[Sema] Reword warning for constant captures that are not required

This is one of the darker corners of C++, make it clear that this is
about constants and rephrase it a bit.

Before: lambda capture 'i' is not required to be captured for this use
After:  lambda capture of constant 'i' is not required for this use
llvm-svn: 337152

Author: d0k

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -341,8 +341,8 @@ def warn_unneeded_member_function : Warning<
   InGroup<UnneededMemberFunction>, DefaultIgnore;
 def warn_unused_private_field: Warning<"private field %0 is not used">,
   InGroup<UnusedPrivateField>, DefaultIgnore;
-def warn_unused_lambda_capture: Warning<"lambda capture %0 is not "
-  "%select{used|required to be captured for this use}1">,
+def warn_unused_lambda_capture: Warning<"lambda capture "
+  "%select{|of constant }1%0 is not %select{used|required for this use}1">,
   InGroup<UnusedLambdaCapture>, DefaultIgnore;
 
 def warn_parameter_size: Warning<

clang/test/SemaCXX/warn-unused-lambda-capture.cpp

@@ -41,9 +41,9 @@ void test() {
   auto explicit_by_value_used = [i] { return i + 1; };
   auto explicit_by_value_used_void = [i] { (void)i; };
   auto explicit_by_value_unused = [i] {}; // expected-warning{{lambda capture 'i' is not used}}
-  auto explicit_by_value_unused_sizeof = [i] { return sizeof(i); }; // expected-warning{{lambda capture 'i' is not required to be captured for this use}}
-  auto explicit_by_value_unused_decltype = [i] { decltype(i) j = 0; }; // expected-warning{{lambda capture 'i' is not required to be captured for this use}}
-  auto explicit_by_value_unused_const = [k] { return k + 1; };         // expected-warning{{lambda capture 'k' is not required to be captured for this use}}
+  auto explicit_by_value_unused_sizeof = [i] { return sizeof(i); }; // expected-warning{{lambda capture of constant 'i' is not required for this use}}
+  auto explicit_by_value_unused_decltype = [i] { decltype(i) j = 0; }; // expected-warning{{lambda capture of constant 'i' is not required for this use}}
+  auto explicit_by_value_unused_const = [k] { return k + 1; };         // expected-warning{{lambda capture of constant 'k' is not required for this use}}
 
   auto explicit_by_reference_used = [&i] { i++; };
   auto explicit_by_reference_unused = [&i] {}; // expected-warning{{lambda capture 'i' is not used}}
@@ -146,10 +146,10 @@ void test_templated() {
   auto explicit_by_value_used_void = [i] { (void)i; };
 
   auto explicit_by_value_unused = [i] {}; // expected-warning{{lambda capture 'i' is not used}}
-  auto explicit_by_value_unused_sizeof = [i] { return sizeof(i); }; // expected-warning{{lambda capture 'i' is not required to be captured for this use}}
+  auto explicit_by_value_unused_sizeof = [i] { return sizeof(i); }; // expected-warning{{lambda capture of constant 'i' is not required for this use}}
   auto explicit_by_value_unused_decltype = [i] { decltype(i) j = 0; }; // expected-warning{{lambda capture 'i' is not used}}
-  auto explicit_by_value_unused_const = [k] { return k + 1; };         // expected-warning{{lambda capture 'k' is not required to be captured for this use}}
-  auto explicit_by_value_unused_const_generic = [k](auto c) { return k + 1; }; // expected-warning{{lambda capture 'k' is not required to be captured for this use}}
+  auto explicit_by_value_unused_const = [k] { return k + 1; };         // expected-warning{{lambda capture of constant 'k' is not required for this use}}
+  auto explicit_by_value_unused_const_generic = [k](auto c) { return k + 1; }; // expected-warning{{lambda capture of constant 'k' is not required for this use}}
 
   auto explicit_by_reference_used = [&i] { i++; };
   auto explicit_by_reference_unused = [&i] {}; // expected-warning{{lambda capture 'i' is not used}}