Improve alignment of "info threads" output, align "Target Id" column

It's long annoyed me that "info threads"'s columns are misaligned.

Particularly the "Target Id" column's content is usually longer than
the specified column width, so the table ends up with the "Frame"
column misaligned.  For example, currently we get this:

 (gdb) info threads
   Id   Target Id         Frame
   1    Thread 0x7ffff7fb5740 (LWP 9056) "threads" 0x00007ffff7bc28ad in __pthread_join (threadid=140737345763072, thread_return=0x7fffffffd3e8) at pthread_join.c:90
   2    Thread 0x7ffff7803700 (LWP 9060) "function0" thread_function0 (arg=0x0) at threads.c:90
 * 3    Thread 0x7ffff7002700 (LWP 9061) "threads" thread_function1 (arg=0x1) at threads.c:106

The fact that the "Frame" heading is in a weird spot is particularly
annoying.

This commit turns the above into into this:

 (gdb) info threads
   Id   Target Id                                    Frame
   1    Thread 0x7ffff7fb5740 (LWP 7548) "threads"   0x00007ffff7bc28ad in __pthread_join (threadid=140737345763072, thread_return=0x7fffffffd3e8) at pthread_join.c:90
   2    Thread 0x7ffff7803700 (LWP 7555) "function0" thread_function0 (arg=0x0) at threads.c:91
 * 3    Thread 0x7ffff7002700 (LWP 7557) "threads"   thread_function1 (arg=0x1) at threads.c:104

It does that by computing the max width of the "Target Id" column and
using that as column width when creating the table.

This results in calling target_pid_to_str / target_extra_thread_info /
target_thread_name twice for each thread, but I think that it doesn't
matter in practice performance-wise, because the remote target caches
the info, and with native targets it shouldn't be noticeable.  It
could matter if we have many threads (say, thousands), but then "info
threads" is practically useless in such a scenario anyway -- better
thread filtering and aggregation would be necessary.

(Note: I have an old branch somewhere where I attempted at making
gdb's "info threads"-like tables follow a model/view design, so that a
general framework took care of issues like these, but it's incomplete
and a much bigger change.  This patch doesn't prevent going in that
direction in the future, of course.)

gdb/ChangeLog:
2018-06-29  Pedro Alves  <palves@redhat.com>

	* thread.c (thread_target_id_str): New, factored out from ...
	(print_thread_info_1): ... here.  Use it to compute the max
	"Target Id" column width.

gdb/testsuite/ChangeLog:
2018-06-29  Pedro Alves  <palves@redhat.com>

	* gdb.threads/names.exp: Adjust expected "info threads" output.

1 files changed, 43 insertions, 22 deletions

diff --git a/gdb/thread.c b/gdb/thread.c
index 77b497e..fd92e78 100644
--- a/gdb/thread.c
+++ b/gdb/thread.c
@@ -1119,6 +1119,26 @@ should_print_thread (const char *requested_threads, int default_inf_num,
   return 1;
 }
 
+/* Return the string to display in "info threads"'s "Target Id"
+   column, for TP.  */
+
+static std::string
+thread_target_id_str (thread_info *tp)
+{
+  const char *target_id = target_pid_to_str (tp->ptid);
+  const char *extra_info = target_extra_thread_info (tp);
+  const char *name = tp->name != nullptr ? tp->name : target_thread_name (tp);
+
+  if (extra_info != nullptr && name != nullptr)
+    return string_printf ("%s \"%s\" (%s)", target_id, name, extra_info);
+  else if (extra_info != nullptr)
+    return string_printf ("%s (%s)", target_id, extra_info);
+  else if (name != nullptr)
+    return string_printf ("%s \"%s\"", target_id, name);
+  else
+    return target_id;
+}
+
 /* Like print_thread_info, but in addition, GLOBAL_IDS indicates
    whether REQUESTED_THREADS is a list of global or per-inferior
    thread ids.  */
@@ -1129,7 +1149,6 @@ print_thread_info_1 (struct ui_out *uiout, const char *requested_threads,
 		     int show_global_ids)
 {
   struct thread_info *tp;
-  const char *extra_info, *name, *target_id;
   struct inferior *inf;
   int default_inf_num = current_inferior ()->num;
 
@@ -1155,6 +1174,9 @@ print_thread_info_1 (struct ui_out *uiout, const char *requested_threads,
     else
       {
 	int n_threads = 0;
+	/* The width of the "Target Id" column.  Grown below to
+	   accommodate the largest entry.  */
+	size_t target_id_col_width = 17;
 
 	ALL_THREADS (tp)
 	  {
@@ -1162,6 +1184,13 @@ print_thread_info_1 (struct ui_out *uiout, const char *requested_threads,
 				      global_ids, pid, tp))
 	      continue;
 
+	    if (!uiout->is_mi_like_p ())
+	      {
+		target_id_col_width
+		  = std::max (target_id_col_width,
+			      thread_target_id_str (tp).size ());
+	      }
+
 	    ++n_threads;
 	  }
 
@@ -1182,7 +1211,8 @@ print_thread_info_1 (struct ui_out *uiout, const char *requested_threads,
 	uiout->table_header (4, ui_left, "id-in-tg", "Id");
 	if (show_global_ids)
 	  uiout->table_header (4, ui_left, "id", "GId");
-	uiout->table_header (17, ui_left, "target-id", "Target Id");
+	uiout->table_header (target_id_col_width, ui_left,
+			     "target-id", "Target Id");
 	uiout->table_header (1, ui_left, "frame", "Frame");
 	uiout->table_body ();
       }
@@ -1224,33 +1254,24 @@ print_thread_info_1 (struct ui_out *uiout, const char *requested_threads,
 	   shared by several fields.  For MI, we do the right thing
 	   instead.  */
 
-	target_id = target_pid_to_str (tp->ptid);
-	extra_info = target_extra_thread_info (tp);
-	name = tp->name ? tp->name : target_thread_name (tp);
-
 	if (uiout->is_mi_like_p ())
 	  {
-	    uiout->field_string ("target-id", target_id);
-	    if (extra_info)
+	    uiout->field_string ("target-id", target_pid_to_str (tp->ptid));
+
+	    const char *extra_info = target_extra_thread_info (tp);
+	    if (extra_info != nullptr)
 	      uiout->field_string ("details", extra_info);
-	    if (name)
+
+	    const char *name = (tp->name != nullptr
+				? tp->name
+				: target_thread_name (tp));
+	    if (name != NULL)
 	      uiout->field_string ("name", name);
 	  }
 	else
 	  {
-	    std::string contents;
-
-	    if (extra_info && name)
-	      contents = string_printf ("%s \"%s\" (%s)", target_id,
-					name, extra_info);
-	    else if (extra_info)
-	      contents = string_printf ("%s (%s)", target_id, extra_info);
-	    else if (name)
-	      contents = string_printf ("%s \"%s\"", target_id, name);
-	    else
-	      contents = target_id;
-
-	    uiout->field_string ("target-id", contents.c_str ());
+	    uiout->field_string ("target-id",
+				 thread_target_id_str (tp).c_str ());
 	  }
 
 	if (tp->state == THREAD_RUNNING)