[gcc/devel/c++-modules] Block-scope externs disallowed

[Nathan Sidwell <nathan@gcc.gnu.org>]

https://gcc.gnu.org/g:3152c118ca04efb2605cc796b1be58d75a6465b2

commit 3152c118ca04efb2605cc796b1be58d75a6465b2
Author: Nathan Sidwell <nathan@acm.org>
Date:   Fri Oct 9 08:21:30 2020 -0700

    Block-scope externs disallowed
    
            gcc/cp/
            * decl.c (start_decl): Reject block-scope extern in module
            purview.
            gcc/testsuite/
            * g++.dg/modules/local-extern-1.C: New.

Diff:
---
 ChangeLog.modules                             |  7 +++++++
 gcc/cp/decl.c                                 | 11 ++++++++---
 gcc/testsuite/g++.dg/modules/local-extern-1.C | 20 ++++++++++++++++++++
 3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/ChangeLog.modules b/ChangeLog.modules
index 61dcf53141b..40a31624223 100644
--- a/ChangeLog.modules
+++ b/ChangeLog.modules
@@ -1,5 +1,12 @@
 2020-10-09  Nathan Sidwell  <nathan@acm.org>
 
+	Block-scope externs disallowed
+	gcc/cp/
+	* decl.c (start_decl): Reject block-scope extern in module
+	purview.
+	gcc/testsuite/
+	* g++.dg/modules/local-extern-1.C: New.
+
 	Remove unused code
 	gcc/cp/
 	* friend.c (add_friend): Remove #if'd out code
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 169204e26bb..baa32d71123 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -5445,9 +5445,14 @@ start_decl (const cp_declarator *declarator,
 
   if ((DECL_EXTERNAL (decl) || TREE_CODE (decl) == FUNCTION_DECL)
       && current_function_decl)
-    /* A function-scope decl of some namespace-scope decl.  */
-    // FIXME: This is ill-formed in a named module
-    DECL_LOCAL_DECL_P (decl) = true;
+    {
+      /* A function-scope decl of some namespace-scope decl.  */
+      DECL_LOCAL_DECL_P (decl) = true;
+      if (named_module_purview_p ())
+	error_at (declarator->id_loc,
+		  "block-scope extern declaration %q#D not permitted"
+		  " in module purview", decl);
+    }
 
   /* Enter this declaration into the symbol table.  Don't push the plain
      VAR_DECL for a variable template.  */
diff --git a/gcc/testsuite/g++.dg/modules/local-extern-1.C b/gcc/testsuite/g++.dg/modules/local-extern-1.C
new file mode 100644
index 00000000000..7b016053d36
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/local-extern-1.C
@@ -0,0 +1,20 @@
+// { dg-additional-options "-fmodules-ts -Wno-pedantic" }
+
+module;
+# 4 __FILE__ 1
+inline void frob ()
+{
+  extern int bob; // OK
+}
+
+# 11 "" 2
+export module bob;
+// { dg-module-cmi !bob }
+
+inline void dob ()
+{
+  extern int bob; // { dg-error "block-scope extern" }
+}
+
+
+// { dg-prune-output "not writing module" }