On Thu, 10 Aug 2023, Jason Merrill wrote: > On 8/10/23 16:40, Patrick Palka wrote: > > On Thu, 10 Aug 2023, Jason Merrill wrote: > > > > > On 8/10/23 12:09, Patrick Palka wrote: > > > > Booststrapped and regtested on x86_64-pc-linux-gnu, does this look OK > > > > for > > > > trunk and perhaps 13? > > > > > > > > -- >8 -- > > > > > > > > We shouldn't issue a "declared static but never defined" warning > > > > for a deduction guide (declared in an anonymous namespace). > > > > > > > > PR c++/106604 > > > > > > > > gcc/cp/ChangeLog: > > > > > > > > * decl.cc (wrapup_namespace_globals): Don't issue a > > > > -Wunused-function warning for a deduction guide. > > > > > > Maybe instead of special casing this here we could set DECL_INITIAL on > > > deduction guides so they look defined? > > > > That seems to work, but it requires some tweaks in duplicate_decls to keep > > saying "declared" instead of "defined" when diagnosing a deduction guide > > redeclaration. I'm not sure which approach is preferable? > > I'm not sure it matters which we say; the restriction that you can't repeat a > deduction guide makes it more like a definition anyway (even if [basic.def] > disagrees). Is the diagnostic worse apart from that word? Ah, makes sense. So we can also remove the special case for them in the redeclaration checking code after we give them a dummy DECL_INITIAL. Like so? Here's a before/after for the diagnostic with the below patch: Before src/gcc/testsuite/g++.dg/cpp1z/class-deduction74.C:11:1: error: deduction guide ‘S()-> S’ redeclared 11 | S() -> S; // { dg-error "redefinition" } | ^ src/gcc/testsuite/g++.dg/cpp1z/class-deduction74.C:10:1: note: ‘S()-> S’ previously declared here 10 | S() -> S; // { dg-message "previously defined here|old declaration" } | ^ After src/gcc/testsuite/g++.dg/cpp1z/class-deduction74.C:11:1: error: redefinition of ‘S()-> S’ 11 | S() -> S; // { dg-error "redefinition" } | ^ src/gcc/testsuite/g++.dg/cpp1z/class-deduction74.C:10:1: note: ‘S()-> S’ previously defined here 10 | S() -> S; // { dg-message "previously defined here|old declaration" } | ^ -- >8 -- Subject: [PATCH] c++: bogus warning w/ deduction guide in anon ns [PR106604] Here we're unintentionally issuing a "declared static but never defined" warning for a deduction guide declared in an anonymous namespace. This patch fixes this by giving deduction guides a dummy DECL_INITIAL, which suppresses the warning and also allows us to simplify redeclaration checking for them. Co-authored-by: Jason Merrill PR c++/106604 gcc/cp/ChangeLog: * decl.cc (redeclaration_error_message): Remove special handling for deduction guides. (grokfndecl): Give deduction guides a dummy DECL_INITIAL. gcc/testsuite/ChangeLog: * g++.dg/cpp1z/class-deduction74.C: Expect "defined" instead of "declared" in diagnostics for a repeated deduction guide. * g++.dg/cpp1z/class-deduction116.C: New test. --- gcc/cp/decl.cc | 14 ++++++-------- gcc/testsuite/g++.dg/cpp1z/class-deduction116.C | 8 ++++++++ gcc/testsuite/g++.dg/cpp1z/class-deduction74.C | 14 +++++++------- 3 files changed, 21 insertions(+), 15 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction116.C diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc index 792ab330dd0..3ada5516c58 100644 --- a/gcc/cp/decl.cc +++ b/gcc/cp/decl.cc @@ -3297,10 +3297,6 @@ redeclaration_error_message (tree newdecl, tree olddecl) } } - if (deduction_guide_p (olddecl) - && deduction_guide_p (newdecl)) - return G_("deduction guide %q+D redeclared"); - /* [class.compare.default]: A definition of a comparison operator as defaulted that appears in a class shall be the first declaration of that function. */ @@ -3355,10 +3351,6 @@ redeclaration_error_message (tree newdecl, tree olddecl) } } - if (deduction_guide_p (olddecl) - && deduction_guide_p (newdecl)) - return G_("deduction guide %q+D redeclared"); - /* Core issue #226 (C++11): If a friend function template declaration specifies a @@ -10352,6 +10344,12 @@ grokfndecl (tree ctype, DECL_CXX_DESTRUCTOR_P (decl) = 1; DECL_NAME (decl) = dtor_identifier; break; + case sfk_deduction_guide: + /* Give deduction guides a definition even though they don't really + have one: the restriction that you can't repeat a deduction guide + makes them more like a definition anyway. */ + DECL_INITIAL (decl) = void_node; + break; default: break; } diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction116.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction116.C new file mode 100644 index 00000000000..00f6d5fef41 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction116.C @@ -0,0 +1,8 @@ +// PR c++/106604 +// { dg-do compile { target c++17 } } +// { dg-additional-options "-Wunused-function" } + +namespace { + template struct A { A(...); }; + A(bool) -> A; // { dg-bogus "never defined" } +} diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction74.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction74.C index fe113819a95..7bab882da7d 100644 --- a/gcc/testsuite/g++.dg/cpp1z/class-deduction74.C +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction74.C @@ -7,20 +7,20 @@ template struct S { }; template struct X { }; -S() -> S; // { dg-message "previously declared here|old declaration" } -S() -> S; // { dg-error "redeclared" } +S() -> S; // { dg-message "previously defined here|old declaration" } +S() -> S; // { dg-error "redefinition" } X() -> X; S() -> S; // { dg-error "ambiguating new declaration of" } -S(bool) -> S; // { dg-message "previously declared here" } -explicit S(bool) -> S; // { dg-error "redeclared" } +S(bool) -> S; // { dg-message "previously defined here" } +explicit S(bool) -> S; // { dg-error "redefinition" } -explicit S(char) -> S; // { dg-message "previously declared here" } -S(char) -> S; // { dg-error "redeclared" } +explicit S(char) -> S; // { dg-message "previously defined here" } +S(char) -> S; // { dg-error "redefinition" } template S(T, T) -> S; // { dg-message "previously declared here" } template X(T, T) -> X; -template S(T, T) -> S; // { dg-error "redeclared" } +template S(T, T) -> S; // { dg-error "redefinition" } // OK: Use SFINAE. template S(T) -> S; -- 2.42.0.rc1