PR32673: Don't wrap parameter packs in SubstTemplateTypeParmPackType nodes when forming implicit deduction guides.

Doing so thwarts template type deduction. Instead, substitute the pack directly
by picking "slice 0" of the resulting expansion.

llvm-svn: 300805

clang/include/clang/AST/TypeLoc.h

@@ -1544,7 +1544,11 @@ class DependentSizedArrayTypeLoc :
     public InheritingConcreteTypeLoc<ArrayTypeLoc,
                                      DependentSizedArrayTypeLoc,
                                      DependentSizedArrayType> {
-
+public:
+  void initializeLocal(ASTContext &Context, SourceLocation Loc) {
+    ArrayTypeLoc::initializeLocal(Context, Loc);
+    setSizeExpr(getTypePtr()->getSizeExpr());
+  }
 };
 
 class VariableArrayTypeLoc :

clang/lib/Sema/SemaTemplate.cpp

@@ -1636,11 +1636,22 @@ private:
   transformFunctionTypeParam(ParmVarDecl *OldParam,
                              MultiLevelTemplateArgumentList &Args) {
     TypeSourceInfo *OldDI = OldParam->getTypeSourceInfo();
-    TypeSourceInfo *NewDI =
-        Args.getNumLevels()
-            ? SemaRef.SubstType(OldDI, Args, OldParam->getLocation(),
-                                OldParam->getDeclName())
-            : OldDI;
+    TypeSourceInfo *NewDI;
+    if (!Args.getNumLevels())
+      NewDI = OldDI;
+    else if (auto PackTL = OldDI->getTypeLoc().getAs<PackExpansionTypeLoc>()) {
+      // Expand out the one and only element in each inner pack.
+      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, 0);
+      NewDI =
+          SemaRef.SubstType(PackTL.getPatternLoc(), Args,
+                            OldParam->getLocation(), OldParam->getDeclName());
+      if (!NewDI) return nullptr;
+      NewDI =
+          SemaRef.CheckPackExpansion(NewDI, PackTL.getEllipsisLoc(),
+                                     PackTL.getTypePtr()->getNumExpansions());
+    } else
+      NewDI = SemaRef.SubstType(OldDI, Args, OldParam->getLocation(),
+                                OldParam->getDeclName());
     if (!NewDI)
       return nullptr;
 

clang/test/SemaCXX/cxx1z-class-template-argument-deduction.cpp

@@ -213,3 +213,38 @@ namespace transform_params {
   };
   D d(Y<0, 1, 2>{});
 }
+
+namespace variadic {
+  int arr3[3], arr4[4];
+
+  // PR32673
+  template<typename T> struct A {
+    template<typename ...U> A(T, U...);
+  };
+  A a(1, 2, 3);
+
+  template<typename T> struct B {
+    template<int ...N> B(T, int (&...r)[N]);
+  };
+  B b(1, arr3, arr4);
+
+  template<typename T> struct C {
+    template<template<typename> typename ...U> C(T, U<int>...);
+  };
+  C c(1, a, b);
+
+  template<typename ...U> struct X {
+    template<typename T> X(T, U...);
+  };
+  X x(1, 2, 3);
+
+  template<int ...N> struct Y {
+    template<typename T> Y(T, int (&...r)[N]);
+  };
+  Y y(1, arr3, arr4);
+
+  template<template<typename> typename ...U> struct Z {
+    template<typename T> Z(T, U<int>...);
+  };
+  Z z(1, a, b);
+}