From 91ddee6bf045b1c6144d14233abdb96127186ec3 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Sun, 10 May 2020 20:32:21 +0200
Subject: [PATCH 01/11] nix: Implement basic bash completion

---
 Makefile                   |  1 +
 misc/bash/completion.sh    |  7 +++++
 misc/bash/local.mk         |  1 +
 src/libmain/common-args.cc | 10 ++++++-
 src/libutil/args.cc        | 55 ++++++++++++++++++++++++++++++++++++--
 src/libutil/args.hh        |  4 +++
 src/libutil/hash.cc        |  3 +++
 src/libutil/hash.hh        |  2 ++
 src/nix/main.cc            | 16 ++++++++++-
 9 files changed, 95 insertions(+), 4 deletions(-)
 create mode 100644 misc/bash/completion.sh
 create mode 100644 misc/bash/local.mk

diff --git a/Makefile b/Makefile
index e3057c36c..545397b23 100644
--- a/Makefile
+++ b/Makefile
@@ -11,6 +11,7 @@ makefiles = \
   src/resolve-system-dependencies/local.mk \
   scripts/local.mk \
   corepkgs/local.mk \
+  misc/bash/local.mk \
   misc/systemd/local.mk \
   misc/launchd/local.mk \
   misc/upstart/local.mk \
diff --git a/misc/bash/completion.sh b/misc/bash/completion.sh
new file mode 100644
index 000000000..097353b50
--- /dev/null
+++ b/misc/bash/completion.sh
@@ -0,0 +1,7 @@
+function _complete_nix {
+    while IFS= read -r line; do
+        COMPREPLY+=("$line")
+    done < <(NIX_GET_COMPLETIONS=$COMP_CWORD "${COMP_WORDS[@]}")
+}
+
+complete -F _complete_nix nix
diff --git a/misc/bash/local.mk b/misc/bash/local.mk
new file mode 100644
index 000000000..99ada5108
--- /dev/null
+++ b/misc/bash/local.mk
@@ -0,0 +1 @@
+$(eval $(call install-file-as, $(d)/completion.sh, $(datarootdir)/bash-completion/completions/_nix3, 0644))
diff --git a/src/libmain/common-args.cc b/src/libmain/common-args.cc
index 51e199ea5..f3f508ff4 100644
--- a/src/libmain/common-args.cc
+++ b/src/libmain/common-args.cc
@@ -31,9 +31,17 @@ MixCommonArgs::MixCommonArgs(const string & programName)
         .labels = {"name", "value"},
         .handler = {[](std::string name, std::string value) {
             try {
+                if (auto prefix = needsCompletion(name)) {
+                    std::map<std::string, Config::SettingInfo> settings;
+                    globalConfig.getSettings(settings);
+                    for (auto & s : settings)
+                        if (hasPrefix(s.first, *prefix))
+                            completions->insert(s.first);
+                }
                 globalConfig.set(name, value);
             } catch (UsageError & e) {
-                warn(e.what());
+                if (!completions)
+                    warn(e.what());
             }
         }},
     });
diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index f829415d1..ceaabcfca 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -13,6 +13,19 @@ void Args::addFlag(Flag && flag_)
     if (flag->shortName) shortFlags[flag->shortName] = flag;
 }
 
+std::shared_ptr<std::set<std::string>> completions;
+
+std::string completionMarker = "___COMPLETE___";
+
+std::optional<std::string> needsCompletion(std::string_view s)
+{
+    if (!completions) return {};
+    auto i = s.find(completionMarker);
+    if (i != std::string::npos)
+        return std::string(s.begin(), i);
+    return {};
+}
+
 void Args::parseCmdline(const Strings & _cmdline)
 {
     Strings pendingArgs;
@@ -20,6 +33,13 @@ void Args::parseCmdline(const Strings & _cmdline)
 
     Strings cmdline(_cmdline);
 
+    if (auto s = getEnv("NIX_GET_COMPLETIONS")) {
+        size_t n = std::stoi(*s);
+        assert(n > 0 && n <= cmdline.size());
+        *std::next(cmdline.begin(), n - 1) += completionMarker;
+        completions = std::make_shared<decltype(completions)::element_type>();
+    }
+
     for (auto pos = cmdline.begin(); pos != cmdline.end(); ) {
 
         auto arg = *pos;
@@ -99,18 +119,32 @@ bool Args::processFlag(Strings::iterator & pos, Strings::iterator end)
     auto process = [&](const std::string & name, const Flag & flag) -> bool {
         ++pos;
         std::vector<std::string> args;
+        bool anyNeedsCompletion = false;
         for (size_t n = 0 ; n < flag.handler.arity; ++n) {
             if (pos == end) {
                 if (flag.handler.arity == ArityAny) break;
-                throw UsageError("flag '%s' requires %d argument(s)", name, flag.handler.arity);
+                if (anyNeedsCompletion)
+                    args.push_back("");
+                else
+                    throw UsageError("flag '%s' requires %d argument(s)", name, flag.handler.arity);
+            } else {
+                if (needsCompletion(*pos))
+                    anyNeedsCompletion = true;
+                args.push_back(*pos++);
             }
-            args.push_back(*pos++);
         }
         flag.handler.fun(std::move(args));
         return true;
     };
 
     if (string(*pos, 0, 2) == "--") {
+        if (auto prefix = needsCompletion(*pos)) {
+            for (auto & [name, flag] : longFlags) {
+                if (!hiddenCategories.count(flag->category)
+                    && hasPrefix(name, std::string(*prefix, 2)))
+                    completions->insert("--" + name);
+            }
+        }
         auto i = longFlags.find(string(*pos, 2));
         if (i == longFlags.end()) return false;
         return process("--" + i->first, *i->second);
@@ -123,6 +157,14 @@ bool Args::processFlag(Strings::iterator & pos, Strings::iterator end)
         return process(std::string("-") + c, *i->second);
     }
 
+    if (auto prefix = needsCompletion(*pos)) {
+        if (prefix == "-") {
+            completions->insert("--");
+            for (auto & [flag, _] : shortFlags)
+                completions->insert(std::string("-") + flag);
+        }
+    }
+
     return false;
 }
 
@@ -161,6 +203,10 @@ Args::Flag Args::Flag::mkHashTypeFlag(std::string && longName, HashType * ht)
         .description = "hash algorithm ('md5', 'sha1', 'sha256', or 'sha512')",
         .labels = {"hash-algo"},
         .handler = {[ht](std::string s) {
+            if (auto prefix = needsCompletion(s))
+                for (auto & type : hashTypes)
+                    if (hasPrefix(type, *prefix))
+                        completions->insert(type);
             *ht = parseHashType(s);
             if (*ht == htUnknown)
                 throw UsageError("unknown hash type '%1%'", s);
@@ -217,6 +263,11 @@ MultiCommand::MultiCommand(const Commands & commands)
 {
     expectedArgs.push_back(ExpectedArg{"command", 1, true, [=](std::vector<std::string> ss) {
         assert(!command);
+        if (auto prefix = needsCompletion(ss[0])) {
+            for (auto & [name, command] : commands)
+                if (hasPrefix(name, *prefix))
+                    completions->insert(name);
+        }
         auto i = commands.find(ss[0]);
         if (i == commands.end())
             throw UsageError("'%s' is not a recognised command", ss[0]);
diff --git a/src/libutil/args.hh b/src/libutil/args.hh
index 1932e6a8a..ae2875e72 100644
--- a/src/libutil/args.hh
+++ b/src/libutil/args.hh
@@ -256,4 +256,8 @@ typedef std::vector<std::pair<std::string, std::string>> Table2;
 
 void printTable(std::ostream & out, const Table2 & table);
 
+extern std::shared_ptr<std::set<std::string>> completions;
+
+std::optional<std::string> needsCompletion(std::string_view s);
+
 }
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 7caee1da7..606c78ed7 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -16,6 +16,9 @@
 namespace nix {
 
 
+std::set<std::string> hashTypes = { "md5", "sha1", "sha256", "sha512" };
+
+
 void Hash::init()
 {
     if (type == htMD5) hashSize = md5HashSize;
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index ea9fca3e7..e1a16ba22 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -18,6 +18,8 @@ const int sha1HashSize = 20;
 const int sha256HashSize = 32;
 const int sha512HashSize = 64;
 
+extern std::set<std::string> hashTypes;
+
 extern const string base32Chars;
 
 enum Base : int { Base64, Base32, Base16, SRI };
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 3915a4896..c491bc264 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -166,7 +166,21 @@ void mainWrapped(int argc, char * * argv)
 
     NixArgs args;
 
-    args.parseCmdline(argvToStrings(argc, argv));
+    Finally printCompletions([&]()
+    {
+        if (completions) {
+            for (auto & s : *completions)
+                std::cout << s << "\n";
+        }
+    });
+
+    try {
+        args.parseCmdline(argvToStrings(argc, argv));
+    } catch (UsageError &) {
+        if (!completions) throw;
+    }
+
+    if (completions) return;
 
     settings.requireExperimentalFeature("nix-command");
 

From e0c19ee620c53b52ca7cf69c19d414d782338be1 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Sun, 10 May 2020 21:35:07 +0200
Subject: [PATCH 02/11] Add completion for paths

---
 misc/bash/completion.sh | 10 ++++++++-
 src/libutil/args.cc     | 48 ++++++++++++++++++++++++++++++++++++++++-
 src/libutil/args.hh     | 12 +++++++++--
 src/nix/build.cc        |  1 +
 src/nix/cat.cc          |  4 ++--
 src/nix/command.cc      |  1 +
 src/nix/hash.cc         |  2 +-
 src/nix/installables.cc |  3 ++-
 src/nix/ls.cc           |  4 ++--
 src/nix/main.cc         |  5 +++--
 src/nix/repl.cc         |  2 +-
 src/nix/run.cc          |  2 +-
 src/nix/sigs.cc         |  3 ++-
 13 files changed, 82 insertions(+), 15 deletions(-)

diff --git a/misc/bash/completion.sh b/misc/bash/completion.sh
index 097353b50..93298c369 100644
--- a/misc/bash/completion.sh
+++ b/misc/bash/completion.sh
@@ -1,6 +1,14 @@
 function _complete_nix {
+    local have_type
     while IFS= read -r line; do
-        COMPREPLY+=("$line")
+        if [[ -z $have_type ]]; then
+            have_type=1
+            if [[ $line = filenames ]]; then
+                compopt -o filenames
+            fi
+        else
+            COMPREPLY+=("$line")
+        fi
     done < <(NIX_GET_COMPLETIONS=$COMP_CWORD "${COMP_WORDS[@]}")
 }
 
diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index ceaabcfca..320b1b4b2 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -1,6 +1,8 @@
 #include "args.hh"
 #include "hash.hh"
 
+#include <glob.h>
+
 namespace nix {
 
 void Args::addFlag(Flag && flag_)
@@ -13,6 +15,7 @@ void Args::addFlag(Flag && flag_)
     if (flag->shortName) shortFlags[flag->shortName] = flag;
 }
 
+bool pathCompletions = false;
 std::shared_ptr<std::set<std::string>> completions;
 
 std::string completionMarker = "___COMPLETE___";
@@ -128,8 +131,11 @@ bool Args::processFlag(Strings::iterator & pos, Strings::iterator end)
                 else
                     throw UsageError("flag '%s' requires %d argument(s)", name, flag.handler.arity);
             } else {
-                if (needsCompletion(*pos))
+                if (needsCompletion(*pos)) {
+                    if (flag.completer)
+                        flag.completer(n, *pos);
                     anyNeedsCompletion = true;
+                }
                 args.push_back(*pos++);
             }
         }
@@ -214,6 +220,46 @@ Args::Flag Args::Flag::mkHashTypeFlag(std::string && longName, HashType * ht)
     };
 }
 
+void completePath(size_t, std::string_view s)
+{
+    if (auto prefix = needsCompletion(s)) {
+        pathCompletions = true;
+        glob_t globbuf;
+        if (glob((*prefix + "*").c_str(), GLOB_NOESCAPE | GLOB_TILDE, nullptr, &globbuf) == 0) {
+            for (size_t i = 0; i < globbuf.gl_pathc; ++i)
+                completions->insert(globbuf.gl_pathv[i]);
+            globfree(&globbuf);
+        }
+    }
+}
+
+void Args::expectPathArg(const std::string & label, string * dest, bool optional)
+{
+    expectedArgs.push_back({
+        .label = label,
+        .arity = 1,
+        .optional = optional,
+        .handler = {[=](std::vector<std::string> ss) {
+            completePath(0, ss[0]);
+            *dest = ss[0];
+        }}
+    });
+}
+
+void Args::expectPathArgs(const std::string & label, std::vector<std::string> * dest)
+{
+    expectedArgs.push_back({
+        .label = label,
+        .arity = 0,
+        .optional = false,
+        .handler = {[=](std::vector<std::string> ss) {
+            for (auto & s : ss)
+                completePath(0, s);
+            *dest = std::move(ss);
+        }}
+    });
+}
+
 Strings argvToStrings(int argc, char * * argv)
 {
     Strings args;
diff --git a/src/libutil/args.hh b/src/libutil/args.hh
index ae2875e72..f93459c96 100644
--- a/src/libutil/args.hh
+++ b/src/libutil/args.hh
@@ -83,6 +83,7 @@ protected:
         std::string category;
         Strings labels;
         Handler handler;
+        std::function<void(size_t, std::string_view)> completer;
 
         static Flag mkHashTypeFlag(std::string && longName, HashType * ht);
     };
@@ -98,8 +99,8 @@ protected:
     struct ExpectedArg
     {
         std::string label;
-        size_t arity; // 0 = any
-        bool optional;
+        size_t arity = 0; // 0 = any
+        bool optional = false;
         std::function<void(std::vector<std::string>)> handler;
     };
 
@@ -182,6 +183,8 @@ public:
         }});
     }
 
+    void expectPathArg(const std::string & label, string * dest, bool optional = false);
+
     /* Expect 0 or more arguments. */
     void expectArgs(const std::string & label, std::vector<std::string> * dest)
     {
@@ -190,6 +193,8 @@ public:
         }});
     }
 
+    void expectPathArgs(const std::string & label, std::vector<std::string> * dest);
+
     friend class MultiCommand;
 };
 
@@ -257,7 +262,10 @@ typedef std::vector<std::pair<std::string, std::string>> Table2;
 void printTable(std::ostream & out, const Table2 & table);
 
 extern std::shared_ptr<std::set<std::string>> completions;
+extern bool pathCompletions;
 
 std::optional<std::string> needsCompletion(std::string_view s);
 
+void completePath(size_t, std::string_view s);
+
 }
diff --git a/src/nix/build.cc b/src/nix/build.cc
index 83d47acd4..474337208 100644
--- a/src/nix/build.cc
+++ b/src/nix/build.cc
@@ -18,6 +18,7 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixProfile
             .description = "path of the symlink to the build result",
             .labels = {"path"},
             .handler = {&outLink},
+            .completer = completePath
         });
 
         addFlag({
diff --git a/src/nix/cat.cc b/src/nix/cat.cc
index fd91f2036..eeee1e529 100644
--- a/src/nix/cat.cc
+++ b/src/nix/cat.cc
@@ -25,7 +25,7 @@ struct CmdCatStore : StoreCommand, MixCat
 {
     CmdCatStore()
     {
-        expectArg("path", &path);
+        expectPathArg("path", &path);
     }
 
     std::string description() override
@@ -47,7 +47,7 @@ struct CmdCatNar : StoreCommand, MixCat
 
     CmdCatNar()
     {
-        expectArg("nar", &narPath);
+        expectPathArg("nar", &narPath);
         expectArg("path", &path);
     }
 
diff --git a/src/nix/command.cc b/src/nix/command.cc
index 71b027719..803a36e84 100644
--- a/src/nix/command.cc
+++ b/src/nix/command.cc
@@ -108,6 +108,7 @@ MixProfile::MixProfile()
         .description = "profile to update",
         .labels = {"path"},
         .handler = {&profile},
+        .completer = completePath
     });
 }
 
diff --git a/src/nix/hash.cc b/src/nix/hash.cc
index 366314227..0f460c668 100644
--- a/src/nix/hash.cc
+++ b/src/nix/hash.cc
@@ -31,7 +31,7 @@ struct CmdHash : Command
             .labels({"modulus"})
             .dest(&modulus);
         #endif
-        expectArgs("paths", &paths);
+        expectPathArgs("paths", &paths);
     }
 
     std::string description() override
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 57060e9b1..c144a7e70 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -77,7 +77,8 @@ SourceExprCommand::SourceExprCommand()
         .shortName = 'f',
         .description = "evaluate FILE rather than the default",
         .labels = {"file"},
-        .handler = {&file}
+        .handler = {&file},
+        .completer = completePath
     });
 
     addFlag({
diff --git a/src/nix/ls.cc b/src/nix/ls.cc
index b9716a6a1..aac082422 100644
--- a/src/nix/ls.cc
+++ b/src/nix/ls.cc
@@ -85,7 +85,7 @@ struct CmdLsStore : StoreCommand, MixLs
 {
     CmdLsStore()
     {
-        expectArg("path", &path);
+        expectPathArg("path", &path);
     }
 
     Examples examples() override
@@ -117,7 +117,7 @@ struct CmdLsNar : Command, MixLs
 
     CmdLsNar()
     {
-        expectArg("nar", &narPath);
+        expectPathArg("nar", &narPath);
         expectArg("path", &path);
     }
 
diff --git a/src/nix/main.cc b/src/nix/main.cc
index c491bc264..fffdeab90 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -68,7 +68,7 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
         addFlag({
             .longName = "help",
             .description = "show usage information",
-            .handler = {[&]() { showHelpAndExit(); }},
+            .handler = {[&]() { if (!completions) showHelpAndExit(); }},
         });
 
         addFlag({
@@ -96,7 +96,7 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
         addFlag({
             .longName = "version",
             .description = "show version information",
-            .handler = {[&]() { printVersion(programName); }},
+            .handler = {[&]() { if (!completions) printVersion(programName); }},
         });
 
         addFlag({
@@ -169,6 +169,7 @@ void mainWrapped(int argc, char * * argv)
     Finally printCompletions([&]()
     {
         if (completions) {
+            std::cout << (pathCompletions ? "filenames\n" : "no-filenames\n");
             for (auto & s : *completions)
                 std::cout << s << "\n";
         }
diff --git a/src/nix/repl.cc b/src/nix/repl.cc
index 0a6a7ab19..2e7b14d08 100644
--- a/src/nix/repl.cc
+++ b/src/nix/repl.cc
@@ -767,7 +767,7 @@ struct CmdRepl : StoreCommand, MixEvalArgs
 
     CmdRepl()
     {
-        expectArgs("files", &files);
+        expectPathArgs("files", &files);
     }
 
     std::string description() override
diff --git a/src/nix/run.cc b/src/nix/run.cc
index 3e2c8b4f3..3701ffe3d 100644
--- a/src/nix/run.cc
+++ b/src/nix/run.cc
@@ -149,7 +149,7 @@ struct CmdRun : InstallableCommand, RunCommon
 
     CmdRun()
     {
-        expectArgs("args", &args);
+        expectPathArgs("args", &args);
     }
 
     std::string description() override
diff --git a/src/nix/sigs.cc b/src/nix/sigs.cc
index 6c9b9a792..7821a5432 100644
--- a/src/nix/sigs.cc
+++ b/src/nix/sigs.cc
@@ -105,7 +105,8 @@ struct CmdSignPaths : StorePathsCommand
             .shortName = 'k',
             .description = "file containing the secret signing key",
             .labels = {"file"},
-            .handler = {&secretKeyFile}
+            .handler = {&secretKeyFile},
+            .completer = completePath
         });
     }
 

From 0884f180f5ca8a864e6db5256eaa10646e87d671 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Sun, 10 May 2020 21:50:32 +0200
Subject: [PATCH 03/11] Simplify

---
 src/libfetchers/registry.cc |  2 +-
 src/libmain/common-args.cc  | 16 +++++++++-------
 src/libutil/args.cc         | 28 +++++++++++-----------------
 src/libutil/util.cc         |  2 +-
 src/libutil/util.hh         |  2 +-
 5 files changed, 23 insertions(+), 27 deletions(-)

diff --git a/src/libfetchers/registry.cc b/src/libfetchers/registry.cc
index 77d3b3378..f6760d2d0 100644
--- a/src/libfetchers/registry.cc
+++ b/src/libfetchers/registry.cc
@@ -155,7 +155,7 @@ void overrideRegistry(
 static std::shared_ptr<Registry> getGlobalRegistry(ref<Store> store)
 {
     static auto reg = [&]() {
-        auto path = settings.flakeRegistry;
+        auto path = settings.flakeRegistry.get();
 
         if (!hasPrefix(path, "/")) {
             auto storePath = downloadFile(store, path, "flake-registry.json", false).storePath;
diff --git a/src/libmain/common-args.cc b/src/libmain/common-args.cc
index f3f508ff4..51a61f1ca 100644
--- a/src/libmain/common-args.cc
+++ b/src/libmain/common-args.cc
@@ -31,19 +31,21 @@ MixCommonArgs::MixCommonArgs(const string & programName)
         .labels = {"name", "value"},
         .handler = {[](std::string name, std::string value) {
             try {
-                if (auto prefix = needsCompletion(name)) {
-                    std::map<std::string, Config::SettingInfo> settings;
-                    globalConfig.getSettings(settings);
-                    for (auto & s : settings)
-                        if (hasPrefix(s.first, *prefix))
-                            completions->insert(s.first);
-                }
                 globalConfig.set(name, value);
             } catch (UsageError & e) {
                 if (!completions)
                     warn(e.what());
             }
         }},
+        .completer = [](size_t index, std::string_view prefix) {
+            if (index == 0) {
+                std::map<std::string, Config::SettingInfo> settings;
+                globalConfig.getSettings(settings);
+                for (auto & s : settings)
+                    if (hasPrefix(s.first, prefix))
+                        completions->insert(s.first);
+            }
+        }
     });
 
     addFlag({
diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index 320b1b4b2..257b4b6c4 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -122,22 +122,15 @@ bool Args::processFlag(Strings::iterator & pos, Strings::iterator end)
     auto process = [&](const std::string & name, const Flag & flag) -> bool {
         ++pos;
         std::vector<std::string> args;
-        bool anyNeedsCompletion = false;
         for (size_t n = 0 ; n < flag.handler.arity; ++n) {
             if (pos == end) {
                 if (flag.handler.arity == ArityAny) break;
-                if (anyNeedsCompletion)
-                    args.push_back("");
-                else
-                    throw UsageError("flag '%s' requires %d argument(s)", name, flag.handler.arity);
-            } else {
-                if (needsCompletion(*pos)) {
-                    if (flag.completer)
-                        flag.completer(n, *pos);
-                    anyNeedsCompletion = true;
-                }
-                args.push_back(*pos++);
+                throw UsageError("flag '%s' requires %d argument(s)", name, flag.handler.arity);
             }
+            if (auto prefix = needsCompletion(*pos))
+                if (flag.completer)
+                    flag.completer(n, *prefix);
+            args.push_back(*pos++);
         }
         flag.handler.fun(std::move(args));
         return true;
@@ -209,14 +202,15 @@ Args::Flag Args::Flag::mkHashTypeFlag(std::string && longName, HashType * ht)
         .description = "hash algorithm ('md5', 'sha1', 'sha256', or 'sha512')",
         .labels = {"hash-algo"},
         .handler = {[ht](std::string s) {
-            if (auto prefix = needsCompletion(s))
-                for (auto & type : hashTypes)
-                    if (hasPrefix(type, *prefix))
-                        completions->insert(type);
             *ht = parseHashType(s);
             if (*ht == htUnknown)
                 throw UsageError("unknown hash type '%1%'", s);
-        }}
+        }},
+        .completer = [](size_t index, std::string_view prefix) {
+            for (auto & type : hashTypes)
+                if (hasPrefix(type, prefix))
+                    completions->insert(type);
+        }
     };
 }
 
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 4c8e2b26d..f2782ce69 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -1330,7 +1330,7 @@ bool statusOk(int status)
 }
 
 
-bool hasPrefix(const string & s, const string & prefix)
+bool hasPrefix(std::string_view s, std::string_view prefix)
 {
     return s.compare(0, prefix.size(), prefix) == 0;
 }
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 4be1d4580..a861d5aa6 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -431,7 +431,7 @@ template<class N> bool string2Float(const string & s, N & n)
 
 
 /* Return true iff `s' starts with `prefix'. */
-bool hasPrefix(const string & s, const string & prefix);
+bool hasPrefix(std::string_view s, std::string_view prefix);
 
 
 /* Return true iff `s' ends in `suffix'. */

From 4c3c638a05e52cdc3bd96255873b711a28630288 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 11 May 2020 15:46:18 +0200
Subject: [PATCH 04/11] Cleanup

---
 src/libutil/args.cc     |  90 ++++++++++++-----------------
 src/libutil/args.hh     | 123 +++++++++++++++++++++-------------------
 src/nix/cat.cc          |  12 +++-
 src/nix/command.hh      |   5 +-
 src/nix/hash.cc         |   6 +-
 src/nix/installables.cc |   8 +++
 src/nix/ls.cc           |  12 +++-
 src/nix/repl.cc         |   6 +-
 src/nix/run.cc          |   6 +-
 9 files changed, 145 insertions(+), 123 deletions(-)

diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index 257b4b6c4..c389090ae 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -86,7 +86,7 @@ void Args::printHelp(const string & programName, std::ostream & out)
     for (auto & exp : expectedArgs) {
         std::cout << renderLabels({exp.label});
         // FIXME: handle arity > 1
-        if (exp.arity == 0) std::cout << "...";
+        if (exp.handler.arity == ArityAny) std::cout << "...";
         if (exp.optional) std::cout << "?";
     }
     std::cout << "\n";
@@ -127,8 +127,8 @@ bool Args::processFlag(Strings::iterator & pos, Strings::iterator end)
                 if (flag.handler.arity == ArityAny) break;
                 throw UsageError("flag '%s' requires %d argument(s)", name, flag.handler.arity);
             }
-            if (auto prefix = needsCompletion(*pos))
-                if (flag.completer)
+            if (flag.completer)
+                if (auto prefix = needsCompletion(*pos))
                     flag.completer(n, *prefix);
             args.push_back(*pos++);
         }
@@ -179,12 +179,17 @@ bool Args::processArgs(const Strings & args, bool finish)
 
     bool res = false;
 
-    if ((exp.arity == 0 && finish) ||
-        (exp.arity > 0 && args.size() == exp.arity))
+    if ((exp.handler.arity == ArityAny && finish) ||
+        (exp.handler.arity != ArityAny && args.size() == exp.handler.arity))
     {
         std::vector<std::string> ss;
-        for (auto & s : args) ss.push_back(s);
-        exp.handler(std::move(ss));
+        for (const auto &[n, s] : enumerate(args)) {
+            ss.push_back(s);
+            if (exp.completer)
+                if (auto prefix = needsCompletion(s))
+                    exp.completer(n, *prefix);
+        }
+        exp.handler.fun(ss);
         expectedArgs.pop_front();
         res = true;
     }
@@ -214,46 +219,17 @@ Args::Flag Args::Flag::mkHashTypeFlag(std::string && longName, HashType * ht)
     };
 }
 
-void completePath(size_t, std::string_view s)
+void completePath(size_t, std::string_view prefix)
 {
-    if (auto prefix = needsCompletion(s)) {
-        pathCompletions = true;
-        glob_t globbuf;
-        if (glob((*prefix + "*").c_str(), GLOB_NOESCAPE | GLOB_TILDE, nullptr, &globbuf) == 0) {
-            for (size_t i = 0; i < globbuf.gl_pathc; ++i)
-                completions->insert(globbuf.gl_pathv[i]);
-            globfree(&globbuf);
-        }
+    pathCompletions = true;
+    glob_t globbuf;
+    if (glob((std::string(prefix) + "*").c_str(), GLOB_NOESCAPE | GLOB_TILDE, nullptr, &globbuf) == 0) {
+        for (size_t i = 0; i < globbuf.gl_pathc; ++i)
+            completions->insert(globbuf.gl_pathv[i]);
+        globfree(&globbuf);
     }
 }
 
-void Args::expectPathArg(const std::string & label, string * dest, bool optional)
-{
-    expectedArgs.push_back({
-        .label = label,
-        .arity = 1,
-        .optional = optional,
-        .handler = {[=](std::vector<std::string> ss) {
-            completePath(0, ss[0]);
-            *dest = ss[0];
-        }}
-    });
-}
-
-void Args::expectPathArgs(const std::string & label, std::vector<std::string> * dest)
-{
-    expectedArgs.push_back({
-        .label = label,
-        .arity = 0,
-        .optional = false,
-        .handler = {[=](std::vector<std::string> ss) {
-            for (auto & s : ss)
-                completePath(0, s);
-            *dest = std::move(ss);
-        }}
-    });
-}
-
 Strings argvToStrings(int argc, char * * argv)
 {
     Strings args;
@@ -301,18 +277,22 @@ void Command::printHelp(const string & programName, std::ostream & out)
 MultiCommand::MultiCommand(const Commands & commands)
     : commands(commands)
 {
-    expectedArgs.push_back(ExpectedArg{"command", 1, true, [=](std::vector<std::string> ss) {
-        assert(!command);
-        if (auto prefix = needsCompletion(ss[0])) {
-            for (auto & [name, command] : commands)
-                if (hasPrefix(name, *prefix))
-                    completions->insert(name);
-        }
-        auto i = commands.find(ss[0]);
-        if (i == commands.end())
-            throw UsageError("'%s' is not a recognised command", ss[0]);
-        command = {ss[0], i->second()};
-    }});
+    expectArgs({
+        .label = "command",
+        .optional = true,
+        .handler = {[=](std::string s) {
+            assert(!command);
+            if (auto prefix = needsCompletion(s)) {
+                for (auto & [name, command] : commands)
+                    if (hasPrefix(name, *prefix))
+                        completions->insert(name);
+            }
+            auto i = commands.find(s);
+            if (i == commands.end())
+                throw UsageError("'%s' is not a recognised command", s);
+            command = {s, i->second()};
+        }}
+    });
 
     categories[Command::catDefault] = "Available commands";
 }
diff --git a/src/libutil/args.hh b/src/libutil/args.hh
index f93459c96..250244162 100644
--- a/src/libutil/args.hh
+++ b/src/libutil/args.hh
@@ -28,55 +28,60 @@ protected:
 
     static const size_t ArityAny = std::numeric_limits<size_t>::max();
 
+    struct Handler
+    {
+        std::function<void(std::vector<std::string>)> fun;
+        size_t arity;
+
+        Handler() {}
+
+        Handler(std::function<void(std::vector<std::string>)> && fun)
+            : fun(std::move(fun))
+            , arity(ArityAny)
+        { }
+
+        Handler(std::function<void()> && handler)
+            : fun([handler{std::move(handler)}](std::vector<std::string>) { handler(); })
+            , arity(0)
+        { }
+
+        Handler(std::function<void(std::string)> && handler)
+            : fun([handler{std::move(handler)}](std::vector<std::string> ss) {
+                handler(std::move(ss[0]));
+              })
+            , arity(1)
+        { }
+
+        Handler(std::function<void(std::string, std::string)> && handler)
+            : fun([handler{std::move(handler)}](std::vector<std::string> ss) {
+                handler(std::move(ss[0]), std::move(ss[1]));
+              })
+            , arity(2)
+        { }
+
+        Handler(std::vector<std::string> * dest)
+            : fun([=](std::vector<std::string> ss) { *dest = ss; })
+            , arity(ArityAny)
+        { }
+
+        template<class T>
+        Handler(T * dest)
+            : fun([=](std::vector<std::string> ss) { *dest = ss[0]; })
+            , arity(1)
+        { }
+
+        template<class T>
+        Handler(T * dest, const T & val)
+            : fun([=](std::vector<std::string> ss) { *dest = val; })
+            , arity(0)
+        { }
+    };
+
     /* Flags. */
     struct Flag
     {
         typedef std::shared_ptr<Flag> ptr;
 
-        struct Handler
-        {
-            std::function<void(std::vector<std::string>)> fun;
-            size_t arity;
-
-            Handler() {}
-
-            Handler(std::function<void(std::vector<std::string>)> && fun)
-                : fun(std::move(fun))
-                , arity(ArityAny)
-            { }
-
-            Handler(std::function<void()> && handler)
-                : fun([handler{std::move(handler)}](std::vector<std::string>) { handler(); })
-                , arity(0)
-            { }
-
-            Handler(std::function<void(std::string)> && handler)
-                : fun([handler{std::move(handler)}](std::vector<std::string> ss) {
-                    handler(std::move(ss[0]));
-                  })
-                , arity(1)
-            { }
-
-            Handler(std::function<void(std::string, std::string)> && handler)
-                : fun([handler{std::move(handler)}](std::vector<std::string> ss) {
-                    handler(std::move(ss[0]), std::move(ss[1]));
-                  })
-                , arity(2)
-            { }
-
-            template<class T>
-            Handler(T * dest)
-                : fun([=](std::vector<std::string> ss) { *dest = ss[0]; })
-                , arity(1)
-            { }
-
-            template<class T>
-            Handler(T * dest, const T & val)
-                : fun([=](std::vector<std::string> ss) { *dest = val; })
-                , arity(0)
-            { }
-        };
-
         std::string longName;
         char shortName = 0;
         std::string description;
@@ -99,9 +104,9 @@ protected:
     struct ExpectedArg
     {
         std::string label;
-        size_t arity = 0; // 0 = any
         bool optional = false;
-        std::function<void(std::vector<std::string>)> handler;
+        Handler handler;
+        std::function<void(size_t, std::string_view)> completer;
     };
 
     std::list<ExpectedArg> expectedArgs;
@@ -175,26 +180,30 @@ public:
         });
     }
 
+    void expectArgs(ExpectedArg && arg)
+    {
+        expectedArgs.emplace_back(std::move(arg));
+    }
+
     /* Expect a string argument. */
     void expectArg(const std::string & label, string * dest, bool optional = false)
     {
-        expectedArgs.push_back(ExpectedArg{label, 1, optional, [=](std::vector<std::string> ss) {
-            *dest = ss[0];
-        }});
+        expectArgs({
+            .label = label,
+            .optional = true,
+            .handler = {dest}
+        });
     }
 
-    void expectPathArg(const std::string & label, string * dest, bool optional = false);
-
     /* Expect 0 or more arguments. */
     void expectArgs(const std::string & label, std::vector<std::string> * dest)
     {
-        expectedArgs.push_back(ExpectedArg{label, 0, false, [=](std::vector<std::string> ss) {
-            *dest = std::move(ss);
-        }});
+        expectArgs({
+            .label = label,
+            .handler = {dest}
+        });
     }
 
-    void expectPathArgs(const std::string & label, std::vector<std::string> * dest);
-
     friend class MultiCommand;
 };
 
@@ -266,6 +275,6 @@ extern bool pathCompletions;
 
 std::optional<std::string> needsCompletion(std::string_view s);
 
-void completePath(size_t, std::string_view s);
+void completePath(size_t, std::string_view prefix);
 
 }
diff --git a/src/nix/cat.cc b/src/nix/cat.cc
index eeee1e529..b528a0507 100644
--- a/src/nix/cat.cc
+++ b/src/nix/cat.cc
@@ -25,7 +25,11 @@ struct CmdCatStore : StoreCommand, MixCat
 {
     CmdCatStore()
     {
-        expectPathArg("path", &path);
+        expectArgs({
+            .label = "path",
+            .handler = {&path},
+            .completer = completePath
+        });
     }
 
     std::string description() override
@@ -47,7 +51,11 @@ struct CmdCatNar : StoreCommand, MixCat
 
     CmdCatNar()
     {
-        expectPathArg("nar", &narPath);
+        expectArgs({
+            .label = "nar",
+            .handler = {&narPath},
+            .completer = completePath
+        });
         expectArg("path", &path);
     }
 
diff --git a/src/nix/command.hh b/src/nix/command.hh
index 6b4781303..0738c0f91 100644
--- a/src/nix/command.hh
+++ b/src/nix/command.hh
@@ -73,10 +73,7 @@ struct InstallablesCommand : virtual Args, SourceExprCommand
 {
     std::vector<std::shared_ptr<Installable>> installables;
 
-    InstallablesCommand()
-    {
-        expectArgs("installables", &_installables);
-    }
+    InstallablesCommand();
 
     void prepare() override;
 
diff --git a/src/nix/hash.cc b/src/nix/hash.cc
index 0f460c668..d5636eb47 100644
--- a/src/nix/hash.cc
+++ b/src/nix/hash.cc
@@ -31,7 +31,11 @@ struct CmdHash : Command
             .labels({"modulus"})
             .dest(&modulus);
         #endif
-        expectPathArgs("paths", &paths);
+        expectArgs({
+            .label = "paths",
+            .handler = {&paths},
+            .completer = completePath
+        });
     }
 
     std::string description() override
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index c144a7e70..abc642e11 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -571,6 +571,14 @@ StorePathSet toDerivations(ref<Store> store,
     return drvPaths;
 }
 
+InstallablesCommand::InstallablesCommand()
+{
+    expectArgs({
+        .label = "installables",
+        .handler = {&_installables},
+    });
+}
+
 void InstallablesCommand::prepare()
 {
     if (_installables.empty() && useDefaultInstallables())
diff --git a/src/nix/ls.cc b/src/nix/ls.cc
index aac082422..dc7e370b9 100644
--- a/src/nix/ls.cc
+++ b/src/nix/ls.cc
@@ -85,7 +85,11 @@ struct CmdLsStore : StoreCommand, MixLs
 {
     CmdLsStore()
     {
-        expectPathArg("path", &path);
+        expectArgs({
+            .label = "path",
+            .handler = {&path},
+            .completer = completePath
+        });
     }
 
     Examples examples() override
@@ -117,7 +121,11 @@ struct CmdLsNar : Command, MixLs
 
     CmdLsNar()
     {
-        expectPathArg("nar", &narPath);
+        expectArgs({
+            .label = "nar",
+            .handler = {&narPath},
+            .completer = completePath
+        });
         expectArg("path", &path);
     }
 
diff --git a/src/nix/repl.cc b/src/nix/repl.cc
index 2e7b14d08..c936f9cc2 100644
--- a/src/nix/repl.cc
+++ b/src/nix/repl.cc
@@ -767,7 +767,11 @@ struct CmdRepl : StoreCommand, MixEvalArgs
 
     CmdRepl()
     {
-        expectPathArgs("files", &files);
+        expectArgs({
+            .label = "files",
+            .handler = {&files},
+            .completer = completePath
+        });
     }
 
     std::string description() override
diff --git a/src/nix/run.cc b/src/nix/run.cc
index 3701ffe3d..f9b1298f1 100644
--- a/src/nix/run.cc
+++ b/src/nix/run.cc
@@ -149,7 +149,11 @@ struct CmdRun : InstallableCommand, RunCommon
 
     CmdRun()
     {
-        expectPathArgs("args", &args);
+        expectArgs({
+            .label = "args",
+            .handler = {&args},
+            .completer = completePath
+        });
     }
 
     std::string description() override

From da310fac622612b90f8e511b85b8594b56ec8cdf Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 11 May 2020 21:37:53 +0200
Subject: [PATCH 05/11] Bash completion: Don't break on ':'

---
 misc/bash/completion.sh | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/misc/bash/completion.sh b/misc/bash/completion.sh
index 93298c369..bc184edd6 100644
--- a/misc/bash/completion.sh
+++ b/misc/bash/completion.sh
@@ -1,4 +1,7 @@
 function _complete_nix {
+    local -a words
+    local cword cur
+    _get_comp_words_by_ref -n ':=&' words cword cur
     local have_type
     while IFS= read -r line; do
         if [[ -z $have_type ]]; then
@@ -9,7 +12,8 @@ function _complete_nix {
         else
             COMPREPLY+=("$line")
         fi
-    done < <(NIX_GET_COMPLETIONS=$COMP_CWORD "${COMP_WORDS[@]}")
+    done < <(NIX_GET_COMPLETIONS=$cword "${words[@]}")
+    __ltrim_colon_completions "$cur"
 }
 
 complete -F _complete_nix nix

From e917332d6396fe9808519e7a87916f789b71392a Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 11 May 2020 21:38:17 +0200
Subject: [PATCH 06/11] Shut up warnings while running completers

---
 src/libutil/args.cc | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index c389090ae..ee0c99c2a 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -41,6 +41,7 @@ void Args::parseCmdline(const Strings & _cmdline)
         assert(n > 0 && n <= cmdline.size());
         *std::next(cmdline.begin(), n - 1) += completionMarker;
         completions = std::make_shared<decltype(completions)::element_type>();
+        verbosity = lvlError;
     }
 
     for (auto pos = cmdline.begin(); pos != cmdline.end(); ) {

From 259ff74bdeeaac5a987a4eb88654ba80d9553543 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 11 May 2020 21:49:02 +0200
Subject: [PATCH 07/11] Add completion for installables

This completes flakerefs using the registry (e.g. 'nix<TAB>' => 'nix
nixpkgs') and flake output attributes by evaluating the flake
(e.g. 'dwarffs#nix<TAB>' => 'dwarffs#nixosModules').
---
 src/nix/command.hh      |   7 ++-
 src/nix/installables.cc | 100 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 103 insertions(+), 4 deletions(-)

diff --git a/src/nix/command.hh b/src/nix/command.hh
index 0738c0f91..6a6c3fed9 100644
--- a/src/nix/command.hh
+++ b/src/nix/command.hh
@@ -63,6 +63,8 @@ struct SourceExprCommand : virtual Args, EvalCommand, MixFlakeOptions
     virtual Strings getDefaultFlakeAttrPaths();
 
     virtual Strings getDefaultFlakeAttrPathPrefixes();
+
+    void completeInstallable(std::string_view prefix);
 };
 
 enum RealiseMode { Build, NoBuild, DryRun };
@@ -89,10 +91,7 @@ struct InstallableCommand : virtual Args, SourceExprCommand
 {
     std::shared_ptr<Installable> installable;
 
-    InstallableCommand()
-    {
-        expectArg("installable", &_installable, true);
-    }
+    InstallableCommand();
 
     void prepare() override;
 
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index abc642e11..ade8f83f9 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -11,6 +11,7 @@
 #include "flake/flake.hh"
 #include "eval-cache.hh"
 #include "url.hh"
+#include "registry.hh"
 
 #include <regex>
 #include <queue>
@@ -106,6 +107,91 @@ Strings SourceExprCommand::getDefaultFlakeAttrPathPrefixes()
     };
 }
 
+void SourceExprCommand::completeInstallable(std::string_view prefix)
+{
+    completePath(0, prefix);
+
+    if (file) return; // FIXME
+
+    /* Look for flake output attributes that match the
+       prefix. */
+    try {
+        auto hash = prefix.find('#');
+        if (hash != std::string::npos) {
+            auto fragment = prefix.substr(hash + 1);
+            auto flakeRefS = std::string(prefix.substr(0, hash));
+            // FIXME: do tilde expansion.
+            auto flakeRef = parseFlakeRef(flakeRefS, absPath("."));
+
+            auto state = getEvalState();
+
+            auto evalCache = openEvalCache(*state,
+                std::make_shared<flake::LockedFlake>(lockFlake(*state, flakeRef, lockFlags)),
+                true);
+
+            auto root = evalCache->getRoot();
+
+            /* Complete 'fragment' relative to all the
+               attrpath prefixes as well as the root of the
+               flake. */
+            auto attrPathPrefixes = getDefaultFlakeAttrPathPrefixes();
+            attrPathPrefixes.push_back("");
+
+            for (auto & attrPathPrefixS : attrPathPrefixes) {
+                auto attrPathPrefix = parseAttrPath(*state, attrPathPrefixS);
+                auto attrPathS = attrPathPrefixS + std::string(fragment);
+                auto attrPath = parseAttrPath(*state, attrPathS);
+
+                std::string lastAttr;
+                if (!attrPath.empty() && !hasSuffix(attrPathS, ".")) {
+                    lastAttr = attrPath.back();
+                    attrPath.pop_back();
+                }
+
+                auto attr = root->findAlongAttrPath(attrPath);
+                if (!attr) continue;
+
+                auto attrs = attr->getAttrs();
+                for (auto & attr2 : attrs) {
+                    if (hasPrefix(attr2, lastAttr)) {
+                        auto attrPath2 = attr->getAttrPath(attr2);
+                        /* Strip the attrpath prefix. */
+                        attrPath2.erase(attrPath2.begin(), attrPath2.begin() + attrPathPrefix.size());
+                        completions->insert(flakeRefS + "#" + concatStringsSep(".", attrPath2));
+                    }
+                }
+            }
+
+            /* And add an empty completion for the default
+               attrpaths. */
+            if (fragment.empty()) {
+                for (auto & attrPath : getDefaultFlakeAttrPaths()) {
+                    auto attr = root->findAlongAttrPath(parseAttrPath(*state, attrPath));
+                    if (!attr) continue;
+                    completions->insert(flakeRefS + "#");
+                }
+            }
+        }
+    } catch (Error & e) {
+        warn(e.msg());
+    }
+
+    /* Look for registry entries that match the prefix. */
+    for (auto & registry : fetchers::getRegistries(getStore())) {
+        for (auto & entry : registry->entries) {
+            auto from = entry.from->to_string();
+            if (!hasPrefix(prefix, "flake:") && hasPrefix(from, "flake:")) {
+                std::string from2(from, 6);
+                if (hasPrefix(from2, prefix))
+                    completions->insert(from2);
+            } else {
+                if (hasPrefix(from, prefix))
+                    completions->insert(from);
+            }
+        }
+    }
+}
+
 ref<EvalState> EvalCommand::getEvalState()
 {
     if (!evalState)
@@ -576,6 +662,9 @@ InstallablesCommand::InstallablesCommand()
     expectArgs({
         .label = "installables",
         .handler = {&_installables},
+        .completer = {[&](size_t, std::string_view prefix) {
+            completeInstallable(prefix);
+        }}
     });
 }
 
@@ -588,6 +677,17 @@ void InstallablesCommand::prepare()
     installables = parseInstallables(getStore(), _installables);
 }
 
+InstallableCommand::InstallableCommand()
+{
+    expectArgs({
+        .label = "installable",
+        .handler = {&_installable},
+        .completer = {[&](size_t, std::string_view prefix) {
+            completeInstallable(prefix);
+        }}
+    });
+}
+
 void InstallableCommand::prepare()
 {
     installable = parseInstallable(getStore(), _installable);

From 27d34ef770356f86823ca832f278e72bb0a07982 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 11 May 2020 22:04:13 +0200
Subject: [PATCH 08/11] When completing flakerefs, only return directories

---
 src/libutil/args.cc     | 14 ++++++++++++--
 src/libutil/args.hh     |  2 ++
 src/nix/installables.cc |  2 +-
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index ee0c99c2a..f6740e076 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -220,17 +220,27 @@ Args::Flag Args::Flag::mkHashTypeFlag(std::string && longName, HashType * ht)
     };
 }
 
-void completePath(size_t, std::string_view prefix)
+static void completePath(std::string_view prefix, int flags)
 {
     pathCompletions = true;
     glob_t globbuf;
-    if (glob((std::string(prefix) + "*").c_str(), GLOB_NOESCAPE | GLOB_TILDE, nullptr, &globbuf) == 0) {
+    if (glob((std::string(prefix) + "*").c_str(), GLOB_NOESCAPE | GLOB_TILDE | flags, nullptr, &globbuf) == 0) {
         for (size_t i = 0; i < globbuf.gl_pathc; ++i)
             completions->insert(globbuf.gl_pathv[i]);
         globfree(&globbuf);
     }
 }
 
+void completePath(size_t, std::string_view prefix)
+{
+    completePath(prefix, 0);
+}
+
+void completeDir(size_t, std::string_view prefix)
+{
+    completePath(prefix, GLOB_ONLYDIR);
+}
+
 Strings argvToStrings(int argc, char * * argv)
 {
     Strings args;
diff --git a/src/libutil/args.hh b/src/libutil/args.hh
index 250244162..405ec3d47 100644
--- a/src/libutil/args.hh
+++ b/src/libutil/args.hh
@@ -277,4 +277,6 @@ std::optional<std::string> needsCompletion(std::string_view s);
 
 void completePath(size_t, std::string_view prefix);
 
+void completeDir(size_t, std::string_view prefix);
+
 }
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index ade8f83f9..5ba48d69a 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -109,7 +109,7 @@ Strings SourceExprCommand::getDefaultFlakeAttrPathPrefixes()
 
 void SourceExprCommand::completeInstallable(std::string_view prefix)
 {
-    completePath(0, prefix);
+    completeDir(0, prefix);
 
     if (file) return; // FIXME
 

From 649c2db308f16ce4b2cbefe4a8760577541cfb47 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 11 May 2020 22:10:33 +0200
Subject: [PATCH 09/11] nix flake: Add completion support

---
 src/nix/command.hh      |  2 ++
 src/nix/flake.cc        |  9 ++++++++-
 src/nix/installables.cc | 26 +++++++++++++++++---------
 3 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/src/nix/command.hh b/src/nix/command.hh
index 6a6c3fed9..faa19c8ea 100644
--- a/src/nix/command.hh
+++ b/src/nix/command.hh
@@ -38,6 +38,8 @@ struct EvalCommand : virtual StoreCommand, MixEvalArgs
     ref<EvalState> getEvalState();
 
     std::shared_ptr<EvalState> evalState;
+
+    void completeFlakeRef(std::string_view prefix);
 };
 
 struct MixFlakeOptions : virtual Args
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 6eee781aa..b6cc7eb54 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -28,7 +28,14 @@ public:
 
     FlakeCommand()
     {
-        expectArg("flake-url", &flakeUrl, true);
+        expectArgs({
+            .label = "flake-url",
+            .optional = true,
+            .handler = {&flakeUrl},
+            .completer = {[&](size_t, std::string_view prefix) {
+                completeFlakeRef(prefix);
+            }}
+        });
     }
 
     FlakeRef getFlakeRef()
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 5ba48d69a..2d23b33b7 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -109,8 +109,6 @@ Strings SourceExprCommand::getDefaultFlakeAttrPathPrefixes()
 
 void SourceExprCommand::completeInstallable(std::string_view prefix)
 {
-    completeDir(0, prefix);
-
     if (file) return; // FIXME
 
     /* Look for flake output attributes that match the
@@ -176,6 +174,23 @@ void SourceExprCommand::completeInstallable(std::string_view prefix)
         warn(e.msg());
     }
 
+    completeFlakeRef(prefix);
+}
+
+ref<EvalState> EvalCommand::getEvalState()
+{
+    if (!evalState)
+        evalState = std::make_shared<EvalState>(searchPath, getStore());
+    return ref<EvalState>(evalState);
+}
+
+void EvalCommand::completeFlakeRef(std::string_view prefix)
+{
+    if (prefix == "")
+        completions->insert(".");
+
+    completeDir(0, prefix);
+
     /* Look for registry entries that match the prefix. */
     for (auto & registry : fetchers::getRegistries(getStore())) {
         for (auto & entry : registry->entries) {
@@ -192,13 +207,6 @@ void SourceExprCommand::completeInstallable(std::string_view prefix)
     }
 }
 
-ref<EvalState> EvalCommand::getEvalState()
-{
-    if (!evalState)
-        evalState = std::make_shared<EvalState>(searchPath, getStore());
-    return ref<EvalState>(evalState);
-}
-
 Buildable Installable::toBuildable()
 {
     auto buildables = toBuildables();

From 437614b479dd30200dcdc1950f8d4fdddfef7a61 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 12 May 2020 11:08:59 +0200
Subject: [PATCH 10/11] Fix macOS build

macOS doesn't have GLOB_ONLYDIR.
---
 src/libutil/args.cc | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index f6740e076..8667bd450 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -220,25 +220,35 @@ Args::Flag Args::Flag::mkHashTypeFlag(std::string && longName, HashType * ht)
     };
 }
 
-static void completePath(std::string_view prefix, int flags)
+static void completePath(std::string_view prefix, bool onlyDirs)
 {
     pathCompletions = true;
     glob_t globbuf;
-    if (glob((std::string(prefix) + "*").c_str(), GLOB_NOESCAPE | GLOB_TILDE | flags, nullptr, &globbuf) == 0) {
-        for (size_t i = 0; i < globbuf.gl_pathc; ++i)
+    int flags = GLOB_NOESCAPE | GLOB_TILDE;
+    #ifdef GLOB_ONLYDIR
+    if (onlyDirs)
+        flags |= GLOB_ONLYDIR;
+    #endif
+    if (glob((std::string(prefix) + "*").c_str(), flags, nullptr, &globbuf) == 0) {
+        for (size_t i = 0; i < globbuf.gl_pathc; ++i) {
+            if (onlyDirs) {
+                auto st = lstat(globbuf.gl_pathv[i]);
+                if (!S_ISDIR(st.st_mode)) continue;
+            }
             completions->insert(globbuf.gl_pathv[i]);
+        }
         globfree(&globbuf);
     }
 }
 
 void completePath(size_t, std::string_view prefix)
 {
-    completePath(prefix, 0);
+    completePath(prefix, false);
 }
 
 void completeDir(size_t, std::string_view prefix)
 {
-    completePath(prefix, GLOB_ONLYDIR);
+    completePath(prefix, true);
 }
 
 Strings argvToStrings(int argc, char * * argv)

From b8b2dbf27204bc6ce5f57fa5fc5c76f9265fcee1 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 12 May 2020 11:53:32 +0200
Subject: [PATCH 11/11] Fix InstallableCommand

---
 src/nix/installables.cc | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 2d23b33b7..5385484df 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -689,6 +689,7 @@ InstallableCommand::InstallableCommand()
 {
     expectArgs({
         .label = "installable",
+        .optional = true,
         .handler = {&_installable},
         .completer = {[&](size_t, std::string_view prefix) {
             completeInstallable(prefix);