFlakeRefWithFragment(url, baseDir);
+    auto [flakeRef, fragment] = parseFlakeRefWithFragment(url, baseDir, allowMissing);
     if (fragment != "")
         throw Error("unexpected fragment '%s' in flake reference '%s'", fragment, url);
     return flakeRef;
@@ -66,7 +66,7 @@ std::optional<FlakeRef> maybeParseFlakeRef(
 }
 
 std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
-    const std::string & url, const std::optional<Path> & baseDir)
+    const std::string & url, const std::optional<Path> & baseDir, bool allowMissing)
 {
     using namespace fetchers;
 
@@ -115,17 +115,16 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
         if (!S_ISDIR(lstat(path).st_mode))
             throw BadURL("path '%s' is not a flake (because it's not a directory)", path);
 
+        if (!allowMissing && !pathExists(path + "/flake.nix"))
+            throw BadURL("path '%s' is not a flake (because it doesn't contain a 'flake.nix' file)", path);
+
+        auto fragment = percentDecode(std::string(match[3]));
+
         auto flakeRoot = path;
         std::string subdir;
 
-        while (true) {
+        while (flakeRoot != "/") {
-            if (pathExists(flakeRoot + "/.git")) break;
+            if (pathExists(flakeRoot + "/.git")) {
-            subdir = std::string(baseNameOf(flakeRoot)) + (subdir.empty() ? "" : "/" + subdir);
-            flakeRoot = dirOf(flakeRoot);
-            if (flakeRoot == "/")
-                throw BadURL("path '%s' is not a flake (because it does not reference a Git repository)", path);
-        }
-
                 auto base = std::string("git+file://") + flakeRoot;
 
                 auto parsedURL = ParsedURL{
@@ -137,8 +136,6 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
                     .query = decodeQuery(match[2]),
                 };
 
-        auto fragment = percentDecode(std::string(match[3]));
-
                 if (subdir != "") {
                     if (parsedURL.query.count("dir"))
                         throw Error("flake URL '%s' has an inconsistent 'dir' parameter", url);
@@ -150,6 +147,17 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
                     fragment);
             }
 
+            subdir = std::string(baseNameOf(flakeRoot)) + (subdir.empty() ? "" : "/" + subdir);
+            flakeRoot = dirOf(flakeRoot);
+        }
+
+        fetchers::Attrs attrs;
+        attrs.insert_or_assign("type", "path");
+        attrs.insert_or_assign("path", path);
+
+        return std::make_pair(FlakeRef(inputFromAttrs(attrs), ""), fragment);
+    }
+
     else {
         auto parsedURL = parseURL(url);
         std::string fragment;

src/libexpr/flake/flakeref.hh

@@ -41,13 +41,13 @@ struct FlakeRef
 std::ostream & operator << (std::ostream & str, const FlakeRef & flakeRef);
 
 FlakeRef parseFlakeRef(
-    const std::string & url, const std::optional<Path> & baseDir = {});
+    const std::string & url, const std::optional<Path> & baseDir = {}, bool allowMissing = false);
 
 std::optional<FlakeRef> maybeParseFlake(
     const std::string & url, const std::optional<Path> & baseDir = {});
 
 std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
-    const std::string & url, const std::optional<Path> & baseDir = {});
+    const std::string & url, const std::optional<Path> & baseDir = {}, bool allowMissing = false);
 
 std::optional<std::pair<FlakeRef, std::string>> maybeParseFlakeRefWithFragment(
     const std::string & url, const std::optional<Path> & baseDir = {});

src/libfetchers/path.cc

@@ -32,7 +32,7 @@ struct PathInput : Input
 
     bool isImmutable() const override
     {
-        return (bool) narHash;
+        return narHash || rev;
     }
 
     ParsedURL toURL() const override
@@ -56,9 +56,20 @@ struct PathInput : Input
             attrs.emplace("revCount", *revCount);
         if (lastModified)
             attrs.emplace("lastModified", *lastModified);
+        if (!rev && narHash)
+            attrs.emplace("narHash", narHash->to_string(SRI));
         return attrs;
     }
 
+    std::optional<Path> getSourcePath() const override
+    {
+        return path;
+    }
+
+    void markChangedFile(std::string_view file, std::optional<std::string> commitMsg) const override
+    {
+    }
+
     std::pair<Tree, std::shared_ptr<const Input>> fetchTreeInternal(nix::ref<Store> store) const override
     {
         auto input = std::make_shared<PathInput>(*this);
@@ -74,6 +85,8 @@ struct PathInput : Input
             // FIXME: try to substitute storePath.
             storePath = store->addToStore("source", path);
 
+        input->narHash = store->queryPathInfo(*storePath)->narHash;
+
         return
             {
                 Tree {
@@ -99,6 +112,9 @@ struct PathInputScheme : InputScheme
         auto input = std::make_unique<PathInput>();
         input->path = url.path;
 
+        if (url.authority && *url.authority != "")
+            throw Error("path URL '%s' should not have an authority ('%s')", url.url, *url.authority);
+
         for (auto & [name, value] : url.query)
             if (name == "rev")
                 input->rev = Hash(value, htSHA1);
@@ -114,6 +130,9 @@ struct PathInputScheme : InputScheme
                     throw Error("path URL '%s' has invalid parameter '%s'", url.to_string(), name);
                 input->lastModified = lastModified;
             }
+            else if (name == "narHash")
+                // FIXME: require SRI hash.
+                input->narHash = Hash(value);
             else
                 throw Error("path URL '%s' has unsupported parameter '%s'", url.to_string(), name);
 
@@ -134,6 +153,9 @@ struct PathInputScheme : InputScheme
                 input->revCount = getIntAttr(attrs, "revCount");
             else if (name == "lastModified")
                 input->lastModified = getIntAttr(attrs, "lastModified");
+            else if (name == "narHash")
+                // FIXME: require SRI hash.
+                input->narHash = Hash(getStrAttr(attrs, "narHash"));
             else if (name == "type" || name == "path")
                 ;
             else

src/nix/flake.cc

@@ -551,17 +551,18 @@ struct CmdFlakeInit : virtual Args, Command
     {
         Path flakeDir = absPath(".");
 
-        if (!pathExists(flakeDir + "/.git"))
-            throw Error("the directory '%s' is not a Git repository", flakeDir);
-
         Path flakePath = flakeDir + "/flake.nix";
 
         if (pathExists(flakePath))
             throw Error("file '%s' already exists", flakePath);
 
         writeFile(flakePath,
-#include "flake-template.nix.gen.hh"
+          #include "flake-template.nix.gen.hh"
         );
+
+        if (pathExists(flakeDir + "/.git"))
+            runProgram("git", true,
+                { "-C", flakeDir, "add", "--intent-to-add", "flake.nix" });
     }
 };
 

src/nix/installables.cc

@@ -438,14 +438,6 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
 
     } else {
 
-        auto follow = [&](const std::string & s) -> std::optional<StorePath> {
-            try {
-                return store->followLinksToStorePath(s);
-            } catch (NotInStore &) {
-                return {};
-            }
-        };
-
         for (auto & s : ss) {
             if (hasPrefix(s, "nixpkgs.")) {
                 bool static warned;
@@ -456,23 +448,38 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
             }
 
             else {
-                auto res = maybeParseFlakeRefWithFragment(s, absPath("."));
+                std::exception_ptr ex;
-                if (res) {
+
-                    auto &[flakeRef, fragment] = *res;
+                try {
+                    auto [flakeRef, fragment] = parseFlakeRefWithFragment(s, absPath("."));
                     result.push_back(std::make_shared<InstallableFlake>(
                             *this, std::move(flakeRef),
                             fragment == "" ? getDefaultFlakeAttrPaths() : Strings{fragment},
                             getDefaultFlakeAttrPathPrefixes()));
-                } else {
+                    continue;
-                    std::optional<StorePath> storePath;
+                } catch (...) {
-                    if (s.find('/') != std::string::npos && (storePath = follow(s)))
+                    ex = std::current_exception();
-                        result.push_back(std::make_shared<InstallableStorePath>(store, store->printStorePath(*storePath)));
+                }
-                    else
+
+                if (s.find('/') != std::string::npos) {
+                    try {
+                        result.push_back(std::make_shared<InstallableStorePath>(store, store->printStorePath(store->followLinksToStorePath(s))));
+                        continue;
+                    } catch (NotInStore &) {
+                    } catch (...) {
+                        if (!ex)
+                            ex = std::current_exception();
+                    }
+                }
+
+                std::rethrow_exception(ex);
+
+                /*
                 throw Error(
                     pathExists(s)
                     ? "path '%s' is not a flake or a store path"
                     : "don't know how to handle argument '%s'", s);
-                }
+                */
             }
         }
     }