Add -Wduplicate-protocol for existing diagnostic

[kastiglione]

Summary

Expose a warning flag for warn_duplicate_protocol_def. This allows control
over the severity of duplicate protocol definitions.

For example -Werror=duplicate-protocol or
#pragma clang diagnostic ignored "-Wduplicate-protocol".

[arphaman]

I'm not sure that it's required, but shouldn't we have also have a test that checks for the usage of this flag as well? Adding a test case with #pragma clang diagnostic ignored "-Wduplicate-protocol" and some code to a file like "test/SemaObjC/check-dup-objc-decls-1.m" should be sufficient.

[kastiglione]

@arphaman I wondered whether this called for a test. I'm happy to add one just like that.

[kastiglione]

Added test

[arphaman]

LGTM

[kastiglione]

Thanks @arphaman, are you able to commit this?

[arphaman]

In D26406#590741, @kastiglione wrote:

Thanks @arphaman, are you able to commit this?

Yes, I can commit this for you. Let me know what commit message I should use.

[kastiglione]

@arphaman Thank you. Is the summary here sufficient, or should I elaborate in some way? I'm fine with this summary if you are.

[arphaman]

It seems sufficient enough, I will commit it with the summary. Thanks!

cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td

 def err_forward_superclass : Error<
   "attempting to use the forward class %0 as superclass of %1">;
 def err_no_nsconstant_string_class : Error<
   "cannot find interface declaration for %0">;
 def err_recursive_superclass : Error<
   "trying to recursively use %0 as superclass of %1">;
 def err_conflicting_aliasing_type : Error<"conflicting types for alias %0">;
 def warn_undef_interface : Warning<"cannot find interface declaration for %0">;
-def warn_duplicate_protocol_def : Warning<"duplicate protocol definition of %0 is ignored">;
+def warn_duplicate_protocol_def : Warning<
+  "duplicate protocol definition of %0 is ignored">,
+  InGroup<DiagGroup<"duplicate-protocol">>;
 def err_protocol_has_circular_dependency : Error<
   "protocol has circular dependency">;
 def err_undeclared_protocol : Error<"cannot find protocol declaration for %0">;
 def warn_undef_protocolref : Warning<"cannot find protocol definition for %0">;
 def warn_atprotocol_protocol : Warning<
   "@protocol is using a forward protocol declaration of %0">, InGroup<AtProtocol>;
 def warn_readonly_property : Warning<
   "attribute 'readonly' of property %0 restricts attribute "

cfe/trunk/test/Misc/warning-flags.c

(2) It prevents us adding new warnings to Clang that have no -W flag.  All
     new warnings should have -W flags.
 
     If you add a new warning without a flag, this test will fail.  To fix
     this test, simply add a warning group to that warning.
 
 
 The list of warnings below should NEVER grow.  It should gradually shrink to 0.
 
-CHECK: Warnings without flags (83):
+CHECK: Warnings without flags (82):
 CHECK-NEXT:   ext_excess_initializers
 CHECK-NEXT:   ext_excess_initializers_in_char_array_initializer
 CHECK-NEXT:   ext_expected_semi_decl_list
 CHECK-NEXT:   ext_explicit_specialization_storage_class
 CHECK-NEXT:   ext_initializer_string_for_char_array_too_long
 CHECK-NEXT:   ext_missing_declspec
 CHECK-NEXT:   ext_missing_whitespace_after_macro_name
 CHECK-NEXT:   ext_new_paren_array_nonconst

 CHECK-NEXT:   warn_conv_to_void_not_used
 CHECK-NEXT:   warn_delete_array_type
 CHECK-NEXT:   warn_double_const_requires_fp64
 CHECK-NEXT:   warn_drv_assuming_mfloat_abi_is
 CHECK-NEXT:   warn_drv_clang_unsupported
 CHECK-NEXT:   warn_drv_objc_gc_unsupported
 CHECK-NEXT:   warn_drv_pch_not_first_include
 CHECK-NEXT:   warn_dup_category_def
-CHECK-NEXT:   warn_duplicate_protocol_def
 CHECK-NEXT:   warn_enum_value_overflow
 CHECK-NEXT:   warn_expected_qualified_after_typename
 CHECK-NEXT:   warn_extraneous_char_constant
 CHECK-NEXT:   warn_fe_cc_log_diagnostics_failure
 CHECK-NEXT:   warn_fe_cc_print_header_failure
 CHECK-NEXT:   warn_fe_macro_contains_embedded_newline
 CHECK-NEXT:   warn_file_asm_volatile
 CHECK-NEXT:   warn_ignoring_ftabstop_value

cfe/trunk/test/SemaObjC/check-dup-objc-decls-1.m

 @protocol P -im1; @end
 @protocol Q -im2; @end
 @interface A<P> @end  // expected-note {{previous definition is here}}
 @interface A<Q> @end  // expected-error {{duplicate interface definition for class 'A'}}
 
 @protocol PP<P> @end  // expected-note {{previous definition is here}}
 @protocol PP<Q> @end  // expected-warning {{duplicate protocol definition of 'PP'}}
 
+@protocol DP<P> @end
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wduplicate-protocol"
+@protocol DP<Q> @end
+#pragma clang diagnostic pop
+
 @interface A(Cat)<P> @end // expected-note {{previous definition is here}}
 @interface A(Cat)<Q> @end // expected-warning {{duplicate definition of category 'Cat' on interface 'A'}}
 
 // rdar 7626768
 @class NSString;
 NSString * TestBaz;  // expected-note {{previous definition is here}}
 NSString * const TestBaz;  // expected-error {{redefinition of 'TestBaz' with a different type}}