fortran: Fix arrays of variable length strings for FORTRAN

Before this change resolve_dynamic_array_or_string was called for
all TYPE_CODE_ARRAY and TYPE_CODE_STRING types, but, in the end,
this function always called create_array_type_with_stride, which
creates a TYPE_CODE_ARRAY type.

Suppose we have

subroutine vla_array (arr1, arr2)
  character (len=*):: arr1 (:)
  character (len=5):: arr2 (:)

  print *, arr1 ! break-here
  print *, arr2
end subroutine vla_array

The "print arr1" and "print arr2" command at the "break-here" line
gives the following output:

(gdb) print arr1
$1 = <incomplete type>
(gdb) print arr2
$2 = ('abcde', 'abcde', 'abcde')
(gdb) ptype arr1
type = Type
End Type
(gdb) ptype arr2
type = character*5 (3)

Dwarf info using Intel® Fortran Compiler for such case contains following:
 <1><fd>: Abbrev Number: 12 (DW_TAG_string_type)
    <fe>   DW_AT_name        : (indirect string, offset: 0xd2): .str.ARR1
    <102>   DW_AT_string_length: 3 byte block: 97 23 8 (DW_OP_push_object_address; DW_OP_plus_uconst: 8)

After this change resolve_dynamic_array_or_string now calls
create_array_type_with_stride or create_string_type, so if the
incoming dynamic type is a TYPE_CODE_STRING then we'll get back a
TYPE_CODE_STRING type.  Now gdb shows following:

(gdb) p arr1
$1 = ('abddefghij', 'abddefghij', 'abddefghij', 'abddefghij', 'abddefghij')
(gdb) p arr2
$2 = ('abcde', 'abcde', 'abcde')
(gdb) ptype arr1
type = character*10 (5)
(gdb) ptype arr2
type = character*5 (3)

In case of GFortran, compiler emits DW_TAG_structure_type for string type
arguments of the subroutine and it has only DW_AT_declaration tag.  This
results in <incomplete type> in gdb.  So, following issue is raised in gcc
bugzilla "https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101826".

Fixing above issue introduce regression in gdb.fortran/mixed-lang-stack.exp,
i.e. the test forces the language to C/C++ and print a Fortran string value.
The string value is a dynamic type with code TYPE_CODE_STRING.

Before this commit the dynamic type resolution would always convert this to
a TYPE_CODE_ARRAY of characters, which the C value printing could handle.

But now after this commit we get a TYPE_CODE_STRING, which
neither the C value printing, or the generic value printing code can
support.  And so, I've added support for TYPE_CODE_STRING to the generic
value printing, all characters of strings are printed together till the
first null character.

Lastly, in gdb.opt/fortran-string.exp and gdb.fortran/string-types.exp
tests it expects type of character array in 'character (3)' format but now
after this change we get 'character*3', so tests are updated accordingly.

Approved-By: Tom Tromey <tom@tromey.com>

gdb/gdbtypes.c

@@ -2327,10 +2327,42 @@ resolve_dynamic_array_or_string_1 (struct type *type,
 						    frame, rank - 1,
 						    resolve_p);
     }
+  else if (ary_dim != nullptr && ary_dim->code () == TYPE_CODE_STRING)
+    {
+      /* The following special case for TYPE_CODE_STRING should not be
+	 needed, ideally we would defer resolving the dynamic type of the
+	 array elements until needed later, and indeed, the resolved type
+	 of each array element might be different, so attempting to resolve
+	 the type here makes no sense.
+
+	 However, in Fortran, for arrays of strings, each element must be
+	 the same type, as such, the DWARF for the string length relies on
+	 the object address of the array itself.
+
+	 The problem here is that, when we create values from the dynamic
+	 array type, we resolve the data location, and use that as the
+	 value address, this completely discards the original value
+	 address, and it is this original value address that is the
+	 descriptor for the dynamic array, the very address that the DWARF
+	 needs us to push in order to resolve the dynamic string length.
+
+	 What this means then, is that, given the current state of GDB, if
+	 we don't resolve the string length now, then we will have lost
+	 access to the address of the dynamic object descriptor, and so we
+	 will not be able to resolve the dynamic string later.
+
+	 For now then, we handle special case TYPE_CODE_STRING on behalf of
+	 Fortran, and hope that this doesn't cause problems for anyone
+	 else.  */
+      elt_type = resolve_dynamic_type_internal (type->target_type (),
+						addr_stack, frame, 0);
+    }
   else
     elt_type = type->target_type ();
 
   prop = type->dyn_prop (DYN_PROP_BYTE_STRIDE);
+  if (prop != nullptr && type->code () == TYPE_CODE_STRING)
+    prop = nullptr;
   if (prop != NULL && resolve_p)
     {
       if (dwarf2_evaluate_property (prop, frame, addr_stack, &value))
@@ -2351,6 +2383,9 @@ resolve_dynamic_array_or_string_1 (struct type *type,
     bit_stride = type->field (0).bitsize ();
 
   type_allocator alloc (type, type_allocator::SMASH);
+  if (type->code () == TYPE_CODE_STRING)
+    return create_string_type (alloc, elt_type, range_type);
+  else
     return create_array_type_with_stride (alloc, elt_type, range_type, NULL,
 					  bit_stride);
 }

gdb/testsuite/gdb.fortran/string-types.exp

@@ -52,7 +52,7 @@ with_test_prefix "third breakpoint, first time" {
     # Continue to the third breakpoint.
     gdb_continue_to_breakpoint "continue"
     gdb_test "print s" " = 'foo'"
-    gdb_test "ptype s" "type = character \\(3\\)"
+    gdb_test "ptype s" "type = character\\*3"
 }
 
 with_test_prefix "third breakpoint, second time" {
@@ -65,5 +65,5 @@ with_test_prefix "third breakpoint, second time" {
     # by most users, so seems good enough.
     gdb_continue_to_breakpoint "continue"
     gdb_test "print s" " = 'foo\\\\n\\\\t\\\\r\\\\000bar'"
-    gdb_test "ptype s" "type = character \\(10\\)"
+    gdb_test "ptype s" "type = character\\*10"
 }

gdb/testsuite/gdb.fortran/vla-array.exp

@@ -0,0 +1,60 @@
+# Copyright 2024 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+standard_testfile ".f90"
+load_lib "fortran.exp"
+
+require allow_fortran_tests
+
+if {[prepare_for_testing "failed to prepare" ${testfile} ${srcfile} \
+    {debug f90 quiet}]} {
+    return -1
+}
+
+if ![fortran_runto_main] {
+    untested "could not run to main"
+    return -1
+}
+
+# Try to access vla string / vla string array / string array values.
+gdb_breakpoint [gdb_get_line_number "arr_vla1-print"]
+gdb_continue_to_breakpoint "arr_vla1-print"
+
+# GFortran emits DW_TAG_structure_type for strings and it has only
+# DW_AT_declaration tag.  This results in <incomplete type> in gdb.
+if [test_compiler_info "gfortran*" f90] { setup_xfail *-*-* gcc/101826 }
+gdb_test "print arr_vla1"  \
+    " = \\\('vlaaryvlaary', 'vlaaryvlaary', 'vlaaryvlaary', 'vlaaryvlaary', 'vlaaryvlaary'\\\)"  \
+    "print vla string array"
+
+if [test_compiler_info "gfortran*" f90] { setup_xfail *-*-* gcc/101826 }
+gdb_test "ptype arr_vla1"  \
+    "type = character\\*12 \\(5\\)"  \
+    "print variable length string array type"
+gdb_test "print arr_vla2"  \
+    " = 'vlaary'"  \
+    "print variable length string"
+gdb_test "ptype arr_vla2"  \
+    "type = character\\*6"  \
+    "print variable length string type"
+gdb_test "print arr2"  \
+    " = \\\('vlaaryvla', 'vlaaryvla', 'vlaaryvla'\\\)"  \
+    "print string array"
+gdb_test "ptype arr2"  \
+    "type = character\\*9 \\(3\\)"  \
+    "print string array type"
+gdb_test "print rank(arr_vla1)"  \
+    "$decimal"  \
+    "print string array rank"

gdb/testsuite/gdb.fortran/vla-array.f90

@@ -0,0 +1,45 @@
+! Copyright 2024 Free Software Foundation, Inc.
+!
+! This program is free software; you can redistribute it and/or modify
+! it under the terms of the GNU General Public License as published by
+! the Free Software Foundation; either version 3 of the License, or
+! (at your option) any later version.
+!
+! This program is distributed in the hope that it will be useful,
+! but WITHOUT ANY WARRANTY; without even the implied warranty of
+! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+! GNU General Public License for more details.
+!
+! You should have received a copy of the GNU General Public License
+! along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+subroutine vla_array_func (arr_vla1, arr_vla2, arr2)
+  character (len=*):: arr_vla1 (:)
+  character (len=*):: arr_vla2
+  character (len=9):: arr2 (:)
+
+  print *, arr_vla1    ! arr_vla1-print
+  print *, arr_vla2
+  print *, arr2
+  print *, rank(arr_vla1)
+end subroutine vla_array_func
+
+program vla_array_main
+interface
+  subroutine vla_array_func (arr_vla1, arr_vla2, arr2)
+    character (len=*):: arr_vla1 (:)
+    character (len=*):: arr_vla2
+    character (len=9):: arr2 (:)
+  end subroutine vla_array_func
+end interface
+  character (len=9) :: arr1 (3)
+  character (len=6) :: arr2
+  character (len=12) :: arr3 (5)
+
+  arr1 = 'vlaaryvla'
+  arr2 = 'vlaary'
+  arr3 = 'vlaaryvlaary'
+
+  call vla_array_func (arr3, arr2, arr1)
+
+end program vla_array_main

gdb/testsuite/gdb.opt/fortran-string.exp

@@ -33,5 +33,5 @@ if {![runto f]} {
 
 gdb_test_no_output "set print frame-arguments all"
 gdb_test "frame" ".*s='foo'.*"
-gdb_test "ptype s" "type = character \\(3\\)"
+gdb_test "ptype s" "type = character\\*3"
 gdb_test "p s" "\\$\[0-9\]* = 'foo'"

gdb/valprint.c

@@ -500,6 +500,76 @@ generic_val_print_array (struct value *val,
 
 }
 
+/* generic_val_print helper for TYPE_CODE_STRING.  */
+
+static void
+generic_val_print_string (struct value *val,
+			  struct ui_file *stream, int recurse,
+			  const struct value_print_options *options,
+			  const struct generic_val_print_decorations
+			    *decorations)
+{
+  struct type *type = check_typedef (val->type ());
+  struct type *unresolved_elttype = type->target_type ();
+  struct type *elttype = check_typedef (unresolved_elttype);
+
+  if (type->length () > 0 && unresolved_elttype->length () > 0)
+    {
+      LONGEST low_bound, high_bound;
+
+      if (!get_array_bounds (type, &low_bound, &high_bound))
+	error (_("Could not determine the array high bound"));
+
+      const gdb_byte *valaddr = val->contents_for_printing ().data ();
+      int force_ellipses = 0;
+      enum bfd_endian byte_order = type_byte_order (type);
+      int eltlen, len;
+
+      eltlen = elttype->length ();
+      len = high_bound - low_bound + 1;
+
+      /* If requested, look for the first null char and only
+	 print elements up to it.  */
+      if (options->stop_print_at_null)
+	{
+	  unsigned int print_max_chars = get_print_max_chars (options);
+	  unsigned int temp_len;
+
+	  for (temp_len = 0;
+	      (temp_len < len
+	       && temp_len < print_max_chars
+	       && extract_unsigned_integer (valaddr + temp_len * eltlen,
+					    eltlen, byte_order) != 0);
+	      ++temp_len)
+	      ;
+
+	    /* Force printstr to print ellipses if
+	       we've printed the maximum characters and
+	       the next character is not \000.  */
+	    if (temp_len == print_max_chars && temp_len < len)
+	      {
+		ULONGEST ival
+		  = extract_unsigned_integer (valaddr + temp_len * eltlen,
+					      eltlen, byte_order);
+		if (ival != 0)
+		  force_ellipses = 1;
+	      }
+
+	    len = temp_len;
+	}
+
+	current_language->printstr (stream, unresolved_elttype, valaddr, len,
+				    nullptr, force_ellipses, options);
+    }
+  else
+    {
+      /* Array of unspecified length: treat like pointer to first elt.  */
+      print_unpacked_pointer (type, elttype, val->address (),
+			      stream, options);
+    }
+
+}
+
 /* generic_value_print helper for TYPE_CODE_PTR.  */
 
 static void
@@ -930,6 +1000,10 @@ generic_value_print (struct value *val, struct ui_file *stream, int recurse,
       generic_val_print_array (val, stream, recurse, options, decorations);
       break;
 
+    case TYPE_CODE_STRING:
+      generic_val_print_string (val, stream, recurse, options, decorations);
+      break;
+
     case TYPE_CODE_MEMBERPTR:
       generic_value_print_memberptr (val, stream, recurse, options,
 				     decorations);