On 12/16/21 17:36, Marek Polacek wrote:
For code liketemplate<typename> struct bar; struct bar { int baz; }; bar var; we emit a fairly misleading and unwieldy diagnostic: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ $ g++ -c u.cc u.cc:6:8: error: template argument required for 'struct bar' 6 | struct bar { | ^~~ u.cc:10:5: error: class template argument deduction failed: 10 | bar var; | ^~~ u.cc:10:5: error: no matching function for call to 'bar()' u.cc:3:17: note: candidate: 'template<class> bar()-> bar< <template-parameter-1-1> >' 3 | friend struct bar; | ^~~ u.cc:3:17: note: template argument deduction/substitution failed: u.cc:10:5: note: couldn't deduce template parameter '<template-parameter-1-1>' 10 | bar var; | ^~~ u.cc:3:17: note: candidate: 'template<class> bar(bar< <template-parameter-1-1> >)-> bar< <template-parameter-1-1> >' 3 | friend struct bar; | ^~~ u.cc:3:17: note: template argument deduction/substitution failed: u.cc:10:5: note: candidate expects 1 argument, 0 provided 10 | bar var; | ^~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ but with this patch we get: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ z.C:6:8: error: 'bar' was declared as template but no template header provided 6 | struct bar { | ^~~ z.C:3:17: note: previous declaration here 3 | friend struct bar; | ^~~ z.C:10:5: error: 'bar<...auto...> var' has incomplete type 10 | bar var; | ^~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ which is clearer about what the problem is. I thought it'd be nice to avoid printing the messages about failed CTAD, too. To that end, I'm using CLASSTYPE_ERRONEOUS to suppress CTAD. Not sure if that's entirely kosher.
A bit dubious, but error-recovery often is. Let's go with it.
The other direction (first a non-template class declaration followed by a class template definition) we handle quite well: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ z.C:11:8: error: 'bar' is not a template 11 | struct bar {}; | ^~~ z.C:8:8: note: previous declaration here 8 | struct bar; | ^~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? PR c++/103749 gcc/cp/ChangeLog: * decl.c (lookup_and_check_tag): Give an error when a class was declared as template but no template header has been provided. * pt.c (do_class_deduction): Don't deduce CLASSTYPE_ERRONEOUS types. gcc/testsuite/ChangeLog: * g++.dg/template/redecl4.C: Adjust dg-error. * g++.dg/diagnostic/redeclaration-2.C: New test. --- gcc/cp/decl.c | 11 +++++++++++ gcc/cp/pt.c | 7 +++++++ .../g++.dg/diagnostic/redeclaration-2.C | 19 +++++++++++++++++++ gcc/testsuite/g++.dg/template/redecl4.C | 2 +- 4 files changed, 38 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/g++.dg/diagnostic/redeclaration-2.C diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c index 7ca8770bd02..56fa5b3ffeb 100644 --- a/gcc/cp/decl.c +++ b/gcc/cp/decl.c @@ -15438,6 +15438,17 @@ lookup_and_check_tag (enum tag_types tag_code, tree name, return error_mark_node; }+ if (DECL_CLASS_TEMPLATE_P (decl)+ && !template_header_p + && how == TAG_how::CURRENT_ONLY) + { + error ("%qD was declared as template but no template header provided", + name);
Maybe "class template %qD redeclared as non-template" ? OK with that change.
+ inform (location_of (decl), "previous declaration here"); + CLASSTYPE_ERRONEOUS (TREE_TYPE (decl)) = true; + return error_mark_node; + } + if (DECL_CLASS_TEMPLATE_P (decl) /* If scope is TAG_how::CURRENT_ONLY we're defining a class, so ignore a template template parameter. */ diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index 18c6f118ae6..4f0ae6d5851 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -29601,6 +29601,13 @@ do_class_deduction (tree ptype, tree tmpl, tree init, if (DECL_TEMPLATE_TEMPLATE_PARM_P (tmpl)) return ptype;+ /* If the class was erroneous, don't try to deduce, because that+ can generate a lot of diagnostic. */ + if (TREE_TYPE (tmpl) + && TYPE_LANG_SPECIFIC (TREE_TYPE (tmpl)) + && CLASSTYPE_ERRONEOUS (TREE_TYPE (tmpl))) + return ptype; + /* Wait until the enclosing scope is non-dependent. */ if (DECL_CLASS_SCOPE_P (tmpl) && dependent_type_p (DECL_CONTEXT (tmpl))) diff --git a/gcc/testsuite/g++.dg/diagnostic/redeclaration-2.C b/gcc/testsuite/g++.dg/diagnostic/redeclaration-2.C new file mode 100644 index 00000000000..ac14c2c135f --- /dev/null +++ b/gcc/testsuite/g++.dg/diagnostic/redeclaration-2.C @@ -0,0 +1,19 @@ +// PR c++/103749 + +struct foo { + template<typename> + friend struct bar; +}; + +struct bar { // { dg-error "declared as template" } + int baz; +}; + +template<typename> +struct T; // { dg-message "previous" } + +struct T { // { dg-error "declared as template" } +}; + +bar var; // { dg-error "" } +T t; // { dg-error "" } diff --git a/gcc/testsuite/g++.dg/template/redecl4.C b/gcc/testsuite/g++.dg/template/redecl4.C index 5638bde413d..498ca83a0f4 100644 --- a/gcc/testsuite/g++.dg/template/redecl4.C +++ b/gcc/testsuite/g++.dg/template/redecl4.C @@ -2,4 +2,4 @@ // { dg-do compile }template<int> union A; // { dg-message "previous" }-struct A; // { dg-error "non-template" } +struct A; // { dg-error "declared as template" } base-commit: f91814c22595e1db642140efe030caf2c092ab6f
