[ASTImporter] Import default expression of param before creating the param.

Summary:
The default expression of a parameter variable should be imported before
the parameter variable object is created. Otherwise the function is created
with an incomplete parameter variable (default argument is nullptr) and in
this intermediary state the expression is imported. This import can have
a reference to the incomplete parameter variable that causes crash.

Reviewers: martong, a.sidorin, shafik

Reviewed By: martong

Subscribers: rnkovacs, dkrupp, Szelethus, gamesh411, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D65577

llvm-svn: 368818

1 files changed, 47 insertions, 19 deletions

diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 651c675649e..5b7b5438f6c 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -426,6 +426,9 @@ namespace clang {
 
     Error ImportFunctionDeclBody(FunctionDecl *FromFD, FunctionDecl *ToFD);
 
+    Error ImportDefaultArgOfParmVarDecl(const ParmVarDecl *FromParam,
+                                        ParmVarDecl *ToParam);
+
     template <typename T>
     bool hasSameVisibilityContext(T *Found, T *From);
 
@@ -3841,6 +3844,28 @@ ExpectedDecl ASTNodeImporter::VisitImplicitParamDecl(ImplicitParamDecl *D) {
   return ToParm;
 }
 
+Error ASTNodeImporter::ImportDefaultArgOfParmVarDecl(
+    const ParmVarDecl *FromParam, ParmVarDecl *ToParam) {
+  ToParam->setHasInheritedDefaultArg(FromParam->hasInheritedDefaultArg());
+  ToParam->setKNRPromoted(FromParam->isKNRPromoted());
+
+  if (FromParam->hasUninstantiatedDefaultArg()) {
+    if (auto ToDefArgOrErr = import(FromParam->getUninstantiatedDefaultArg()))
+      ToParam->setUninstantiatedDefaultArg(*ToDefArgOrErr);
+    else
+      return ToDefArgOrErr.takeError();
+  } else if (FromParam->hasUnparsedDefaultArg()) {
+    ToParam->setUnparsedDefaultArg();
+  } else if (FromParam->hasDefaultArg()) {
+    if (auto ToDefArgOrErr = import(FromParam->getDefaultArg()))
+      ToParam->setDefaultArg(*ToDefArgOrErr);
+    else
+      return ToDefArgOrErr.takeError();
+  }
+
+  return Error::success();
+}
+
 ExpectedDecl ASTNodeImporter::VisitParmVarDecl(ParmVarDecl *D) {
   // Parameters are created in the translation unit's context, then moved
   // into the function declaration's context afterward.
@@ -3867,23 +3892,11 @@ ExpectedDecl ASTNodeImporter::VisitParmVarDecl(ParmVarDecl *D) {
                               /*DefaultArg*/ nullptr))
     return ToParm;
 
-  // Set the default argument.
-  ToParm->setHasInheritedDefaultArg(D->hasInheritedDefaultArg());
-  ToParm->setKNRPromoted(D->isKNRPromoted());
-
-  if (D->hasUninstantiatedDefaultArg()) {
-    if (auto ToDefArgOrErr = import(D->getUninstantiatedDefaultArg()))
-      ToParm->setUninstantiatedDefaultArg(*ToDefArgOrErr);
-    else
-      return ToDefArgOrErr.takeError();
-  } else if (D->hasUnparsedDefaultArg()) {
-    ToParm->setUnparsedDefaultArg();
-  } else if (D->hasDefaultArg()) {
-    if (auto ToDefArgOrErr = import(D->getDefaultArg()))
-      ToParm->setDefaultArg(*ToDefArgOrErr);
-    else
-      return ToDefArgOrErr.takeError();
-  }
+  // Set the default argument. It should be no problem if it was already done.
+  // Do not import the default expression before GetImportedOrCreateDecl call
+  // to avoid possible infinite import loop because circular dependency.
+  if (Error Err = ImportDefaultArgOfParmVarDecl(D, ToParm))
+    return std::move(Err);
 
   if (D->isObjCMethodParameter()) {
     ToParm->setObjCMethodScopeInfo(D->getFunctionScopeIndex());
@@ -6939,8 +6952,23 @@ ExpectedStmt ASTNodeImporter::VisitCXXDefaultArgExpr(CXXDefaultArgExpr *E) {
   if (!UsedContextOrErr)
     return UsedContextOrErr.takeError();
 
-  return CXXDefaultArgExpr::Create(
-      Importer.getToContext(), *ToUsedLocOrErr, *ToParamOrErr, *UsedContextOrErr);
+  // Import the default arg if it was not imported yet.
+  // This is needed because it can happen that during the import of the
+  // default expression (from VisitParmVarDecl) the same ParmVarDecl is
+  // encountered here. The default argument for a ParmVarDecl is set in the
+  // ParmVarDecl only after it is imported (set in VisitParmVarDecl if not here,
+  // see VisitParmVarDecl).
+  ParmVarDecl *ToParam = *ToParamOrErr;
+  if (!ToParam->getDefaultArg()) {
+    Optional<ParmVarDecl *> FromParam = Importer.getImportedFromDecl(ToParam);
+    assert(FromParam && "ParmVarDecl was not imported?");
+
+    if (Error Err = ImportDefaultArgOfParmVarDecl(*FromParam, ToParam))
+      return std::move(Err);
+  }
+
+  return CXXDefaultArgExpr::Create(Importer.getToContext(), *ToUsedLocOrErr,
+                                   *ToParamOrErr, *UsedContextOrErr);
 }
 
 ExpectedStmt