[StringUtilities] Fix unicode trimming using Intl.Segmenter [devtools/devtools-frontend : main]

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Connor Clark (Gerrit)

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Dec 18, 2025, 6:58:37 PM (3 days ago) Dec 18

to Paul Irish, Devtools-frontend LUCI CQ, devtools-rev...@chromium.org

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Paul Irish (Gerrit)

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Dec 19, 2025, 8:25:07 PM (2 days ago) Dec 19

to Connor Clark, Devtools-frontend LUCI CQ, devtools-rev...@chromium.org

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File-level comment, Patchset 2 (Latest):

Paul Irish . resolved

played around with this. tried some variants. but in the end what you got here is solid. Nice work

File front_end/core/platform/StringUtilities.test.ts

Line 350, Patchset 2 (Latest):

  it('trimEndWithMaxLength', () => {
    const {trimEndWithMaxLength} = Platform.StringUtilities;

    assert.strictEqual(trimEndWithMaxLength('aaa', 30), 'aaa');
    assert.strictEqual(trimEndWithMaxLength('aaa', 3), 'aaa');
    assert.strictEqual(trimEndWithMaxLength('aaa', 2), 'a…');
    assert.strictEqual(trimEndWithMaxLength('aaa🥳', 4), 'aaa🥳');
    assert.strictEqual(trimEndWithMaxLength('aaa🥳', 3), 'aa…');
    assert.strictEqual(trimEndWithMaxLength('aaa👨‍👨‍👦‍👦', 4), 'aaa👨‍👨‍👦‍👦');
    assert.strictEqual(trimEndWithMaxLength('aaa👨‍👨‍👦‍👦', 3), 'aa…');
    assert.strictEqual(trimEndWithMaxLength('देवनागरी', 5), 'देवनागरी');
    assert.strictEqual(trimEndWithMaxLength('देवनागरी', 4), 'देवना…');

    assert.strictEqual(trimEndWithMaxLength('aaa', 3, ''), 'aaa');
    assert.strictEqual(trimEndWithMaxLength('aaa', 2, ''), 'aa');
    assert.strictEqual(trimEndWithMaxLength('aaa', 1), '…');
    assert.strictEqual(trimEndWithMaxLength('aaa', 0), '…');

    assert.strictEqual(trimEndWithMaxLength('aaaaa', 5, '...'), 'aaaaa');
    assert.strictEqual(trimEndWithMaxLength('aaaaa', 4, '...'), 'a...');
    assert.strictEqual(trimEndWithMaxLength('aaaaa', 3, '...'), '...');
    assert.strictEqual(trimEndWithMaxLength('aaaaa', 1, '...'), '...');

    // NFD.
    assert.strictEqual(trimEndWithMaxLength('caf\u0065\u0301', 4), 'café');
    assert.strictEqual(trimEndWithMaxLength('caf\u0065\u0301', 3), 'ca…');
  });

Paul Irish . unresolved

i was fucking around and got explored some edge cases.. it resulted in this more comprehensive test suite.

and your fn passes all. :)


```suggestion
  describe('trimEndWithMaxLength', () => {
    const {trimEndWithMaxLength} = Platform.StringUtilities;

    it('returns the original string if it fits within maxLength', () => {
      assert.strictEqual(trimEndWithMaxLength('abc', 3), 'abc');
      assert.strictEqual(trimEndWithMaxLength('abc', 10), 'abc');
      assert.strictEqual(trimEndWithMaxLength('', 5), '');
    });

    it('trims the string and adds an ellipsis if it exceeds maxLength', () => {
      assert.strictEqual(trimEndWithMaxLength('abc', 2), 'a…');
      assert.strictEqual(trimEndWithMaxLength('abcdef', 5), 'abcd…');
    });

    it('returns just the ellipsis if maxLength is small', () => {
      assert.strictEqual(trimEndWithMaxLength('abc', 1), '…');
      assert.strictEqual(trimEndWithMaxLength('abc', 0), '…');
    });

    it('returns the empty string if the input is empty and maxLength is 0', () => {
      // Logic check:
      // str.length (0) <= maxLength (0) -> returns str ("")
      assert.strictEqual(trimEndWithMaxLength('', 0), '');
    });

    it('handles unicode surrogate pairs and emojis correctly', () => {
      assert.strictEqual(trimEndWithMaxLength('aaa🥳', 4), 'aaa🥳');
      assert.strictEqual(trimEndWithMaxLength('aaa🥳', 3), 'aa…');
      assert.strictEqual(trimEndWithMaxLength('aaa👨‍👨‍👦‍👦', 4), 'aaa👨‍👨‍👦‍👦');
      assert.strictEqual(trimEndWithMaxLength('aaa👨‍👨‍👦‍👦', 3), 'aa…');
      assert.strictEqual(trimEndWithMaxLength('🇺🇸🇨🇦', 2), '🇺🇸🇨🇦');
      assert.strictEqual(trimEndWithMaxLength('🇺🇸🇨🇦', 1), '…');
    });

    it('handles NFD forms correctly', () => {
      assert.strictEqual(trimEndWithMaxLength('caf\u0065\u0301', 4), 'café');
      assert.strictEqual(trimEndWithMaxLength('caf\u0065\u0301', 3), 'ca…');
    });

    it('handles complex ZWJ sequences', () => {
      const family = '👨‍👩‍👧‍👦'; // 1 grapheme
      // "Start" (5) + Family (1) + "End" (3) = 9 graphemes.
      assert.strictEqual(trimEndWithMaxLength(`Start${family}End`, 9), `Start${family}End`);
      assert.strictEqual(trimEndWithMaxLength(`Start${family}End`, 8), `Start${family}E…`);
      // Max 7. Keep 6 (7-1). "Start" (5) + Family (1).
      assert.strictEqual(trimEndWithMaxLength(`Start${family}End`, 7), `Start${family}…`);
      // "Start" (5) + Family (1) = 6.
      // If limit is 6. "Start" + Family.
      assert.strictEqual(trimEndWithMaxLength(`Start${family}`, 6), `Start${family}`);
      // If limit is 5. "Star…".
      assert.strictEqual(trimEndWithMaxLength(`Start${family}`, 5), 'Star…');
    });

    it('handles devanagari characters', () => {
       assert.strictEqual(trimEndWithMaxLength('देवनागरी', 5), 'देवनागरी');
       assert.strictEqual(trimEndWithMaxLength('देवनागरी', 4), 'देवना…');
    });
  });
```

File front_end/core/platform/StringUtilities.ts

Line 361, Patchset 2 (Latest):export const trimMiddle = (str: string, maxLength: number, ellipsis = '…'): string => {

Paul Irish . unresolved

lets remove this as a param. it's unused in the codebase.

(and moreso.. because if you want to use a flag emoji as an ellipsis character.. you have a few bugs now. )

Line 417, Patchset 2 (Latest):export const trimEndWithMaxLength = (str: string, maxLength: number, ellipsis = '…'): string => {

Paul Irish . unresolved

same remove

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