通过解析器包解析源文件时，如何优雅地跳过包标识？

Question

When I parse go source file with the parser package, the package xxx statement was considered as a normal *ast.Ident. Is there any way to distinguish it from other declarations? Or gracefully ignore the package statement while parsing?

func walk(node ast.Node) bool {
    switch n := node.(type) {
    case *ast.File:
        return true
    case *ast.Ident:
        // I want to check whether it is a package statement 
    case *ast.GenDecl:
        return true
    case *ast.TypeSpec:
        return true
    case *ast.StructType:
        return true
    case *ast.FieldList:
        return true
    case *ast.Field:
        if len(n.Names) > 0 {
            fmt.Println(n.Names[0].String())
        }
    default:
        fmt.Printf("%T
", node)
    }
    return false
}

func parseFile(filename string) error {
    fs := token.NewFileSet()
    f, err := parser.ParseFile(fs, filename, nil, parser.ParseComments)
    if err != nil {
        return err
    }
    ast.Inspect(f, walk)
    return nil
}

Answer 1

To skip over the package identifier, the application must write the code to iterate over the *ast.File children and skip the package identifier in that code:

func walk(node ast.Node) bool {
    switch n := node.(type) {
    case *ast.File:
        walkFileNoPackageName(n)
        // Return false to prevent caller from also 
        // walking children of n.
        return false 
    ... other cases as in question


func walkFileNoPackageName(n *ast.File) {
    if n.Doc != nil {
        ast.Inspect(n.Doc, walk)
    }
    // ast.Inspect(n.Name, walk)  Skip over name
    for _, x := range n.Decls {
        ast.Inspect(x, walk)
    }
}

Run it on the playground.

If you are only interested in package-level declarations in the file, then start the inspection from those declarations:

f, err := parser.ParseFile(fs, filename, nil, parser.ParseComments)
if err != nil {
    return err
}
for _, n := range f.Decls {
    ast.Inspect(n, walk)
}

Use the walk function from the question as is.

Run it on the playground.