fix(i18n): don't treat mustache-style {{tokens}} as named substitutions by thribhuvan003 · Pull Request #2486 · wxt-dev/wxt

thribhuvan003 · 2026-07-04T10:27:47Z

Problem

Since 0.2.6, messages containing mustache-style application tokens ({{targetLanguage}}) are scanned as named substitutions, so the generated types require a substitution object and a plain i18n.t("key") call fails with not assignable to parameter of type never — even when the app intentionally wants the raw localized template back (e.g. AI prompt templates rendered later by the app itself).

Fix

NAMED_SUBSTITUTION_RE now matches single-brace {name} placeholders only, using lookarounds to skip brace groups wrapped in additional braces:

/(?<!\{)\{([A-Za-z0-9_]+)\}(?!\})/g

The regex is shared by the type scanner (getNamedSubstitutionNames) and the runtime (applyNamedSubstitutions), so both stay consistent:

{{selection}} / {{targetLanguage}} → left as literals, not scanned, not substituted
{name} → still scanned and substituted exactly as before
mixed messages ({greeting}, keep {{token}} as-is) → only {greeting} is a substitution

This is the first option proposed in the issue (single-brace only), which keeps 0.2.6 behavior for all existing single-brace users and restores 0.2.5 behavior for mustache templates.

Verification

Added 4 regression tests (scanner + runtime, pure-mustache and mixed cases), using the reproduction strings from the issue.

bun run test: 49 passed (45 existing + 4 new)
bun run check: Oxlint ✔ Publint ✔ TypeScript ✔

Fixes #2482

netlify · 2026-07-04T10:27:51Z

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thribhuvan003 · 2026-07-09T16:03:30Z

friendly bump — still happy to tweak anything if this needs changes. no rush.

pkg-pr-new · 2026-07-31T22:55:47Z

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commit: 77688ce

codecov · 2026-07-31T22:55:53Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.25%. Comparing base (e35d533) to head (77688ce).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2486      +/-   ##
==========================================
+ Coverage   79.19%   79.25%   +0.06%     
==========================================
  Files         134      134              
  Lines        3994     3996       +2     
  Branches      921      923       +2     
==========================================
+ Hits         3163     3167       +4     
+ Misses        735      734       -1     
+ Partials       96       95       -1

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aklinker1

Here's the results from bun bench:

Simple
┌───┬───────────┬──────────────────┬──────────────────┬────────────────────────┬────────────────────────┬─────────┐
│   │ Task name │ Latency avg (ns) │ Latency med (ns) │ Throughput avg (ops/s) │ Throughput med (ops/s) │ Samples │
├───┼───────────┼──────────────────┼──────────────────┼────────────────────────┼────────────────────────┼─────────┤
│ 0 │ Vanilla   │ 2004.0 ± 1.99%   │ 0.00 ± 0.00      │ 489248 ± 0.04%         │ 499013 ± 0             │ 499013  │
│ 1 │ main      │ 2092.5 ± 1.94%   │ 0.00 ± 0.00      │ 468105 ± 0.04%         │ 477890 ± 0             │ 477938  │
│ 2 │ PR        │ 2162.0 ± 1.94%   │ 0.00 ± 0.00      │ 452770 ± 0.04%         │ 462541 ± 0             │ 462541  │
└───┴───────────┴──────────────────┴──────────────────┴────────────────────────┴────────────────────────┴─────────┘

Substitution
┌───┬───────────┬──────────────────┬──────────────────┬────────────────────────┬────────────────────────┬─────────┐
│   │ Task name │ Latency avg (ns) │ Latency med (ns) │ Throughput avg (ops/s) │ Throughput med (ops/s) │ Samples │
├───┼───────────┼──────────────────┼──────────────────┼────────────────────────┼────────────────────────┼─────────┤
│ 0 │ Vanilla   │ 2712.6 ± 1.94%   │ 0.00 ± 0.00      │ 358932 ± 0.05%         │ 368645 ± 0             │ 368645  │
│ 1 │ main      │ 2835.0 ± 1.93%   │ 0.00 ± 0.00      │ 343024 ± 0.05%         │ 352732 ± 0             │ 352732  │
│ 2 │ PR        │ 3124.4 ± 1.93%   │ 0.00 ± 0.00      │ 310389 ± 0.06%         │ 320058 ± 0             │ 320058  │
└───┴───────────┴──────────────────┴──────────────────┴────────────────────────┴────────────────────────┴─────────┘

Named substitution
┌───┬───────────┬──────────────────┬──────────────────┬────────────────────────┬────────────────────────┬─────────┐
│   │ Task name │ Latency avg (ns) │ Latency med (ns) │ Throughput avg (ops/s) │ Throughput med (ops/s) │ Samples │
├───┼───────────┼──────────────────┼──────────────────┼────────────────────────┼────────────────────────┼─────────┤
│ 0 │ Vanilla   │ 2261.7 ± 1.94%   │ 0.00 ± 0.00      │ 432378 ± 0.04%         │ 442136 ± 0             │ 442180  │
│ 1 │ main      │ 3145.5 ± 2.03%   │ 0.00 ± 0.00      │ 308278 ± 0.06%         │ 317919 ± 0             │ 317919  │
│ 2 │ PR        │ 3260.7 ± 2.01%   │ 0.00 ± 0.00      │ 297040 ± 0.06%         │ 306678 ± 0             │ 306678  │
└───┴───────────┴──────────────────┴──────────────────┴────────────────────────┴────────────────────────┴─────────┘

Plural (singular form)
┌───┬───────────┬──────────────────┬──────────────────┬────────────────────────┬────────────────────────┬─────────┐
│   │ Task name │ Latency avg (ns) │ Latency med (ns) │ Throughput avg (ops/s) │ Throughput med (ops/s) │ Samples │
├───┼───────────┼──────────────────┼──────────────────┼────────────────────────┼────────────────────────┼─────────┤
│ 0 │ Vanilla   │ 2354.9 ± 1.94%   │ 0.00 ± 0.00      │ 414908 ± 0.05%         │ 424651 ± 0             │ 424693  │
│ 1 │ main      │ 3157.7 ± 2.03%   │ 0.00 ± 0.00      │ 307037 ± 0.06%         │ 316682 ± 0             │ 316682  │
│ 2 │ PR        │ 3216.2 ± 2.02%   │ 0.00 ± 0.00      │ 301295 ± 0.06%         │ 310927 ± 0             │ 310958  │
└───┴───────────┴──────────────────┴──────────────────┴────────────────────────┴────────────────────────┴─────────┘

Plural (plural form)
┌───┬───────────┬──────────────────┬──────────────────┬────────────────────────┬────────────────────────┬─────────┐
│   │ Task name │ Latency avg (ns) │ Latency med (ns) │ Throughput avg (ops/s) │ Throughput med (ops/s) │ Samples │
├───┼───────────┼──────────────────┼──────────────────┼────────────────────────┼────────────────────────┼─────────┤
│ 0 │ Vanilla   │ 2305.2 ± 2.08%   │ 0.00 ± 0.00      │ 424092 ± 0.04%         │ 433793 ± 0             │ 433793  │
│ 1 │ main      │ 3148.4 ± 2.04%   │ 0.00 ± 0.00      │ 307977 ± 0.06%         │ 317622 ± 0             │ 317622  │
│ 2 │ PR        │ 3244.3 ± 2.01%   │ 0.00 ± 0.00      │ 298591 ± 0.06%         │ 308233 ± 0             │ 308264  │
└───┴───────────┴──────────────────┴──────────────────┴────────────────────────┴────────────────────────┴─────────┘

aklinker1 · 2026-07-31T22:56:17Z

+/**
+ * Matches single-brace `{name}` placeholders only. Double-brace tokens like
+ * `{{name}}` (mustache-style application templates) are left as literals.
+ */
+const NAMED_SUBSTITUTION_RE = /(?<!\{)\{([A-Za-z0-9_]+)\}(?!\})/g;


Shouldn't the solution be to allow escaping them? So instead of only handling {{, we should look for \{.

So you would define a string as "{\\{example}}"

aklinker1 · 2026-07-31T22:56:45Z

+    it('should leave mustache-style tokens unchanged', () => {
+      expect(
+        applyNamedSubstitutions(
+          'Translate {{selection}} into {{targetLanguage}}',


So the tests would look like:

Suggested change

'Translate {{selection}} into {{targetLanguage}}',

'Translate {\\{selection}} into {\\{targetLanguage}}',

thribhuvan003 · 2026-08-02T01:34:35Z

done, went with your escaping suggestion. \{ now escapes a brace, so {\{name}} outputs a literal {{name}} instead of substituting it. that also let me drop the lookbehind regex, so the perf regression you caught is gone. updated the test to the escaped form you suggested too.

aklinker1

Nice yeah, benchmarks look good. Seems comparable or faster. I ran the latest commit and main twice, there's some variation, and this is a different computer. Not sure what happened for the simple PR 2 benchmark lol doesn't seem right.

Simple
┌───┬───────────┬──────────────────┬──────────────────┬────────────────────────┬────────────────────────┬─────────┐
│   │ Task name │ Latency avg (ns) │ Latency med (ns) │ Throughput avg (ops/s) │ Throughput med (ops/s) │ Samples │
├───┼───────────┼──────────────────┼──────────────────┼────────────────────────┼────────────────────────┼─────────┤
│ 0 │ Vanilla   │ 4867.0 ± 10.88%  │ 0.00 ± 0.00      │ 197430 ± 0.09%         │ 205465 ± 0             │ 205486  │
│ 1 │ main #1   │ 6787.5 ± 4.15%   │ 0.00 ± 0.00      │ 138763 ± 0.12%         │ 147329 ± 0             │ 147344  │
│ 2 │ main #2   │ 6073.1 ± 2.01%   │ 0.00 ± 0.00      │ 155396 ± 0.11%         │ 164662 ± 0             │ 164678  │
│ 3 │ PR #1     │ 6555.4 ± 2.16%   │ 0.00 ± 0.00      │ 143534 ± 0.12%         │ 152547 ± 0             │ 152547  │
│ 4 │ PR #2     │ 931.51 ± 1.95%   │ 0.00 ± 0.00      │ 1063616 ± 0.02%        │ 1073523 ± 0            │ 1073630 │
└───┴───────────┴──────────────────┴──────────────────┴────────────────────────┴────────────────────────┴─────────┘

Substitution
┌───┬───────────┬──────────────────┬──────────────────┬────────────────────────┬────────────────────────┬─────────┐
│   │ Task name │ Latency avg (ns) │ Latency med (ns) │ Throughput avg (ops/s) │ Throughput med (ops/s) │ Samples │
├───┼───────────┼──────────────────┼──────────────────┼────────────────────────┼────────────────────────┼─────────┤
│ 0 │ Vanilla   │ 7471.3 ± 2.97%   │ 0.00 ± 0.00      │ 125099 ± 0.14%         │ 133845 ± 0             │ 133845  │
│ 1 │ main #1   │ 9010.5 ± 4.25%   │ 0.00 ± 0.00      │ 102606 ± 0.16%         │ 110982 ± 0             │ 110993  │
│ 2 │ main #2   │ 7104.7 ± 9.07%   │ 0.00 ± 0.00      │ 132726 ± 0.12%         │ 140752 ± 0             │ 140780  │
│ 3 │ PR #1     │ 8408.1 ± 3.46%   │ 0.00 ± 0.00      │ 110510 ± 0.15%         │ 118933 ± 0             │ 118945  │
│ 4 │ PR #2     │ 8498.3 ± 4.30%   │ 0.00 ± 0.00      │ 109344 ± 0.15%         │ 117671 ± 0             │ 117683  │
└───┴───────────┴──────────────────┴──────────────────┴────────────────────────┴────────────────────────┴─────────┘

Named substitution
┌───┬───────────┬──────────────────┬──────────────────┬────────────────────────┬────────────────────────┬─────────┐
│   │ Task name │ Latency avg (ns) │ Latency med (ns) │ Throughput avg (ops/s) │ Throughput med (ops/s) │ Samples │
├───┼───────────┼──────────────────┼──────────────────┼────────────────────────┼────────────────────────┼─────────┤
│ 0 │ Vanilla   │ 6818.6 ± 2.34%   │ 0.00 ± 0.00      │ 137849 ± 0.12%         │ 146658 ± 0             │ 146658  │
│ 1 │ main #1   │ 9700.9 ± 3.90%   │ 0.00 ± 0.00      │ 94679 ± 0.17%          │ 103083 ± 0             │ 103083  │
│ 2 │ main #2   │ 8999.5 ± 2.03%   │ 0.00 ± 0.00      │ 102192 ± 0.17%         │ 111117 ± 0             │ 111128  │
│ 3 │ PR #1     │ 10025 ± 3.00%    │ 0.00 ± 0.00      │ 91082 ± 0.18%          │ 99751 ± 0              │ 99771   │
│ 4 │ PR #2     │ 8797.9 ± 7.96%   │ 0.00 ± 0.00      │ 105439 ± 0.15%         │ 113663 ± 0             │ 113663  │
└───┴───────────┴──────────────────┴──────────────────┴────────────────────────┴────────────────────────┴─────────┘

Plural (singular form)
┌───┬───────────┬──────────────────┬──────────────────┬────────────────────────┬────────────────────────┬─────────┐
│   │ Task name │ Latency avg (ns) │ Latency med (ns) │ Throughput avg (ops/s) │ Throughput med (ops/s) │ Samples │
├───┼───────────┼──────────────────┼──────────────────┼────────────────────────┼────────────────────────┼─────────┤
│ 0 │ Vanilla   │ 7465.6 ± 2.89%   │ 0.00 ± 0.00      │ 125470 ± 0.13%         │ 133948 ± 0             │ 133961  │
│ 1 │ main #1   │ 9743.4 ± 4.41%   │ 0.00 ± 0.00      │ 94243 ± 0.17%          │ 102634 ± 0             │ 102644  │
│ 2 │ main #2   │ 9252.2 ± 2.40%   │ 0.00 ± 0.00      │ 99238 ± 0.17%          │ 108082 ± 0             │ 108093  │
│ 3 │ PR #1     │ 9526.3 ± 2.30%   │ 0.00 ± 0.00      │ 96542 ± 0.17%          │ 104973 ± 0             │ 104983  │
│ 4 │ PR #2     │ 8369.8 ± 3.90%   │ 0.00 ± 0.00      │ 110833 ± 0.15%         │ 119477 ± 0             │ 119489  │
└───┴───────────┴──────────────────┴──────────────────┴────────────────────────┴────────────────────────┴─────────┘

Plural (plural form)
┌───┬───────────┬──────────────────┬──────────────────┬────────────────────────┬────────────────────────┬─────────┐
│   │ Task name │ Latency avg (ns) │ Latency med (ns) │ Throughput avg (ops/s) │ Throughput med (ops/s) │ Samples │
├───┼───────────┼──────────────────┼──────────────────┼────────────────────────┼────────────────────────┼─────────┤
│ 0 │ Vanilla   │ 6797.9 ± 2.23%   │ 0.00 ± 0.00      │ 138301 ± 0.12%         │ 147103 ± 0             │ 147118  │
│ 1 │ main #1   │ 8604.1 ± 4.34%   │ 0.00 ± 0.00      │ 107954 ± 0.15%         │ 116223 ± 0             │ 116235  │
│ 2 │ main #2   │ 9080.1 ± 1.99%   │ 0.00 ± 0.00      │ 101217 ± 0.17%         │ 110131 ± 0             │ 110153  │
│ 3 │ PR #1     │ 10370 ± 3.06%    │ 0.00 ± 0.00      │ 88218 ± 0.18%          │ 96432 ± 0              │ 96519   │
│ 4 │ PR #2     │ 9103.0 ± 2.59%   │ 0.00 ± 0.00      │ 101082 ± 0.17%         │ 109854 ± 0             │ 109865  │
└───┴───────────┴──────────────────┴──────────────────┴────────────────────────┴────────────────────────┴─────────┘

aklinker1 · 2026-08-02T02:12:56Z

Wait, does escaping also prevent \{example} from being replaced in general? Or does this only handle the mustache style {{?

#2486 (comment)

thribhuvan003 · 2026-08-03T05:44:00Z

yeah, it's general. \{ escapes any single opening brace, not just the double. so \{example} stays literal even if you pass an example substitution, and a plain {example} still gets replaced. the mustache case is just that same escape on the first brace: {\{example}} outputs {{example}}.

thribhuvan003 requested a review from aklinker1 as a code owner July 4, 2026 10:27

github-actions Bot assigned thribhuvan003 Jul 4, 2026

github-actions Bot added the pkg/i18n Includes changes to the `packages/i18n` directory label Jul 4, 2026

aklinker1 requested changes Jul 31, 2026

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fix(i18n): allow escaping braces to keep tokens literal in substitutions

77688ce

thribhuvan003 force-pushed the fix/i18n-mustache-literal-tokens branch from 12a3f7e to 77688ce Compare August 2, 2026 01:30

aklinker1 previously approved these changes Aug 2, 2026

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fix(i18n): don't treat mustache-style {{tokens}} as named substitutions - #2486

fix(i18n): don't treat mustache-style {{tokens}} as named substitutions#2486
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