Thanks!

Pull request overview

This PR aligns @babel/code-frame column handling with Babel AST locations by treating columns as 0-based, and updates internal Babel callers/tests to remove prior + 1 compensations.

Changes:

• Update @babel/code-frame marker calculations to interpret column as 0-based (including allowing column 0 as a valid value).
• Remove loc.column + 1 adjustments in @babel/core and @babel/traverse call sites.
• Update and extend @babel/code-frame tests to use 0-based columns (including new coverage for column 0).

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

packages/babel-code-frame/src/common.ts:65

• getMarkerLines now uses column: null as a sentinel and tests pass column: null, but the exported Location/NodeLocation types still require column: number. This makes the public TS types inconsistent with the runtime API and forces @ts-expect-error workarounds. Consider updating Location so column is optional or number | null (and similarly for loc.end) so consumers can pass column 0 and also omit columns without type casts.

  const startLoc: Location = {
    // @ts-expect-error default value
    column: null,
    // @ts-expect-error default value
    line: -1,
    ...loc.start,
  };

packages/babel-code-frame/src/common.ts:106

• In the multi-line case, middle-line marker lengths are computed using source[lineNumber - i].length. Since lineNumber is startLine + i, lineNumber - i always equals startLine, so for spans of more than 3 lines every middle line will incorrectly use the first line’s length. This should use the current line’s length (e.g. the same indexing approach as the first-line branch) so markers cover the full middle line correctly.

      } else {
        const sourceLength = source[lineNumber - i].length;

        markerLines[lineNumber] = [0, sourceLength];
      }

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Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

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Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated no new comments.

packages/babel-code-frame/src/common.ts:65

• getMarkerLines now uses column: null as the sentinel for “no column”, and tests/usage in this repo pass column: null, but the exported Location/NodeLocation types still require column: number. This forces @ts-expect-error internally and means TS consumers can’t represent the supported null/omitted-column cases without casting. Consider updating the public types (e.g., column?: number | null) so the runtime API and typings stay in sync, and so column 0 remains a valid numeric position.

  const startLoc: Location = {
    // @ts-expect-error default value
    column: null,
    // @ts-expect-error default value
    line: -1,
    ...loc.start,
  };

packages/babel-code-frame/src/common.ts:117

• In the single-line range case, markerLines[startLine] = [startColumn, endColumn - startColumn] will produce NaN (and later break marker rendering) if either startColumn or endColumn is null/undefined. Since this PR explicitly introduces null as a valid sentinel for missing columns, it would be safer to guard here (e.g., treat missing columns as “no column”/whole-line highlight, or normalize missing startColumn to 0 when endColumn is provided).

    if (startColumn === endColumn) {
      if (startColumn != null) {
        markerLines[startLine] = [startColumn, 0];
      } else {
        markerLines[startLine] = true;
      }
    } else {
      markerLines[startLine] = [startColumn, endColumn - startColumn];
    }

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Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated no new comments.

packages/babel-code-frame/src/common.ts:66

• getMarkerLines now relies on column: null as the sentinel to represent “no column” (and the tests also pass column: null), but the TypeScript Location/NodeLocation types still declare column: number, forcing @ts-expect-error here. This leaks into the public codeFrameColumns signature and makes it hard for TS consumers to express “no column” or column: null without casts. Consider updating the types (e.g., column?: number | null) so the implementation and public API are type-safe and you can drop the @ts-expect-error defaults.

  const startLoc: Location = {
    // @ts-expect-error default value
    column: null,
    // @ts-expect-error default value
    line: -1,
    ...loc.start,
  };
  const endLoc: Location = {

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Thank you. The changes now look good to me. Could you open a docs PR to babel/website?