[dev.typeparams] go/types: cleanups around receiver type checks

This is a port of CL 333770 to go/types, adjusted for the error
reporting API and to not support compiler error messages. An error
message changed (to 'invalid receiver type' from just 'invalid
receiver'), so a test had to be adjusted.

Change-Id: I166e8831d8c9f98ebfb0270fe5221586fc112825
Reviewed-on: https://go-review.googlesource.com/c/go/+/335079
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/types/signature.go

@@ -199,30 +199,40 @@ func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast
 
 		// spec: "The receiver type must be of the form T or *T where T is a type name."
 		// (ignore invalid types - error was reported before)
-		if t := rtyp; t != Typ[Invalid] {
+		if rtyp != Typ[Invalid] {
 			var err string
-			if T := asNamed(t); T != nil {
+			switch T := rtyp.(type) {
+			case *Named:
 				// spec: "The type denoted by T is called the receiver base type; it must not
 				// be a pointer or interface type and it must be declared in the same package
 				// as the method."
 				if T.obj.pkg != check.pkg {
 					err = "type not defined in this package"
 				} else {
-					switch u := optype(T).(type) {
-					case *Basic:
-						// unsafe.Pointer is treated like a regular pointer
-						if u.kind == UnsafePointer {
-							err = "unsafe.Pointer"
+					// The underlying type of a receiver base type can be a type parameter;
+					// e.g. for methods with a generic receiver T[P] with type T[P any] P.
+					underIs(T, func(u Type) bool {
+						switch u := u.(type) {
+						case *Basic:
+							// unsafe.Pointer is treated like a regular pointer
+							if u.kind == UnsafePointer {
+								err = "unsafe.Pointer"
+								return false
+							}
+						case *Pointer, *Interface:
+							err = "pointer or interface type"
+							return false
 						}
-					case *Pointer, *Interface:
-						err = "pointer or interface type"
-					}
+						return true
+					})
 				}
-			} else {
+			case *Basic:
 				err = "basic or unnamed type"
+			default:
+				check.errorf(recv, _InvalidRecv, "invalid receiver type %s", recv.typ)
 			}
 			if err != "" {
-				check.errorf(recv, _InvalidRecv, "invalid receiver %s (%s)", recv.typ, err)
+				check.errorf(recv, _InvalidRecv, "invalid receiver type %s (%s)", recv.typ, err)
 				// ok to continue
 			}
 		}

src/go/types/testdata/examples/methods.go2

@@ -6,6 +6,8 @@
 
 package p
 
+import "unsafe"
+
 // Parameterized types may have methods.
 type T1[A any] struct{ a A }
 
@@ -94,3 +96,18 @@ func (_ T2[_, _, _]) _() int { return 42 }
 type T0 struct{}
 func (T0) _() {}
 func (T1[A]) _() {}
+
+// A generic receiver type may constrain its type parameter such
+// that it must be a pointer type. Such receiver types are not
+// permitted.
+type T3a[P interface{ ~int | ~string | ~float64 }] P
+
+func (T3a[_]) m() {} // this is ok
+
+type T3b[P interface{ ~unsafe.Pointer }] P
+
+func (T3b /* ERROR invalid receiver */ [_]) m() {}
+
+type T3c[P interface{ *int | *string }] P
+
+func (T3c /* ERROR invalid receiver */ [_]) m() {}

src/go/types/testdata/fixedbugs/issue28251.src

@@ -60,6 +60,6 @@ type (
         T11 = T
 )
 
-func (T9 /* ERROR invalid receiver \*\*T */ ) m9() {}
+func (T9 /* ERROR invalid receiver type \*\*T */ ) m9() {}
 func _() { (T{}).m9 /* ERROR has no field or method m9 */ () }
 func _() { (&T{}).m9 /* ERROR has no field or method m9 */ () }