Ast Grep

ast-grep Code Search

Use the ast_grep tool for all ast-grep operations. It has three modes: pattern, rule, and inspect. The tool description contains the full syntax reference — this skill teaches the workflow for writing effective searches.

Workflow

1. Understand the query

Before writing anything, clarify:

• What code pattern or structure is the target?
• Which programming language?
• Are there variations or edge cases to include/exclude?

2. Start with pattern mode

Always try the simplest approach first:

ast_grep({ mode: "pattern", pattern: "console.log($MSG)", lang: "javascript" })

If a single pattern matches what you need, stop here. Don't over-engineer.

3. Escalate to rule mode only when needed

Use rule mode when you need:

• Relational logic: "X inside Y" or "X containing Y" → has/inside with stopBy: end
• Negation: "X without Y" → not + has
• Alternatives: "X or Y" → any
• Combinations: "X and Y and Z" → all

ast_grep({
  mode: "rule",
  lang: "typescript",
  rule: "kind: function_declaration\nhas:\n  pattern: await $EXPR\n  stopBy: end"
})

4. Debug with inspect mode

When rules don't match, use inspect to understand the AST:

ast_grep({
  mode: "inspect",
  pattern: "async function foo() { await bar(); }",
  lang: "javascript",
  inspect_format: "ast"
})

This reveals the correct kind names. Common mistakes:

• Wrong kind value (e.g. arrow_function vs function_declaration)
• Missing stopBy: end on has/inside (search stops too early)
• Pattern too specific (use metavariables to generalize)

5. Iterate

The cycle is: pattern → inspect → rule → inspect → refine. Each step should make the rule more precise. Don't write a complex rule in one shot.

Key Principles

• stopBy: end is mandatory on has and inside rules. Without it, the search stops at the first non-matching node instead of traversing the full subtree.
• Prefer pattern over kind when the code structure is unambiguous. kind + relational rules are for when patterns can't express the constraint.
• Use all for ordered metavariable binding. If rule B depends on a metavariable captured by rule A, put A before B in an all array.
• Non-capturing wildcards ($_VAR) avoid unnecessary binding. Use when you need to match "something" but don't care what.
• $$$ matches zero or more nodes. Use in function args ($$$ARGS), statement blocks ($$$BODY), etc.

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