[clang-tidy] Add test support for the fix description.

[hokein]

Summary

Add a new annotation "CHECK-FIX-DESCRIPTIONS" to lit test to
verify the fix description provided by checks.

[hokein]

cleanup

[alexfh]

clang-tools-extra/test/clang-tidy/check_clang_tidy.py

109 ↗

(On Diff #195385)

Wait, how do "check descriptions" differ from notes?

[hokein]

Use CHECK-NOTES.

[hokein]

Based on our last offline discussion, it is possible to use CHECK-NOTES to verify fix descriptions. However, CHECK-NOTES enforce sto verify all note diagnostic messages, some existing tests will be failed because they don't cover all notes (the number is not large, only ~60), I'll update the tests when updating the relative checks.

Finally (after every check provides fix descriptions), we may deprecate CHECK-MESSAGES, and in favor of CHECK-NOTES.

clang-tools-extra/test/clang-tidy/misc-unused-using-decls.cpp

 };
 template <typename T>
 T ff() { T t; return t; }
 } // namespace ns
 
 // ----- Using declarations -----
 // eol-comments aren't removed (yet)
 using n::A; // A
-// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: using decl 'A' is unused
+// CHECK-NOTES: :[[@LINE-1]]:10: warning: using decl 'A' is unused
+// CHECK-NOTES: [[@LINE-2]]:10: note: remove the using
 // CHECK-FIXES: {{^}}// A
 using n::B;
 using n::C;
 using n::D;
 using n::E; // E
-// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: using decl 'E' is unused
+// CHECK-NOTES: :[[@LINE-1]]:10: warning: using decl 'E' is unused
+// CHECK-NOTES: [[@LINE-2]]:10: note: remove the using
 // CHECK-FIXES: {{^}}// E
 using n::F;
 using n::G;
 using n::H;
 using n::I;
 int I::ii = 1;
 class Derived : public n::Base {
  public:
   using Base::f;
 };
 using n::UsedInstance;
 using n::UsedFunc;
 using n::UsedTemplateFunc;
 using n::UnusedInstance; // UnusedInstance
-// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: using decl 'UnusedInstance' is unused
+// CHECK-NOTES: :[[@LINE-1]]:10: warning: using decl 'UnusedInstance' is unused
+// CHECK-NOTES: [[@LINE-2]]:10: note: remove the using
 // CHECK-FIXES: {{^}}// UnusedInstance
 using n::UnusedFunc; // UnusedFunc
-// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: using decl 'UnusedFunc' is unused
+// CHECK-NOTES: :[[@LINE-1]]:10: warning: using decl 'UnusedFunc' is unused
+// CHECK-NOTES: [[@LINE-2]]:10: note: remove the using
 // CHECK-FIXES: {{^}}// UnusedFunc
 using n::cout;
 using n::endl;
 
 using n::UsedInTemplateFunc;
 using n::J;
 template <typename T> void Callee() {
   J<T> j;
   UsedInTemplateFunc<T>();
 }
 
 using n::OverloadFunc; // OverloadFunc
-// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: using decl 'OverloadFunc' is unused
+// CHECK-NOTES: :[[@LINE-1]]:10: warning: using decl 'OverloadFunc' is unused
+// CHECK-NOTES: [[@LINE-2]]:10: note: remove the using
 // CHECK-FIXES: {{^}}// OverloadFunc
 
 #define DEFINE_INT(name)        \
   namespace INT {               \
   static const int _##name = 1; \
   }                             \
   using INT::_##name
 DEFINE_INT(test);

 }
 
 void IgnoreFunctionScope() {
 // Using-decls defined in function scope will be ignored.
 using n::H;
 }
 
 using n::Color1;
-// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: using decl 'Color1' is unused
+// CHECK-NOTES: :[[@LINE-1]]:10: warning: using decl 'Color1' is unused
+// CHECK-NOTES: [[@LINE-2]]:10: note: remove the using
 using n::Green;
-// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: using decl 'Green' is unused
+// CHECK-NOTES: :[[@LINE-1]]:10: warning: using decl 'Green' is unused
+// CHECK-NOTES: [[@LINE-2]]:10: note: remove the using
 using n::Color2;
 using n::Color3;
 using n::Blue;
 
 using ns::AA;
 using ns::ff;
 
 using n::K;
 
 using n::N;
 
 // FIXME: Currently non-type template arguments are not supported.
 using n::Constant;
-// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: using decl 'Constant' is unused
-
+// CHECK-NOTES: :[[@LINE-1]]:10: warning: using decl 'Constant' is unused
+// CHECK-NOTES: [[@LINE-2]]:10: note: remove the using
 // ----- Usages -----
 void f(B b);
 void g() {
   vector<C> data;
   D::i = 1;
   F<int> f;
   void (*func)() = &G::func;
   int *i = &H::i;