[Parser] (C++) Make -Wextra-semi slightly more useful

Summary:
Let's suppose the `-Weverything` is passed.

Given code like
```
void F() {}
;
```
If the code is compiled with `-std=c++03`, it would diagnose that extra sema:
```
<source>:2:1: warning: extra ';' outside of a function is a C++11 extension [-Wc++11-extra-semi]
;
^~
```
If the code is compiled with `-std=c++11`, it also would diagnose that extra sema:
```
<source>:2:1: warning: extra ';' outside of a function is incompatible with C++98 [-Wc++98-compat-pedantic]
;
^~
```

But, let's suppose the C++11 or higher is used, and the used does not care
about `-Wc++98-compat-pedantic`, so he disables that diagnostic.
And that silences the complaint about extra `;` too.
And there is no way to re-enable that particular diagnostic, passing `-Wextra-semi` does nothing...

Now, there is also a related `no newline at end of file` diagnostic, which is also emitted by `-Wc++98-compat-pedantic`
```
<source>:2:2: warning: C++98 requires newline at end of file [-Wc++98-compat-pedantic]
;
 ^
```
But unlike the previous case, if `-Wno-c++98-compat-pedantic` is passed, that diagnostic stays displayed:
```
<source>:2:2: warning: no newline at end of file [-Wnewline-eof]
;
 ^
```

This diff refactors the code so `-Wc++98-compat-extra-semi` can be re-enabled, after the `-Wc++98-compat-pedantic` was disabled.
This seems ugly, but there does not seem to be any saner way.

Testing: `$ ninja check-clang`

Reviewers: rsmith, rtrieu, aaron.ballman

Reviewed By: aaron.ballman

Subscribers: jordan_rose, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D43162

llvm-svn: 327558

2 files changed, 5 insertions, 2 deletions

diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 2d471f1fa5a..c6f98cbade4 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -151,8 +151,10 @@ def Exceptions : DiagGroup<"exceptions">;
 def GNUEmptyInitializer : DiagGroup<"gnu-empty-initializer">;
 def GNUEmptyStruct : DiagGroup<"gnu-empty-struct">;
 def ExtraTokens : DiagGroup<"extra-tokens">;
+def CXX98CompatExtraSemi : DiagGroup<"c++98-compat-extra-semi">;
 def CXX11ExtraSemi : DiagGroup<"c++11-extra-semi">;
-def ExtraSemi : DiagGroup<"extra-semi", [CXX11ExtraSemi]>;
+def ExtraSemi : DiagGroup<"extra-semi", [CXX98CompatExtraSemi,
+                                         CXX11ExtraSemi]>;
 
 def GNUFlexibleArrayInitializer : DiagGroup<"gnu-flexible-array-initializer">;
 def GNUFlexibleArrayUnionMember : DiagGroup<"gnu-flexible-array-union-member">;
@@ -196,6 +198,7 @@ def CXX98Compat : DiagGroup<"c++98-compat",
 def CXX98CompatPedantic : DiagGroup<"c++98-compat-pedantic",
                                     [CXX98Compat,
                                      CXX98CompatBindToTemporaryCopy,
+                                     CXX98CompatExtraSemi,
                                      CXXPre14CompatPedantic,
                                      CXXPre17CompatPedantic,
                                      CXXPre2aCompatPedantic]>;
diff --git a/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td
index e60f3ae64b2..40c84d4afdd 100644
--- a/clang/include/clang/Basic/DiagnosticParseKinds.td
+++ b/clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -39,7 +39,7 @@ def ext_empty_translation_unit : Extension<
   InGroup<DiagGroup<"empty-translation-unit">>;
 def warn_cxx98_compat_top_level_semi : Warning<
   "extra ';' outside of a function is incompatible with C++98">,
-  InGroup<CXX98CompatPedantic>, DefaultIgnore;
+  InGroup<CXX98CompatExtraSemi>, DefaultIgnore;
 def ext_extra_semi : Extension<
   "extra ';' %select{"
   "outside of a function|"