Implement implicit auto keyword injection in clang itself.

Co-authored-by: Axel Naumann <Axel.Naumann@cern.ch>
Co-authored-by: Javier Lopez-Gomez <javier.lopez.gomez@cern.ch>

Author: 3 people

clang/lib/Sema/SemaExpr.cpp

@@ -15654,6 +15654,46 @@ ExprResult Sema::CreateBuiltinBinOp(SourceLocation OpLoc,
 
   switch (Opc) {
   case BO_Assign:
+    // ROOT hack: we want to support constructs like n = new TNamed() and if n
+    // wasn't declared we should declare it.
+    if (DeclRefExpr* DRE = dyn_cast<DeclRefExpr>(LHSExpr)) {
+      if (VarDecl* VD = dyn_cast<VarDecl>(DRE->getDecl())) {
+        if (const AutoType* aTy = dyn_cast<AutoType>(VD->getType().getTypePtr())) {
+          if (const AnnotateAttr* A = VD->getAttr<AnnotateAttr>()) {
+            // If the deduction didn't take place and it is our special
+            // annotation
+            if (!aTy->isDeduced() && A->getAnnotation().equals("__Auto")) {
+              QualType ResTy;
+              ASTContext& C = getASTContext();
+              TypeSourceInfo* TrivialTSI
+                = C.getTrivialTypeSourceInfo(VD->getType());
+              TemplateDeductionInfo Info(RHSExpr->getExprLoc());
+              TemplateDeductionResult Result =
+                  DeduceAutoType(TrivialTSI->getTypeLoc(), RHSExpr, ResTy, Info);
+              if (Result != TDK_Success && Result != TDK_AlreadyDiagnosed) {
+                 Diag(VD->getLocation(), diag::err_auto_var_requires_init)
+                    << VD->getDeclName() << VD->getType();
+                 VD->setInvalidDecl();
+
+                 return ExprError();
+              }
+              if (!ResTy.isNull()) {
+                VD->setTypeSourceInfo(C.getTrivialTypeSourceInfo(ResTy));
+                VD->setType(ResTy);
+              }
+              VD->setInit(DefaultLvalueConversion(RHSExpr).get());
+              PushOnScopeChains(VD, getCurScope(), /*Add to ctx*/true);
+
+              // Here we need to return 'something' to make the parser happy.
+              // A reference to the decl is semantically closest to what we want.
+              return BuildDeclRefExpr(VD, VD->getType(), VK_LValue,
+                                      SourceLocation());
+            }
+          }
+        }
+      }
+    }
+
     ResultTy = CheckAssignmentOperands(LHS.get(), RHS, OpLoc, QualType(), Opc);
     if (getLangOpts().CPlusPlus &&
         LHS.get()->getObjectKind() != OK_ObjCProperty) {