[PATCH] fortran: Fix host association in module procedure interface bodies [PR79330]

[Gonzalosilvalde]

Named constants from the host scope were not accessible in module
procedure interface bodies, causing bind(C, name=...) expressions
referencing such constants to fail.  The compiler treated the constant
as an implicitly typed REAL(4) variable instead of resolving it from
the enclosing module scope.

The fix sets has_import_set on the current namespace when a module
procedure is detected inside an interface block, before bind(C) is
parsed, so that symbol lookup can reach the host scope.

gcc/fortran/ChangeLog:

        PR fortran/79330
        * decl.cc (gfc_match_subroutine): Set has_import_set when
        matching a module procedure inside an interface block.
        (gfc_match_function_decl): Likewise.

gcc/testsuite/ChangeLog:

        PR fortran/79330
        * gfortran.dg/bind_c_module_proc.f90: New test.
---
 gcc/fortran/decl.cc                            | 12 ++++++++++--
 .../gfortran.dg/bind_c_module_proc.f90         | 18 ++++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gfortran.dg/bind_c_module_proc.f90

diff --git a/gcc/fortran/decl.cc b/gcc/fortran/decl.cc
index 454b65f2c47..faf404d994a 100644
--- a/gcc/fortran/decl.cc
+++ b/gcc/fortran/decl.cc
@@ -8191,7 +8191,11 @@ gfc_match_function_decl (void)
     sym = sym->result;
 
   if (current_attr.module_procedure)
-    sym->attr.module_procedure = 1;
+    {
+      sym->attr.module_procedure = 1;
+      if (gfc_current_state () == COMP_INTERFACE)
+        gfc_current_ns->has_import_set = 1;
+    }
 
   gfc_new_block = sym;
 
@@ -8687,7 +8691,11 @@ gfc_match_subroutine (void)
                                             &gfc_current_locus);
 
   if (current_attr.module_procedure)
-    sym->attr.module_procedure = 1;
+    {
+      sym->attr.module_procedure = 1;
+      if (gfc_current_state () == COMP_INTERFACE)
+        gfc_current_ns->has_import_set = 1;
+    }
 
   if (add_hidden_procptr_result (sym))
     sym = sym->result;
diff --git a/gcc/testsuite/gfortran.dg/bind_c_module_proc.f90 
b/gcc/testsuite/gfortran.dg/bind_c_module_proc.f90
new file mode 100644
index 00000000000..2df933f3c14
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/bind_c_module_proc.f90
@@ -0,0 +1,18 @@
+! { dg-do compile }
+! PR fortran/79330
+! Verify that named constants from the host scope are accessible
+! in module procedure interface bodies for bind(C, name=...).
+
+module m
+  implicit none
+  character(len=*), parameter :: PREFIX = "_gfortran_"
+  interface
+    module subroutine sub() bind(C, name=PREFIX//"caf_sub")
+      implicit none
+    end subroutine
+    module function func() result(r) bind(C, name=PREFIX//"caf_func")
+      implicit none
+      integer :: r
+    end function
+  end interface
+end module
-- 
2.47.3