Add --context flag for diffs.

Allows specifying the number of lines of context to show around diffs.
The logic was already in place, just some plumbing was needed.

CHANGELOG.md

@@ -80,6 +80,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * `jj branch list` now supports a `--tracked/-t` option which can be used to
   show tracked branches only. Omits local Git-tracking branches by default.
 
+* `jj diff/interdiff/obslog` now accept a `--context` flag for the number of
+  lines of context to show.
+
 ### Fixed bugs
 
 * On Windows, symlinks in the repo are now materialized as regular files in the

cli/src/commands/diff.rs

@@ -50,6 +50,9 @@ pub(crate) struct DiffArgs {
     paths: Vec<String>,
     #[command(flatten)]
     format: DiffFormatArgs,
+    /// Number of lines of context to show.
+    #[arg(long)]
+    context: Option<usize>,
 }
 
 #[instrument(skip_all)]
@@ -84,6 +87,7 @@ pub(crate) fn cmd_diff(
         &to_tree,
         matcher.as_ref(),
         &diff_formats,
+        args.context.unwrap_or(3),
     )?;
     Ok(())
 }

cli/src/commands/interdiff.rs

@@ -39,6 +39,9 @@ pub(crate) struct InterdiffArgs {
     paths: Vec<String>,
     #[command(flatten)]
     format: DiffFormatArgs,
+    /// Number of lines of context to show.
+    #[arg(long)]
+    context: Option<usize>,
 }
 
 #[instrument(skip_all)]
@@ -64,5 +67,6 @@ pub(crate) fn cmd_interdiff(
         &to_tree,
         matcher.as_ref(),
         &diff_formats,
+        args.context.unwrap_or(3),
     )
 }

cli/src/commands/obslog.rs

@@ -53,6 +53,9 @@ pub(crate) struct ObslogArgs {
     patch: bool,
     #[command(flatten)]
     diff_format: DiffFormatArgs,
+    /// Number of lines of context to show.
+    #[arg(long)]
+    context: Option<usize>,
 }
 
 #[instrument(skip_all)]
@@ -114,6 +117,7 @@ pub(crate) fn cmd_obslog(
                     &workspace_command,
                     &commit,
                     &diff_formats,
+                    args.context,
                 )?;
             }
             let node_symbol = if Some(commit.id()) == wc_commit_id {
@@ -133,7 +137,14 @@ pub(crate) fn cmd_obslog(
             with_content_format
                 .write(formatter, |formatter| template.format(&commit, formatter))?;
             if !diff_formats.is_empty() {
-                show_predecessor_patch(ui, formatter, &workspace_command, &commit, &diff_formats)?;
+                show_predecessor_patch(
+                    ui,
+                    formatter,
+                    &workspace_command,
+                    &commit,
+                    &diff_formats,
+                    args.context,
+                )?;
             }
         }
     }
@@ -147,6 +158,7 @@ fn show_predecessor_patch(
     workspace_command: &WorkspaceCommandHelper,
     commit: &Commit,
     diff_formats: &[DiffFormat],
+    num_context_lines: Option<usize>,
 ) -> Result<(), CommandError> {
     let predecessors = commit.predecessors();
     let predecessor = match predecessors.first() {
@@ -164,5 +176,6 @@ fn show_predecessor_patch(
         &tree,
         &EverythingMatcher,
         diff_formats,
+        num_context_lines.unwrap_or(3),
     )
 }

cli/src/description_util.rs

@@ -110,6 +110,7 @@ pub fn description_template_for_commit(
         to_tree,
         &EverythingMatcher,
         &[DiffFormat::Summary],
+        3,
     )?;
     let mut template_chunks = Vec::new();
     if !intro.is_empty() {

cli/src/diff_util.rs

@@ -175,6 +175,7 @@ pub fn show_diff(
     to_tree: &MergedTree,
     matcher: &dyn Matcher,
     formats: &[DiffFormat],
+    num_context_lines: usize,
 ) -> Result<(), CommandError> {
     for format in formats {
         match format {
@@ -192,11 +193,11 @@ pub fn show_diff(
             }
             DiffFormat::Git => {
                 let tree_diff = from_tree.diff_stream(to_tree, matcher);
-                show_git_diff(formatter, workspace_command, tree_diff)?;
+                show_git_diff(formatter, workspace_command, num_context_lines, tree_diff)?;
             }
             DiffFormat::ColorWords => {
                 let tree_diff = from_tree.diff_stream(to_tree, matcher);
-                show_color_words_diff(formatter, workspace_command, tree_diff)?;
+                show_color_words_diff(formatter, workspace_command, num_context_lines, tree_diff)?;
             }
             DiffFormat::Tool(tool) => {
                 merge_tools::generate_diff(ui, formatter.raw(), from_tree, to_tree, matcher, tool)?;
@@ -225,16 +226,17 @@ pub fn show_patch(
         &to_tree,
         matcher,
         formats,
+        3,
     )
 }
 
 fn show_color_words_diff_hunks(
     left: &[u8],
     right: &[u8],
+    num_context_lines: usize,
     formatter: &mut dyn Formatter,
 ) -> io::Result<()> {
     const SKIPPED_CONTEXT_LINE: &str = "    ...\n";
-    let num_context_lines = 3;
     let mut context = VecDeque::new();
     // Have we printed "..." for any skipped context?
     let mut skipped_context = false;
@@ -429,6 +431,7 @@ fn basic_diff_file_type(value: &MaterializedTreeValue) -> &'static str {
 pub fn show_color_words_diff(
     formatter: &mut dyn Formatter,
     workspace_command: &WorkspaceCommandHelper,
+    num_context_lines: usize,
     tree_diff: TreeDiffStream,
 ) -> Result<(), CommandError> {
     formatter.push_label("diff")?;
@@ -449,7 +452,12 @@ pub fn show_color_words_diff(
                 } else if right_content.is_binary {
                     writeln!(formatter.labeled("binary"), "    (binary)")?;
                 } else {
-                    show_color_words_diff_hunks(&[], &right_content.contents, formatter)?;
+                    show_color_words_diff_hunks(
+                        &[],
+                        &right_content.contents,
+                        num_context_lines,
+                        formatter,
+                    )?;
                 }
             } else if right_value.is_present() {
                 let description = match (&left_value, &right_value) {
@@ -508,6 +516,7 @@ pub fn show_color_words_diff(
                     show_color_words_diff_hunks(
                         &left_content.contents,
                         &right_content.contents,
+                        num_context_lines,
                         formatter,
                     )?;
                 }
@@ -523,7 +532,12 @@ pub fn show_color_words_diff(
                 } else if left_content.is_binary {
                     writeln!(formatter.labeled("binary"), "    (binary)")?;
                 } else {
-                    show_color_words_diff_hunks(&left_content.contents, &[], formatter)?;
+                    show_color_words_diff_hunks(
+                        &left_content.contents,
+                        &[],
+                        num_context_lines,
+                        formatter,
+                    )?;
                 }
             }
         }
@@ -694,8 +708,9 @@ fn show_unified_diff_hunks(
     formatter: &mut dyn Formatter,
     left_content: &[u8],
     right_content: &[u8],
+    num_context_lines: usize,
 ) -> Result<(), CommandError> {
-    for hunk in unified_diff_hunks(left_content, right_content, 3) {
+    for hunk in unified_diff_hunks(left_content, right_content, num_context_lines) {
         writeln!(
             formatter.labeled("hunk_header"),
             "@@ -{},{} +{},{} @@",
@@ -760,6 +775,7 @@ fn materialized_diff_stream<'a>(
 pub fn show_git_diff(
     formatter: &mut dyn Formatter,
     workspace_command: &WorkspaceCommandHelper,
+    num_context_lines: usize,
     tree_diff: TreeDiffStream,
 ) -> Result<(), CommandError> {
     formatter.push_label("diff")?;
@@ -778,7 +794,7 @@ pub fn show_git_diff(
                     writeln!(formatter, "--- /dev/null")?;
                     writeln!(formatter, "+++ b/{path_string}")
                 })?;
-                show_unified_diff_hunks(formatter, &[], &right_part.content)?;
+                show_unified_diff_hunks(formatter, &[], &right_part.content, num_context_lines)?;
             } else if right_value.is_present() {
                 let left_part = git_diff_part(&path, left_value)?;
                 let right_part = git_diff_part(&path, right_value)?;
@@ -803,7 +819,12 @@ pub fn show_git_diff(
                     }
                     Ok(())
                 })?;
-                show_unified_diff_hunks(formatter, &left_part.content, &right_part.content)?;
+                show_unified_diff_hunks(
+                    formatter,
+                    &left_part.content,
+                    &right_part.content,
+                    num_context_lines,
+                )?;
             } else {
                 let left_part = git_diff_part(&path, left_value)?;
                 formatter.with_label("file_header", |formatter| {
@@ -813,7 +834,7 @@ pub fn show_git_diff(
                     writeln!(formatter, "--- a/{path_string}")?;
                     writeln!(formatter, "+++ /dev/null")
                 })?;
-                show_unified_diff_hunks(formatter, &left_part.content, &[])?;
+                show_unified_diff_hunks(formatter, &left_part.content, &[], num_context_lines)?;
             }
         }
         Ok::<(), CommandError>(())

cli/tests/cli-reference@.md.snap

@@ -655,6 +655,7 @@ With the `--from` and/or `--to` options, shows the difference from/to the given
   Possible values: `true`, `false`
 
 * `--tool <TOOL>` — Generate diff by external command
+* `--context <CONTEXT>` — Number of lines of context to show
 
 
 
@@ -1000,6 +1001,7 @@ This excludes changes from other commits by temporarily rebasing `--from` onto `
   Possible values: `true`, `false`
 
 * `--tool <TOOL>` — Generate diff by external command
+* `--context <CONTEXT>` — Number of lines of context to show
 
 
 
@@ -1221,6 +1223,7 @@ Show how a change has evolved as it's been updated, rebased, etc.
   Possible values: `true`, `false`
 
 * `--tool <TOOL>` — Generate diff by external command
+* `--context <CONTEXT>` — Number of lines of context to show