go/types/typeutil: make IntuitiveMethodSet(*C) nonempty for concrete types C

This fixes a bug in guru describe.

Also, add a test of IntuitiveMethodSet.

Change-Id: Ied3780807afd88e664fdb186619499670529fe33
Reviewed-on: https://go-review.googlesource.com/20166
Reviewed-by: Daniel Morsing <daniel.morsing@gmail.com>

cmd/guru/testdata/src/describe/main.go

@@ -37,6 +37,9 @@ func main() { // @describe func-def-main "main"
 	_ = d.f    // @describe func-ref-d.f "d.f"
 	_ = i.f    // @describe func-ref-i.f "i.f"
 
+	var dptr *D // @describe ptr-with-nonptr-methods "dptr"
+	_ = dptr
+
 	// var objects
 	anon := func() {
 		_ = d // @describe ref-lexical-d "d"

cmd/guru/testdata/src/describe/main.golden

@@ -84,6 +84,14 @@ defined here
 reference to interface method func (I).f()
 defined here
 
+-------- @describe ptr-with-nonptr-methods --------
+definition of var dptr *D
+Method set:
+	method (*D) f()
+Fields:
+	Field        int
+	AnotherField string
+
 -------- @describe ref-lexical-d --------
 reference to var d D
 defined here

go/types/typeutil/ui.go

@@ -10,23 +10,36 @@ package typeutil
 
 import "go/types"
 
-// IntuitiveMethodSet returns the intuitive method set of a type, T.
+// IntuitiveMethodSet returns the intuitive method set of a type T,
+// which is the set of methods you can call on an addressable value of
+// that type.
 //
-// The result contains MethodSet(T) and additionally, if T is a
-// concrete type, methods belonging to *T if there is no identically
-// named method on T itself.  This corresponds to user intuition about
-// method sets; this function is intended only for user interfaces.
+// The result always contains MethodSet(T), and is exactly MethodSet(T)
+// for interface types and for pointer-to-concrete types.
+// For all other concrete types T, the result additionally
+// contains each method belonging to *T if there is no identically
+// named method on T itself.
+//
+// This corresponds to user intuition about method sets;
+// this function is intended only for user interfaces.
 //
 // The order of the result is as for types.MethodSet(T).
 //
 func IntuitiveMethodSet(T types.Type, msets *MethodSetCache) []*types.Selection {
+	isPointerToConcrete := func(T types.Type) bool {
+		ptr, ok := T.(*types.Pointer)
+		return ok && !types.IsInterface(ptr.Elem())
+	}
+
 	var result []*types.Selection
 	mset := msets.MethodSet(T)
-	if _, ok := T.Underlying().(*types.Interface); ok {
+	if types.IsInterface(T) || isPointerToConcrete(T) {
 		for i, n := 0, mset.Len(); i < n; i++ {
 			result = append(result, mset.At(i))
 		}
 	} else {
+		// T is some other concrete type.
+		// Report methods of T and *T, preferring those of T.
 		pmset := msets.MethodSet(types.NewPointer(T))
 		for i, n := 0, pmset.Len(); i < n; i++ {
 			meth := pmset.At(i)
@@ -35,6 +48,7 @@ func IntuitiveMethodSet(T types.Type, msets *MethodSetCache) []*types.Selection
 			}
 			result = append(result, meth)
 		}
+
 	}
 	return result
 }

go/types/typeutil/ui_test.go

@@ -0,0 +1,63 @@
+// +build go1.5
+
+package typeutil_test
+
+import (
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"go/types"
+	"strings"
+	"testing"
+
+	"golang.org/x/tools/go/types/typeutil"
+)
+
+func TestIntuitiveMethodSet(t *testing.T) {
+	const source = `
+package P
+type A int
+func (A) f()
+func (*A) g()
+`
+
+	fset := token.NewFileSet()
+	f, err := parser.ParseFile(fset, "hello.go", source, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var conf types.Config
+	pkg, err := conf.Check("P", fset, []*ast.File{f}, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	qual := types.RelativeTo(pkg)
+
+	for _, test := range []struct {
+		expr string // type expression
+		want string // intuitive method set
+	}{
+		{"A", "(A).f (*A).g"},
+		{"*A", "(*A).f (*A).g"},
+		{"error", "(error).Error"},
+		{"*error", ""},
+		{"struct{A}", "(struct{A}).f (*struct{A}).g"},
+		{"*struct{A}", "(*struct{A}).f (*struct{A}).g"},
+	} {
+		tv, err := types.Eval(fset, pkg, 0, test.expr)
+		if err != nil {
+			t.Errorf("Eval(%s) failed: %v", test.expr, err)
+		}
+		var names []string
+		for _, m := range typeutil.IntuitiveMethodSet(tv.Type, nil) {
+			name := fmt.Sprintf("(%s).%s", types.TypeString(m.Recv(), qual), m.Obj().Name())
+			names = append(names, name)
+		}
+		got := strings.Join(names, " ")
+		if got != test.want {
+			t.Errorf("IntuitiveMethodSet(%s) = %q, want %q", test.expr, got, test.want)
+		}
+	}
+}