[clang] Enable the -Wdangling-capture diagnostic by default. (llvm#11…

…9685)

We have tested this diagnostics internally, and we don't find see any
issues.

clang/docs/ReleaseNotes.rst

@@ -666,6 +666,15 @@ Improvements to Clang's diagnostics
       bool operator==(const C&) = default;
     };
 
+- Clang now emits `-Wdangling-capture` diangostic when a STL container captures a dangling reference.
+
+  .. code-block:: c++
+
+    void test() {
+      std::vector<std::string_view> views;
+      views.push_back(std::string("123")); // warning
+    }
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -10237,10 +10237,10 @@ def warn_dangling_pointer_assignment : Warning<
    InGroup<DanglingAssignment>;
 def warn_dangling_reference_captured : Warning<
    "object whose reference is captured by '%0' will be destroyed at the end of "
-   "the full-expression">, InGroup<DanglingCapture>, DefaultIgnore;
+   "the full-expression">, InGroup<DanglingCapture>;
 def warn_dangling_reference_captured_by_unknown : Warning<
    "object whose reference is captured will be destroyed at the end of "
-   "the full-expression">, InGroup<DanglingCapture>, DefaultIgnore;
+   "the full-expression">, InGroup<DanglingCapture>;
 
 // For non-floating point, expressions of the form x == x or x != x
 // should result in a warning, since these always evaluate to a constant.