Give string literals const element typesin C++, and cope with the deprecated C++ conversion from a string literal to a pointer-to-non-const-character

llvm-svn: 56137

3 files changed, 49 insertions, 0 deletions

diff --git a/clang/lib/Sema/Sema.h b/clang/lib/Sema/Sema.h
index f45e49ff018..e562547a8ee 100644
--- a/clang/lib/Sema/Sema.h
+++ b/clang/lib/Sema/Sema.h
@@ -890,6 +890,8 @@ private:
   // blcok pointer types.
   AssignConvertType CheckBlockPointerTypesForAssignment(QualType lhsType, 
                                                         QualType rhsType);
+
+  bool IsStringLiteralToNonConstPointerConversion(Expr *From, QualType ToType);
   
   /// the following "Check" methods will return a valid/converted QualType
   /// or a null QualType (indicating an error diagnostic was issued).
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 017e19df6c1..f0765d538d6 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -290,6 +290,10 @@ Sema::ActOnStringLiteral(const Token *StringToks, unsigned NumStringToks) {
   QualType StrTy = Context.CharTy;
   if (Literal.AnyWide) StrTy = Context.getWCharType();
   if (Literal.Pascal) StrTy = Context.UnsignedCharTy;
+
+  // A C++ string literal has a const-qualified element type (C++ 2.13.4p1).
+  if (getLangOptions().CPlusPlus)
+    StrTy.addConst();
   
   // Get an array type for the string, according to C99 6.4.5.  This includes
   // the nul terminator character as well as the string length for pascal
@@ -3066,6 +3070,18 @@ bool Sema::DiagnoseAssignmentResult(AssignConvertType ConvTy,
     DiagKind = diag::ext_typecheck_convert_pointer_void_func;
     break;
   case CompatiblePointerDiscardsQualifiers:
+    // If the qualifiers lost were because we were applying the
+    // (deprecated) C++ conversion from a string literal to a char*
+    // (or wchar_t*), then there was no error (C++ 4.2p2).  FIXME:
+    // Ideally, this check would be performed in
+    // CheckPointerTypesForAssignment. However, that would require a
+    // bit of refactoring (so that the second argument is an
+    // expression, rather than a type), which should be done as part
+    // of a larger effort to fix CheckPointerTypesForAssignment for
+    // C++ semantics.
+    if (getLangOptions().CPlusPlus &&
+        IsStringLiteralToNonConstPointerConversion(SrcExpr, DstType))
+      return false;
     DiagKind = diag::ext_typecheck_convert_discards_qualifiers;
     break;
   case IntToBlockPointer:
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index a7e36c95fcd..c8a21f7d53f 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -202,3 +202,34 @@ bool Sema::CheckCXXBooleanCondition(Expr *&CondExpr) {
                 Ty.getAsString(), CondExpr->getSourceRange());
   return false;
 }
+
+/// Helper function to determine whether this is the (deprecated) C++
+/// conversion from a string literal to a pointer to non-const char or
+/// non-const wchar_t (for narrow and wide string literals,
+/// respectively).
+bool 
+Sema::IsStringLiteralToNonConstPointerConversion(Expr *From, QualType ToType) {
+  // Look inside the implicit cast, if it exists.
+  if (ImplicitCastExpr *Cast = dyn_cast<ImplicitCastExpr>(From))
+    From = Cast->getSubExpr();
+
+  // A string literal (2.13.4) that is not a wide string literal can
+  // be converted to an rvalue of type "pointer to char"; a wide
+  // string literal can be converted to an rvalue of type "pointer
+  // to wchar_t" (C++ 4.2p2).
+  if (StringLiteral *StrLit = dyn_cast<StringLiteral>(From))
+    if (const PointerType *ToPtrType = ToType->getAsPointerType())
+      if (const BuiltinType *ToPointeeType 
+          = ToPtrType->getPointeeType()->getAsBuiltinType()) {
+        // This conversion is considered only when there is an
+        // explicit appropriate pointer target type (C++ 4.2p2).
+        if (ToPtrType->getPointeeType().getCVRQualifiers() == 0 &&
+            ((StrLit->isWide() && ToPointeeType->isWideCharType()) ||
+             (!StrLit->isWide() &&
+              (ToPointeeType->getKind() == BuiltinType::Char_U ||
+               ToPointeeType->getKind() == BuiltinType::Char_S))))
+          return true;
+      }
+
+  return false;
+}