[Clang] Do not defer variable template instantiation for undeduced types

clang/docs/ReleaseNotes.rst

@@ -743,6 +743,7 @@ Bug Fixes to C++ Support
   in a ``constexpr`` function. (#GH131432)
 - Fixed an incorrect TreeTransform for calls to ``consteval`` functions if a conversion template is present. (#GH137885)
 - Clang now emits a warning when class template argument deduction for alias templates is used in C++17. (#GH133806)
+- Fixed a missed initializer instantiation bug for variable templates. (#GH134526), (#GH138122)
 - Fix a crash when checking the template template parameters of a dependent lambda appearing in an alias declaration.
   (#GH136432), (#GH137014), (#GH138018)
 - Fixed an assertion when trying to constant-fold various builtins when the argument

clang/lib/Sema/SemaExpr.cpp

@@ -20158,9 +20158,10 @@ static void DoMarkVarDeclReferenced(
           Var->setTemplateSpecializationKind(TSK, PointOfInstantiation);
       }
 
-      if (UsableInConstantExpr) {
+      if (UsableInConstantExpr || Var->getType()->isUndeducedType()) {
         // Do not defer instantiations of variables that could be used in a
         // constant expression.
+        // The type deduction also needs a complete initializer.
         SemaRef.runWithSufficientStackSpace(PointOfInstantiation, [&] {
           SemaRef.InstantiateVariableDefinition(PointOfInstantiation, Var);
         });

clang/test/CodeGenCXX/cxx1z-inline-variables.cpp

@@ -1,5 +1,19 @@
 // RUN: %clang_cc1 -std=c++1z %s -emit-llvm -o - -triple x86_64-linux-gnu | FileCheck %s
 
+template <typename T> struct InlineAuto {
+  template <typename G> inline static auto var = 5;
+};
+int inlineauto = InlineAuto<int>::var<int>;
+// CHECK: @_ZN10InlineAutoIiE3varIiEE = {{.*}}i32 5{{.*}}comdat
+
+template <typename> struct PartialInlineAuto {
+  template <typename, typename> inline static auto var = 6;
+  template <typename T> inline static auto var<int, T> = 7;
+};
+
+int partialinlineauto = PartialInlineAuto<int>::var<int, int>;
+// CHECK: @_ZN17PartialInlineAutoIiE3varIiiEE = {{.*}}i32 7{{.*}}comdat
+
 struct Q {
   // CHECK: @_ZN1Q1kE = linkonce_odr constant i32 5, comdat
   static constexpr int k = 5;

clang/test/SemaTemplate/cxx17-inline-variables.cpp

@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -std=c++17 -verify %s
-// expected-no-diagnostics
+
 template<bool> struct DominatorTreeBase {
   static constexpr bool IsPostDominator = true;
 };
@@ -27,3 +27,45 @@ template <typename T> constexpr int A<T>::n = sizeof(A) + sizeof(T);
 template <typename T> inline constexpr int A<T>::m = sizeof(A) + sizeof(T);
 static_assert(A<int>().f() == 5);
 static_assert(A<int>().g() == 5);
+
+namespace GH135032 {
+
+template <typename T> struct InlineAuto {
+  template <typename G> inline static auto var = 5;
+};
+
+template <typename> struct PartialInlineAuto {
+  template <typename, typename> inline static auto var = 6;
+  template <typename T> inline static auto var<int, T> = 7;
+};
+
+int inline_auto = InlineAuto<int>::var<int>;
+int partial_inline_auto = PartialInlineAuto<int>::var<int, int>;
+
+}
+
+namespace GH140773 {
+template <class T> class ConstString { // #ConstString
+  ConstString(typename T::type) {} // #ConstString-Ctor
+};
+
+template <class = int>
+struct Foo {
+  template <char>
+  static constexpr ConstString kFilename{[] { // #kFileName
+    return 42;
+  }};
+};
+
+// We don't want to instantiate the member template until it's used!
+Foo<> foo;
+
+auto X = Foo<>::kFilename<'a'>;
+// expected-error@#kFileName {{no viable constructor}}
+// expected-note@-2 {{in instantiation of static data member}}
+// expected-note@#ConstString-Ctor {{candidate template ignored}}
+// expected-note@#ConstString-Ctor {{implicit deduction guide}}
+// expected-note@#ConstString {{candidate template ignored}}
+// expected-note@#ConstString {{implicit deduction guide}}
+
+}