diff: Allow setting the default level of context in config.

CHANGELOG.md

@@ -73,6 +73,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
    belonging to a remote. This option can be combined with `--tracked` or
    `--conflicted`.
 
+* Added the config settings `diff.color-words.context` and `diff.git.context` to
+  control the default number of lines of context shown.
+
 ### Fixed bugs
 
 * Error on `trunk()` revset resolution is now handled gracefully.

cli/src/config-schema.json

@@ -288,6 +288,22 @@
                             "type": "integer",
                             "description": "Maximum number of removed/added word alternation to inline",
                             "default": 3
+                        },
+                        "context": {
+                            "type": "integer",
+                            "description": "Number of lines of context to show",
+                            "default": 3
+                        }
+                    }
+                },
+                "git": {
+                    "type": "object",
+                    "description": "Options for git diffs",
+                    "properties": {
+                        "context": {
+                            "type": "integer",
+                            "description": "Number of lines of context to show",
+                            "default": 3
                         }
                     }
                 }

cli/src/config/misc.toml

@@ -8,6 +8,10 @@ unamend = ["unsquash"]
 
 [diff.color-words]
 max-inline-alternation = 3
+context = 3
+
+[diff.git]
+context = 3
 
 [ui]
 # TODO: delete ui.allow-filesets in jj 0.26+

cli/src/diff_util.rs

@@ -184,7 +184,7 @@ fn diff_formats_from_args(
         formats.push(DiffFormat::NameOnly);
     }
     if args.git {
-        let options = UnifiedDiffOptions::from_args(args);
+        let options = UnifiedDiffOptions::from_settings_and_args(settings, args)?;
         formats.push(DiffFormat::Git(Box::new(options)));
     }
     if args.color_words {
@@ -230,7 +230,7 @@ fn default_diff_format(
         "types" => Ok(DiffFormat::Types),
         "name-only" => Ok(DiffFormat::NameOnly),
         "git" => {
-            let options = UnifiedDiffOptions::from_args(args);
+            let options = UnifiedDiffOptions::from_settings_and_args(settings, args)?;
             Ok(DiffFormat::Git(Box::new(options)))
         }
         "color-words" => {
@@ -520,8 +520,11 @@ impl ColorWordsDiffOptions {
                 })?),
             }
         };
+        let context = args
+            .context
+            .map_or_else(|| config.get("diff.color-words.context"), Ok)?;
         Ok(ColorWordsDiffOptions {
-            context: args.context.unwrap_or(DEFAULT_CONTEXT_LINES),
+            context,
             line_diff: LineDiffOptions::from_args(args),
             max_inline_alternation,
         })
@@ -1212,11 +1215,17 @@ pub struct UnifiedDiffOptions {
 }
 
 impl UnifiedDiffOptions {
-    fn from_args(args: &DiffFormatArgs) -> Self {
+    fn from_settings_and_args(
-        UnifiedDiffOptions {
+        settings: &UserSettings,
-            context: args.context.unwrap_or(DEFAULT_CONTEXT_LINES),
+        args: &DiffFormatArgs,
+    ) -> Result<Self, config::ConfigError> {
+        let context = args
+            .context
+            .map_or_else(|| settings.config().get("diff.git.context"), Ok)?;
+        Ok(UnifiedDiffOptions {
+            context,
             line_diff: LineDiffOptions::from_args(args),
-        }
+        })
     }
 }
 

cli/tests/test_diff_command.rs

@@ -1736,6 +1736,100 @@ fn test_diff_skipped_context() {
     "###);
 }
 
+#[test]
+fn test_diff_skipped_context_from_settings_color_words() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "repo"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    test_env.add_config(
+        r#"
+[diff.color-words]
+context = 0
+        "#,
+    );
+
+    std::fs::write(repo_path.join("file1"), "a\nb\nc\nd\ne").unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["describe", "-m", "=== First commit"]);
+
+    test_env.jj_cmd_ok(&repo_path, &["new", "@", "-m", "=== Must show 0 context"]);
+    std::fs::write(repo_path.join("file1"), "a\nb\nC\nd\ne").unwrap();
+
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &["log", "-Tdescription", "-p", "--no-graph", "--reversed"],
+    );
+    insta::assert_snapshot!(stdout, @r#"
+    === First commit
+    Added regular file file1:
+            1: a
+            2: b
+            3: c
+            4: d
+            5: e
+    === Must show 0 context
+    Modified regular file file1:
+        ...
+       3    3: cC
+        ...
+    "#);
+}
+
+#[test]
+fn test_diff_skipped_context_from_settings_git() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "repo"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    test_env.add_config(
+        r#"
+[diff.git]
+context = 0
+        "#,
+    );
+
+    std::fs::write(repo_path.join("file1"), "a\nb\nc\nd\ne").unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["describe", "-m", "=== First commit"]);
+
+    test_env.jj_cmd_ok(&repo_path, &["new", "@", "-m", "=== Must show 0 context"]);
+    std::fs::write(repo_path.join("file1"), "a\nb\nC\nd\ne").unwrap();
+
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &[
+            "log",
+            "-Tdescription",
+            "-p",
+            "--git",
+            "--no-graph",
+            "--reversed",
+        ],
+    );
+    insta::assert_snapshot!(stdout, @r#"
+    === First commit
+    diff --git a/file1 b/file1
+    new file mode 100644
+    index 0000000000..0fec236860
+    --- /dev/null
+    +++ b/file1
+    @@ -1,0 +1,5 @@
+    +a
+    +b
+    +c
+    +d
+    +e
+    \ No newline at end of file
+    === Must show 0 context
+    diff --git a/file1 b/file1
+    index 0fec236860..b7615dae52 100644
+    --- a/file1
+    +++ b/file1
+    @@ -3,1 +3,1 @@
+    -c
+    +C
+    "#);
+}
+
 #[test]
 fn test_diff_skipped_context_nondefault() {
     let test_env = TestEnvironment::default();

docs/config.md

@@ -204,7 +204,8 @@ ui.diff.format = "git"
 
 In color-words diffs, changed words are displayed inline by default. Because
 it's difficult to read a diff line with many removed/added words, there's a
-threshold to switch to traditional separate-line format.
+threshold to switch to traditional separate-line format. You can also change
+the default number of lines of context shown.
 
 * `max-inline-alternation`: Maximum number of removed/added word alternation to
   inline. For example, `<added> ... <added>` sequence has 1 alternation, so the
@@ -219,10 +220,23 @@ threshold to switch to traditional separate-line format.
   The default is `3`.
 
   **This parameter is experimental.** The definition is subject to change.
+* `context`: Number of lines of context to show in the diff. The default is `3`.
 
 ```toml
 [diff.color-words]
 max-inline-alternation = 3
+context = 3
+```
+
+#### Git diff options
+
+In git diffs you can change the default number of lines of context shown.
+
+* `context`: Number of lines of context to show in the diff. The default is `3`.
+
+```toml
+[diff.git]
+context = 3
 ```
 
 ### Generating diffs by external command