Support pathspecs in --cut

Sometimes I want to extract a small number of changes from a commit
that touches loads of files. Since the cut mode prompts about every
single file, there is no convenient way to do this.

Teach --cut about pathspec arguments.  This allows to use

	git revise --cut my-commit -- path/to/my/file
	a

to extract to a separate commit all changes in the given file.

In future we could support pathspecs in other subcommands.

docs/man.rst

@@ -10,6 +10,7 @@ SYNOPSIS
 ========
 
 *git revise* [<options>] [<target>]
+*git revise* [<options>] --cut <target> [--] [<pathspec>...]
 
 DESCRIPTION
 ===========
@@ -93,8 +94,9 @@ Main modes of operation
 
 .. option:: -c, --cut
 
-   Interactively select hunks from <target>. The chosen hunks are split into
-   a second commit immediately after the target.
+   Interactively select hunks from <target>, optionally limited by <pathspec>.
+   The chosen hunks are split into a second commit immediately after the
+   target.
 
    After splitting is complete, both commits' messages are edited.
 

gitrevise/tui.py

@@ -19,7 +19,7 @@
 )
 
 
-def build_parser() -> ArgumentParser:
+def build_parser(allow_pathspecs: bool) -> ArgumentParser:
     parser = ArgumentParser(
         description="""\
         Rebase staged changes onto the given commit, and rewrite history to
@@ -36,6 +36,12 @@ def build_parser() -> ArgumentParser:
         nargs="?",
         help="target commit to apply fixups to",
     )
+    if allow_pathspecs:
+        parser.add_argument(
+            "pathspecs",
+            nargs="*",
+            help="make --cut select only from matching files",
+        )
     parser.add_argument("--ref", default="HEAD", help="reference to update")
     parser.add_argument(
         "--reauthor",
@@ -201,7 +207,7 @@ def noninteractive(
 
     # If the commit should be cut, prompt the user to perform the cut.
     if args.cut:
-        current = cut_commit(current)
+        current = cut_commit(current, args.pathspecs)
 
     # Add or remove GPG signatures.
     if repo.sign_commits != bool(current.gpgsig):
@@ -258,7 +264,9 @@ def inner_main(args: Namespace, repo: Repository) -> None:
 
 
 def main(argv: Optional[List[str]] = None) -> None:
-    args = build_parser().parse_args(argv)
+    args = build_parser(allow_pathspecs=True).parse_args(argv)
+    if not args.cut:
+        args = build_parser(allow_pathspecs=False).parse_args(argv)
     try:
         with Repository() as repo:
             inner_main(args, repo)

gitrevise/utils.py

@@ -252,7 +252,7 @@ def update_head(ref: Reference[Commit], new: Commit, expected: Optional[Tree]) -
         )
 
 
-def cut_commit(commit: Commit) -> Commit:
+def cut_commit(commit: Commit, pathspecs: Optional[List[str]] = None) -> Commit:
     """Perform a ``cut`` operation on the given commit, and return the
     modified commit."""
 
@@ -274,7 +274,15 @@ def cut_commit(commit: Commit) -> Commit:
 
     # Run an interactive git-reset to allow picking which pieces of the
     # patch should go into the first part.
-    index.git("reset", "--patch", final_tree.persist().hex(), "--", ".", stdout=None)
+    index.git(
+        "reset",
+        "--patch",
+        final_tree.persist().hex(),
+        "--",
+        *(pathspecs if pathspecs else []),
+        cwd=Path.cwd(),
+        stdout=None,
+    )
 
     # Write out the newly created tree.
     mid_tree = index.tree()

tests/test_cut.py

@@ -1,3 +1,7 @@
+from textwrap import dedent
+
+import pytest
+
 from gitrevise.odb import Repository
 
 from .conftest import bash, editor_main
@@ -84,3 +88,65 @@ def test_cut_root(repo: Repository) -> None:
 
     assert new_u != new
     assert new_u != prev
+
+
+@pytest.mark.parametrize("pathspec", ["subdir/file2", "file2"])
+def test_cut_pathspec(
+    repo: Repository, monkeypatch: pytest.MonkeyPatch, pathspec: str
+) -> None:
+    bash(
+        """
+        echo "Hello, World" >> file1
+        git add file1
+        git commit -m "commit 1"
+
+        echo "Append f1" >> file1
+        mkdir subdir
+        echo "Make f2" >> subdir/file2
+        git add file1 subdir/file2
+        git commit -m "commit 2"
+        """
+    )
+
+    if pathspec == "file2":
+        monkeypatch.chdir(repo.workdir / "subdir")
+    with editor_main(["--cut", "HEAD", pathspec], input=b"y\n") as ed:
+        with ed.next_file() as f:
+            assert f.startswith_dedent("[1] commit 2\n")
+            f.replace_dedent("extracted changes\n")
+
+        with ed.next_file() as f:
+            assert f.startswith_dedent("[2] commit 2\n")
+            f.replace_dedent("remaining changes\n")
+
+    assert (
+        repo.git("show", "HEAD~", "--format=%s").decode()
+        == dedent(
+            """
+        extracted changes
+
+        diff --git a/subdir/file2 b/subdir/file2
+        new file mode 100644
+        index 0000000..93350fe
+        --- /dev/null
+        +++ b/subdir/file2
+        @@ -0,0 +1 @@
+        +Make f2"""
+        )[1:]
+    )
+
+    assert (
+        repo.git("show", "HEAD", "--format=%s").decode()
+        == dedent(
+            """
+        remaining changes
+
+        diff --git a/file1 b/file1
+        index 3fa0d4b..ada44cf 100644
+        --- a/file1
+        +++ b/file1
+        @@ -1 +1,2 @@
+         Hello, World
+        +Append f1"""
+        )[1:]
+    )

tests/test_edit.py

@@ -1,12 +1,10 @@
-from subprocess import CalledProcessError
-
-import pytest
-
 from gitrevise.odb import Repository
 
 from .conftest import main
 
+
+# pylint: disable=unused-argument
 def test_edit_illegal_extra_argument(repo: Repository) -> None:
-    p = main(["--edit", "HEAD", "HEAD"], check=False, capture_output=True)
-    assert b'error: unrecognized arguments' in p.stderr
-    assert p.returncode != 0
+    process = main(["--edit", "HEAD", "HEAD"], check=False, capture_output=True)
+    assert b"error: unrecognized arguments" in process.stderr
+    assert process.returncode != 0