[dev.go2go] go/types: add missing instantiation checks for function type arguments

Fixes #40684.

Change-Id: If642edbf321973729a8d5b36b4bf61e3fae7ee3a
Reviewed-on: https://go-review.googlesource.com/c/go/+/251557
Run-TryBot: Robert Griesemer <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>

Author: griesemer

src/go/types/call.go

@@ -204,6 +204,8 @@ func (check *Checker) exprOrTypeList(elist []ast.Expr) (xlist []*operand, ok boo
 			break
 		}
 
+		check.instantiatedOperand(&x)
+
 		// exactly one (possibly invalid or comma-ok) value or type
 		xlist = []*operand{&x}
 
@@ -220,6 +222,7 @@ func (check *Checker) exprOrTypeList(elist []ast.Expr) (xlist []*operand, ok boo
 				ntypes = len(xlist) // make 'if' condition fail below (no additional error in this case)
 			case typexpr:
 				ntypes++
+				check.instantiatedOperand(&x)
 			}
 		}
 		if 0 < ntypes && ntypes < len(xlist) {
@@ -521,10 +524,7 @@ func (check *Checker) selector(x *operand, e *ast.SelectorExpr) {
 		goto Error
 	}
 
-	if x.mode == typexpr && isGeneric(x.typ) {
-		check.errorf(e.Pos(), "cannot use generic type %s without instantiation", x.typ)
-		goto Error
-	}
+	check.instantiatedOperand(x)
 
 	obj, index, indirect = check.lookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel)
 	if obj == nil {
@@ -774,3 +774,11 @@ func (check *Checker) useLHS(arg ...ast.Expr) {
 		}
 	}
 }
+
+// instantiatedOperand reports an error of x is an uninstantiated (generic) type and sets x.typ to Typ[Invalid].
+func (check *Checker) instantiatedOperand(x *operand) {
+	if x.mode == typexpr && isGeneric(x.typ) {
+		check.errorf(x.pos(), "cannot use generic type %s without instantiation", x.typ)
+		x.typ = Typ[Invalid]
+	}
+}

src/go/types/expr.go

@@ -1340,10 +1340,9 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 						x.mode = typexpr
 					}
 					return expression
-				} else {
-					check.errorf(x.pos(), "%s is not a generic type", x.typ)
-					goto Error
 				}
+				check.errorf(x.pos(), "%s is not a generic type", x.typ)
+				goto Error
 			}
 
 			if sig := x.typ.Signature(); sig != nil {

src/go/types/fixedbugs/issue40038.go2

@@ -11,5 +11,5 @@ func (A[T]) m(A[T])
 func f[P interface{m(P)}]()
 
 func _() {
-	_ = f[A]
+	_ = f[A[int]]
 }

src/go/types/fixedbugs/issue40684.go2

@@ -0,0 +1,15 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type T[_ any] int
+
+func f[_ any]()
+func g[_, _ any]()
+
+func _() {
+	_ = f[T /* ERROR without instantiation */ ]
+	_ = g[T /* ERROR without instantiation */ , T /* ERROR without instantiation */ ]
+}

src/go/types/typexpr.go

@@ -582,10 +582,7 @@ func (check *Checker) typeOrNil(e ast.Expr) Type {
 	case novalue:
 		check.errorf(x.pos(), "%s used as type", &x)
 	case typexpr:
-		if isGeneric(x.typ) {
-			check.errorf(e.Pos(), "cannot use generic type %s without instantiation", x.typ)
-			return Typ[Invalid]
-		}
+		check.instantiatedOperand(&x)
 		return x.typ
 	case value:
 		if x.isNil() {