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perf: fix double regex pass in UnquoteYAMLKey causing ~2x compile slowdown #22459

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Merged
pelikhan merged 4 commits into from
Mar 23, 2026
Merged

perf: fix double regex pass in UnquoteYAMLKey causing ~2x compile slowdown #22459

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88665b2
Initial plan
Copilot Mar 23, 2026
3d7220c
fix: resolve performance regression in UnquoteYAMLKey by using single…
Copilot Mar 23, 2026
17d774e
test: add BenchmarkUnquoteYAMLKey to guard against double-pass regex …
Copilot Mar 23, 2026
49a7b57
Merge branch 'main' into copilot/fix-regression-compile-memory-usage
pelikhan Mar 23, 2026
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14 changes: 3 additions & 11 deletions pkg/workflow/yaml.go
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Original file line number Diff line number Diff line change
Expand Up @@ -146,17 +146,9 @@ func UnquoteYAMLKey(yamlStr string, key string) string {
re = regexp.MustCompile(pattern)
unquoteYAMLKeyCache.Store(key, re)
}
return re.ReplaceAllStringFunc(yamlStr, func(match string) string {
// Find the submatch groups
submatches := re.FindStringSubmatch(match)
if len(submatches) >= 3 {
// submatches[0] is the full match
// submatches[1] is the line start (^ or \n)
// submatches[2] is the whitespace
return submatches[1] + submatches[2] + key + ":"
}
return match
})
// Use ReplaceAllString with capture group references for a single-pass replacement.
// ${1} = line start (^ or \n), ${2} = optional whitespace
return re.ReplaceAllString(yamlStr, "${1}${2}"+key+":")
Comment on lines +149 to +151
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Copilot AI Mar 23, 2026

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regexp.Regexp.ReplaceAllString treats $ in the replacement string as a capture-group expansion. Since key is concatenated directly into the replacement, keys containing $ (e.g. user-provided frontmatter keys) would be corrupted by unintended backref expansion. Escape $ in key before building the replacement (e.g. replace $ with $$), or use an API that performs literal insertion for the dynamic portion.

Suggested change
// Use ReplaceAllString with capture group references for a single-pass replacement.
// ${1} = line start (^ or \n), ${2} = optional whitespace
return re.ReplaceAllString(yamlStr, "${1}${2}"+key+":")
// Escape '$' in the key so it is treated literally in the replacement string,
// not as a backreference marker by regexp.ReplaceAllString.
escapedKey := strings.ReplaceAll(key, "$", "$$")
// Use ReplaceAllString with capture group references for a single-pass replacement.
// ${1} = line start (^ or \n), ${2} = optional whitespace
return re.ReplaceAllString(yamlStr, "${1}${2}"+escapedKey+":")

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}

// MarshalWithFieldOrder marshals a map to YAML with fields in a specific order.
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30 changes: 30 additions & 0 deletions pkg/workflow/yaml_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -407,6 +407,36 @@ func TestExtractTopLevelYAMLSectionWithOrdering(t *testing.T) {
}
}

// BenchmarkUnquoteYAMLKey measures single-pass regex replacement performance.
// This benchmark guards against regressions where the implementation calls
// FindStringSubmatch inside a ReplaceAllStringFunc callback (double regex pass).
func BenchmarkUnquoteYAMLKey(b *testing.B) {
// A realistic workflow YAML with the "on" key quoted by the marshaler
yamlStr := `"on":
push:
branches:
- main
pull_request:
types:
- opened
- synchronize
issues:
types:
- opened
workflow_dispatch:
jobs:
agent:
runs-on: ubuntu-latest
steps:
- name: Run
run: echo hello
`
b.ReportAllocs()
for b.Loop() {
_ = UnquoteYAMLKey(yamlStr, "on")
}
}

func TestFormatYAMLValue(t *testing.T) {
tests := []struct {
name string
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