Allow arbitrary capability name in Thread Safety Analysis

Restricting the names of capabilities to only "role" or "mutex" makes
for awkward diagnostic text, such as with:
https://chromium-review.googlesource.com/c/chromium/src/+/1948098/19/base/sequence_checker_unittest.nc#33

Author: etiennep-chromium

clang/include/clang/Basic/Attr.td

@@ -2567,10 +2567,6 @@ def Capability : InheritableAttr {
   let Accessors = [Accessor<"isShared",
                     [Clang<"shared_capability", 0>]>];
   let Documentation = [Undocumented];
-  let AdditionalMembers = [{
-    bool isMutex() const { return getName().equals_lower("mutex"); }
-    bool isRole() const { return getName().equals_lower("role"); }
-  }];
 }
 
 def AssertCapability : InheritableAttr {

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -3252,9 +3252,6 @@ def warn_at_available_unchecked_use : Warning<
   InGroup<DiagGroup<"unsupported-availability-guard">>;
 
 // Thread Safety Attributes
-def warn_invalid_capability_name : Warning<
-  "invalid capability name '%0'; capability name must be 'mutex' or 'role'">,
-  InGroup<ThreadSafetyAttributes>, DefaultIgnore;
 def warn_thread_attribute_ignored : Warning<
   "ignoring %0 attribute because its argument is invalid">,
   InGroup<ThreadSafetyAttributes>, DefaultIgnore;

clang/lib/Sema/SemaDeclAttr.cpp

@@ -6195,11 +6195,6 @@ static void handleCapabilityAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
       !S.checkStringLiteralArgumentAttr(AL, 0, N, &LiteralLoc))
     return;
 
-  // Currently, there are only two names allowed for a capability: role and
-  // mutex (case insensitive). Diagnose other capability names.
-  if (!N.equals_lower("mutex") && !N.equals_lower("role"))
-    S.Diag(LiteralLoc, diag::warn_invalid_capability_name) << N;
-
   D->addAttr(::new (S.Context) CapabilityAttr(S.Context, AL, N));
 }
 

clang/test/Sema/attr-capabilities.c

@@ -1,5 +1,6 @@
 // RUN: %clang_cc1 -fsyntax-only -Wthread-safety -verify %s
 
+typedef int __attribute__((capability("role"))) ThreadRole;
 typedef int __attribute__((capability("role"))) ThreadRole;
 struct __attribute__((shared_capability("mutex"))) Mutex {};
 struct NotACapability {};
@@ -8,8 +9,8 @@ struct NotACapability {};
 union __attribute__((capability("mutex"))) MutexUnion { int a; char* b; };
 typedef union { int a; char* b; } __attribute__((capability("mutex"))) MutexUnion2;
 
-// Test an invalid capability name
-struct __attribute__((capability("wrong"))) IncorrectName {}; // expected-warning {{invalid capability name 'wrong'; capability name must be 'mutex' or 'role'}}
+// Test a different capability name
+struct __attribute__((capability("custom"))) CustomName {};
 
 int Test1 __attribute__((capability("test1")));  // expected-error {{'capability' attribute only applies to structs, unions, classes, and typedefs}}
 int Test2 __attribute__((shared_capability("test2"))); // expected-error {{'shared_capability' attribute only applies to structs, unions, classes, and typedefs}}