Re: [Patch, Fortran] C prototypes for functions returning C function pointers

[Thomas Koenig]

Hi Harald,

the attached patch contains a chunk changing resolve.cc
that is neither described in the suggested commit message,
and it fails to compile here:

../../gcc-trunk/gcc/fortran/resolve.cc: In function 'void
check_c_funptr_assign_interface(gfc_expr*, gfc_expr*)':
../../gcc-trunk/gcc/fortran/resolve.cc:12248:48: error: 'gfc_expr' {aka
'struct gfc_expr'} has no member named 'is_c_interop'
12248 |   if (rhs->expr_type != EXPR_FUNCTION || !rhs->is_c_interop)
       |                                                ^~~~~~~~~~~~

Can you please check whether you inadvertently added something
that was not planned or tested?

I sent out the wrong version of the patch, sorry (one which contained
an intermediate stage of something I tried, and then abandoned).

Here is the one that actually in my tree, and that I regression-tested.

Best regards

        Thomas



diff --git a/gcc/fortran/dump-parse-tree.cc b/gcc/fortran/dump-parse-tree.cc
index 1a15757b57b..3e4a30fe0de 100644
--- a/gcc/fortran/dump-parse-tree.cc
+++ b/gcc/fortran/dump-parse-tree.cc
@@ -4038,6 +4038,7 @@ static void write_interop_decl (gfc_symbol *);
 static void write_proc (gfc_symbol *, bool);
 static void show_external_symbol (gfc_gsymbol *, void *);
 static void write_type (gfc_symbol *sym);
+static void write_funptr_fcn (gfc_symbol *);
 
 /* Do we need to write out an #include <ISO_Fortran_binding.h> or not?  */
 
@@ -4379,9 +4380,10 @@ write_type (gfc_symbol *sym)
 {
   gfc_component *c;
 
-  /* Don't dump our iso c module.  */
+  /* Don't dump our iso c module, nor vtypes.  */
 
-  if (sym->from_intmod == INTMOD_ISO_C_BINDING || sym->attr.flavor != FL_DERIVED)
+  if (sym->from_intmod == INTMOD_ISO_C_BINDING || sym->attr.flavor != FL_DERIVED
+      || sym->attr.vtype)
     return;
 
   fprintf (dumpfile, "typedef struct %s {\n", sym->name);
@@ -4495,6 +4497,18 @@ write_formal_arglist (gfc_symbol *sym, bool bind_c)
 
 }
 
+/* Write out an interoperable function returning a function pointer.  Better
+   handled separately.  As we know nothing about the type, assume
+   a C default return of int.  */
+
+static void
+write_funptr_fcn (gfc_symbol *sym)
+{
+  fprintf (dumpfile, "void (*%s (", sym->binding_label);
+  write_formal_arglist (sym, 1);
+  fputs (")) ();\n", dumpfile);
+}
+
 /* Write out a procedure, including its arguments.  */
 static void
 write_proc (gfc_symbol *sym, bool bind_c)
@@ -4552,7 +4566,13 @@ write_interop_decl (gfc_symbol *sym)
   else if (sym->attr.flavor == FL_DERIVED)
     write_type (sym);
   else if (sym->attr.flavor == FL_PROCEDURE)
-    write_proc (sym, true);
+    {
+      if (sym->ts.type == BT_DERIVED
+	  && strcmp (sym->ts.u.derived->name, "c_funptr") == 0)
+	write_funptr_fcn (sym);
+      else
+	write_proc (sym, true);
+    }
 }
 
 /* This section deals with dumping the global symbol tree.  */