getFuncDeclResultTypes

scratch_1.go

package main

import (
	"fmt"
	"go/ast"
	"go/parser"
)
import "golang.org/x/tools/go/loader"

func main() {
	source := `
package main

import "fmt"

type s struct{}

func (s s)Println(x string) {}


func increment(v int) int {
	return v + 1
}

func main(){
  fmt.Println("xxx")

  {
      fmt := s{}
      fmt.Println("yyy")
  }

  fmt.Println("xxx")
}
`

	lo := loader.Config{ParserMode: parser.ParseComments}
	astf, err := lo.ParseFile("main.go", source)
	if err != nil {
		panic(err)
	}
	lo.CreateFromFiles("main", astf)

	prog, err := lo.Load()
	if err != nil {
		panic(err)
	}
	targetPkgName := "fmt"
	targetFuncName := "Println"
	targetPkg := prog.Package(targetPkgName)

	if types, ok := getFuncDeclResultTypes(targetPkg, targetFuncName); ok {
		fmt.Println(types)
	}
}

func getFuncDeclResultTypes(packageInfo *loader.PackageInfo, funcName string) (types []string, ok bool) {
	funcDecl, ok := getFuncDecl(packageInfo, funcName)
	if !ok {
		return nil, false
	}

	results := funcDecl.Type.Results.List
	for _, result := range results {
		if typeIdent, ok := result.Type.(*ast.Ident); ok {
			types = append(types, typeIdent.Name)
		}
	}
	return types, true
}

func getFuncDecl(packageInfo *loader.PackageInfo, funcName string) (*ast.FuncDecl, bool) {
	for _, file := range packageInfo.Files {
		ast.FileExports(file)
		for _, decl := range file.Decls {
			if funcDecl, ok := decl.(*ast.FuncDecl); ok {
				if funcDecl.Name.Name == funcName {
					return funcDecl, true
				}
			}
		}
	}
	return nil, false
}