Support dynamically computed convenience variables in get_internalvar_integer

When using $_thread in info threads to showonly the current thread,
you get this error:
```
(gdb) info thread $_thread
Convenience variable must have integer value.
Args must be numbers or '$' variables.
```

It's because $_thread is a dynamically computed convenience
variable, which isn't supported yet by get_internalvar_integer.

Now the output looks like this:
```
(gdb) info threads $_thread
  Id   Target Id           Frame
* 1    Thread 10640.0x2680 main () at C:/src/repos/binutils-gdb.git/gdb/testsuite/gdb.base/gdbvars.c:21
```

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=17600
Approved-By: Tom Tromey <tom@tromey.com>

3 files changed, 28 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.base/gdbvars.exp b/gdb/testsuite/gdb.base/gdbvars.exp
index cb6656c..d4b2860 100644
--- a/gdb/testsuite/gdb.base/gdbvars.exp
+++ b/gdb/testsuite/gdb.base/gdbvars.exp
@@ -158,6 +158,11 @@ proc test_with_program {} {
 	"Set a new convenience variable to a program variable"
     gdb_test "print /x \$prog_var" " = $hex" \
 	"Print contents of new convenience variable of program variable"
+
+    # Test $_thread/$_inferior convenience variables in various commands.
+    gdb_test "info threads \$_thread" "\\* 1 .* main.*"
+    gdb_test "info inferiors \$_inferior" "\\* 1 .* process.*"
+    gdb_test "break foo_int thread \$_thread" "Breakpoint \[0-9\]*.*"
 }
 
 gdb_test_no_output "set print sevenbit-strings"
diff --git a/gdb/thread.c b/gdb/thread.c
index c0ed64e..85bdbaa 100644
--- a/gdb/thread.c
+++ b/gdb/thread.c
@@ -1129,6 +1129,10 @@ print_thread_info_1 (struct ui_out *uiout, const char *requested_threads,
 
 	for (thread_info *tp : all_threads ())
 	  {
+	    /* In case REQUESTED_THREADS contains $_thread.  */
+	    if (current_thread != nullptr)
+	      switch_to_thread (current_thread);
+
 	    if (!should_print_thread (requested_threads, default_inf_num,
 				      global_ids, pid, tp))
 	      continue;
@@ -1176,6 +1180,10 @@ print_thread_info_1 (struct ui_out *uiout, const char *requested_threads,
 	  if (tp == current_thread && tp->state == THREAD_EXITED)
 	    current_exited = true;
 
+	  /* In case REQUESTED_THREADS contains $_thread.  */
+	  if (current_thread != nullptr)
+	    switch_to_thread (current_thread);
+
 	  if (!should_print_thread (requested_threads, default_inf_num,
 				    global_ids, pid, tp))
 	    continue;
diff --git a/gdb/value.c b/gdb/value.c
index 1a39855..e9308b0 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -2119,6 +2119,21 @@ get_internalvar_integer (struct internalvar *var, LONGEST *result)
 	}
     }
 
+  if (var->kind == INTERNALVAR_MAKE_VALUE)
+    {
+      struct gdbarch *gdbarch = get_current_arch ();
+      struct value *val
+	= (*var->u.make_value.functions->make_value) (gdbarch, var,
+						      var->u.make_value.data);
+      struct type *type = check_typedef (val->type ());
+
+      if (type->code () == TYPE_CODE_INT)
+	{
+	  *result = value_as_long (val);
+	  return 1;
+	}
+    }
+
   return 0;
 }