cmd/compile, go/types: allow `any` anywhere (as a type)

Adjust types2 and go/types and some test cases.

Because `any` is not treated specially anymore in constraint
position we get additional errors in constraints if `any` is
used before Go1.18 (in addition to the error that type parameter
lists are not permitted before Go1.18).

Fixes #33232.

Change-Id: I85590c6094b07c3e494fef319e3a38d0217cf6f0
Reviewed-on: https://go-review.googlesource.com/c/go/+/351456
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 9 insertions, 10 deletions

diff --git a/test/typeparam/tparam1.go b/test/typeparam/tparam1.go
index 698877a6f0..3b4260c102 100644
--- a/test/typeparam/tparam1.go
+++ b/test/typeparam/tparam1.go
@@ -8,11 +8,10 @@
 
 package tparam1
 
-// The predeclared identifier "any" is only visible as a constraint
-// in a type parameter list.
-var _ any     // ERROR "cannot use any outside constraint position"
-func _(_ any) // ERROR "cannot use any outside constraint position"
-type _[_ any /* ok here */] struct{}
+// The predeclared identifier "any" may be used in place of interface{}.
+var _ any
+func _(_ any)
+type _[_ any] struct{}
 
 const N = 10
 
@@ -24,16 +23,16 @@ type (
 	_[T1, T2 any, T3 any] struct{}
 )
 
-func _[T any]() {}
-func _[T, T any]() {} // ERROR "T redeclared"
+func _[T any]()             {}
+func _[T, T any]()          {} // ERROR "T redeclared"
 func _[T1, T2 any](x T1) T2 { panic(0) }
 
 // Type parameters are visible from opening [ to end of function.
 type C interface{}
 
-func _[T interface{}]() {}
-func _[T C]() {}
-func _[T struct{}]() {}// ERROR "not an interface"
+func _[T interface{}]()        {}
+func _[T C]()                  {}
+func _[T struct{}]()           {} // ERROR "not an interface"
 func _[T interface{ m() T }]() {}
 func _[T1 interface{ m() T2 }, T2 interface{ m() T1 }]() {
 	var _ T1