refactor(tasks): improve terminal diff output with context lines

crates/oxc_formatter/Cargo.toml

@@ -37,6 +37,7 @@ unicode-width = { workspace = true }
 
 [dev-dependencies]
 insta = { workspace = true }
+oxc_tasks_common = { path = "../../tasks/common" }
 pico-args = { workspace = true }
 serde_json = { workspace = true }
 serde = { workspace = true, features = ["derive"] }

crates/oxc_formatter/examples/formatter.rs

@@ -9,6 +9,7 @@
 //! ```bash
 //! cargo run -p oxc_formatter --example formatter [filename]
 //! cargo run -p oxc_formatter --example formatter -- --no-semi [filename]
+//! cargo run -p oxc_formatter --example formatter -- --diff [filename]
 //! ```
 
 use std::{fs, path::Path};
@@ -19,13 +20,15 @@ use oxc_formatter::{
 };
 use oxc_parser::Parser;
 use oxc_span::SourceType;
+use oxc_tasks_common::print_diff_in_terminal;
 use pico_args::Arguments;
 
 /// Format a JavaScript or TypeScript file
 fn main() -> Result<(), String> {
     let mut args = Arguments::from_env();
     let no_semi = args.contains("--no-semi");
     let show_ir = args.contains("--ir");
+    let show_diff = args.contains("--diff");
     let print_width = args.opt_value_from_str::<&'static str, u16>("--print-width").unwrap_or(None);
     let name = args.free_from_str().unwrap_or_else(|_| "test.js".to_string());
 
@@ -68,9 +71,17 @@ fn main() -> Result<(), String> {
         println!("--- End IR ---\n");
     }
 
-    println!("--- Formatted Code ---");
     let code = formatted.print().map_err(|e| e.to_string())?.into_code();
-    println!("{code}");
-    println!("--- End Formatted Code ---");
+
+    if show_diff {
+        println!("--- Diff ---");
+        print_diff_in_terminal(&source_text, &code);
+        println!("--- End Diff ---");
+    } else {
+        println!("--- Formatted Code ---");
+        println!("{code}");
+        println!("--- End Formatted Code ---");
+    }
+
     Ok(())
 }

crates/oxc_transformer_plugins/src/module_runner_transform.rs

@@ -857,7 +857,7 @@ mod test {
     use oxc_parser::Parser;
     use oxc_semantic::SemanticBuilder;
     use oxc_span::SourceType;
-    use oxc_tasks_common::print_diff_in_terminal;
+    use oxc_tasks_common::print_text_diff;
     use oxc_transformer::{JsxRuntime, TransformOptions, Transformer};
 
     use super::ModuleRunnerTransform;
@@ -921,7 +921,7 @@ mod test {
         let result = transform(source_text, false).unwrap().code;
         if result != expected {
             let diff = TextDiff::from_lines(&expected, &result);
-            print_diff_in_terminal(&diff);
+            print_text_diff(&diff);
             panic!("Expected code does not match the result");
         }
     }
@@ -932,7 +932,7 @@ mod test {
         let result = transform(source_text, true).unwrap().code;
         if result != expected {
             let diff = TextDiff::from_lines(&expected, &result);
-            print_diff_in_terminal(&diff);
+            print_text_diff(&diff);
             panic!("Expected code does not match the result");
         }
     }
@@ -944,7 +944,7 @@ mod test {
             transform(source_text, false).unwrap();
         if code != expected {
             let diff = TextDiff::from_lines(&expected, &code);
-            print_diff_in_terminal(&diff);
+            print_text_diff(&diff);
             panic!("Expected code does not match the result");
         }
         for dep in deps {

tasks/common/src/diff.rs

@@ -1,19 +1,98 @@
+use std::collections::VecDeque;
+
 use console::Style;
 use similar::{ChangeTag, DiffableStr, TextDiff};
 
-pub fn print_diff_in_terminal<T>(diff: &TextDiff<T>)
-where
-    T: DiffableStr + ?Sized,
-{
-    for op in diff.ops() {
-        for change in diff.iter_changes(op) {
-            let (sign, style) = match change.tag() {
-                ChangeTag::Delete => ("-", Style::new().red()),
-                ChangeTag::Insert => ("+", Style::new().green()),
-                // ChangeTag::Equal => (" ", Style::new()),
-                ChangeTag::Equal => continue,
-            };
-            print!("{}{}", style.apply_to(sign).bold(), style.apply_to(change));
+const CONTEXT_LINES: usize = 3;
+
+/// Prints a colored diff to the terminal with context lines around changes.
+///
+/// Features:
+/// - 3 lines of context above and below each change
+/// - Line numbers in a gutter with `│` separator
+/// - Blank line between adjacent hunks
+/// - `...` separator when lines are skipped between hunks
+/// - Colors: red (`-`) for deletions, green (`+`) for insertions, dim for context
+///
+/// Example output:
+/// ```text
+///     1 │fn main() {
+///     2 │    let x = 1;
+/// -   3 │    let y = 2;
+/// +   3 │    let y = 3;
+///     4 │    println!("{}", x + y);
+///     5 │}
+/// ...
+///    42 │fn other() {
+/// -  43 │    old_code();
+/// +  43 │    new_code();
+///    44 │}
+/// ```
+pub fn print_diff_in_terminal(expected: &str, result: &str) {
+    let diff = TextDiff::from_lines(expected, result);
+    print_text_diff(&diff);
+}
+
+/// Prints an existing `TextDiff` to the terminal.
+/// Use this when you need access to the `TextDiff` for other operations (e.g., `diff.ratio()`).
+pub fn print_text_diff<T: DiffableStr + ?Sized>(diff: &TextDiff<T>) {
+    let mut context_buffer: VecDeque<_> = VecDeque::with_capacity(CONTEXT_LINES);
+    let mut trailing_remaining = 0;
+    let mut has_printed = false;
+    let mut had_gap = false;
+    let mut needs_separator = false;
+
+    for change in diff.ops().iter().flat_map(|op| diff.iter_changes(op)) {
+        let tag = change.tag();
+
+        if tag == ChangeTag::Equal {
+            if trailing_remaining > 0 {
+                print_line(tag, change.new_index(), &change.to_string());
+                trailing_remaining -= 1;
+                needs_separator = true;
+            } else {
+                if context_buffer.len() == CONTEXT_LINES {
+                    context_buffer.pop_front();
+                    had_gap = true;
+                }
+                context_buffer.push_back((tag, change.new_index(), change.to_string()));
+            }
+            continue;
+        }
+
+        if has_printed && (needs_separator || !context_buffer.is_empty()) {
+            if had_gap {
+                println!("{}", Style::new().cyan().apply_to("..."));
+            } else {
+                println!();
+            }
+        }
+
+        while let Some((tag, line_num, content)) = context_buffer.pop_front() {
+            print_line(tag, line_num, &content);
         }
+
+        let line_num =
+            if tag == ChangeTag::Delete { change.old_index() } else { change.new_index() };
+        print_line(tag, line_num, &change.to_string());
+
+        has_printed = true;
+        had_gap = false;
+        needs_separator = false;
+        trailing_remaining = CONTEXT_LINES;
     }
 }
+
+fn print_line(tag: ChangeTag, line_num: Option<usize>, content: &str) {
+    let (sign, style) = match tag {
+        ChangeTag::Delete => ("-", Style::new().red()),
+        ChangeTag::Insert => ("+", Style::new().green()),
+        ChangeTag::Equal => (" ", Style::new().dim()),
+    };
+    print!(
+        "{}{} │{}",
+        style.apply_to(sign).bold(),
+        Style::new().dim().apply_to(format!("{:>4}", line_num.map_or(0, |n| n + 1))),
+        style.apply_to(content)
+    );
+}

tasks/common/src/lib.rs

@@ -6,7 +6,7 @@ mod request;
 mod snapshot;
 mod test_file;
 
-pub use diff::print_diff_in_terminal;
+pub use diff::{print_diff_in_terminal, print_text_diff};
 
 pub use crate::{request::agent, snapshot::Snapshot, test_file::*};
 

tasks/prettier_conformance/src/lib.rs

@@ -301,7 +301,7 @@ impl TestRunner {
                             "{}",
                             path.strip_prefix(fixtures_root()).unwrap().to_string_lossy()
                         );
-                        oxc_tasks_common::print_diff_in_terminal(&diff);
+                        oxc_tasks_common::print_text_diff(&diff);
                     }
                     println!();
                 }

tasks/transform_conformance/src/test_case.rs

@@ -14,7 +14,7 @@ use oxc::{
     span::{SourceType, VALID_EXTENSIONS},
     transformer::{BabelOptions, HelperLoaderMode, TransformOptions},
 };
-use oxc_tasks_common::{normalize_path, print_diff_in_terminal, project_root};
+use oxc_tasks_common::{normalize_path, print_text_diff, project_root};
 
 use crate::{
     TestRunnerOptions,
@@ -363,7 +363,7 @@ impl TestCase {
                     if !passed {
                         let diff = TextDiff::from_lines(&output, actual_errors);
                         println!("Diff:\n");
-                        print_diff_in_terminal(&diff);
+                        print_text_diff(&diff);
                     }
                 }
             } else {
@@ -378,7 +378,7 @@ impl TestCase {
                 if !passed {
                     let diff = TextDiff::from_lines(&output, &self.transformed_code);
                     println!("Diff:\n");
-                    print_diff_in_terminal(&diff);
+                    print_text_diff(&diff);
                 }
             }