[gdb] Fix printing of unresolved dynamic type

When debugging gdb in batch mode with executable mixed-lang-stack and doing a
backtrace at breakpt:
...
$ gdb --args gdb \
  -batch \
  outputs/gdb.fortran/mixed-lang-stack/mixed-lang-stack \
  -ex "b breakpt" \
  -ex r \
  -ex bt
...
and stopping at resolve_dynamic_type to print the type:
...
(gdb) b resolve_dynamic_type
Breakpoint 1 at 0x6b020c: file gdbtypes.c, line 2633.
(gdb) commands
Type commands for breakpoint(s) 1, one per line.
End with a line saying just "end".
>call recursive_dump_type (type, 0)
>continue
>end
(gdb) run
...
we eventually run into an assert for the dynamic type of "str":
...
Thread 1 "gdb" hit Breakpoint 1, resolve_dynamic_type (type=0x22204f0, \
  valaddr=..., addr=4199408) at gdbtypes.c:2633
2633        = {check_typedef (type), valaddr, addr, NULL};
type node 0x22204f0
name '<NULL>' (0x0)
code 0xd (TYPE_CODE_STRING)
length 0
  ...
    nfields 0 0x22204b0
gdbtypes.h:526: internal-error: LONGEST dynamic_prop::const_val() const: \
  Assertion `m_kind == PROP_CONST' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
...
when trying to print the high bound of a TYPE_CODE_RANGE, which has m_kind
PROP_LOCEXPR, while the code in resolve_dynamic_type assumes PROP_CONST.

Fix this by extending the printing of TYPE_CODE_RANGE to allow
PROP_LOCEXPR/PROP_LOCLIST as well, such that we have instead:
...
    nfields 0 0x1fbc020
    low 1  high (dynamic)
...

Tested on x86_64-linux.

gdb/ChangeLog:

2020-08-17  Tom de Vries  <tdevries@suse.de>

	PR gdb/26393
	* gdbtypes.c (dump_dynamic_prop): New function.
	(recursive_dump_type): Use dump_dynamic_prop for TYPE_CODE_RANGE.

2 files changed, 34 insertions, 7 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 9cc7e44..3e733a7 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2020-08-17  Tom de Vries  <tdevries@suse.de>
+
+	PR gdb/26393
+	* gdbtypes.c (dump_dynamic_prop): New function.
+	(recursive_dump_type): Use dump_dynamic_prop for TYPE_CODE_RANGE.
+
 2020-08-15  Tom de Vries  <tdevries@suse.de>
 
 	PR backtrace/26390
diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index da1c58c..c1eb03d 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -4856,6 +4856,29 @@ print_gnat_stuff (struct type *type, int spaces)
 
 static struct obstack dont_print_type_obstack;
 
+/* Print the dynamic_prop PROP.  */
+
+static void
+dump_dynamic_prop (dynamic_prop const& prop)
+{
+  switch (prop.kind ())
+    {
+    case PROP_CONST:
+      printf_filtered ("%s", plongest (prop.const_val ()));
+      break;
+    case PROP_UNDEFINED:
+      printf_filtered ("(undefined)");
+      break;
+    case PROP_LOCEXPR:
+    case PROP_LOCLIST:
+      printf_filtered ("(dynamic)");
+      break;
+    default:
+      gdb_assert_not_reached ("unhandled prop kind");
+      break;
+    }
+}
+
 void
 recursive_dump_type (struct type *type, int spaces)
 {
@@ -5115,13 +5138,11 @@ recursive_dump_type (struct type *type, int spaces)
     }
   if (type->code () == TYPE_CODE_RANGE)
     {
-      printfi_filtered (spaces, "low %s%s  high %s%s\n",
-			plongest (type->bounds ()->low.const_val ()),
-			(type->bounds ()->low.kind () == PROP_UNDEFINED
-			 ? " (undefined)" : ""),
-			plongest (type->bounds ()->high.const_val ()),
-			(type->bounds ()->high.kind () == PROP_UNDEFINED
-			 ? " (undefined)" : ""));
+      printfi_filtered (spaces, "low ");
+      dump_dynamic_prop (type->bounds ()->low);
+      printf_filtered ("  high ");
+      dump_dynamic_prop (type->bounds ()->high);
+      printf_filtered ("\n");
     }
 
   switch (TYPE_SPECIFIC_FIELD (type))