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[string_scanner] Extract LineScannerMixin and deduplicate eager scanning logic - #2569

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natebosch merged 9 commits into
dart-lang:mainfrom
amanmaurya92:refactor-string-scanner-mixin
Sep 22, 2026
Merged

natebosch merged 9 commits into
dart-lang:mainfrom
amanmaurya92:refactor-string-scanner-mixin

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Description

This PR refactors LineScanner and EagerSpanScanner in package:string_scanner to share eager line and column tracking implementation via LineScannerMixin:

  • Deduplication: Extracted shared line/column state tracking, position= setter logic, _adjustLineAndColumn, scanChar, readChar, and scan into mixin LineScannerMixin on StringScanner.
  • EagerSpanScanner cleanup: Updated EagerSpanScanner to use with LineScannerMixin, eliminating ~120 lines of duplicate regex-based state tracking and removing the legacy TODO(nweiz) tracking sdk#23770.
  • Zero Breaking Changes: Preserves existing class contracts, behavior, and public API compatibility.
  • Changelog: Added an entry in pkgs/string_scanner/CHANGELOG.md.

Verification

  • dart analyze: 0 issues found.
  • dart test: All 185 tests passed across line_scanner, span_scanner, string_scanner, and error_test.
  • dart format: Code formatted according to Dart style guide.

  • I’ve reviewed the contributor guide and applied the relevant portions to this PR.
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Note: The Dart team is trialing Gemini Code Assist. Don't take its comments as final Dart team feedback. Use the suggestions if they're helpful; otherwise, wait for a human reviewer.

@amanmaurya92
amanmaurya92 requested a review from a team as a code owner August 30, 2026 19:11

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Code Review

This pull request refactors the line and column tracking logic by introducing a new LineScannerMixin on StringScanner. This mixin is then used by both LineScanner and EagerSpanScanner, successfully eliminating a significant amount of duplicated code. The feedback suggests adding a code example to the documentation of the newly introduced public LineScannerMixin to comply with the repository's style guide.

@amanmaurya92 amanmaurya92 changed the title [string_scanner] Extract LineScannerMixin and deduplicate eager scann… [string_scanner] Extract LineScannerMixin and deduplicate eager scanning logic Sep 8, 2026
@amanmaurya92

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@natebosch can you please review this patch? it is code cleanup

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@kevmoo Hi Kevin, could you please approve the workflow runs for CI when you get a chance? Thanks!

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kevmoo commented Sep 12, 2026

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Also introduces a new public mixin type. Which seems nice.

Add `show` clauses to the public library exports to make the public API
surface area explicit.

Move the `EagerSpanScanner` which is not public into `line_spanner.dart`
so the shared mixin can be private. Add a dependency on `package:meeta`
and mark it as `@internal`.

Remove some redundancy in docs.

Remove the changelog since it's no longer user facing.
@natebosch

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Also introduces a new public mixin type. Which seems nice.

I disagree. I think we should hide it (so I did).

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Refactor makes sense. 👍

@natebosch
natebosch merged commit 8ccf8cc into dart-lang:main Sep 22, 2026
22 checks passed
copybara-service Bot pushed a commit to dart-lang/sdk that referenced this pull request Oct 6, 2026
Revisions updated by `dart tools/rev_sdk_deps.dart`.

native (https://github.com/dart-lang/native/compare/f628b26..27f7678):
  27f767827  Mon Sep 28 14:51:28 2026 +0200  Daco Harkes  [hooks_runner] Remove `KernelAssets` and `Target` (dart-lang/native#3703)
  ddc7d6deb  Mon Sep 28 05:40:03 2026 +0200  Jakob Kordež  [ffigen] Skip typedefs to function pointers with unsupported parameter types (dart-lang/native#3694)
  177d283d9  Mon Sep 28 04:30:28 2026 +0200  Jakob Kordež  [ffigen] Generate bindings for C++ enums, structs and unions nested in namespaces and records (dart-lang/native#3644)
  5ee8f67d8  Mon Sep 28 11:39:14 2026 +1000  Liam Appelbe  [objective_c] Clarify block isolate scoping (dart-lang/native#3692)
  25f090116  Fri Sep 25 12:09:12 2026 +1000  Liam Appelbe  [ffigen][jnigen] Deprecate YAML config (dart-lang/native#3654)
  8364413eb  Fri Sep 25 10:09:50 2026 +1000  Liam Appelbe  [jnigen] Document nullability (dart-lang/native#3690)
  e8d518574  Thu Sep 24 18:02:46 2026 +1000  Liam Appelbe  [ffigen] Code snippet-ify ffigen and objective_c (dart-lang/native#3685)
  663385955  Thu Sep 24 03:21:53 2026 +0300  Manar Elhabbal  [ffigen] prevent setting both cpp and objectiveC in ffigenerator (dart-lang/native#3687)
  1cf40952a  Thu Sep 24 09:27:09 2026 +1000  Liam Appelbe  [objective_c] Remove arm64e build hack (dart-lang/native#3680)
  c44550b6e  Wed Sep 23 13:01:33 2026 +0200  Simon Binder  [web_assets] Scaffold package (dart-lang/native#3610)
  57b4bad69  Wed Sep 23 16:21:27 2026 +1000  Liam Appelbe  [swift2objc] Code snippet-ify swift2objc (dart-lang/native#3684)
  5cee1d0be  Wed Sep 23 10:16:29 2026 +0530  Rachit Vikram Singh  [ffigen] Add Input.appendCompilerOptions to append clang args to defaults (`#3630`) (dart-lang/native#3676)
  225a648df  Wed Sep 23 14:37:13 2026 +1000  Liam Appelbe  [jnigen] Code snippet-ify jnigen and co (dart-lang/native#3641)
  2030decf9  Wed Sep 23 13:51:24 2026 +1000  Liam Appelbe  [infra] Move snippets_tool to its own package (dart-lang/native#3683)
  6fa2beea2  Wed Sep 23 12:14:28 2026 +1000  Liam Appelbe  [objective_c] Revert `#3664` (dart-lang/native#3681)
  ed7605f8a  Tue Sep 22 12:03:22 2026 +0530  Sivapriya  [jni] Add deep conversion utils (dart-lang/native#3635)
  8574b7422  Tue Sep 22 08:31:11 2026 +0200  Lukas Klingsbo  [ffigen] Allow package:cli_util 0.5.x and 0.6.x (dart-lang/native#3673)

test (https://github.com/dart-lang/test/compare/9946c95..4f92d53):
  4f92d530  Fri Sep 25 16:46:22 2026 -0700  Nate Bosch  Unskip a test on windows (dart-lang/test#2772)
  7fb84866  Fri Sep 25 14:52:39 2026 -0700  Nate Bosch  Bundle skips at the end of the GitHub reporter (dart-lang/test#2768)
  603e5ec5  Thu Sep 24 14:00:41 2026 -0700  Nate Bosch  Clean up the runner's temporary directories (dart-lang/test#2763)
  4bf04d90  Thu Sep 24 12:41:15 2026 -0700  Nate Bosch  Refactor signal handling in executable.dart (dart-lang/test#2765)
  2c660a84  Tue Sep 22 15:33:34 2026 -0700  Nate Bosch  Regenerate mono_repo output (dart-lang/test#2767)

tools (https://github.com/dart-lang/tools/compare/3614ce0..d87eaf7):
  d87eaf79  Thu Sep 24 08:31:33 2026 -0700  Kevin Moore  fix(benchmark_harness): migrate subprocess spawning to package:cli_util (dart-lang/tools#2585)
  8ccf8ccf  Wed Sep 23 05:09:10 2026 +0530  Aman Maurya  [string_scanner] Extract a mixin for LineScanner and deduplicate eager scanning logic (dart-lang/tools#2569)
  afcdd6d9  Tue Sep 22 15:38:07 2026 +0200  Morgan :)  Document that watch events converge on filesystem state. (dart-lang/tools#2607)
  f2157cbc  Tue Sep 22 04:52:58 2026 +0300  Hasan Armoush  [code_builder] Add null-aware cascades, cascade index, and fluent cascade helpers (dart-lang/tools#2540)

web (https://github.com/dart-lang/web/compare/e5c6c02..ec71a4c):
  ec71a4c  Mon Sep 28 10:07:01 2026 -0700  Kevin Moore  [js_interop_gen] Require `code_builder: ^4.12.0` and update golden headers (dart-lang/web#576)

[email protected]

Change-Id: I766bc5b2b1297e3251990821bb73387ba685e39b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/556320
Commit-Queue: Nate Bosch <[email protected]>
Reviewed-by: Brian Quinlan <[email protected]>
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3 participants