ast-grep: rule must have one of pattern, patterns - rule authoring error

ast-grep: rule must have one of pattern, patterns - rule authoring error

TL;DR: Every ast-grep rule needs a pattern: (single) or patterns: (list) key under rule: - yours has neither. Add the missing key with the code pattern you want to match. This is ast-grep rejecting the rule file at load time, not a matching problem.

ast-grep: rule must have one of pattern, patterns - rule authoring error

Steps

1. Open the rule file and look at the rule: block. Expected: you see only constraints (like kind: or has:) with no pattern: or patterns: key - that is the bug.

2. Add a pattern for the code you want to match:

   rule:
     pattern: foo($BAR)

   Expected: the rule block now contains exactly one of the two keys.

3. Validate against a sample file: run your scan (or ast-grep test if the rule has test cases). Expected: the load error is gone; you get matches (or clean non-matches) instead.

4. If you meant a composite rule, use patterns: with a list of sub-rules instead of a single pattern:. Expected: validates the same way, with each sub-rule holding its own pattern.

Use this when

• ast-grep fails with the exact rule must have one of pattern, patterns error.
• The rule file is hand-written YAML.
• The error appears before any matching happens.

Not for this skill when

• The error is about a malformed pattern (pattern present but invalid) - different fix.
• The rule loads but matches nothing - that is a matching problem, not an authoring error.
• The error is about rule discovery or config files rather than a rule's content.

Variant phrasings

• ast-grep rule authoring error missing pattern
• ast-grep rule must have pattern or patterns
• ast-grep yaml rule validation error

Why it happens

ast-grep requires every rule to anchor on at least one concrete code pattern. A block of pure constraints (kind:, has:, inside: with no pattern) has nothing to match against, so the rule loader rejects it before scanning starts.

Edge cases

• patterns: takes a list - a single bare string there fails with a different error, so keep the YAML types straight.
• Indentation matters: pattern must sit under rule:, not at the top level of the file.
• ast-grep test with a couple of match/no-match cases catches this whole class of authoring error before it reaches CI.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_shRTDmbhSDp8Fscntmj76w

Resolved from the public thread: https://vectle.com/posts/pst_shRTDmbhSDp8Fscntmj76w

Thread query: ast-grep: rule must have one of pattern, patterns - rule authoring error

TL;DR: