[PATCH] D26893: [Sema] Fix assert on valid during template argument deduction

[Erik Pilkington via cfe-commits]

erik.pilkington created this revision.
erik.pilkington added a reviewer: rsmith.
erik.pilkington added a subscriber: cfe-commits.

This patch fixes an assert that fired when diagnosing a failed template argument deduction attempt. The problem is that when deducing template arguments for a template specialization, if there are insufficient template arguments, we return `Sema::TDK_TooFewArguments`, which is meant to be used with call arguments, not template arguments and therefore confuses the diagnostic handling. This patch fixes the assert by instead returning `Sema::TDK_MiscellaneousDeductionFailure`.

This fixes a regression introduced in r274077, recorded by PR31043. Thanks!


https://reviews.llvm.org/D26893

Files:
  lib/Sema/SemaTemplateDeduction.cpp
  test/SemaTemplate/deduction.cpp


Index: test/SemaTemplate/deduction.cpp
===================================================================
--- test/SemaTemplate/deduction.cpp
+++ test/SemaTemplate/deduction.cpp
@@ -273,3 +273,13 @@
   }
   void g() { f(X<int*, nullptr>()); }
 }
+
+namespace PR31043 {
+template <class... Ts>
+struct tuple {};
+
+template <class T>
+int foo(tuple<T>); // expected-note{{candidate template ignored: failed template argument deduction}}
+
+int z = foo(tuple<>{}); // expected-error{{no matching function call to 'foo'}}
+}
Index: lib/Sema/SemaTemplateDeduction.cpp
===================================================================
--- lib/Sema/SemaTemplateDeduction.cpp
+++ lib/Sema/SemaTemplateDeduction.cpp
@@ -1921,8 +1921,9 @@
 
       // Check whether we have enough arguments.
       if (!hasTemplateArgumentForDeduction(Args, ArgIdx, NumArgs))
-        return NumberOfArgumentsMustMatch ? Sema::TDK_TooFewArguments
-                                          : Sema::TDK_Success;
+        return NumberOfArgumentsMustMatch
+                   ? Sema::TDK_MiscellaneousDeductionFailure
+                   : Sema::TDK_Success;
 
       if (Args[ArgIdx].isPackExpansion()) {
         // FIXME: We follow the logic of C++0x [temp.deduct.type]p22 here,


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