c++: Check module attachment instead of just purview when necessary [PR112631]

Block-scope declarations of functions or extern values are not allowed
when attached to a named module. Similarly, class member functions are
not inline if attached to a named module. However, in both these cases
we currently only check if the declaration is within the module purview;
it is possible for such a declaration to occur within the module purview
but not be attached to a named module (e.g. in an 'extern "C++"' block).
This patch makes the required adjustments.

	PR c++/112631

gcc/cp/ChangeLog:

	* cp-tree.h (named_module_attach_p): New function.
	* decl.cc (start_decl): Check for attachment not purview.
	(grokmethod): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/block-decl-1_a.C: New test.
	* g++.dg/modules/block-decl-1_b.C: New test.
	* g++.dg/modules/block-decl-2.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>

5 files changed, 47 insertions, 5 deletions

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 14895bc..0591386 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7381,6 +7381,8 @@ inline bool module_attach_p ()
 
 inline bool named_module_purview_p ()
 { return named_module_p () && module_purview_p (); }
+inline bool named_module_attach_p ()
+{ return named_module_p () && module_attach_p (); }
 
 /* We're currently exporting declarations.  */
 inline bool module_exporting_p ()
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index dbc3df2..7a97b86 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -6092,10 +6092,10 @@ start_decl (const cp_declarator *declarator,
     {
       /* A function-scope decl of some namespace-scope decl.  */
       DECL_LOCAL_DECL_P (decl) = true;
-      if (named_module_purview_p ())
+      if (named_module_attach_p ())
 	error_at (declarator->id_loc,
-		  "block-scope extern declaration %q#D not permitted"
-		  " in module purview", decl);
+		  "block-scope extern declaration %q#D must not be"
+		  " attached to a named module", decl);
     }
 
   /* Enter this declaration into the symbol table.  Don't push the plain
@@ -18907,10 +18907,10 @@ grokmethod (cp_decl_specifier_seq *declspecs,
   check_template_shadow (fndecl);
 
   /* p1779 ABI-Isolation makes inline not a default for in-class
-     definitions in named module purview.  If the user explicitly
+     definitions attached to a named module.  If the user explicitly
      made it inline, grokdeclarator will already have done the right
      things.  */
-  if ((!named_module_purview_p ()
+  if ((!named_module_attach_p ()
        || flag_module_implicit_inline
       /* Lambda's operator function remains inline.  */
        || LAMBDA_TYPE_P (DECL_CONTEXT (fndecl)))
diff --git a/gcc/testsuite/g++.dg/modules/block-decl-1_a.C b/gcc/testsuite/g++.dg/modules/block-decl-1_a.C
new file mode 100644
index 0000000..e7ffc62
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/block-decl-1_a.C
@@ -0,0 +1,9 @@
+// { dg-additional-options "-fmodules-ts" }
+// { dg-module-cmi bla }
+
+export module bla;
+
+export extern "C++" inline void fun() {
+  void oops();  // { dg-bogus "block-scope extern declaration" }
+  oops();
+}
diff --git a/gcc/testsuite/g++.dg/modules/block-decl-1_b.C b/gcc/testsuite/g++.dg/modules/block-decl-1_b.C
new file mode 100644
index 0000000..c0d724f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/block-decl-1_b.C
@@ -0,0 +1,10 @@
+// { dg-module-do link }
+// { dg-additional-options "-fmodules-ts" }
+
+import bla;
+
+void oops() {}
+
+int main() {
+  fun();
+}
diff --git a/gcc/testsuite/g++.dg/modules/block-decl-2.C b/gcc/testsuite/g++.dg/modules/block-decl-2.C
new file mode 100644
index 0000000..974e26f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/block-decl-2.C
@@ -0,0 +1,21 @@
+// { dg-additional-options "-fmodules-ts" }
+// { dg-module-cmi !mod }
+
+export module mod;
+
+namespace {
+  void internal() {}
+}
+
+export extern "C++" auto foo() {
+  struct X {
+    // `foo` is not attached to a named module, and as such
+    // `X::f` should be implicitly `inline` here
+    void f() {  // { dg-error "references internal linkage entity" }
+      internal();
+    }
+  };
+  return X{};
+}
+
+// { dg-prune-output "failed to write compiled module" }