brave-core/docs/best-practices/plaster.md

Plaster

✅ Plaster Patch Patterns Should Match Specific Context

Plaster patch config re_pattern should generally match method names or other relevant context to ensure a single, targeted match. Simple patterns can be used when the intention is to match all instances of a particular pattern in a file.

# ❌ WRONG - overly broad pattern that might match multiple locations
re_pattern: 'return false;'

# ✅ CORRECT - matches method name and context for targeted replacement
re_pattern: 'bool IsFeatureEnabled[\(\)\S\s\{\}]+?(return false);\s+^\}'

# ✅ ALSO CORRECT - simple pattern when all instances should match
# (Use this intentionally when you want to replace every occurrence)
re_pattern: 'kOldConstant'

Matching specific context (method names, surrounding code) makes patches more maintainable and prevents accidental matches during Chromium updates. Use broad patterns only when you explicitly intend to replace all occurrences.

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✅ Use pattern for Simple Symbol Replacement, re_pattern for Context-Aware Matches

Only use pattern for simple matches—generally a single symbol name that you want to replace globally. If you need more context (including whitespace), then re_pattern is more appropriate.

# ✅ CORRECT - simple symbol replacement with pattern for all instances of a constant
pattern: 'kOldConstantName'
replace: 'kNewConstantName'

# ✅ CORRECT - simple symbol replacement with pattern for all instances of a method call
pattern: 'ChromiumMethod'
replace: 'BraveMethod'

# ✅ CORRECT - re_pattern handles flexible whitespace
re_pattern: '(^\s+)(ChromiumMethod\(\))'
replace: '\1BraveMethod()'

# ❌ WRONG - pattern requires exact whitespace match, fragile to upstream changes
pattern: '    MyMethod()'  # Breaks if upstream changes indentation
replace: '    BraveMethod()'

# ✅ CORRECT - re_pattern handles flexible whitespace
re_pattern: '(if\s+\()MyMethod\(\)([\S\s]+?{)'
replace: '\1BraveMethod()\2'

# ❌ WRONG - pattern includes additional context
pattern: 'if (MyMethod() && my_bool) {'  # Breaks if upstream changes indentation
replace: 'if (BraveMethod() && my_bool) {'

Using pattern for simple symbol names keeps configs readable and maintainable. Reserve re_pattern for when you need regex features like whitespace matching, character classes, or structural patterns.

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