x/tools/go/types/typeutil: wrong computed method set

[dotaheor]

What version of Go are you using (go version)?

$ go version
go version go1.13.7 linux/amd64

What did you do?

package main

import (
	"fmt"
	"go/ast"
	"go/importer"
	"go/parser"
	"go/token"
	"go/types"
	"log"
	"reflect"
	
	"golang.org/x/tools/go/types/typeutil"
)

const input = `
package abc

type Conn struct {
	frameReader
	PayloadType int
}

type frameReader interface {
	PayloadType() byte
}
`

var fset = token.NewFileSet()

func main() {
	f, err := parser.ParseFile(fset, "hello.go", input, 0)
	if err != nil {
		log.Fatal(err)
	}

	conf := types.Config{Importer: importer.Default()}
	info := &types.Info{Types: make(map[ast.Expr]types.TypeAndValue)}
	pkg, err := conf.Check("cmd/hello", fset, []*ast.File{f}, info)
	if err != nil {
		log.Fatal(err)
	}
	
	ct := pkg.Scope().Lookup("Conn").Type()
	
	var cache typeutil.MethodSetCache
	var methetset = cache.MethodSet(ct)
	fmt.Println(methetset)
		// MethodSet {
		// 	method (cmd/hello.Conn) PayloadType() byte
		// }
	
	fmt.Println(reflect.TypeOf(Conn{}).NumMethod())
		// 0
}

type Conn struct {
	frameReader
	PayloadType int
}

type frameReader interface {
	PayloadType() byte
}

What did you expect to see?

Type Conn has no methods.

What did you see instead?

Type Conn has one method.

[ianlancetaylor]

But Conn does have a method, from the embedded frameReader type. Why should it have no methods?

[dotaheor]

But reflect says it hasn't.

[ianlancetaylor]

Did you reverse "what did you expect to see" and "what did you see instead"?

Hmmm, looks like you did. When I run the program, it prints 0 for NumMethod.

[ianlancetaylor]

Oh, sorry, I get it now. The method should be hidden by the field of the same name. The reflect package sees that, but golang.org/x/tools/go/types/typeutil does not.

We appreciate the bug reports, but it will save time if you can say more clearly what the issue is, rather than leaving us to work it out. Thanks.

[ianlancetaylor]

CC @griesemer

[griesemer]

Smaller reproducer: https://play.golang.org/p/TRM-fN9nvVd

The primary function types.LookupFieldOrMethod correctly reports a field, but types.NewMethodSet returns the method. Looks like a bug in the method set computation.

(As an aside, types.NewMethodSet is not directly used by go/types, so there's no danger of go/typesdirectly being compromised by this - it was requested forx/tools/go/types/typeutil`. I should have said no at that time... :-)