[go_router] Support nested parentheses, groups, and lookaround assertions in path parameters by MaximeRougieux · Pull Request #12571 · flutter/packages

MaximeRougieux · 2026-08-24T13:43:27Z

Fixes [go_router] path parameters regex can't use grouping flutter#117307
Fixes an issue that prevented developers to use all kinds of groups in regexp patterns

Example:
/tags/:slug((?!politics|economy)[^/]+) should match /tags/culture and not match /tags/politics, but the current behavior is that the internal parenthesis are unhandled and the pattern is then used literally :

/tags/flutter -> No match
/tags/politics -> No match
/tags/flutter((?!politics|economy))[^/]+) -> Match, slug="flutter"

Disclosure: I did the investigation and fix using AI, which i carefully reviewed and tried to improve as much as I could according to the AI contribution guidelines. I think it's still better to mention it

A few things to note:

Not a big fan of the "string-scanner" to find the closing parenthesis, but this is unachievable with a regex and needed for the fix to work as expected, and it's tested
You might be wondering why the _escapeGroup function is completely gone (and why it was there in the first place if we can just remove it like that). The AI retraces this to when the repository transitioned from using the path_to_regexp package to having the functions in the codebase. This package seems to be using positional group matching, whereas go_router relies on named group matching, so escaping characters like :,- or ! is unnecessary as they can't disrupt the matching from working as expected.

Pre-Review Checklist

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Code Review

This pull request refactors path parameter parsing in go_router by replacing the _parameterRegExp regular expression with a custom scanner (_pathParametersOf and _closingParenIndex) to correctly handle nested parentheses, escaped characters, and character classes within parameter constraints. It introduces a _PathParameter class and updates patternToRegExp and patternToPath to use the new scanner. Unit tests are added to verify the parsing of nested groups, group constructs, and parentheses in character classes. There are no review comments, and I have no feedback to provide.

Piinks

Hey @MaximeRougieux thanks for contributing! One required step before we can move this forward: go_router uses the batched release process. Please add a pending changelog entry under packages/go_router/pending_changelogs/

MaximeRougieux · 2026-08-28T12:44:04Z

Hi @Piinks, I added the pending changelog, do you want me to squash it with the other commit or is it fine like that?

Piinks · 2026-09-02T21:00:01Z

Hi @Piinks, I added the pending changelog, do you want me to squash it with the other commit or is it fine like that?

No it's fine. Everything gets squashed when merged

Piinks

Thanks for working on this @MaximeRougieux!

I noticed a couple things to address:

The 4 tests added in path_utils_test.dart cover non-capturing groups (?: and lookaheads (?!, but none test an actual capturing group with alternation like (FOO|BAR) or the reproduction pattern from #117307 (r'/details/:id((FOO|BAR)[0-9a-zA-Z]{10})'). Please add a test for this in test/path_utils_test.dart.
The PR title mentions "capturing groups like (?!, (?: and (?=", but (?: is explicitly non-capturing and (?!/(?= are zero-width lookaround assertions. Could you update the PR title to:
[go_router] Support nested parentheses, groups, and lookaround assertions in path parameters
- In the description example /tags/:slug((?!politics|economy)), lookaheads are zero-width and do not consume characters, so without a trailing segment pattern like [^/]+, it won't match /tags/culture. Updating the example to /tags/:slug((?!politics|economy)[^/]+) will avoid confusion for reviewers and future archaeologists. :)
In packages/go_router/pending_changelogs/fix_lookahead_path_params.yaml, please adjust the entry to follow repo conventions (complete sentence ending in a period, accurate scope):
```
changelog: |
  - Fixes path parameter regex parsing to support nested parentheses, grouping constructs, and lookahead assertions in GoRoute paths.
version: patch
```

I think go_router_builder has a duplicate copy of path_utils.dart that has the same issue; would you like to follow up with an issue/PR to port this fix there as well?

MaximeRougieux · 2026-09-04T08:50:59Z

Hey @Piinks, thanks for the review!
Sure thing, I'll send the PR to go_router_builder after i've fixed everything and i'll reference it here 👌

MaximeRougieux · 2026-09-05T00:07:42Z

@Piinks everything should be good now, let me know if you need anything else on these PR

Piinks

LGTM thank you!

Piinks

It looks like there are some failing checks, can you take a look?

MaximeRougieux · 2026-09-11T12:20:22Z

It looks like there are some failing checks, can you take a look?

The logs are difficult to understand but it seems there was a class MockPlatform extends Mock implements Platform somewhere in the tool's code that triggered a compilation error during the job executions. I couldn't find it in the code so it could have been a temporary failure on main. I rebased just in case, could you start the CI/CD again please?

MaximeRougieux · 2026-09-21T15:56:39Z

@Piinks could you please relaunch the CI regarding this comment please?

Piinks · 2026-09-24T22:44:33Z

Added!

MaximeRougieux · 2026-09-25T16:19:26Z

@Piinks it seems to have failed again on some unrelated ci change 😅 I rebased again, can you try reading the CI/CD label ? Third time will hopefully be the charm

Piinks · 2026-09-25T17:32:31Z

@Piinks it seems to have failed again on some unrelated ci change 😅 I rebased again, can you try reading the CI/CD label ? Third time will hopefully be the charm

Have you tried running the tests locally?

MaximeRougieux · 2026-09-28T13:23:56Z

@Piinks it seems to have failed again on some unrelated ci change 😅 I rebased again, can you try reading the CI/CD label ? Third time will hopefully be the charm

Have you tried running the tests locally?

Yes, if you refer to go_router local tests, and to be clear they did not fail on this PR, the failing check was ci.yaml validation with a log i don't remember (and i can't find it in the check history).

It seemed like an unrelated failure, I assume rerunning the CI will work (unless it hits another issue of the same kind)

MaximeRougieux · 2026-10-12T14:31:01Z

@Piinks it seems everything is finally passing here, thanks for your help!

Piinks

LGTM thank you!

MaximeRougieux · 2026-10-22T09:13:25Z

Hi @elliette! Could you have a look on this when you have time please? Thanks! 😇

elliette

Looks good! One small request - it looks like the documentation at

packages/packages/go_router/lib/src/route.dart

Lines 373 to 374 in 6c3361d

    
             /// The regular expression is interpreted as a Dart [RegExp] pattern and must 
        
             /// not contain nested parentheses.

is now out-of-date - do you mind updating it to remove the line about not supporting nested parentheses? Thanks!

… (?: and (?=

…gExp

MaximeRougieux · 2026-10-26T14:40:24Z

Hi @elliette, thanks for the review!
I updated the doc comment and rebased the branch (no conflicts and the test suite passes locally), it should be good after another CI/CD run 🙂

github-actions Bot added p: go_router triage-framework Should be looked at in framework triage labels Aug 24, 2026

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MaximeRougieux mentioned this pull request Aug 24, 2026

[go_router] path parameters regex can't use grouping flutter/flutter#117307

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MaximeRougieux changed the title ~~[go_router] Support capturing groups in path pattern regexp like (?!, (?: and (?=~~ [go_router] Support nested parentheses, groups, and lookaround assertions in path parameters Sep 4, 2026

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Piinks added the CICD Run CI/CD label Sep 10, 2026

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MaximeRougieux force-pushed the fix/go-router-lookahead-path-params branch from d695165 to 7ce8c1c Compare September 11, 2026 12:13

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Piinks added the CICD Run CI/CD label Sep 24, 2026

MaximeRougieux force-pushed the fix/go-router-lookahead-path-params branch from 7ce8c1c to 131f1a6 Compare September 25, 2026 16:17

flutter-dashboard Bot removed the CICD Run CI/CD label Sep 25, 2026

MaximeRougieux force-pushed the fix/go-router-lookahead-path-params branch from 131f1a6 to 8b8ff6e Compare September 28, 2026 13:56

Piinks added the CICD Run CI/CD label Sep 28, 2026

Piinks approved these changes Oct 12, 2026

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Piinks requested a review from elliette October 12, 2026 19:25

elliette approved these changes Oct 22, 2026

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MaximeRougieux added 5 commits October 26, 2026 14:45

[go_router] Support capturing groups in path pattern regexp like (?!,…

73a1646

… (?: and (?=

[go_router] Add changelog entry for path param regexp fix

07a4de9

[go_router] Add a test for capturing group alternation in patternToRe…

9652c82

…gExp

[go_router] Reword changelog

9b92431

[go_router] Fix doc comment on GoRoute.path

2a12b0b

MaximeRougieux force-pushed the fix/go-router-lookahead-path-params branch from 8b8ff6e to 2a12b0b Compare October 26, 2026 14:37

flutter-dashboard Bot removed the CICD Run CI/CD label Oct 26, 2026

elliette added CICD Run CI/CD autosubmit Merge PR when tree becomes green via auto submit App labels Oct 30, 2026

auto-submit Bot merged commit c81561e into flutter:main Oct 30, 2026
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engine-flutter-autoroll mentioned this pull request Nov 2, 2026

Roll Packages from 3742a4eecd6b to 3f34a6f7a79b (8 revisions) flutter/flutter#195795

Merged

	/// The regular expression is interpreted as a Dart [RegExp] pattern and must
	/// not contain nested parentheses.

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