go/types, types2: types in method expressions must be instantiated

Use varType instead of instantiatedOperand to check if the type of a method expressions is instantiated.

This removes the last usage of instantiatedOperand, so it can be deleted.

Fixes #48048

Change-Id: I2b219dafe2bba3603100bb8f25b8ff4e8ef53841
Reviewed-on: https://go-review.googlesource.com/c/go/+/345970
Trust: Robert Griesemer <[email protected]>
Trust: Matthew Dempsky <[email protected]>
Run-TryBot: Robert Griesemer <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>

Author: qmuntal

src/cmd/compile/internal/types2/call.go

@@ -479,7 +479,9 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr) {
 		goto Error
 	}
 
-	check.instantiatedOperand(x)
+	if x.mode == typexpr {
+		x.typ = check.varType(e.X)
+	}
 
 	obj, index, indirect = LookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel)
 	if obj == nil {
@@ -718,11 +720,3 @@ func (check *Checker) useLHS(arg ...syntax.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, "cannot use generic type %s without instantiation", x.typ)
-		x.typ = Typ[Invalid]
-	}
-}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue48048.go2

@@ -0,0 +1,15 @@
+// Copyright 2021 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[P any] struct{}
+
+func (T[_]) A() {}
+
+var _ = (T[int]).A
+var _ = (*T[int]).A
+
+var _ = (T /* ERROR cannot use generic type */).A
+var _ = (*T /* ERROR cannot use generic type */).A

src/go/types/call.go

@@ -470,7 +470,9 @@ func (check *Checker) selector(x *operand, e *ast.SelectorExpr) {
 		goto Error
 	}
 
-	check.instantiatedOperand(x)
+	if x.mode == typexpr {
+		x.typ = check.varType(e.X)
+	}
 
 	obj, index, indirect = LookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel)
 	if obj == nil {
@@ -745,11 +747,3 @@ 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, _Todo, "cannot use generic type %s without instantiation", x.typ)
-		x.typ = Typ[Invalid]
-	}
-}

src/go/types/testdata/fixedbugs/issue48048.go2

@@ -0,0 +1,15 @@
+// Copyright 2021 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[P any] struct{}
+
+func (T[_]) A() {}
+
+var _ = (T[int]).A
+var _ = (*T[int]).A
+
+var _ = (T /* ERROR cannot use generic type */).A
+var _ = (*T /* ERROR cannot use generic type */).A