Add :depth option to git deps

lib/mix/lib/mix/scm/git.ex

@@ -125,14 +125,18 @@ defmodule Mix.SCM.Git do
     sparse_toggle(opts)
     update_origin(opts[:git])
 
+    rev = get_lock_rev(opts[:lock], opts) || get_opts_rev(opts)
+
     # Fetch external data
     ["--git-dir=.git", "fetch", "--force", "--quiet"]
     |> Kernel.++(progress_switch(git_version()))
     |> Kernel.++(tags_switch(opts[:tag]))
+    |> Kernel.++(depth_switch(opts[:depth]))
+    |> Kernel.++(if rev, do: ["origin", rev], else: [])
     |> git!()
 
     # Migrate the Git repo
-    rev = get_lock_rev(opts[:lock], opts) || get_opts_rev(opts) || default_branch()
+    rev = rev || default_branch()
     git!(["--git-dir=.git", "checkout", "--quiet", rev])
 
     if opts[:submodules] do
@@ -164,7 +168,7 @@ defmodule Mix.SCM.Git do
   defp sparse_toggle(opts) do
     cond do
       sparse = opts[:sparse] ->
-        sparse_check(git_version())
+        check_sparse_support(git_version())
         git!(["--git-dir=.git", "config", "core.sparsecheckout", "true"])
         File.mkdir_p!(".git/info")
         File.write!(".git/info/sparse-checkout", sparse)
@@ -180,27 +184,50 @@ defmodule Mix.SCM.Git do
     end
   end
 
-  defp sparse_check(version) do
-    unless {1, 7, 4} <= version do
-      version = version |> Tuple.to_list() |> Enum.join(".")
+  @min_git_version_sparse {1, 7, 4}
+  @min_git_version_depth {1, 5, 0}
+  @min_git_version_progress {1, 7, 1}
+
+  defp check_sparse_support(version) do
+    ensure_feature_compatibility(version, @min_git_version_sparse, "sparse checkout")
+  end
+
+  defp check_depth_support(version) do
+    ensure_feature_compatibility(version, @min_git_version_depth, "depth (shallow clone)")
+  end
 
+  defp ensure_feature_compatibility(version, required_version, feature) do
+    unless required_version <= version do
       Mix.raise(
-        "Git >= 1.7.4 is required to use sparse checkout. " <>
-          "You are running version #{version}"
+        "Git >= #{format_version(required_version)} is required to use #{feature}. " <>
+          "You are running version #{format_version(version)}"
       )
     end
   end
 
   defp progress_switch(version) do
-    if {1, 7, 1} <= version, do: ["--progress"], else: []
+    if @min_git_version_progress <= version, do: ["--progress"], else: []
   end
 
   defp tags_switch(nil), do: []
   defp tags_switch(_), do: ["--tags"]
 
+  defp depth_switch(nil), do: []
+
+  defp depth_switch(n) when is_integer(n) and n > 0 do
+    check_depth_support(git_version())
+    ["--depth=#{n}"]
+  end
+
   ## Helpers
 
   defp validate_git_options(opts) do
+    opts
+    |> validate_refspec()
+    |> validate_depth()
+  end
+
+  defp validate_refspec(opts) do
     case Keyword.take(opts, [:branch, :ref, :tag]) do
       [] ->
         opts
@@ -222,6 +249,22 @@ defmodule Mix.SCM.Git do
     end
   end
 
+  defp validate_depth(opts) do
+    case Keyword.take(opts, [:depth]) do
+      [] ->
+        opts
+
+      [{:depth, depth}] when is_integer(depth) and depth > 0 ->
+        opts
+
+      invalid_depth ->
+        Mix.raise(
+          "The depth must be a positive integer, and be specified only once, got: #{inspect(invalid_depth)}. " <>
+            "Error on Git dependency: #{redact_uri(opts[:git])}"
+        )
+    end
+  end
+
   defp get_lock(opts) do
     %{rev: rev} = get_rev_info()
     {:git, opts[:git], rev, get_lock_opts(opts)}
@@ -238,7 +281,7 @@ defmodule Mix.SCM.Git do
   defp get_lock_rev(_, _), do: nil
 
   defp get_lock_opts(opts) do
-    lock_opts = Keyword.take(opts, [:branch, :ref, :tag, :sparse, :subdir])
+    lock_opts = Keyword.take(opts, [:branch, :ref, :tag, :sparse, :subdir, :depth])
 
     if opts[:submodules] do
       lock_opts ++ [submodules: true]
@@ -248,11 +291,7 @@ defmodule Mix.SCM.Git do
   end
 
   defp get_opts_rev(opts) do
-    if branch = opts[:branch] do
-      "origin/#{branch}"
-    else
-      opts[:ref] || opts[:tag]
-    end
+    opts[:branch] || opts[:ref] || opts[:tag]
   end
 
   defp redact_uri(git) do
@@ -282,6 +321,8 @@ defmodule Mix.SCM.Git do
   end
 
   defp default_branch() do
+    # Note: the `set-head -a` command requires the remote reference to be
+    # fetched first.
     git!(["--git-dir=.git", "remote", "set-head", "origin", "-a"])
     "origin/HEAD"
   end
@@ -328,9 +369,17 @@ defmodule Mix.SCM.Git do
     end
   end
 
-  # Also invoked by lib/mix/test/test_helper.exs
+  # Invoked by lib/mix/test/test_helper.exs
   @doc false
-  def git_version do
+  def unsupported_options do
+    git_version = git_version()
+
+    []
+    |> Kernel.++(if git_version < @min_git_version_sparse, do: [:sparse], else: [])
+    |> Kernel.++(if git_version < @min_git_version_depth, do: [:depth], else: [])
+  end
+
+  defp git_version do
     case Mix.State.fetch(:git_version) do
       {:ok, version} ->
         version
@@ -354,6 +403,10 @@ defmodule Mix.SCM.Git do
     |> List.to_tuple()
   end
 
+  defp format_version(version) do
+    version |> Tuple.to_list() |> Enum.join(".")
+  end
+
   defp to_integer(string) do
     {int, _} = Integer.parse(string)
     int

lib/mix/lib/mix/tasks/deps.ex

@@ -120,6 +120,10 @@ defmodule Mix.Tasks.Deps do
     * `:subdir` - (since v1.13.0) search for the project in the given directory
       relative to the git checkout. This is similar to `:sparse` option but instead
       of a doing a sparse checkout it does a full checkout.
+    * `:depth` - (since v1.17.0) creates a shallow clone of the Git repository,
+      limiting the history to the specified number of commits. This can significantly
+      improve clone speed for large repositories when full history is not needed.
+      The value must be a positive integer, typically `1`.
 
   If your Git repository requires authentication, such as basic username:password
   HTTP authentication via URLs, it can be achieved via Git configuration, keeping

lib/mix/test/mix/scm/git_test.exs

@@ -32,7 +32,7 @@ defmodule Mix.SCM.GitTest do
              "https://github.com/elixir-lang/some_dep.git - v1"
 
     assert Mix.SCM.Git.format(Keyword.put(opts, :branch, "b")) ==
-             "https://github.com/elixir-lang/some_dep.git - origin/b"
+             "https://github.com/elixir-lang/some_dep.git - b"
 
     assert Mix.SCM.Git.format(Keyword.put(opts, :ref, "abcdef")) ==
              "https://github.com/elixir-lang/some_dep.git - abcdef"

lib/mix/test/mix/tasks/deps.git_test.exs

@@ -478,6 +478,207 @@ defmodule Mix.Tasks.DepsGitTest do
     purge([GitRepo, GitRepo.MixProject])
   end
 
+  describe "Git depth option" do
+    @describetag :git_depth
+
+    test "gets and updates Git repos with depth option" do
+      Process.put(:git_repo_opts, depth: 1)
+
+      in_fixture("no_mixfile", fn ->
+        Mix.Project.push(GitApp)
+
+        Mix.Tasks.Deps.Get.run([])
+        message = "* Getting git_repo (#{fixture_path("git_repo")})"
+        assert_received {:mix_shell, :info, [^message]}
+        assert_shallow("deps/git_repo", 1)
+
+        # Expand depth
+        update_dep(depth: 2)
+        Mix.Tasks.Deps.Get.run([])
+        assert_shallow("deps/git_repo", 2)
+
+        # Reduce depth
+        update_dep(depth: 1)
+        Mix.Tasks.Deps.Get.run([])
+        assert_shallow("deps/git_repo", 1)
+      end)
+    end
+
+    test "with tag" do
+      Process.put(:git_repo_opts, depth: 1, tag: "with_module")
+
+      in_fixture("no_mixfile", fn ->
+        Mix.Project.push(GitApp)
+
+        Mix.Tasks.Deps.Get.run([])
+        message = "* Getting git_repo (#{fixture_path("git_repo")} - with_module)"
+        assert_received {:mix_shell, :info, [^message]}
+        assert_shallow("deps/git_repo", 1)
+      end)
+    end
+
+    test "with branch" do
+      Process.put(:git_repo_opts, depth: 1, branch: "main")
+
+      in_fixture("no_mixfile", fn ->
+        Mix.Project.push(GitApp)
+
+        Mix.Tasks.Deps.Get.run([])
+        message = "* Getting git_repo (#{fixture_path("git_repo")} - main)"
+        assert_received {:mix_shell, :info, [^message]}
+        assert_shallow("deps/git_repo", 1)
+      end)
+    end
+
+    test "with ref" do
+      [last, _ | _] = get_git_repo_revs("git_repo")
+
+      Process.put(:git_repo_opts, depth: 1, ref: last)
+
+      in_fixture("no_mixfile", fn ->
+        Mix.Project.push(GitApp)
+
+        Mix.Tasks.Deps.Get.run([])
+        message = "* Getting git_repo (#{fixture_path("git_repo")} - #{last})"
+        assert_received {:mix_shell, :info, [^message]}
+        assert_shallow("deps/git_repo", 1)
+      end)
+    end
+
+    test "changing refspec updates retaining depth" do
+      [last, first | _] = get_git_repo_revs("git_repo")
+
+      Process.put(:git_repo_opts, ref: first, depth: 1)
+
+      in_fixture("no_mixfile", fn ->
+        Mix.Project.push(GitApp)
+
+        Mix.Tasks.Deps.Get.run([])
+        message = "* Getting git_repo (#{fixture_path("git_repo")} - #{first})"
+        assert_received {:mix_shell, :info, [^message]}
+        assert_shallow("deps/git_repo", 1)
+        assert File.read!("mix.lock") =~ first
+
+        # Change refspec
+        update_dep(ref: last, depth: 1)
+        Mix.Tasks.Deps.Get.run([])
+        assert_shallow("deps/git_repo", 1)
+        assert File.read!("mix.lock") =~ last
+      end)
+    end
+
+    test "removing depth retains shallow repository" do
+      # For compatibility and simplicity, we follow Git's behavior and do not
+      # attempt to unshallow an existing repository. This should not be a
+      # problem, because all we guarantee is that the correct source code is
+      # available whenever mix.exs or mix.lock change. If one wanted to have a
+      # full clone, they can always run `deps.clean` and `deps.get` again.
+      Process.put(:git_repo_opts, depth: 1)
+
+      in_fixture("no_mixfile", fn ->
+        Mix.Project.push(GitApp)
+
+        Mix.Tasks.Deps.Get.run([])
+        message = "* Getting git_repo (#{fixture_path("git_repo")})"
+        assert_received {:mix_shell, :info, [^message]}
+        assert_shallow("deps/git_repo", 1)
+
+        # Remove depth
+        update_dep([])
+        Mix.Tasks.Deps.Get.run([])
+        refute File.read!("mix.lock") =~ "depth:"
+        assert File.exists?("deps/git_repo/.git/shallow")
+
+        assert System.cmd("git", ~w[--git-dir=deps/git_repo/.git rev-list --count HEAD]) ==
+                 {"1\n", 0}
+      end)
+    end
+
+    @tag :git_sparse
+    test "with sparse checkout" do
+      Process.put(:git_repo_opts, sparse: "sparse_dir", depth: 1)
+
+      in_fixture("no_mixfile", fn ->
+        Mix.Project.push(GitApp)
+
+        Mix.Tasks.Deps.Get.run([])
+        message = "* Getting git_repo (#{fixture_path("git_repo")})"
+        assert_received {:mix_shell, :info, [^message]}
+        assert_shallow("deps/git_repo", 1)
+
+        refute File.exists?("deps/git_repo/mix.exs")
+        assert File.exists?("deps/git_repo/sparse_dir/mix.exs")
+        assert File.read!("mix.lock") =~ "sparse: \"sparse_dir\""
+      end)
+    end
+
+    test "with subdir" do
+      Process.put(:git_repo_opts, subdir: "sparse_dir", depth: 1)
+
+      in_fixture("no_mixfile", fn ->
+        Mix.Project.push(GitApp)
+
+        Mix.Tasks.Deps.Get.run([])
+        message = "* Getting git_repo (#{fixture_path("git_repo")})"
+        assert_received {:mix_shell, :info, [^message]}
+        assert_shallow("deps/git_repo", 1)
+
+        assert File.exists?("deps/git_repo/mix.exs")
+        assert File.exists?("deps/git_repo/sparse_dir/mix.exs")
+        assert File.read!("mix.lock") =~ "subdir: \"sparse_dir\""
+      end)
+    end
+
+    test "does not affect submodules depth" do
+      # The expectation is that we can add an explicit option in the future,
+      # just like git-clone has `--shallow-submodules`.
+      Process.put(:git_repo_opts, submodules: true, depth: 1)
+
+      in_fixture("no_mixfile", fn ->
+        Mix.Project.push(GitApp)
+
+        Mix.Tasks.Deps.Get.run([])
+        message = "* Getting git_repo (#{fixture_path("git_repo")})"
+        assert_received {:mix_shell, :info, [^message]}
+        assert_shallow("deps/git_repo", 1)
+
+        assert File.read!("mix.lock") =~ "submodules: true"
+        # TODO: assert submodule is not shallow. This would likely require
+        # changes to the fixtures. Apparently, not even the submodules-specific
+        # tests check that the cloned repo contains submodules as expected.
+      end)
+    end
+
+    defp update_dep(git_repo_opts) do
+      # Flush the errors we got, move to a clean slate
+      Mix.shell().flush()
+      Mix.Task.clear()
+      Process.put(:git_repo_opts, git_repo_opts)
+      Mix.Project.pop()
+      Mix.Project.push(GitApp)
+    end
+
+    defp assert_shallow(repo_path, depth) do
+      assert File.read!("mix.lock") =~ "depth: #{depth}"
+
+      # Check if the repository is a shallow clone
+      assert File.exists?(repo_path <> "/.git/shallow")
+
+      # Check the number of commits in the current branch.
+      #
+      # We could consider all branches with `git rev-list --count --all`, as in
+      # practice there should be only a single branch. However, the test fixture
+      # sets up two branches, and that brings us to an interesting situation:
+      # instead of guaranteeing that the `:depth` option would keep the
+      # repository lean even after refspec changes, we only guarantee the number
+      # of commits in the current branch, perhaps leaving more objects around
+      # than strictly necessary. This allows us to keep the implementation
+      # simple, while still providing a reasonable guarantee.
+      assert System.cmd("git", ~w[--git-dir=#{repo_path}/.git rev-list --count HEAD]) ==
+               {"#{depth}\n", 0}
+    end
+  end
+
   defp refresh(post_config) do
     %{name: name, file: file} = Mix.Project.pop()
     Mix.ProjectStack.post_config(post_config)