Enforce restrictions that 'main' is not allowed to be deleted, or to be used by

the program, in C++. (We allow the latter as an extension, since we've always
permitted it, and GCC does the same, and our supported C++ ABIs don't do
anything special in main.)

llvm-svn: 199782

3 files changed, 16 insertions, 3 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index c08d87d59a8..9dac4d53024 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -6809,6 +6809,8 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     }
 
     // If a function is defined as defaulted or deleted, mark it as such now.
+    // FIXME: Does this ever happen? ActOnStartOfFunctionDef forces the function
+    // definition kind to FDK_Definition.
     switch (D.getFunctionDefinitionKind()) {
       case FDK_Declaration:
       case FDK_Definition:
@@ -7670,8 +7672,9 @@ static SourceRange getResultSourceRange(const FunctionDecl *FD) {
 }
 
 void Sema::CheckMain(FunctionDecl* FD, const DeclSpec& DS) {
-  // C++11 [basic.start.main]p3:  A program that declares main to be inline,
-  //   static or constexpr is ill-formed.
+  // C++11 [basic.start.main]p3:
+  //   A program that [...] declares main to be inline, static or
+  //   constexpr is ill-formed.
   // C11 6.7.4p4:  In a hosted environment, no function specifier(s) shall
   //   appear in a declaration of main.
   // static main is not an error under C99, but we should warn about it.
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 39d71e20163..76b9d669d42 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -11984,6 +11984,11 @@ void Sema::SetDeclDeleted(Decl *Dcl, SourceLocation DelLoc) {
     }
   }
 
+  // C++11 [basic.start.main]p3:
+  //   A program that defines main as deleted [...] is ill-formed.
+  if (Fn->isMain())
+    Diag(DelLoc, diag::err_deleted_main);
+
   Fn->setDeletedAsWritten();
 }
 
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 3640c5ad24b..ff54b6b24e4 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -264,13 +264,18 @@ bool Sema::DiagnoseUseOfDecl(NamedDecl *D, SourceLocation Loc,
       SmallVectorImpl<PartialDiagnosticAt> &Suppressed = Pos->second;
       for (unsigned I = 0, N = Suppressed.size(); I != N; ++I)
         Diag(Suppressed[I].first, Suppressed[I].second);
-      
+
       // Clear out the list of suppressed diagnostics, so that we don't emit
       // them again for this specialization. However, we don't obsolete this
       // entry from the table, because we want to avoid ever emitting these
       // diagnostics again.
       Suppressed.clear();
     }
+
+    // C++ [basic.start.main]p3:
+    //   The function 'main' shall not be used within a program.
+    if (cast<FunctionDecl>(D)->isMain())
+      Diag(Loc, diag::ext_main_used);
   }
 
   // See if this is an auto-typed variable whose initializer we are parsing.