================
@@ -1880,16 +1880,70 @@ Sema::ConditionResult
Parser::ParseCXXCondition(StmtResult *InitStmt,
return Sema::ConditionError();
}
+ if (!getLangOpts().CPlusPlus && Tok.is(tok::kw___extension__)) {
+ // In C, the first clause of a condition may be a declaration used as an
+ // init-statement (C2y), and that declaration may be prefixed by one or
more
+ // __extension__ markers. Consume them up front -- mirroring
block-statement
+ // parsing -- so the disambiguation below sees the real start of the
+ // declaration. The markers also silence extension diagnostics for the rest
+ // of the condition, including the diagnostic for the init-statement
+ // extension itself.
+ std::optional<ExtensionRAIIObject> ExtensionGuard;
+ ExtensionGuard.emplace(Diags);
+ while (TryConsumeToken(tok::kw___extension__))
+ ;
+ }
+
ParsedAttributes attrs(AttrFactory);
- MaybeParseCXX11Attributes(attrs);
+ bool ParsedAttrs = MaybeParseCXX11Attributes(attrs);
+ if (!getLangOpts().CPlusPlus)
----------------
bassiounix wrote:
Ok after investigating the behavior of the current code, we do want to parse
this in C mode only because in C++ this code will raise an error and a warning
in case we used `[[]]` or any attributes only in the init stmt.
```cpp
if ([[]]; true) {}
if (__attribute__((assume(1 > 0))); true) {}
if (__attribute__(()); true) {}
```
But we do handle `[[]];` in C mode since we parse CXX11 attributes and check
them down with the existence of `;`
```cpp
// Handle 'if (; true)' and 'if ([[...]]; true)'.
if (Tok.is(tok::semi)) {
```
Yes GNU attributes are handled for `ConditionOrInitStatement::InitStmtDecl`,
but since it has C++ specific code it raises error/warnings on empty
declarations, which is not desired in C mode.
We can go ahead and suppress these reports but it will cause a parsing behavior
that's completely wrong rejecting valid code like `__attribute__((...))
__attribute__((...)) int x;`. If we wanted to handle that we should have a
state somewhere to know what to accept and what to reject, which will alter
functions' signature and becomes a messy edit.
The best way to go around it in my opinion is to catch that case before even
entering `ConditionOrInitStatement::InitStmtDecl` and handle it in `if
(Tok.is(tok::semi)) {` like we already do with `[[]]` by
`MaybeParseCXX11Attributes(attrs);`.
And since this is only a valid case in C mode, we don't want to do that in C++
mode and let the compiler report empty init stmt like desired.
https://github.com/llvm/llvm-project/pull/198244
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