rsmith added a comment.
Maybe you could refactor the check to something like:
if (Name.isIdentifier() && Name.getAsIdentifierInfo()->isStr("main")
NewVD->getDeclContext()->getRedeclContext()->isTranslationUnit() &&
!getLangOpts().Freestanding && !NewVD->getDescribedVarTemplate()) {
if (getLangOpts().CPlusPlus)
Diag1;
else if (NewVD->hasExternalFormalLinkage())
Diag2;
}
================
Comment at: include/clang/Basic/DiagnosticSemaKinds.td:514
@@ +513,3 @@
+def err_main_global_variable : Error<"main can't be declared as global
variable">;
+def warn_main_redefined : Warning<"external-linkage variable named 'main' has "
+ "undefined behavior">, InGroup<Main>;
----------------
Hyphenating 'external linkage' is unusual; how about 'variable named 'main'
with external linkage has undefined behavior'?
================
Comment at: lib/Sema/SemaDecl.cpp:6113
@@ +6112,3 @@
+ // A program that declares a variable main at global scope is ill-formed.
+ if (getLangOpts().CPlusPlus && !getLangOpts().Freestanding &&
+ NewVD->hasGlobalStorage() && !NewVD->isStaticLocal() &&
----------------
The freestanding check should apply in C too.
================
Comment at: lib/Sema/SemaDecl.cpp:6114-6116
@@ +6113,5 @@
+ if (getLangOpts().CPlusPlus && !getLangOpts().Freestanding &&
+ NewVD->hasGlobalStorage() && !NewVD->isStaticLocal() &&
+ !NewVD->isStaticDataMember() && !NewVD->getDescribedVarTemplate()
&&
+ NewVD->getDeclContext()->isTranslationUnit())
+ Diag(D.getLocStart(), diag::err_main_global_variable);
----------------
The only checks you need here are: 1) DeclContext's redecl context is the
translation unit, and 2) NewVD is not a variable template. All the other checks
are implied by the DC check. I'd suggest factoring these out into the main
check.
================
Comment at: lib/Sema/SemaDecl.cpp:6116
@@ +6115,3 @@
+ !NewVD->isStaticDataMember() && !NewVD->getDescribedVarTemplate()
&&
+ NewVD->getDeclContext()->isTranslationUnit())
+ Diag(D.getLocStart(), diag::err_main_global_variable);
----------------
You need to check `NewVD->getDeclContext()->getRedeclContext()`, in case there
are `LinkageSpecDecl`s surrounding the variable (`extern "C++" int main;`).
================
Comment at: lib/Sema/SemaDecl.cpp:6121
@@ +6120,3 @@
+ // behavior.
+ if (!getLangOpts().CPlusPlus && NewVD->isExternC())
+ Diag(D.getLocStart(), diag::warn_main_redefined);
----------------
It's weird to ask `isExternC` from C. Use `hasExternalFormalLinkage` instead.
http://reviews.llvm.org/D11658
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