go/types: determine hasPtrRecv property from source rather than type

LookupFieldOrMethod needs to know if a method receiver is a pointer
type. Until now this was computed from the the method signature's
receiver, which required the method signature to be type-checked.
Furthermore, it required the receiver to be set before the method
signature was fully type-checked in some cases (see issue #6638).

This CL remembers this property during object resolution, when we
know it from the source.

With this CL, method signatures don't need to be type-checked before
they can be looked up; this is a first step towards separating
type checking of types and type-checking of associated methods.

Updates #23203.
Updates #26854.

Change-Id: Ie3eb7976e8fe8176ea1b284fa7471a4b7000f80b
Reviewed-on: https://go-review.googlesource.com/c/139422
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

src/go/types/methodset.go

@@ -255,8 +255,17 @@ func (s methodSet) add(list []*Func, index []int, indirect bool, multiples bool)
 }
 
 // ptrRecv reports whether the receiver is of the form *T.
-// The receiver must exist.
 func ptrRecv(f *Func) bool {
-	_, isPtr := deref(f.typ.(*Signature).recv.typ)
-	return isPtr
+	// If a method's type is set, use that as the source of truth for the receiver.
+	if f.typ != nil {
+		_, isPtr := deref(f.typ.(*Signature).recv.typ)
+		return isPtr
+	}
+
+	// If a method's type is not set it may be a method/function that is:
+	// 1) client-supplied (via NewFunc with no signature), or
+	// 2) internally created but not yet type-checked.
+	// For case 1) we can't do anything; the client must know what they are doing.
+	// For case 2) we can use the information gathered by the resolver.
+	return f.hasPtrRecv
 }

src/go/types/object.go

@@ -294,6 +294,7 @@ func (*Var) isDependency() {} // a variable may be a dependency of an initializa
 // An abstract method may belong to many interfaces due to embedding.
 type Func struct {
 	object
+	hasPtrRecv bool // only valid for methods that don't have a type yet
 }
 
 // NewFunc returns a new function with the given signature, representing
@@ -304,7 +305,7 @@ func NewFunc(pos token.Pos, pkg *Package, name string, sig *Signature) *Func {
 	if sig != nil {
 		typ = sig
 	}
-	return &Func{object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}}
+	return &Func{object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, false}
 }
 
 // FullName returns the package- or receiver-type-qualified name of

src/go/types/resolver.go

@@ -465,6 +465,8 @@ func (check *Checker) collectObjects() {
 			typ := unparen(list[0].Type)
 			if ptr, _ := typ.(*ast.StarExpr); ptr != nil {
 				typ = unparen(ptr.X)
+				// TODO(gri): This may not be sufficient. See issue #27995.
+				f.hasPtrRecv = true
 			}
 			if base, _ := typ.(*ast.Ident); base != nil {
 				// base is a potential base type name; determine

src/go/types/typexpr.go

@@ -558,9 +558,13 @@ func (check *Checker) interfaceType(ityp *Interface, iface *ast.InterfaceType, d
 			pos := name.Pos()
 			// Don't type-check signature yet - use an
 			// empty signature now and update it later.
-			// Since we know the receiver, set it up now
-			// (required to avoid crash in ptrRecv; see
-			// e.g. test case for issue 6638).
+			// But set up receiver since we know it and
+			// its position, and because interface method
+			// signatures don't get a receiver via regular
+			// type-checking (there isn't a receiver in the
+			// the method's AST). Setting the correct receiver
+			// type is also important for ptrRecv() (see methodset.go).
+			//
 			// TODO(gri) Consider marking methods signatures
 			// as incomplete, for better error messages. See
 			// also the T4 and T5 tests in testdata/cycles2.src.