nix flake clone: Support all input types

For input types that have no concept of cloning, we now default to
copying the entire source tree.

Author: edolstra

src/libfetchers/fetchers.cc

@@ -6,6 +6,7 @@
 #include "nix/fetchers/fetch-settings.hh"
 #include "nix/fetchers/fetch-to-store.hh"
 #include "nix/util/url.hh"
+#include "nix/util/archive.hh"
 
 #include <nlohmann/json.hpp>
 
@@ -377,10 +378,10 @@ Input Input::applyOverrides(std::optional<std::string> ref, std::optional<Hash>
     return scheme->applyOverrides(*this, ref, rev);
 }
 
-void Input::clone(const Settings & settings, const std::filesystem::path & destDir) const
+void Input::clone(const Settings & settings, ref<Store> store, const std::filesystem::path & destDir) const
 {
     assert(scheme);
-    scheme->clone(settings, *this, destDir);
+    scheme->clone(settings, store, *this, destDir);
 }
 
 std::optional<std::filesystem::path> Input::getSourcePath() const
@@ -493,9 +494,19 @@ void InputScheme::putFile(
     throw Error("input '%s' does not support modifying file '%s'", input.to_string(), path);
 }
 
-void InputScheme::clone(const Settings & settings, const Input & input, const std::filesystem::path & destDir) const
+void InputScheme::clone(
+    const Settings & settings, ref<Store> store, const Input & input, const std::filesystem::path & destDir) const
 {
-    throw Error("do not know how to clone input '%s'", input.to_string());
+    if (std::filesystem::exists(destDir))
+        throw Error("cannot clone into existing path %s", destDir);
+
+    auto [accessor, input2] = getAccessor(settings, store, input);
+
+    Activity act(*logger, lvlTalkative, actUnknown, fmt("copying '%s' to %s...", input2.to_string(), destDir));
+
+    auto source = sinkToSource([&](Sink & sink) { accessor->dumpPath(CanonPath::root, sink); });
+
+    restorePath(destDir, *source);
 }
 
 std::optional<ExperimentalFeature> InputScheme::experimentalFeature() const

src/libfetchers/git.cc

@@ -278,7 +278,8 @@ struct GitInputScheme : InputScheme
         return res;
     }
 
-    void clone(const Settings & settings, const Input & input, const std::filesystem::path & destDir) const override
+    void clone(const Settings & settings, ref<Store> store, const Input & input, const std::filesystem::path & destDir)
+        const override
     {
         auto repoInfo = getRepoInfo(input);
 

src/libfetchers/github.cc

@@ -426,12 +426,13 @@ struct GitHubInputScheme : GitArchiveInputScheme
         return DownloadUrl{parseURL(url), headers};
     }
 
-    void clone(const Settings & settings, const Input & input, const std::filesystem::path & destDir) const override
+    void clone(const Settings & settings, ref<Store> store, const Input & input, const std::filesystem::path & destDir)
+        const override
     {
         auto host = getHost(input);
         Input::fromURL(settings, fmt("git+https://%s/%s/%s.git", host, getOwner(input), getRepo(input)))
             .applyOverrides(input.getRef(), input.getRev())
-            .clone(settings, destDir);
+            .clone(settings, store, destDir);
     }
 };
 
@@ -507,15 +508,16 @@ struct GitLabInputScheme : GitArchiveInputScheme
         return DownloadUrl{parseURL(url), headers};
     }
 
-    void clone(const Settings & settings, const Input & input, const std::filesystem::path & destDir) const override
+    void clone(const Settings & settings, ref<Store> store, const Input & input, const std::filesystem::path & destDir)
+        const override
     {
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("gitlab.com");
         // FIXME: get username somewhere
         Input::fromURL(
             settings,
             fmt("git+https://%s/%s/%s.git", host, getStrAttr(input.attrs, "owner"), getStrAttr(input.attrs, "repo")))
             .applyOverrides(input.getRef(), input.getRev())
-            .clone(settings, destDir);
+            .clone(settings, store, destDir);
     }
 };
 
@@ -596,14 +598,15 @@ struct SourceHutInputScheme : GitArchiveInputScheme
         return DownloadUrl{parseURL(url), headers};
     }
 
-    void clone(const Settings & settings, const Input & input, const std::filesystem::path & destDir) const override
+    void clone(const Settings & settings, ref<Store> store, const Input & input, const std::filesystem::path & destDir)
+        const override
     {
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("git.sr.ht");
         Input::fromURL(
             settings,
             fmt("git+https://%s/%s/%s", host, getStrAttr(input.attrs, "owner"), getStrAttr(input.attrs, "repo")))
             .applyOverrides(input.getRef(), input.getRev())
-            .clone(settings, destDir);
+            .clone(settings, store, destDir);
     }
 };
 

src/libfetchers/include/nix/fetchers/fetchers.hh

@@ -143,7 +143,7 @@ public:
 
     Input applyOverrides(std::optional<std::string> ref, std::optional<Hash> rev) const;
 
-    void clone(const Settings & settings, const std::filesystem::path & destDir) const;
+    void clone(const Settings & settings, ref<Store> store, const std::filesystem::path & destDir) const;
 
     std::optional<std::filesystem::path> getSourcePath() const;
 
@@ -216,7 +216,8 @@ struct InputScheme
 
     virtual Input applyOverrides(const Input & input, std::optional<std::string> ref, std::optional<Hash> rev) const;
 
-    virtual void clone(const Settings & settings, const Input & input, const std::filesystem::path & destDir) const;
+    virtual void clone(
+        const Settings & settings, ref<Store> store, const Input & input, const std::filesystem::path & destDir) const;
 
     virtual std::optional<std::filesystem::path> getSourcePath(const Input & input) const;
 

src/nix/flake.cc

@@ -1049,7 +1049,7 @@ struct CmdFlakeClone : FlakeCommand
         if (destDir.empty())
             throw Error("missing flag '--dest'");
 
-        getFlakeRef().resolve(fetchSettings, store).input.clone(fetchSettings, destDir);
+        getFlakeRef().resolve(fetchSettings, store).input.clone(fetchSettings, store, destDir);
     }
 };
 

tests/functional/flakes/flakes.sh

@@ -369,6 +369,10 @@ tar cfz "$TEST_ROOT"/flake.tar.gz -C "$TEST_ROOT" flake5
 
 nix build -o "$TEST_ROOT"/result file://"$TEST_ROOT"/flake.tar.gz
 
+nix flake clone "file://$TEST_ROOT/flake.tar.gz" --dest "$TEST_ROOT/unpacked"
+[[ -e $TEST_ROOT/unpacked/flake.nix ]]
+expectStderr 1 nix flake clone "file://$TEST_ROOT/flake.tar.gz" --dest "$TEST_ROOT/unpacked" | grep 'existing path'
+
 # Building with a tarball URL containing a SRI hash should also work.
 url=$(nix flake metadata --json file://"$TEST_ROOT"/flake.tar.gz | jq -r .url)
 [[ $url =~ sha256- ]]