Add command flake clone

src/libexpr/primops/flake.cc

@@ -146,17 +146,19 @@ std::shared_ptr<FlakeRegistry> getFlagRegistry()
     return std::make_shared<FlakeRegistry>();
 }
 
-const std::vector<std::shared_ptr<FlakeRegistry>> EvalState::getFlakeRegistries()
+// This always returns a vector with globalReg, userReg, localReg, flakeReg.
+// If one of them doesn't exist, the registry is left empty but does exist.
+const Registries EvalState::getFlakeRegistries()
 {
-    std::vector<std::shared_ptr<FlakeRegistry>> registries;
-    registries.push_back(getGlobalRegistry());
+    Registries registries;
+    registries.push_back(getGlobalRegistry()); // TODO (Nick): Doesn't this break immutability?
     registries.push_back(getUserRegistry());
+    registries.push_back(std::make_shared<FlakeRegistry>()); // local
     registries.push_back(getFlagRegistry());
     return registries;
 }
 
-static FlakeRef lookupFlake(EvalState & state, const FlakeRef & flakeRef,
-    const std::vector<std::shared_ptr<FlakeRegistry>> & registries,
+static FlakeRef lookupFlake(EvalState & state, const FlakeRef & flakeRef, const Registries & registries,
     std::vector<FlakeRef> pastSearches = {})
 {
     if (registries.empty() && !flakeRef.isDirect())
@@ -462,4 +464,35 @@ static void prim_getFlake(EvalState & state, const Pos & pos, Value * * args, Va
 
 static RegisterPrimOp r2("getFlake", 1, prim_getFlake);
 
+void gitCloneFlake (std::string flakeUri, EvalState & state, Registries registries,
+    Path endDirectory)
+{
+    FlakeRef flakeRef(flakeUri);
+    flakeRef = lookupFlake(state, flakeRef, registries);
+
+    std::string uri;
+
+    Strings args = {"clone"};
+
+    if (auto refData = std::get_if<FlakeRef::IsGitHub>(&flakeRef.data)) {
+        uri = "git@github.com:" + refData->owner + "/" + refData->repo + ".git";
+        args.push_back(uri);
+        if (flakeRef.ref) {
+            args.push_back("--branch");
+            args.push_back(*flakeRef.ref);
+        }
+    } else if (auto refData = std::get_if<FlakeRef::IsGit>(&flakeRef.data)) {
+        args.push_back(refData->uri);
+        if (flakeRef.ref) {
+            args.push_back("--branch");
+            args.push_back(*flakeRef.ref);
+        }
+    }
+
+    if (endDirectory != "")
+        args.push_back(endDirectory);
+
+    runProgram("git", true, args);
+}
+
 }

src/libexpr/primops/flake.hh

@@ -27,6 +27,8 @@ struct LockFile
     std::map<FlakeId, FlakeRef> nonFlakeEntries;
 };
 
+typedef std::vector<std::shared_ptr<FlakeRegistry>> Registries;
+
 Path getUserRegistryPath();
 
 enum RegistryAccess { DisallowRegistry, AllowRegistry, AllowRegistryAtTop };
@@ -86,4 +88,5 @@ Dependencies resolveFlake(EvalState &, const FlakeRef &, RegistryAccess registry
 
 void updateLockFile(EvalState &, const Path & path);
 
+void gitCloneFlake (std::string flakeUri, EvalState &, Registries, Path);
 }

src/libexpr/primops/flakeref.hh

@@ -67,6 +67,7 @@ namespace nix {
        https://example.org/my/repo.git
        https://example.org/my/repo.git?ref=release-1.2.3
        https://example.org/my/repo.git?rev=e72daba8250068216d79d2aeef40d4d95aff6666
+       git://github.com/edolstra/dwarffs.git\?ref=flake\&rev=2efca4bc9da70fb001b26c3dc858c6397d3c4817
 
    * /path.git(\?attr(&attr)*)?
 

src/libutil/util.cc

@@ -962,12 +962,14 @@ std::vector<char *> stringsToCharPtrs(const Strings & ss)
     return res;
 }
 
-
+// Output = "standard out" output stream
 string runProgram(Path program, bool searchPath, const Strings & args,
     const std::optional<std::string> & input)
 {
     RunOptions opts(program, args);
     opts.searchPath = searchPath;
+    // This allows you to refer to a program with a pathname relative to the
+    // PATH variable.
     opts.input = input;
 
     auto res = runProgram(opts);
@@ -978,6 +980,7 @@ string runProgram(Path program, bool searchPath, const Strings & args,
     return res.second;
 }
 
+// Output = error code + "standard out" output stream
 std::pair<int, std::string> runProgram(const RunOptions & options_)
 {
     RunOptions options(options_);
@@ -1028,6 +1031,8 @@ void runProgram2(const RunOptions & options)
 
         if (options.searchPath)
             execvp(options.program.c_str(), stringsToCharPtrs(args_).data());
+            // This allows you to refer to a program with a pathname relative
+            // to the PATH variable.
         else
             execv(options.program.c_str(), stringsToCharPtrs(args_).data());
 

src/nix/flake.cc

@@ -280,6 +280,34 @@ struct CmdFlakeInit : virtual Args, Command
     }
 };
 
+struct CmdFlakeClone : StoreCommand, FlakeCommand, MixEvalArgs
+{
+    Path endDirectory = "";
+
+    std::string name() override
+    {
+        return "clone";
+    }
+
+    std::string description() override
+    {
+        return "clone flake repository";
+    }
+
+    CmdFlakeClone()
+    {
+        expectArg("end-dir", &endDirectory, true);
+    }
+
+    void run(nix::ref<nix::Store> store) override
+    {
+        auto evalState = std::make_shared<EvalState>(searchPath, store);
+
+        Registries registries = evalState->getFlakeRegistries();
+        gitCloneFlake(flakeUri, *evalState, registries, endDirectory);
+    }
+};
+
 struct CmdFlake : virtual MultiCommand, virtual Command
 {
     CmdFlake()
@@ -291,6 +319,7 @@ struct CmdFlake : virtual MultiCommand, virtual Command
             , make_ref<CmdFlakeRemove>()
             , make_ref<CmdFlakePin>()
             , make_ref<CmdFlakeInit>()
+            , make_ref<CmdFlakeClone>()
           })
     {
     }