[PATCH] D40284: [Sema] Improve diagnostics for template arg deduction

[Jacob Bandes-Storch via Phabricator via cfe-commits]

jtbandes updated this revision to Diff 124033.
jtbandes added a comment.

@erik.pilkington Updated to use a wrapper function. This is definitely less invasive, but it could defeat some optimizations (any approach that checks the return value will defeat tail recursion, I suppose...)


https://reviews.llvm.org/D40284

Files:
  lib/Sema/SemaTemplateDeduction.cpp
  test/CXX/temp/temp.fct.spec/temp.deduct/temp.deduct.call/basic.cpp


Index: test/CXX/temp/temp.fct.spec/temp.deduct/temp.deduct.call/basic.cpp
===================================================================
--- test/CXX/temp/temp.fct.spec/temp.deduct/temp.deduct.call/basic.cpp
+++ test/CXX/temp/temp.fct.spec/temp.deduct/temp.deduct.call/basic.cpp
@@ -45,3 +45,11 @@
     func(foo<int>()); // expected-error {{no matching function}}
   }
 }
+
+namespace test4 {
+  // expected-note at +1 {{candidate template ignored: could not match 'int [N]' against 'int []'}}
+  template<int N> void f1(int (&arr)[N]);
+  template<int N> void f2(int (&arr)[]) {
+    f1(arr); // expected-error {{no matching function}}
+  }
+}
Index: lib/Sema/SemaTemplateDeduction.cpp
===================================================================
--- lib/Sema/SemaTemplateDeduction.cpp
+++ lib/Sema/SemaTemplateDeduction.cpp
@@ -1056,6 +1056,12 @@
   return false;
 }
 
+static Sema::TemplateDeductionResult DeduceTemplateArgumentsByTypeMatchInner(
+    Sema &S, TemplateParameterList *TemplateParams, QualType ParamIn,
+    QualType ArgIn, TemplateDeductionInfo &Info,
+    SmallVectorImpl<DeducedTemplateArgument> &Deduced, unsigned TDF,
+    bool PartialOrdering, bool DeducedFromArrayBound);
+
 /// \brief Deduce the template arguments by comparing the parameter type and
 /// the argument type (C++ [temp.deduct.type]).
 ///
@@ -1080,15 +1086,34 @@
 /// \returns the result of template argument deduction so far. Note that a
 /// "success" result means that template argument deduction has not yet failed,
 /// but it may still fail, later, for other reasons.
-static Sema::TemplateDeductionResult
-DeduceTemplateArgumentsByTypeMatch(Sema &S,
-                                   TemplateParameterList *TemplateParams,
-                                   QualType ParamIn, QualType ArgIn,
-                                   TemplateDeductionInfo &Info,
-                            SmallVectorImpl<DeducedTemplateArgument> &Deduced,
-                                   unsigned TDF,
-                                   bool PartialOrdering,
-                                   bool DeducedFromArrayBound) {
+static Sema::TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch(
+    Sema &S, TemplateParameterList *TemplateParams, QualType ParamIn,
+    QualType ArgIn, TemplateDeductionInfo &Info,
+    SmallVectorImpl<DeducedTemplateArgument> &Deduced, unsigned TDF,
+    bool PartialOrdering, bool DeducedFromArrayBound) {
+  // Because DeduceTemplateArgumentsByTypeMatchInner is recursive, and tends to
+  // modify Info.FirstArg and SecondArg even when deduction succeeds, save the
+  // original values and restore them if no error occurred.
+  const auto OriginalFirstArg = Info.FirstArg;
+  const auto OriginalSecondArg = Info.SecondArg;
+
+  const auto Result = DeduceTemplateArgumentsByTypeMatchInner(
+      S, TemplateParams, ParamIn, ArgIn, Info, Deduced, TDF, PartialOrdering,
+      DeducedFromArrayBound);
+
+  if (Result == Sema::TDK_Success) {
+    Info.FirstArg = OriginalFirstArg;
+    Info.SecondArg = OriginalSecondArg;
+  }
+  return Result;
+}
+
+/// \see DeduceTemplateArgumentsByTypeMatch()
+static Sema::TemplateDeductionResult DeduceTemplateArgumentsByTypeMatchInner(
+    Sema &S, TemplateParameterList *TemplateParams, QualType ParamIn,
+    QualType ArgIn, TemplateDeductionInfo &Info,
+    SmallVectorImpl<DeducedTemplateArgument> &Deduced, unsigned TDF,
+    bool PartialOrdering, bool DeducedFromArrayBound) {
   // We only want to look at the canonical types, since typedefs and
   // sugar are not part of template argument deduction.
   QualType Param = S.Context.getCanonicalType(ParamIn);


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