Go

This page curates a list of example ast-grep rules to check and to rewrite Go code.

Find function declarations with names of certain pattern

• Playground Link

Description

ast-grep can find function declarations by their names. But not all names can be matched by a meta variable pattern. For instance, you cannot use a meta variable pattern to find function declarations whose names start with a specific prefix, e.g. TestAbs with the prefix Test. Attempting Test$_ will fail because it is not a valid syntax.

Instead, you can use a YAML rule to use the regex atomic rule.

YAML

id: test-functions
language: go
rule:
  kind: function_declaration
  has:
    field: name
    regex: Test.*

Example

package abs
import "testing"
func TestAbs(t *testing.T) {
    got := Abs(-1)
    if got != 1 {
        t.Errorf("Abs(-1) = %d; want 1", got)
    }
}

Contributed by

kevinkjt2000 on Discord.

Match Function Call in Golang

• Playground Link

Description

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

A plain pattern like fmt.Println($A) will not work. This is because Golang syntax also allows type conversions, e.g. int(3.14), that look like function calls.

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: func t() { fmt.Println($A) }. Then, we can use the selector call_expression to match only function calls.

YAML

id: match-function-call
language: go
rule:
  pattern:
    context: 'func t() { fmt.Println($A) }'
    selector: call_expression

Example

func main() {
    fmt.Println("OK")
}

Contributed by

Inspired by QuantumGhost from ast-grep/ast-grep#646