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Fix implementation of [temp.param]p14's first sentence. #83487
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The first sentence says: If a template-parameter of a class template, variable template, or alias template has a default template-argument, each subsequent template-parameter shall either have a default template-argument supplied or be a template parameter pack. However, we were only testing for "not a function function template", and referring to an older version of the standard. As far as I can tell, CWG2032 added the variable-template, and the alias-template pre-dates the standard on github. This patch started as a bug fix for llvm#83461 , but ended up fixing a number of similar cases, so those are validated as well.
@llvm/pr-subscribers-clang Author: Erich Keane (erichkeane) ChangesThe first sentence says: If a template-parameter of a class template, variable template, or alias template has a default template-argument, each subsequent template-parameter shall either have a default template-argument supplied or be a template parameter pack. However, we were only testing for "not a function function template", and referring to an older version of the standard. As far as I can tell, CWG2032 added the variable-template, and the alias-template pre-dates the standard on github. This patch started as a bug fix for #83461 , but ended up fixing a number of similar cases, so those are validated as well. Full diff: https://github.com/llvm/llvm-project/pull/83487.diff 2 Files Affected:
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index e91033dd886891..a7910bda874c8d 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -3141,12 +3141,14 @@ bool Sema::CheckTemplateParameterList(TemplateParameterList *NewParams,
diag::note_template_param_prev_default_arg_in_other_module)
<< PrevModuleName;
Invalid = true;
- } else if (MissingDefaultArg && TPC != TPC_FunctionTemplate) {
- // C++ [temp.param]p11:
- // If a template-parameter of a class template has a default
- // template-argument, each subsequent template-parameter shall either
- // have a default template-argument supplied or be a template parameter
- // pack.
+ } else if (MissingDefaultArg &&
+ (TPC == TPC_ClassTemplate || TPC == TPC_FriendClassTemplate ||
+ TPC == TPC_VarTemplate || TPC == TPC_TypeAliasTemplate)) {
+ // C++ 23[temp.param]p14:
+ // If a template-parameter of a class template, variable template, or
+ // alias template has a default template argument, each subsequent
+ // template-parameter shall either have a default template argument
+ // supplied or be a template parameter pack.
Diag((*NewParam)->getLocation(),
diag::err_template_param_default_arg_missing);
Diag(PreviousDefaultArgLoc, diag::note_template_param_prev_default_arg);
diff --git a/clang/test/SemaCXX/GH83461.cpp b/clang/test/SemaCXX/GH83461.cpp
new file mode 100644
index 00000000000000..509535e883e6d9
--- /dev/null
+++ b/clang/test/SemaCXX/GH83461.cpp
@@ -0,0 +1,60 @@
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s
+
+struct S {
+ template<typename Ty = int>
+ friend void foo(auto){}
+
+ template<typename Ty = int, typename Tz>
+ friend void foo2(){}
+};
+
+template<typename T>
+struct TemplS {
+ template<typename Ty = int>
+ friend void foo3(auto){}
+
+ template<typename Ty = int, typename Tz>
+ friend void foo4(){}
+};
+
+void Inst() {
+ TemplS<int>();
+}
+// expected-error@+2{{template parameter missing a default argument}}
+// expected-note@+1{{previous default template argument defined here}}
+template<typename T = int, typename U>
+struct ClassTempl{};
+
+struct HasFriendClassTempl {
+ // expected-error@+1{{default template argument not permitted on a friend template}}
+ template<typename T = int, typename U>
+ friend struct Friend;
+
+ // expected-error@+3{{cannot define a type in a friend declaration}}
+ // expected-error@+1{{default template argument not permitted on a friend template}}
+ template<typename T = int, typename U>
+ friend struct Friend2{};
+};
+
+template<typename Ty>
+struct HasFriendClassTempl2 {
+ // expected-error@+3{{template parameter missing a default argument}}
+ // expected-note@+2{{previous default template argument defined here}}
+ // expected-note@#INST2{{in instantiation of template class}}
+ template<typename T = int, typename U>
+ friend struct Friend;
+};
+
+void Inst2() {
+ HasFriendClassTempl2<int>(); // #INST2
+}
+
+// expected-error@+2{{template parameter missing a default argument}}
+// expected-note@+1{{previous default template argument defined here}}
+template<typename T = int, typename U>
+static constexpr U VarTempl;
+
+// expected-error@+2{{template parameter missing a default argument}}
+// expected-note@+1{{previous default template argument defined here}}
+template<typename T = int, typename U>
+using TypeAlias = U;
|
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The changes look correct to me, but I think we should add a DR test for this so that we can properly regenerate cxx_dr_status.html
Also, the changes should come with a release note.
Ooof, yeah, forgot the release note. @Endilll has volunteered to do the DR test in a separate commit, as this only fixes the 1st half of the DR, so I'm not sure it actually fixes all of it. |
My plan is to add tests to this PR, but if you want to land this sooner, I can do tests in a separate PR. |
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Thanks for the details, then LGTM with a release note added when landing.
The first sentence says:
If a template-parameter of a class template, variable template, or alias template has a default template-argument, each subsequent template-parameter shall either have a default template-argument supplied or be a template parameter pack.
However, we were only testing for "not a function function template", and referring to an older version of the standard. As far as I can tell, CWG2032 added the variable-template, and the alias-template pre-dates the standard on github.
This patch started as a bug fix for #83461 , but ended up fixing a number of similar cases, so those are validated as well.