cmd/compile, go/*: move method type parameter checks from parsers to type checkers

The parsers (cmd/compile/internal/syntax and go/parser) always accepted
type parameters on methods for parser robustness but reported an error.

With this change, the parsers accept the type parameters on methods,
and then the type checkers (cmd/compile/internal/types2 and go/types)
complain about them.

Add test case for method type parameters when running the parsers only.
Adjust some existing test cases as needed.

This change is a necessary first step towards implementing generic
methods but does not enable them.

For #77273.

Change-Id: I291fcf0aef0c917c74b32131c88b9e4ed71c5060
Reviewed-on: https://go-review.googlesource.com/c/go/+/738441
Reviewed-by: Mark Freeman <markfreeman@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Griesemer <gri@google.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/test/typeparam/issue50317.go b/test/typeparam/issue50317.go
index c33c4f061c..a7d0c38484 100644
--- a/test/typeparam/issue50317.go
+++ b/test/typeparam/issue50317.go
@@ -8,8 +8,8 @@ package p
 
 type S struct{}
 
-func (S) _[_ any]() {} // ERROR "method must have no type parameters"
+func (S) _[_ any]() {} // ERROR "method _ must have no type parameters"
 
 type _ interface {
-	m[_ any]() // ERROR "method must have no type parameters"
+	m[_ any]() // ERROR "interface method must have no type parameters"
 }