log: add -p/--patch option to show diff along with commit meta data

"log -p | less" is the option I often use with hg/git to find interesting
bits from the changelog, and I think it's also valid with jj. Unlike
"hg log -p --stat", "jj log -p --summary" does not show both diff summary
and patch to reflect the internal structure. This behavoir is arguable and
may be changed later.

The logic of show_patch() is extracted from cmd_show().

CHANGELOG.md

@@ -39,6 +39,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   operation rebased A as A', then B would be automatically rebased on top of
   A'). See #111 for more examples.
 
+* `jj log` now accepts `-p`/`--patch` option.
+
 ## [0.3.3] - 2022-03-16
 
 No changes, only trying to get the automated build to work.

src/commands.rs

@@ -1067,6 +1067,11 @@ struct LogArgs {
     /// documented and is likely to change)
     #[clap(long, short = 'T')]
     template: Option<String>,
+    /// Show patch
+    #[clap(long, short = 'p')]
+    patch: bool,
+    #[clap(flatten)]
+    format: DiffFormat,
 }
 
 /// Show how a change has evolved
@@ -2663,6 +2668,7 @@ fn cmd_log(ui: &mut Ui, command: &CommandHelper, args: &LogArgs) -> Result<(), C
 
     let revset_expression = workspace_command.parse_revset(ui, &args.revisions)?;
     let repo = workspace_command.repo();
+    let workspace_root = workspace_command.workspace_root();
     let workspace_id = workspace_command.workspace_id();
     let checkout_id = repo.view().get_checkout(&workspace_id);
     let revset = revset_expression.evaluate(repo.as_repo_ref(), Some(&workspace_id))?;
@@ -2710,6 +2716,7 @@ fn cmd_log(ui: &mut Ui, command: &CommandHelper, args: &LogArgs) -> Result<(), C
             }
             let mut buffer = vec![];
             let commit_id = index_entry.commit_id();
+            let commit = store.get_commit(&commit_id).unwrap();
             let is_checkout = Some(&commit_id) == checkout_id;
             {
                 let writer = Box::new(&mut buffer);
@@ -2717,7 +2724,6 @@ fn cmd_log(ui: &mut Ui, command: &CommandHelper, args: &LogArgs) -> Result<(), C
                 if is_checkout {
                     formatter.add_label("checkout".to_string())?;
                 }
-                let commit = store.get_commit(&commit_id).unwrap();
                 template.format(&commit, formatter.as_mut())?;
                 if is_checkout {
                     formatter.remove_label()?;
@@ -2726,6 +2732,18 @@ fn cmd_log(ui: &mut Ui, command: &CommandHelper, args: &LogArgs) -> Result<(), C
             if !buffer.ends_with(b"\n") {
                 buffer.push(b'\n');
             }
+            if args.patch {
+                let writer = Box::new(&mut buffer);
+                let mut formatter = ui.new_formatter(writer);
+                show_patch(
+                    ui,
+                    formatter.as_mut(),
+                    repo,
+                    &commit,
+                    workspace_root,
+                    &args.format,
+                )?;
+            }
             let node_symbol = if is_checkout { b"@" } else { b"o" };
             graph.add_node(
                 &index_entry.position(),
@@ -2738,12 +2756,32 @@ fn cmd_log(ui: &mut Ui, command: &CommandHelper, args: &LogArgs) -> Result<(), C
         for index_entry in revset.iter() {
             let commit = store.get_commit(&index_entry.commit_id()).unwrap();
             template.format(&commit, formatter)?;
+            // TODO: should --summary (without --patch) show diff summary as in hg log
+            // --stat?
+            if args.patch {
+                show_patch(ui, formatter, repo, &commit, workspace_root, &args.format)?;
+            }
         }
     }
 
     Ok(())
 }
 
+fn show_patch(
+    ui: &Ui,
+    formatter: &mut dyn Formatter,
+    repo: &Arc<ReadonlyRepo>,
+    commit: &Commit,
+    workspace_root: &Path,
+    args: &DiffFormat,
+) -> Result<(), CommandError> {
+    let parents = commit.parents();
+    let from_tree = merge_commit_trees(repo.as_repo_ref(), &parents);
+    let to_tree = commit.tree();
+    let diff_iterator = from_tree.diff(&to_tree, &EverythingMatcher);
+    show_diff(ui, formatter, repo, workspace_root, args, diff_iterator)
+}
+
 fn cmd_obslog(ui: &mut Ui, command: &CommandHelper, args: &ObslogArgs) -> Result<(), CommandError> {
     let mut workspace_command = command.workspace_helper(ui)?;
 

tests/test_log_command.rs

@@ -0,0 +1,77 @@
+// 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 jujutsu::testutils::TestEnvironment;
+
+#[test]
+fn test_log_with_or_without_diff() {
+    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, &["describe", "-m", "add a file"]);
+    test_env.jj_cmd_success(&repo_path, &["new", "-m", "a new commit"]);
+    std::fs::write(repo_path.join("file1"), "foo\nbar\n").unwrap();
+
+    let stdout = test_env.jj_cmd_success(&repo_path, &["log", "-T", "description"]);
+    insta::assert_snapshot!(stdout, @r###"
+    @ a new commit
+    o add a file
+    o
+    "###);
+
+    let stdout = test_env.jj_cmd_success(&repo_path, &["log", "-T", "description", "-p"]);
+    insta::assert_snapshot!(stdout, @r###"
+    @ a new commit
+    | Modified regular file file1:
+    |    1    1: foo
+    |         2: bar
+    o add a file
+    | Added regular file file1:
+    |         1: foo
+    o 
+    "###);
+
+    let stdout = test_env.jj_cmd_success(&repo_path, &["log", "-T", "description", "--no-graph"]);
+    insta::assert_snapshot!(stdout, @r###"
+    a new commit
+    add a file
+
+    "###);
+
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &["log", "-T", "description", "--no-graph", "-p", "--git"],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    a new commit
+    diff --git a/file1 b/file1
+    index 257cc5642c...3bd1f0e297 100644
+    --- a/file1
+    +++ b/file1
+    @@ -1,1 +1,2 @@
+     foo
+    +bar
+    add a file
+    diff --git a/file1 b/file1
+    new file mode 100644
+    index 0000000000..257cc5642c
+    --- /dev/null
+    +++ b/file1
+    @@ -1,0 +1,1 @@
+    +foo
+
+    "###);
+}