Fortran: host association issue with symbol in COMMON block [PR108454]

When resolving a flavorless symbol that is already registered with a COMMON
block, and which neither has the intrinsic, generic, or external attribute,
skip searching among interfaces to avoid false resolution to a derived type
of the same name.

	PR fortran/108454

gcc/fortran/ChangeLog:

	* resolve.cc (resolve_common_blocks): Initialize variable.
	(resolve_symbol): If a symbol is already registered with a COMMON
	block, do not search for an interface with the same name.

gcc/testsuite/ChangeLog:

	* gfortran.dg/common_29.f90: New test.

2 files changed, 42 insertions, 1 deletions

diff --git a/gcc/fortran/resolve.cc b/gcc/fortran/resolve.cc
index 12a623da..f2eef12 100644
--- a/gcc/fortran/resolve.cc
+++ b/gcc/fortran/resolve.cc
@@ -1049,7 +1049,7 @@ resolve_common_vars (gfc_common_head *common_block, bool named_common)
 static void
 resolve_common_blocks (gfc_symtree *common_root)
 {
-  gfc_symbol *sym;
+  gfc_symbol *sym = NULL;
   gfc_gsymbol * gsym;
 
   if (common_root == NULL)
@@ -17693,6 +17693,12 @@ resolve_symbol (gfc_symbol *sym)
 	  && sym->attr.if_source == IFSRC_UNKNOWN
 	  && sym->ts.type == BT_UNKNOWN))
     {
+      /* A symbol in a common block might not have been resolved yet properly.
+	 Do not try to find an interface with the same name.  */
+      if (sym->attr.flavor == FL_UNKNOWN && !sym->attr.intrinsic
+	  && !sym->attr.generic && !sym->attr.external
+	  && sym->attr.in_common)
+	goto skip_interfaces;
 
     /* If we find that a flavorless symbol is an interface in one of the
        parent namespaces, find its symtree in this namespace, free the
@@ -17716,6 +17722,7 @@ resolve_symbol (gfc_symbol *sym)
 	    }
 	}
 
+skip_interfaces:
       /* Otherwise give it a flavor according to such attributes as
 	 it has.  */
       if (sym->attr.flavor == FL_UNKNOWN && sym->attr.external == 0
diff --git a/gcc/testsuite/gfortran.dg/common_29.f90 b/gcc/testsuite/gfortran.dg/common_29.f90
new file mode 100644
index 0000000..66f2a18
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/common_29.f90
@@ -0,0 +1,34 @@
+! { dg-do compile }
+! PR fortran/108454
+!
+! Contributed by G.Steinmetz
+
+module m
+  type t
+  end type
+contains
+  subroutine s
+    common t
+  end
+end
+
+module m2
+  implicit none
+  type t
+  end type
+contains
+  subroutine s
+    real :: t
+    common /com/ t
+  end
+end
+
+module m3
+  type t
+  end type
+contains
+  subroutine s
+    type(t) :: x  ! { dg-error "cannot be host associated at .1." }
+    common t      ! { dg-error "incompatible object of the same name" }
+  end
+end