[Parse/Sema] Diagnose invalid attributes for GenericTypeParamDecl

Previously, invalid attributes were silently accepted and ignored.

https://bugs.swift.org/browse/SR-8202

Author: rintaro

include/swift/AST/Attr.def

@@ -114,7 +114,7 @@ DECL_ATTR(_silgen_name, SILGenName,
   0)
 DECL_ATTR(available, Available,
   OnAbstractFunction | OnGenericType | OnVar | OnSubscript | OnEnumElement |
-  OnExtension |
+  OnExtension | OnGenericTypeParam |
   AllowMultipleAttributes | LongAttribute,
   1)
 CONTEXTUAL_SIMPLE_DECL_ATTR(final, Final,

lib/Sema/TypeCheckGeneric.cpp

@@ -427,6 +427,7 @@ TypeChecker::prepareGenericParamList(GenericParamList *gp,
 
   unsigned depth = gp->getDepth();
   for (auto paramDecl : *gp) {
+    checkDeclAttributesEarly(paramDecl);
     paramDecl->setDepth(depth);
     if (!paramDecl->hasAccess())
       paramDecl->setAccess(access);

test/Parse/invalid.swift

@@ -150,3 +150,10 @@ func sr8202_bar(@available(iOS, deprecated: 0) x: Int) {} // expected-error {{'@
 func sr8202_baz(@discardableResult x: Int) {} // expected-error {{'@discardableResult' attribute cannot be applied to this declaration}}
 func sr8202_qux(@objcMembers x: String) {} // expected-error {{@objcMembers may only be used on 'class' declarations}}
 func sr8202_quux(@weak x: String) {} // expected-error {{'weak' is a declaration modifier, not an attribute}} expected-error {{'weak' may only be used on 'var' declarations}}
+
+class sr8202_cls<@NSApplicationMain T: AnyObject> {} // expected-error {{@NSApplicationMain may only be used on 'class' declarations}}
+func sr8202_func<@discardableResult T>(x: T) {} // expected-error {{'@discardableResult' attribute cannot be applied to this declaration}}
+enum sr8202_enum<@indirect T> {} // expected-error {{'indirect' is a declaration modifier, not an attribute}} expected-error {{'indirect' modifier cannot be applied to this declaration}}
+protocol P {
+  @available(swift, introduced: 4.2) associatedtype Assoc // expected-error {{'@availability' attribute cannot be applied to this declaration}}
+}