cli: add interdiff command

Add the `jj interdiff` command for comparing only the diffs of commits.
Its args are identical to that of `jj diff`, minus `--revision` (because
interdiff always requires two commits).

Like `jj obslog -p`, Changes introduced by intervening commits are
ignored by rebasing `--from` onto `--to` 's parents.

CHANGELOG.md

@@ -56,6 +56,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### New features
 
+* The new `jj interdiff` command compares the changes in commits, ignoring
+  changes from intervening commits.
+
 * `jj rebase` now accepts a `--branch/-b <revision>` argument, which can be used
   instead of `-r` or `-s` to specify which commits to rebase. It will rebase the
   whole branch, relative to the destination. The default mode has changed from

src/commands.rs

@@ -1101,6 +1101,7 @@ enum Commands {
     Status(StatusArgs),
     Log(LogArgs),
     Obslog(ObslogArgs),
+    Interdiff(InterdiffArgs),
     Describe(DescribeArgs),
     Close(CloseArgs),
     Open(OpenArgs),
@@ -1323,6 +1324,26 @@ struct ObslogArgs {
     diff_format: DiffFormatArgs,
 }
 
+/// Compare the changes of two commits
+///
+/// This excludes changes from other commits by temporarily rebasing `--from`
+/// onto `--to`'s parents. If you wish to compare the same change across
+/// versions, consider `jj obslog -p` instead.
+#[derive(clap::Args, Clone, Debug)]
+#[clap(group(ArgGroup::new("to_diff").args(&["from", "to"]).multiple(true).required(true)))]
+struct InterdiffArgs {
+    /// Show changes from this revision
+    #[clap(long)]
+    from: Option<String>,
+    /// Show changes to this revision
+    #[clap(long)]
+    to: Option<String>,
+    /// Restrict the diff to these paths
+    paths: Vec<String>,
+    #[clap(flatten)]
+    format: DiffFormatArgs,
+}
+
 /// Edit the change description
 ///
 /// Starts an editor to let you edit the description of a change. The editor
@@ -3235,6 +3256,27 @@ fn show_predecessor_patch(
     show_diff(formatter, workspace_command, diff_iterator, diff_format)
 }
 
+fn cmd_interdiff(
+    ui: &mut Ui,
+    command: &CommandHelper,
+    args: &InterdiffArgs,
+) -> Result<(), CommandError> {
+    let workspace_command = command.workspace_helper(ui)?;
+    let from = workspace_command.resolve_single_rev(args.from.as_deref().unwrap_or("@"))?;
+    let to = workspace_command.resolve_single_rev(args.to.as_deref().unwrap_or("@"))?;
+
+    let from_tree = rebase_to_dest_parent(&workspace_command, &from, &to)?;
+    let workspace_root = workspace_command.workspace_root();
+    let matcher = matcher_from_values(ui, workspace_root, &args.paths)?;
+    let diff_iterator = from_tree.diff(&to.tree(), matcher.as_ref());
+    show_diff(
+        ui.stdout_formatter().as_mut(),
+        &workspace_command,
+        diff_iterator,
+        diff_format_for(ui, &args.format),
+    )
+}
+
 fn rebase_to_dest_parent(
     workspace_command: &WorkspaceCommandHelper,
     source: &Commit,
@@ -5499,6 +5541,7 @@ where
         Commands::Show(sub_args) => cmd_show(ui, &command_helper, sub_args),
         Commands::Status(sub_args) => cmd_status(ui, &command_helper, sub_args),
         Commands::Log(sub_args) => cmd_log(ui, &command_helper, sub_args),
+        Commands::Interdiff(sub_args) => cmd_interdiff(ui, &command_helper, sub_args),
         Commands::Obslog(sub_args) => cmd_obslog(ui, &command_helper, sub_args),
         Commands::Describe(sub_args) => cmd_describe(ui, &command_helper, sub_args),
         Commands::Close(sub_args) => cmd_close(ui, &command_helper, sub_args),

tests/test_interdiff_command.rs

@@ -0,0 +1,168 @@
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use common::TestEnvironment;
+
+pub mod common;
+
+#[test]
+fn test_interdiff_basic() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    std::fs::write(repo_path.join("file1"), "foo\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["new"]);
+    std::fs::write(repo_path.join("file2"), "foo\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["branch", "create", "left"]);
+
+    test_env.jj_cmd_success(&repo_path, &["checkout", "root"]);
+    std::fs::write(repo_path.join("file3"), "foo\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["new"]);
+    std::fs::write(repo_path.join("file2"), "foo\nbar\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["branch", "create", "right"]);
+
+    // implicit --to
+    let stdout = test_env.jj_cmd_success(&repo_path, &["interdiff", "--from", "left"]);
+    insta::assert_snapshot!(stdout, @r###"
+    Modified regular file file2:
+       1    1: foo
+            2: bar
+    "###);
+
+    // explicit --to
+    test_env.jj_cmd_success(&repo_path, &["checkout", "@-"]);
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &["interdiff", "--from", "left", "--to", "right"],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    Modified regular file file2:
+       1    1: foo
+            2: bar
+    "###);
+    test_env.jj_cmd_success(&repo_path, &["undo"]);
+
+    // formats specifiers
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &["interdiff", "--from", "left", "--to", "right", "-s"],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    M file2
+    "###);
+
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &["interdiff", "--from", "left", "--to", "right", "--git"],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    diff --git a/file2 b/file2
+    index 257cc5642c...3bd1f0e297 100644
+    --- a/file2
+    +++ b/file2
+    @@ -1,1 +1,2 @@
+     foo
+    +bar
+    "###);
+}
+
+#[test]
+fn test_interdiff_paths() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    std::fs::write(repo_path.join("file1"), "foo\n").unwrap();
+    std::fs::write(repo_path.join("file2"), "foo\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["new"]);
+    std::fs::write(repo_path.join("file1"), "bar\n").unwrap();
+    std::fs::write(repo_path.join("file2"), "bar\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["branch", "create", "left"]);
+
+    test_env.jj_cmd_success(&repo_path, &["checkout", "root"]);
+    std::fs::write(repo_path.join("file1"), "foo\n").unwrap();
+    std::fs::write(repo_path.join("file2"), "foo\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["new"]);
+    std::fs::write(repo_path.join("file1"), "baz\n").unwrap();
+    std::fs::write(repo_path.join("file2"), "baz\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["branch", "create", "right"]);
+
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &["interdiff", "--from", "left", "--to", "right", "file1"],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    Modified regular file file1:
+       1    1: barbaz
+    "###);
+
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &[
+            "interdiff",
+            "--from",
+            "left",
+            "--to",
+            "right",
+            "file1",
+            "file2",
+        ],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    Modified regular file file1:
+       1    1: barbaz
+    Modified regular file file2:
+       1    1: barbaz
+    "###);
+}
+
+#[test]
+fn test_interdiff_conflicting() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    std::fs::write(repo_path.join("file"), "foo\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["new"]);
+    std::fs::write(repo_path.join("file"), "bar\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["branch", "create", "left"]);
+
+    test_env.jj_cmd_success(&repo_path, &["checkout", "root"]);
+    std::fs::write(repo_path.join("file"), "abc\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["new"]);
+    std::fs::write(repo_path.join("file"), "def\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["branch", "create", "right"]);
+
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &["interdiff", "--from", "left", "--to", "right", "--git"],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    diff --git a/file b/file
+    index f845ab93f0...24c5735c3e 100644
+    --- a/file
+    +++ b/file
+    @@ -1,8 +1,1 @@
+    -<<<<<<<
+    --------
+    -+++++++
+    --foo
+    -+abc
+    -+++++++
+    -bar
+    ->>>>>>>
+    +def
+    "###);
+}