[Sema] Fixes an assertion failure while instantiation a template with an incomplete typo corrected type

[Mordante]

Summary

This fixes bug 35682. When a template in instantiated with an incomplete typo corrected type an assertion can trigger if the -ferror-limit is used to reduce the number of errors. The issue can be reproduced with the following code:

#include <utility>
        
using SetKeyType = String;                                                      
std::pair<SetKeyType, int> v;

and compiled with: clang -stdlib=libc++ -ferror-limit=1 -c bug.cc
This requires the stdlib=libc++ option, without it the assertion does not trigger. Neither does it trigger when the -ferror-limit=1 is not used. The test case is based on this sample but no longer requires the -stdlib=libc++ option.

[lebedev.ri]

Test?

clang/lib/Sema/SemaTemplate.cpp

732

no else after return

[Mordante]

Thanks for feedback. I'll whether I can find a way to generate a nice test case.

clang/lib/Sema/SemaTemplate.cpp

732

Will do in the next update.

[Mordante]

Fixes @lebedev.ri's remark and adds the requested test.
While working on the test I discovered the initial assumption in bug 35682 was incorrect. Updated the title and summary accordingly.

[lebedev.ri]

clang/test/SemaTemplate/instantiate-incomplete-typo-suggested-error-limit.cpp

10–11

Please don't pull in any external headers - just mock what you need.

[Mordante]

Remove the includes from the test.
Changed the std::is_constructible to is_same since the latter is easier to mock.

[lebedev.ri]

Test looks good, adding a few more potential reviewers..

[Mordante]

Update bug number references:

• Removed from the source
• Use PR35682 in the test

Note: I tried to use -verify instead of FileCheck but that doesn't seem to work well since -ferror-limit 1 reports no line number. Other tests with -ferror-limit 1 also use FileCheck.

[aaron.ballman]

clang/lib/Sema/SemaTemplate.cpp

727

The call to std::move() shouldn't be necessary.

clang/test/SemaTemplate/instantiate-incomplete-typo-suggested-error-limit.cpp

2

Do you intend to test %clang_cc1 instead? Can the test be rewritten to use -verify rather than FileCheck? If the test crashes or asserts, that will cause the test to fail anyway, so it doesn't seem like it needs to FileCheck.

[Mordante]

clang/test/SemaTemplate/instantiate-incomplete-typo-suggested-error-limit.cpp

2

As discussed on IRC this is not possible due to the fact there is an error without line number.
(frontend): too many errors emitted, stopping now

[Mordante]

Removes the unnecessary std::move as suggested by @aaron.ballman.

[aaron.ballman]

LGTM!

[Mordante]

Thanks for the review.
Could you commit this patch? I don't have commit access.

[aaron.ballman]

In D64644#1661417, @Mordante wrote:

Thanks for the review.
Could you commit this patch? I don't have commit access.

Happy to do so -- I've commit in r371320.

clang/lib/Sema/SemaTemplate.cpp

Sema::ActOnDependentIdExpression(const CXXScopeSpec &SS,
   return BuildDependentDeclRefExpr(SS, TemplateKWLoc, NameInfo, TemplateArgs);
 }
 
 ExprResult
 Sema::BuildDependentDeclRefExpr(const CXXScopeSpec &SS,
                                 SourceLocation TemplateKWLoc,
                                 const DeclarationNameInfo &NameInfo,
                                 const TemplateArgumentListInfo *TemplateArgs) {
+  // DependentScopeDeclRefExpr::Create requires a valid QualifierLoc
+  NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
+  if (!QualifierLoc)
+    return ExprError();
+
   return DependentScopeDeclRefExpr::Create(
-      Context, SS.getWithLocInContext(Context), TemplateKWLoc, NameInfo,
-      TemplateArgs);
+      Context, QualifierLoc, TemplateKWLoc, NameInfo, TemplateArgs);
 }
 
 
 /// Determine whether we would be unable to instantiate this template (because
 /// it either has no definition, or is in the process of being instantiated).
 bool Sema::DiagnoseUninstantiableTemplate(SourceLocation PointOfInstantiation,
                                           NamedDecl *Instantiation,
                                           bool InstantiatedFromMember,
                                           const NamedDecl *Pattern,
                                           const NamedDecl *PatternDef,
                                           TemplateSpecializationKind TSK,
                                           bool Complain /*= true*/) {
   assert(isa<TagDecl>(Instantiation) || isa<FunctionDecl>(Instantiation) ||

clang/test/SemaTemplate/instantiate-incomplete-typo-suggested-error-limit.cpp

+// RUN: not %clang -fsyntax-only -std=c++11 -ferror-limit=1 %s 2>&1 | FileCheck %s
+
+// Test case for PR35682.
+// The issue be caused by the typo correction that changes String to the
+// incomplete type string. The example is based on the std::pair code and
+// reduced to a minimal test case. When using std::pair the issue can only be
+// reproduced when using the -stdlib=libc++ compiler option.
+
+template <class T> class allocator;
+
+template <class charT> struct char_traits;
+
+template <class CharT, class Traits = char_traits<CharT>,
+          class Allocator = allocator<CharT>>
+class basic_string;
+typedef basic_string<char, char_traits<char>, allocator<char>> string;
+
+template <bool, class Tp = void> struct enable_if {};
+template <class Tp> struct enable_if<true, Tp> { typedef Tp type; };
+
+template <class Tp, Tp v> struct integral_constant {
+  static constexpr const Tp value = v;
+  typedef Tp value_type;
+  typedef integral_constant type;
+
+  constexpr operator value_type() const noexcept { return value; }
+  constexpr value_type operator()() const noexcept { return value; }
+};
+
+template <class Tp, Tp v> constexpr const Tp integral_constant<Tp, v>::value;
+
+using true_type = integral_constant<bool, true>;
+using false_type = integral_constant<bool, false>;
+
+template <class Tp, class Up> struct is_same : public false_type {};
+template <class Tp> struct is_same<Tp, Tp> : public true_type {};
+
+template <class T> struct single {
+  typedef T first_type;
+
+  T first;
+
+  struct CheckArgs {
+    template <class U1> static constexpr bool enable_implicit() {
+      return is_same<first_type, U1>::value;
+    }
+  };
+
+  template <class U1,
+            typename enable_if<CheckArgs::template enable_implicit<U1>(),
+                               bool>::type = false>
+  single(U1 &&u1);
+};
+
+using SetKeyType = String;
+single<SetKeyType> v;
+
+// CHECK: error: unknown type name 'String'; did you mean 'string'?
+// CHECK: fatal error: too many errors emitted, stopping now [-ferror-limit=]
+// CHECK-NOT: Assertion{{.*}}failed