Fix parsing of keys containing literal [] inside bracket groups

[techouse]

Problem

qs splits bracket groups with a regex that forbids [] inside a group:

var child = /(\[[^[][^\]]*])/g; // original: /(\[[^[\]]*])/g

This causes keys like search[withbracket[]] to split into "[withbracket]", then "[]", leaving the inner [] detached from the literal segment. Downstream, it can no longer be treated as a single literal key.

Repro

// expected:
qs.parse('search[withbracket[]]=foobar');
// => { search: { 'withbracket[]': 'foobar' } }

// actual (today):
// inner [] is split out, so the key can’t be treated as one literal segment

Fix approach

Backport splitKeyIntoSegments from qs_dart and replace the regex child matcher with a balanced bracket splitter that treats [] inside a bracket group as literal content (only outer [] act as array push). This preserves withbracket[] as a single segment.

Notes

• Does not change existing semantics for [] at the outermost level (array push).
• Honors existing options: allowDots, depth, strictDepth, allowPrototypes, etc.

Test snippet

t.test('parses keys with literal [] inside a bracket group (#493)', function (st) {
    // A bracket pair inside a bracket group should be treated literally as part of the key
    st.deepEqual(
        qs.parse('search[withbracket[]]=foobar'),
        { search: { 'withbracket[]': 'foobar' } },
        'treats inner [] literally when inside a bracket group'
    );

    // Single-level variant
    st.deepEqual(
        qs.parse('a[b[]]=c'),
        { a: { 'b[]': 'c' } },
        'keeps "b[]" as a literal key'
    );

    // Nested with an array push on the outer level
    st.deepEqual(
        qs.parse('list[][x[]]=y'),
        { list: [{ 'x[]': 'y' }] },
        'preserves inner [] while still treating outer [] as array push'
    );

    // Multiple nested bracket pairs: inner [] remains literal as part of the key
    st.deepEqual(
        qs.parse('a[b[c[]]]=d'),
        { a: { 'b[c[]]': 'd' } },
        'treats "b[c[]]" as a literal key inside the bracket group'
    );

    // Depth limits with literal brackets: preserve inner [] while limiting bracket-group parsing
    st.deepEqual(
        qs.parse('a[b[c[]]][d]=e', { depth: 1 }),
        { a: { 'b[c[]]': { '[d]': 'e' } } },
        'respects depth: 1 and preserves literal inner [] in the parsed key'
    );

    // Unterminated inner bracket group is wrapped as a literal remainder segment
    st.deepEqual(
        qs.parse('a[[]b=c'),
        { a: { '[[]b': 'c' } },
        'handles unterminated inner bracket groups without throwing'
    );

    st.end();
});

---

Fixes #493

[techouse]

@ljharb, it seems some of the tests fail because the runners are unable to download a specific Node version, i.e.

curl: (56) OpenSSL SSL_read: Connection reset by peer, errno 104
download from https://nodejs.org/dist/v5.3.0/node-v5.3.0-linux-x64.tar.xz failed
grep: /home/runner/.nvm/.cache/bin/node-v5.3.0-linux-x64/node-v5.3.0-linux-x64.tar.xz: No such file or directory

curl: (92) HTTP/2 stream 0 was not closed cleanly: INTERNAL_ERROR (err 2)
download from https://nodejs.org/dist/v13.13.0/node-v13.13.0-linux-x64.tar.xz failed
grep: /home/runner/.nvm/.cache/bin/node-v13.13.0-linux-x64/node-v13.13.0-linux-x64.tar.xz: No such file or directory

[techouse]

@ljharb, have you had a chance to look at this yet? 😊

[Copilot]

Pull Request Overview

This PR implements bracket balancing in the query string parser to correctly handle literal [] characters inside bracket groups. Previously, bracket pairs within a bracket group could cause parsing issues. The new implementation uses a level counter to properly balance opening and closing brackets, treating inner bracket pairs as literal parts of keys.

Key Changes

• Refactored parseKeys function to extract bracket parsing logic into a new splitKeyIntoSegments helper function
• Implemented bracket-balancing algorithm that uses a level counter to track nested brackets
• Added test cases validating that [] inside bracket groups are treated as literal key characters

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
lib/parse.js	Replaced regex-based bracket parsing with bracket-balancing algorithm that correctly handles nested [] within bracket groups
test/parse.js	Added test case covering three scenarios: basic nested brackets, single-level variant, and array push with nested brackets

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[ljharb]

This is pretty hard to review. Could you perhaps make a refactoring commit that makes the majority of the changes, and then a fix commit with the test and the thing that makes the test pass?

[techouse]

This is pretty hard to review. Could you perhaps make a refactoring commit that makes the majority of the changes, and then a fix commit with the test and the thing that makes the test pass?

@ljharb done. 😇

I have split the parse key processing into a refactor-only commit followed by the nested-bracket fix plus its regression tests so it now has the structure you have asked for.

[Copilot]

Pull Request Overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

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[techouse]

Thanks for the review, @ljharb 😇

I have pushed updates to align with main semantics and addressed each thread below:

• restored depth <= 0 behavior (including prototype guard) in splitKeyIntoSegments
• switched strict depth checks to options.strictDepth === true
• removed the remainder !== '.' special-case and simplified tail handling
• applied the naming/style suggestions

I have also added regression coverage for depth-0 behavior (allowDots normalization and prototype guarding).

The merge conflicts were quite the challenge (this PR is from August!), so I hope I didn't mess up somewhere 😅

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

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[Copilot]

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

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