[PATCH] D150258: [clang][parser] Fix namespace dropping after malformed declarations

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added a comment.

Thank you for working on this! FWIW, I verified that the precommit CI failures are unrelated to this patch.

Can you add a release note to `clang/docs/ReleaseNotes.rst` about the fix?



================
Comment at: clang/lib/Parse/ParseDecl.cpp:2179-2180
 
-        if (isDeclarationSpecifier(ImplicitTypenameContext::No)) {
+        if (isDeclarationSpecifier(ImplicitTypenameContext::No) ||
+            Tok.is(tok::kw_namespace)) {
           // If there is an invalid declaration specifier right after the
----------------
It'd help to update the comment below since it doesn't mention why namespaces are handled specially.


================
Comment at: clang/lib/Parse/ParseDecl.cpp:2306-2310
     // Otherwise things are very confused and we skip to recover.
     if (!isDeclarationSpecifier(ImplicitTypenameContext::No)) {
-      SkipUntil(tok::r_brace, StopAtSemi | StopBeforeMatch);
-      TryConsumeToken(tok::semi);
+      SkipMalformedDecl();
     }
   }
----------------
Changes for our coding style.

There seems to be some unfortunate interplay here though. Consider:
```
void bar() namespace foo { int i; }

int main() {
  foo::i = 12;
}
```
Calling `SkipMalformedDecl()` changes the behavior for this test case because we don't recover as well. With your patch applied, this gives us two diagnostics:
```
C:\Users\aballman\OneDrive - Intel Corporation\Desktop\test.cpp:1:11: error: expected ';' after top level declarator
void bar() namespace foo { int i; }
          ^
          ;
C:\Users\aballman\OneDrive - Intel Corporation\Desktop\test.cpp:4:3: error: use of undeclared identifier 'foo'
  foo::i = 12;
  ^
2 errors generated.
```
If the `namespace` keyword is on its own line, then we recover gracefully and don't emit the "use of undeclared identifier" warning.

While this is technically a regression in behavior for this test case, I think the overall changes are still an improvement. I suspect not a whole lot of code puts `namespace` somewhere other than the start of a line (same for `inline namespace` which has the same behavior with your patch).


================
Comment at: clang/lib/Parse/ParseTemplate.cpp:278
   if (!DeclaratorInfo.hasName()) {
-    // If so, skip until the semi-colon or a }.
-    SkipUntil(tok::r_brace, StopAtSemi | StopBeforeMatch);
-    if (Tok.is(tok::semi))
-      ConsumeToken();
+    SkipMalformedDecl();
     return nullptr;
----------------
We'll have the same sort of recovery issues here unless the namespace is on its own line, but that also seems like a highly unlikely scenario.


================
Comment at: clang/test/Parser/cxx-namespace-after-missing-semicolon.cpp:1
+// RUN: %clang_cc1 -verify %s
+
----------------



================
Comment at: clang/test/Parser/cxx-template-recovery.cpp:1
+// RUN: %clang_cc1 -verify %s
+
----------------



Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D150258/new/

https://reviews.llvm.org/D150258