c++: modules and explicit(bool) [PR103752]

We weren't streaming a C++20 dependent explicit-specifier.

	PR c++/103752

gcc/cp/ChangeLog:

	* module.cc (trees_out::core_vals): Stream explicit specifier.
	(trees_in::core_vals): Likewise.
	* pt.cc (store_explicit_specifier): No longer static.
	(tsubst_function_decl): Clear DECL_HAS_DEPENDENT_EXPLICIT_SPEC_P.
	* cp-tree.h (lookup_explicit_specifier): Declare.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/explicit-bool-1_b.C: New test.
	* g++.dg/modules/explicit-bool-1_a.H: New test.

5 files changed, 48 insertions, 2 deletions

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index f09055e..f253b32 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7420,6 +7420,7 @@ extern bool copy_guide_p			(const_tree);
 extern bool template_guide_p			(const_tree);
 extern bool builtin_guide_p			(const_tree);
 extern void store_explicit_specifier		(tree, tree);
+extern tree lookup_explicit_specifier		(tree);
 extern void walk_specializations		(bool,
 						 void (*)(bool, spec_entry *,
 							  void *),
diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 81ceef9..3cf0af1 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -6034,6 +6034,9 @@ trees_out::core_vals (tree t)
       WT (t->function_decl.function_specific_target);
       WT (t->function_decl.function_specific_optimization);
       WT (t->function_decl.vindex);
+
+      if (DECL_HAS_DEPENDENT_EXPLICIT_SPEC_P (t))
+	WT (lookup_explicit_specifier (t));
       break;
 
     case USING_DECL:
@@ -6531,6 +6534,13 @@ trees_in::core_vals (tree t)
 	RT (t->function_decl.function_specific_target);
 	RT (t->function_decl.function_specific_optimization);
 	RT (t->function_decl.vindex);
+
+	if (DECL_HAS_DEPENDENT_EXPLICIT_SPEC_P (t))
+	  {
+	    tree spec;
+	    RT (spec);
+	    store_explicit_specifier (t, spec);
+	  }
       }
       break;
 
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 862f337..5c995da 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -13870,7 +13870,7 @@ store_explicit_specifier (tree v, tree t)
 
 /* Lookup an element in EXPLICIT_SPECIFIER_MAP.  */
 
-static tree
+tree
 lookup_explicit_specifier (tree v)
 {
   return *explicit_specifier_map->get (v);
@@ -14103,7 +14103,13 @@ tsubst_function_decl (tree t, tree args, tsubst_flags_t complain,
 				    /*function_p=*/false,
 				    /*i_c_e_p=*/true);
       spec = build_explicit_specifier (spec, complain);
-      DECL_NONCONVERTING_P (r) = (spec == boolean_true_node);
+      if (instantiation_dependent_expression_p (spec))
+	store_explicit_specifier (r, spec);
+      else
+	{
+	  DECL_NONCONVERTING_P (r) = (spec == boolean_true_node);
+	  DECL_HAS_DEPENDENT_EXPLICIT_SPEC_P (r) = false;
+	}
     }
 
   /* OpenMP UDRs have the only argument a reference to the declared
diff --git a/gcc/testsuite/g++.dg/modules/explicit-bool-1_a.H b/gcc/testsuite/g++.dg/modules/explicit-bool-1_a.H
new file mode 100644
index 0000000..db49721
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/explicit-bool-1_a.H
@@ -0,0 +1,23 @@
+// PR c++/103752
+// { dg-additional-options -fmodule-header }
+// { dg-require-effective-target c++20 }
+
+template<typename _T1, typename _T2>
+struct pair
+{
+        constexpr
+      explicit(__is_same(_T1, _T2))
+      pair()
+      { }
+
+        _T1 first;
+        _T2 second;
+};
+
+struct string
+{
+  string() { }
+  string(const char* s) : s(s) { }
+
+  const char* s = "";
+};
diff --git a/gcc/testsuite/g++.dg/modules/explicit-bool-1_b.C b/gcc/testsuite/g++.dg/modules/explicit-bool-1_b.C
new file mode 100644
index 0000000..27bfdee
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/explicit-bool-1_b.C
@@ -0,0 +1,6 @@
+// { dg-additional-options -fmodules-ts }
+// { dg-require-effective-target c++20 }
+
+export module x;
+import "explicit-bool-1_a.H";
+pair<string, string> environment;