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/obslog.rs

@@ -133,7 +133,13 @@ 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,
+                )?;
             }
         }
     }

cli/src/diff_util.rs

@@ -44,6 +44,8 @@ use crate::merge_tools::{self, ExternalMergeTool};
 use crate::text_util;
 use crate::ui::Ui;
 
+const DEFAULT_CONTEXT_LINES: usize = 3;
+
 #[derive(clap::Args, Clone, Debug)]
 #[command(next_help_heading = "Diff Formatting Options")]
 #[command(group(clap::ArgGroup::new("short-format").args(&["summary", "stat", "types"])))]
@@ -73,15 +75,18 @@ pub struct DiffFormatArgs {
     /// Generate diff by external command
     #[arg(long)]
     pub tool: Option<String>,
+    /// Number of lines of context to show.
+    #[arg(long)]
+    context: Option<usize>,
 }
 
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub enum DiffFormat {
     Summary,
     Stat,
     Types,
-    Git,
-    ColorWords,
+    Git(usize),
+    ColorWords(usize),
     Tool(Box<ExternalMergeTool>),
 }
 
@@ -121,8 +126,14 @@ fn diff_formats_from_args(
     let mut formats = [
         (args.summary, DiffFormat::Summary),
         (args.types, DiffFormat::Types),
-        (args.git, DiffFormat::Git),
-        (args.color_words, DiffFormat::ColorWords),
+        (
+            args.git,
+            DiffFormat::Git(args.context.unwrap_or(DEFAULT_CONTEXT_LINES)),
+        ),
+        (
+            args.color_words,
+            DiffFormat::ColorWords(args.context.unwrap_or(DEFAULT_CONTEXT_LINES)),
+        ),
         (args.stat, DiffFormat::Stat),
     ]
     .into_iter()
@@ -158,8 +169,8 @@ fn default_diff_format(settings: &UserSettings) -> Result<DiffFormat, config::Co
     match name.as_ref() {
         "summary" => Ok(DiffFormat::Summary),
         "types" => Ok(DiffFormat::Types),
-        "git" => Ok(DiffFormat::Git),
-        "color-words" => Ok(DiffFormat::ColorWords),
+        "git" => Ok(DiffFormat::Git(DEFAULT_CONTEXT_LINES)),
+        "color-words" => Ok(DiffFormat::ColorWords(DEFAULT_CONTEXT_LINES)),
         "stat" => Ok(DiffFormat::Stat),
         _ => Err(config::ConfigError::Message(format!(
             "invalid diff format: {name}"
@@ -190,13 +201,13 @@ pub fn show_diff(
                 let tree_diff = from_tree.diff_stream(to_tree, matcher);
                 show_types(formatter, workspace_command, tree_diff)?;
             }
-            DiffFormat::Git => {
+            DiffFormat::Git(num_context_lines) => {
                 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 => {
+            DiffFormat::ColorWords(num_context_lines) => {
                 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)?;
@@ -231,10 +242,10 @@ pub fn show_patch(
 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 +440,7 @@ 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 +461,12 @@ 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 +525,7 @@ pub fn show_color_words_diff(
                     show_color_words_diff_hunks(
                         &left_content.contents,
                         &right_content.contents,
+                        num_context_lines,
                         formatter,
                     )?;
                 }
@@ -523,7 +541,12 @@ 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 +717,9 @@ 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 +784,7 @@ 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 +803,7 @@ 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 +828,12 @@ 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 +843,7 @@ 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
 
 
 
@@ -1051,6 +1053,7 @@ Show commit history
   Possible values: `true`, `false`
 
 * `--tool <TOOL>` — Generate diff by external command
+* `--context <CONTEXT>` — Number of lines of context to show
 
 
 
@@ -1221,6 +1224,7 @@ 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
 
 
 
@@ -1592,6 +1596,7 @@ Show commit description and changes in a revision
   Possible values: `true`, `false`
 
 * `--tool <TOOL>` — Generate diff by external command
+* `--context <CONTEXT>` — Number of lines of context to show