Match Function Call in C

• Playground Link

Description

One of the common questions of ast-grep is to match function calls in C.

A plain pattern like test($A) will not work. This is because tree-sitter-c parse the code snippet into macro_type_specifier, see the pattern output.

To avoid this ambiguity, ast-grep lets us write a contextual pattern, which is a pattern inside a larger code snippet. We can use context to write a pattern like this: test($A);. Then, we can use the selector call_expression to match only function calls.

YAML

id: match-function-call
language: c
rule:
  pattern:
    context: $M($$$);
    selector: call_expression

Example

#define test(x) (2*x)
int a = test(2);
int main(){
    int b = test(2);
}

Caveat

Note, tree-sitter-c parses code differently when it receives code fragment. For example,

• test(a) is parsed as macro_type_specifier
• test(a); is parsed as expression_statement -> call_expression
• int b = test(a) is parsed as declaration -> init_declarator -> call_expression

The behavior is controlled by how the tree-sitter parser is written. And tree-sitter-c behaves differently from tree-sitter-cpp.

Please file issues on tree-sitter-c repo if you want to change the behavior. ast-grep will respect changes and decision from upstream authors.