[PATCH] Fortran: diagnose USE associated symbols in COMMON blocks [PR108453]

[Harald Anlauf <anlauf@gmx.de>]

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Dear all,

a USE associated symbol shall not appear in a COMMON block
(F2018:C8121) and needs to be diagnosed.  The patch is
fairly obvious.

Regtested on x86_64-pc-linux-gnu.  OK for mainline?

As the PR is marked as a 10/11/12/13 regression,
I plan to backport as appropriate.

Thanks,
Harald


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From 3f0e4b23038ade2cd14d93b0705af93848ee45c2 Mon Sep 17 00:00:00 2001
From: Harald Anlauf <anlauf@gmx.de>
Date: Sat, 28 Jan 2023 17:59:23 +0100
Subject: [PATCH] Fortran: diagnose USE associated symbols in COMMON blocks
 [PR108453]

gcc/fortran/ChangeLog:

	PR fortran/108453
	* match.cc (gfc_match_common): A USE associated name shall not appear
	in a COMMON block (F2018:C8121).

gcc/testsuite/ChangeLog:

	PR fortran/108453
	* gfortran.dg/common_27.f90: New test.
---
 gcc/fortran/match.cc                    | 10 ++++++++++
 gcc/testsuite/gfortran.dg/common_27.f90 | 14 ++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 gcc/testsuite/gfortran.dg/common_27.f90

diff --git a/gcc/fortran/match.cc b/gcc/fortran/match.cc
index 5e933c12931..5eb6d0e1c1d 100644
--- a/gcc/fortran/match.cc
+++ b/gcc/fortran/match.cc
@@ -5345,6 +5345,16 @@ gfc_match_common (void)
 		goto cleanup;
 	    }

+	  /* F2018:R874:  common-block-object is variable-name [ (array-spec) ]
+	     F2018:C8121: A variable-name shall not be a name made accessible
+	     by use association.  */
+	  if (sym->attr.use_assoc)
+	    {
+	      gfc_error ("Symbol %qs at %C is USE associated from module %qs "
+			 "and cannot occur in COMMON", sym->name, sym->module);
+	      goto cleanup;
+	    }
+
 	  /* Deal with an optional array specification after the
 	     symbol name.  */
 	  m = gfc_match_array_spec (&as, true, true);
diff --git a/gcc/testsuite/gfortran.dg/common_27.f90 b/gcc/testsuite/gfortran.dg/common_27.f90
new file mode 100644
index 00000000000..dcde5de2bd2
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/common_27.f90
@@ -0,0 +1,14 @@
+! { dg-do compile }
+! PR fortran/108453 - a use associated variable cannot occur in COMMON
+! Contributed by G.Steinmetz
+
+module m
+  type t
+  end type
+  real :: r
+end
+program p
+  use m, only: t, r
+  common t      ! { dg-error "USE associated from module" }
+  common /cm/ r ! { dg-error "USE associated from module" }
+end
--
2.35.3