merge_tools: enable :builtin as default diff/merge editor

CHANGELOG.md

@@ -30,6 +30,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   `jj log -T 'description ++ "\0"' --no-graph` to output descriptions only, but
   be able to tell where the boundaries are
 
+* jj now bundles a TUI tool to use as the default diff and merge editors. (The
+  previous default was `meld`.)
+
 ### Fixed bugs
 
 ## [0.9.0] - 2023-09-06

cli/src/diff_util.rs

@@ -35,7 +35,7 @@ use unicode_width::UnicodeWidthStr as _;
 
 use crate::cli_util::{CommandError, WorkspaceCommandHelper};
 use crate::formatter::Formatter;
-use crate::merge_tools::{self, ExternalMergeTool};
+use crate::merge_tools::{self, ExternalMergeTool, MergeTool};
 use crate::text_util;
 use crate::ui::Ui;
 
@@ -124,8 +124,13 @@ fn diff_formats_from_args(
     .collect_vec();
     if let Some(name) = &args.tool {
         let tool = merge_tools::get_tool_config(settings, name)?
-            .unwrap_or_else(|| ExternalMergeTool::with_program(name));
+            .unwrap_or_else(|| MergeTool::External(ExternalMergeTool::with_program(name)));
-        formats.push(DiffFormat::Tool(Box::new(tool)));
+        match tool {
+            MergeTool::Builtin => {}
+            MergeTool::External(tool) => {
+                formats.push(DiffFormat::Tool(Box::new(tool)));
+            }
+        }
     }
     Ok(formats)
 }
@@ -135,8 +140,13 @@ fn default_diff_format(settings: &UserSettings) -> Result<DiffFormat, config::Co
     if let Some(args) = config.get("ui.diff.tool").optional()? {
         // External "tool" overrides the internal "format" option.
         let tool = merge_tools::get_tool_config_from_args(settings, &args)?
-            .unwrap_or_else(|| ExternalMergeTool::with_diff_args(&args));
+            .unwrap_or_else(|| MergeTool::External(ExternalMergeTool::with_diff_args(&args)));
-        return Ok(DiffFormat::Tool(Box::new(tool)));
+        match tool {
+            MergeTool::Builtin => {}
+            MergeTool::External(tool) => {
+                return Ok(DiffFormat::Tool(Box::new(tool)));
+            }
+        }
     }
     let name = if let Some(name) = config.get_string("ui.diff.format").optional()? {
         name

cli/src/merge_tools/mod.rs

@@ -33,6 +33,8 @@ pub use self::external::{generate_diff, ExternalMergeTool};
 use crate::config::CommandNameAndArgs;
 use crate::ui::Ui;
 
+const BUILTIN_EDITOR_NAME: &str = ":builtin";
+
 #[derive(Debug, Error)]
 pub enum DiffEditError {
     #[error(transparent)]
@@ -166,7 +168,7 @@ fn editor_args_from_settings(
     if let Some(args) = settings.config().get(key).optional()? {
         Ok(args)
     } else {
-        let default_editor = "meld";
+        let default_editor = BUILTIN_EDITOR_NAME;
         writeln!(
             ui.hint(),
             "Using default editor '{default_editor}'; you can change this by setting {key}"
@@ -180,7 +182,11 @@ fn editor_args_from_settings(
 pub fn get_tool_config(
     settings: &UserSettings,
     name: &str,
-) -> Result<Option<ExternalMergeTool>, ConfigError> {
+) -> Result<Option<MergeTool>, ConfigError> {
+    if name == BUILTIN_EDITOR_NAME {
+        return Ok(Some(MergeTool::Builtin));
+    }
+
     const TABLE_KEY: &str = "merge-tools";
     let tools_table = settings.config().get_table(TABLE_KEY)?;
     if let Some(v) = tools_table.get(name) {
@@ -193,7 +199,7 @@ pub fn get_tool_config(
         if result.program.is_empty() {
             result.program.clone_from(&name.to_string());
         };
-        Ok(Some(result))
+        Ok(Some(MergeTool::External(result)))
     } else {
         Ok(None)
     }
@@ -204,7 +210,7 @@ pub fn get_tool_config(
 pub fn get_tool_config_from_args(
     settings: &UserSettings,
     args: &CommandNameAndArgs,
-) -> Result<Option<ExternalMergeTool>, ConfigError> {
+) -> Result<Option<MergeTool>, ConfigError> {
     match args {
         CommandNameAndArgs::String(name) => get_tool_config(settings, name),
         CommandNameAndArgs::Vec(_) | CommandNameAndArgs::Structured { .. } => Ok(None),
@@ -217,8 +223,8 @@ fn get_diff_editor_from_settings(
 ) -> Result<MergeTool, ExternalToolError> {
     let args = editor_args_from_settings(ui, settings, "ui.diff-editor")?;
     let editor = get_tool_config_from_args(settings, &args)?
-        .unwrap_or_else(|| ExternalMergeTool::with_edit_args(&args));
+        .unwrap_or_else(|| MergeTool::External(ExternalMergeTool::with_edit_args(&args)));
-    Ok(MergeTool::External(editor))
+    Ok(editor)
 }
 
 fn get_merge_tool_from_settings(
@@ -226,14 +232,15 @@ fn get_merge_tool_from_settings(
     settings: &UserSettings,
 ) -> Result<MergeTool, ExternalToolError> {
     let args = editor_args_from_settings(ui, settings, "ui.merge-editor")?;
-    let editor = get_tool_config_from_args(settings, &args)?
+    let mergetool = get_tool_config_from_args(settings, &args)?
-        .unwrap_or_else(|| ExternalMergeTool::with_merge_args(&args));
+        .unwrap_or_else(|| MergeTool::External(ExternalMergeTool::with_merge_args(&args)));
-    if editor.merge_args.is_empty() {
+    match mergetool {
-        Err(ExternalToolError::MergeArgsNotConfigured {
+        MergeTool::External(mergetool) if mergetool.merge_args.is_empty() => {
-            tool_name: args.to_string(),
+            Err(ExternalToolError::MergeArgsNotConfigured {
-        })
+                tool_name: args.to_string(),
-    } else {
+            })
-        Ok(MergeTool::External(editor))
+        }
+        mergetool => Ok(mergetool),
     }
 }
 
@@ -260,30 +267,7 @@ mod tests {
         };
 
         // Default
-        insta::assert_debug_snapshot!(get("").unwrap(), @r###"
+        insta::assert_debug_snapshot!(get("").unwrap(), @"Builtin");
-        External(
-            ExternalMergeTool {
-                program: "meld",
-                diff_args: [
-                    "$left",
-                    "$right",
-                ],
-                edit_args: [
-                    "$left",
-                    "$right",
-                ],
-                merge_args: [
-                    "$left",
-                    "$base",
-                    "$right",
-                    "-o",
-                    "$output",
-                    "--auto-merge",
-                ],
-                merge_tool_edits_conflict_markers: false,
-            },
-        )
-        "###);
 
         // Just program name, edit_args are filled by default
         insta::assert_debug_snapshot!(get(r#"ui.diff-editor = "my-diff""#).unwrap(), @r###"
@@ -432,30 +416,7 @@ mod tests {
         };
 
         // Default
-        insta::assert_debug_snapshot!(get("").unwrap(), @r###"
+        insta::assert_debug_snapshot!(get("").unwrap(), @"Builtin");
-        External(
-            ExternalMergeTool {
-                program: "meld",
-                diff_args: [
-                    "$left",
-                    "$right",
-                ],
-                edit_args: [
-                    "$left",
-                    "$right",
-                ],
-                merge_args: [
-                    "$left",
-                    "$base",
-                    "$right",
-                    "-o",
-                    "$output",
-                    "--auto-merge",
-                ],
-                merge_tool_edits_conflict_markers: false,
-            },
-        )
-        "###);
 
         // Just program name
         insta::assert_debug_snapshot!(get(r#"ui.merge-editor = "my-merge""#).unwrap_err(), @r###"

docs/config.md

@@ -346,8 +346,9 @@ Obviously, you would only set one line, don't copy them all in!
 
 ## Editing diffs
 
-The `ui.diff-editor` setting affects the tool used for editing diffs (e.g.
+The `ui.diff-editor` setting affects the tool used for editing diffs (e.g.  `jj
-`jj split`, `jj amend -i`). The default is `meld`.
+split`, `jj amend -i`). The default is the special value `:builtin`, which
+launches a TUI tool to edit the diff in your terminal.
 
 `jj` makes the following substitutions:
 
@@ -388,23 +389,6 @@ the directory where the diff editor will be expected to put the result of the
 user's edits. Initially, the contents of `$output` will be the same as the
 contents of `$right`.
 
-### Setting up `scm-diff-editor`
-
-`scm-diff-editor` is a terminal-based diff editor that is part of
-the [git-branchless](https://github.com/arxanas/git-branchless) suite of tools.
-It's a good alternative to Meld, especially if you don't have a graphical
-environment (e.g. when using SSH). To install it:
-
-```shell
-cargo install --git https://github.com/arxanas/git-branchless scm-record --features scm-diff-editor
-```
-
-Then config it as follows:
-
-```toml
-ui.diff-editor = ["scm-diff-editor", "--dir-diff", "$left", "$right"]
-```
-
 ### `JJ-INSTRUCTIONS`
 
 When editing a diff, jj will include a synthetic file called `JJ-INSTRUCTIONS`