From: Volodymyr Sapsai <vsapsai@apple.com>
Date: Mon, 14 May 2018 22:49:44 +0000 (+0000)
Subject: [c++17] Fix assertion on synthesizing deduction guides after a fatal error.
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=82cd820babf3a0f09c8e566a8445b3eee09412f4;p=clang

[c++17] Fix assertion on synthesizing deduction guides after a fatal error.

After a fatal error Sema::InstantiatingTemplate doesn't allow further
instantiation and doesn't push a CodeSynthesisContext. When we tried to
synthesize implicit deduction guides from constructors we hit the
assertion

> Assertion failed: (!CodeSynthesisContexts.empty() && "Cannot perform an instantiation without some context on the " "instantiation stack"), function SubstType, file clang/lib/Sema/SemaTemplateInstantiate.cpp, line 1580.

Fix by avoiding deduction guide synthesis if InstantiatingTemplate is invalid.

rdar://problem/39051732

Reviewers: rsmith

Reviewed By: rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D46446


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@332307 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index 530fc668f2..a5f6b3f026 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -1976,6 +1976,8 @@ void Sema::DeclareImplicitDeductionGuides(TemplateDecl *Template,
   // FIXME: Add a kind for this to give more meaningful diagnostics. But can
   // this substitution process actually fail?
   InstantiatingTemplate BuildingDeductionGuides(*this, Loc, Template);
+  if (BuildingDeductionGuides.isInvalid())
+    return;
 
   // Convert declared constructors into deduction guide templates.
   // FIXME: Skip constructors for which deduction must necessarily fail (those
diff --git a/test/SemaTemplate/instantiate-after-fatal-cxx17.cpp b/test/SemaTemplate/instantiate-after-fatal-cxx17.cpp
new file mode 100644
index 0000000000..3e0ddf1ae6
--- /dev/null
+++ b/test/SemaTemplate/instantiate-after-fatal-cxx17.cpp
@@ -0,0 +1,16 @@
+// RUN: not %clang_cc1 -std=c++17 -fsyntax-only -ferror-limit 1 %s 2>&1 | FileCheck %s
+
+#error Error 1
+#error Error 2
+// CHECK: fatal error: too many errors emitted, stopping now
+
+namespace rdar39051732 {
+
+  template<class T> struct A {
+    template <class U> A(T&, ...);
+  };
+  // Deduction guide triggers constructor instantiation.
+  template<class T> A(const T&, const T&) -> A<T&>;
+
+}
+