fix: improve diagnostic display for syntax errors and large code ranges by fansenze · Pull Request #506 · web-infra-dev/rslint

fansenze · 2026-03-17T02:24:31Z

Summary

Syntax error output: Previously dumped the entire file source text into the error message, making it unreadable. Now renders syntax errors with code snippets (like tsc --pretty), using the same box format as lint rule diagnostics.
Large code range display: Previously showed "Error range is too big. Skipping code block printing." when a diagnostic spanned 13+ lines. Now uses tsc-style folding — shows first 2 lines + .. + last 2 lines, so users always see code context.

Before / After

1. Syntax errors

Before — dumps entire file source into the error string, repeated for each error:

error creating TS program: found 2 syntactic errors. [Expression expected. const x = ;
const y = ;
const z = 1;
 Expression expected. const x = ;
const y = ;
const z = 1;
]

After — each error rendered with TS code, file location, and code snippet:

 TS1109  — [error] Expression expected.
  ╭─┴──────────( index.ts:1:11 )─────
  │ 1 │  const x = ;
  │ 2 │  const y = ;
  ╰────────────────────────────────

 TS1109  — [error] Expression expected.
  ╭─┴──────────( index.ts:2:11 )─────
  │ 1 │  const x = ;
  │ 2 │  const y = ;
  │ 3 │  const z = 1;
  ╰────────────────────────────────

2. Large code range (13+ lines)

Before — code snippet skipped entirely:

 max-lines-per-function  — [error] Function has too many lines (22).
  ╭─┴──────────( index.ts:1:1 )─────
  │  Error range is too big. Skipping code block printing.
  ╰────────────────────────────────

After — first 2 + .. + last 2 lines (tsc-style folding):

 max-lines-per-function  — [error] Function has too many lines (22).
  ╭─┴──────────( index.ts:1:1 )─────
  │  1 │  function reallyLongFunction() {
  │  2 │    const step1 = performStep(1);
  │ .. │
  │ 23 │  }
  │ 24 │
  ╰────────────────────────────────

3. Short code range (unchanged, for comparison)

 no-unused-vars  — [warn] 'unused' is defined but never used
  ╭─┴──────────( index.ts:2:7 )─────
  │ 1 │  const a = 1;
  │ 2 │  const unused = 42;
  │ 3 │  const b = 2;
  ╰────────────────────────────────

Codebox under 5 lines is displayed in full — same behavior as before.

Checklist

Tests updated (or not required).
Documentation updated (or not required).

gemini-code-assist · 2026-03-17T02:24:46Z

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the user experience for diagnostic messages by improving how syntax errors and large code ranges are displayed. The changes aim to provide clearer, more concise, and actionable feedback, aligning the output format with familiar tools like TypeScript's compiler for better readability and debugging.

Highlights

Improved Syntax Error Display: Syntax error messages now use a tsc-like file(line,col): error TS{code}: message format, replacing the previous unreadable full file source dump.
Enhanced Large Code Range Display: Diagnostic messages for large code ranges (5+ lines) now employ tsc-style folding, showing the first two and last two lines with an ellipsis in between, instead of a "Error range is too big" message.

Changelog

cmd/rslint/cmd.go
- Removed the fixed-size buffer and "Error range is too big" message for diagnostic code blocks.
- Implemented a dynamic line buffer and a folding mechanism for diagnostic code blocks that span 5 or more lines, displaying the first two, an ellipsis, and the last two lines.
cmd/rslint/cmd_test.go
- Imported the fmt package.
- Introduced createTestDiagnostic and renderDiagnostic helper functions for easier diagnostic testing.
- Added new test suites (TestPrintDiagnosticFold, TestPrintDiagnosticSingleLine, TestPrintDiagnosticEdgeCases, TestSyntaxErrorFormat, TestSyntaxErrorFormatMultiple) to validate the new diagnostic display and folding logic, as well as the improved syntax error formatting.
internal/utils/create_program.go
- Imported the strings and scanner packages.
- Refactored the syntactic diagnostic error reporting to format messages in a file(line,col): error TS{code}: message style, improving clarity and consistency.

Activity

The author has marked "Tests updated (or not required)." as complete, indicating that new tests were added to cover the changes.

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Code Review

This pull request significantly improves the diagnostic display, making syntax errors more readable and handling large code ranges gracefully with folding. The changes align well with the goal of providing a cleaner, tsc-like output. The implementation is solid, and the new tests are comprehensive. However, I've identified a critical bug in the code folding logic that results in incorrect output and highlighting. I've provided a detailed comment with a suggested fix to address this.

cmd/rslint/cmd.go

- Syntax errors: render with code snippets like tsc --pretty, using the same box format as lint rule diagnostics. Introduce SyntacticError type to carry raw ast.Diagnostic for rich rendering in the CLI. - Large code ranges: replace fixed-size array (13) and "Error range is too big" fallback with dynamic allocation and tsc-style folding (first 2 lines + ... + last 2 lines).

github-actions bot added the release: bug fix label Mar 17, 2026

gemini-code-assist bot reviewed Mar 17, 2026

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cmd/rslint/cmd.go Outdated Show resolved Hide resolved

fansenze force-pushed the fix/diagnostic-display-20260316 branch from 5f990fb to 6cbcf93 Compare March 17, 2026 03:12

fansenze requested a review from hardfist March 17, 2026 03:23

fansenze force-pushed the fix/diagnostic-display-20260316 branch from 6cbcf93 to 6a91c8a Compare March 17, 2026 05:09

hardfist approved these changes Mar 17, 2026

View reviewed changes

fansenze merged commit 2d75a6f into main Mar 17, 2026
14 checks passed

fansenze deleted the fix/diagnostic-display-20260316 branch March 17, 2026 07:25

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fix: improve diagnostic display for syntax errors and large code ranges#506

fix: improve diagnostic display for syntax errors and large code ranges#506
fansenze merged 1 commit intomainfrom
fix/diagnostic-display-20260316

fansenze commented Mar 17, 2026 •

edited

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fansenze commented Mar 17, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Summary

Before / After

1. Syntax errors

2. Large code range (13+ lines)

3. Short code range (unchanged, for comparison)

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gemini-code-assist bot commented Mar 17, 2026

Summary of Changes

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fansenze commented Mar 17, 2026 •

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