alias_ctad_tweaks was expecting that all deduction guides for the class
would be suitable for deduction from the alias definition; in this case, the
deduction guide uses 'true' and the alias B uses 'false', so deduction
fails. But that's OK, we just don't use that deduction guide. I also
noticed that we were giving up on deduction entirely if substitution failed
for some guide; we should only give up on that particular deduction guide.
We ought to give a better diagnostic about this case when deduction fails,
but that can wait.
Tested x86_64-pc-linux-gnu, applying to trunk.
gcc/cp/ChangeLog:
PR c++/99180
PR c++/93295
PR c++/93867
PR c++/99118
PR c++/96873
* pt.c (alias_ctad_tweaks): Handle failure better.
gcc/testsuite/ChangeLog:
PR c++/99180
PR c++/93295
PR c++/93867
PR c++/95486
* g++.dg/cpp2a/class-deduction-alias5.C: New test.
* g++.dg/cpp2a/class-deduction-alias6.C: New test.
* g++.dg/cpp2a/class-deduction-alias7.C: New test.
* g++.dg/cpp2a/class-deduction-alias8.C: New test.
---
gcc/cp/pt.c | 7 ++--
.../g++.dg/cpp2a/class-deduction-alias5.C | 18 +++++++++++
.../g++.dg/cpp2a/class-deduction-alias6.C | 11 +++++++
.../g++.dg/cpp2a/class-deduction-alias7.C | 32 +++++++++++++++++++
.../g++.dg/cpp2a/class-deduction-alias8.C | 14 ++++++++
5 files changed, 79 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias5.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias6.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias7.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias8.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index ff98bc13551..2db27413fdb 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -29039,7 +29039,8 @@ alias_ctad_tweaks (tree tmpl, tree uguides)
unsigned len = TREE_VEC_LENGTH (ftparms);
tree targs = make_tree_vec (len);
int err = unify (ftparms, targs, ret, utype, UNIFY_ALLOW_NONE, false);
- gcc_assert (!err);
+ if (err)
+ continue;
/* The number of parms for f' is the number of parms for A plus
non-deduced parms of f. */
@@ -29072,7 +29073,7 @@ alias_ctad_tweaks (tree tmpl, tree uguides)
guideness, and explicit-specifier. */
tree g = tsubst_decl (DECL_TEMPLATE_RESULT (f), targs, complain);
if (g == error_mark_node)
- return error_mark_node;
+ continue;
DECL_USE_TEMPLATE (g) = 0;
fprime = build_template_decl (g, gtparms, false);
DECL_TEMPLATE_RESULT (fprime) = g;
@@ -29086,7 +29087,7 @@ alias_ctad_tweaks (tree tmpl, tree uguides)
if (ci)
ci = tsubst_constraint_info (ci, targs, complain, in_decl);
if (ci == error_mark_node)
- return error_mark_node;
+ continue;
/* Add a constraint that the return type matches the instantiation of
A with the same template arguments. */
diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias5.C
b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias5.C
new file mode 100644
index 00000000000..69143a3277b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias5.C
@@ -0,0 +1,18 @@
+// PR c++/99180
+// { dg-do compile { target c++17 } }
+
+template <bool, typename... Ts>
+struct A {
+ A(Ts...) {}
+};
+
+template <typename... Ts>
+using B = A<false, Ts...>;
+
+template <typename... Ts>
+A(Ts...) -> A<true, Ts...>;
+
+int main() {
+ B{}; // { dg-error "alias" "" { target c++17_down } }
+ return 0;
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias6.C
b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias6.C
new file mode 100644
index 00000000000..26a38641ab3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias6.C
@@ -0,0 +1,11 @@
+// PR c++/93295
+// { dg-do compile { target c++20 } }
+
+template<typename T, bool B = false>
+struct Foo {
+ Foo(T) {}
+};
+
+template<typename T> Foo(T) -> Foo<T>;
+template<typename T> using Bar = Foo<T, true>;
+Bar b{0};
diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias7.C
b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias7.C
new file mode 100644
index 00000000000..0d8bff7610d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias7.C
@@ -0,0 +1,32 @@
+// PR c++/93867
+// { dg-do compile { target c++20 } }
+
+template <typename CharT, unsigned N>
+struct basic_fixed_string
+{
+ constexpr basic_fixed_string(const CharT *p) {
+ for (int i = 0; i < N; ++i) {
+ m_data[i] = p[i];
+ }
+ }
+
+ CharT m_data[N] {};
+};
+
+template <typename CharT, unsigned N>
+basic_fixed_string(const CharT (&)[N]) -> basic_fixed_string<CharT,N>;
+
+template <unsigned N>
+using fixed_string = basic_fixed_string<char, N>;
+
+template <fixed_string path>
+constexpr int foo()
+{
+ return 42;
+}
+
+int main(int argc, char const *argv[])
+{
+ foo<"hello">();
+ return 0;
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias8.C
b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias8.C
new file mode 100644
index 00000000000..ec005956fa6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias8.C
@@ -0,0 +1,14 @@
+// PR c++/95486
+// { dg-do compile { target c++20 } }
+
+template<class T, class U>
+struct X { X(U) requires __is_same(U, int) {} };
+
+template<class U>
+X(U) -> X<char, U>;
+
+template<class U>
+using Y = X<void, U>;
+
+Y y{1};
+Y z{'a'}; // { dg-error "failed|no match" }
base-commit: a7ce23cec4a4a581b88c226418dc702dcd19bceb
prerequisite-patch-id: 74afe3e9039136cd1275c09f0e3f0d5efcdd8eea
--
2.27.0
