[PATCH 5/5] gdb: remove special case completion word handling for filenames

[Andrew Burgess <aburgess@redhat.com>]

Eli,

CC-ing you directly as the work I'm touching was originally done by
you, see:

  https://sourceware.org/pipermail/gdb-patches/2001-February/007313.html

The original email mentions 4 cases:

  - completion on a file name in a list of file names didn't work;
  - GDB would not always append a slash if the completion is a directory;
  - completion failed when the file name had non-file-name characters,
    such as redirection, around it;
  - on DOS/Windows, completion would fail with files with a drive letter.

I believe I've tested the first 3 of these and they all seem to work
fine still, but I don't have a working Windows machine on which I can
test case #4.  I just wanted to bring this change to your attention in
case you wanted to build/test this and check that completion around
drive letters was still working as expected.

---

This commit removes some code which is special casing the filename
completion logic.  The code in question relates to finding the
beginning of the completion word and was first introduced, or modified
into its existing form in commit 7830cf6fb9571c3357b1a0 (from 2001).

The code being removed moved the start of the completion word backward
until a character in gdb_completer_file_name_break_characters was
found, or until we reached the end of the actual command.

However, I doubt that this is needed any more.  The filename completer
has a corresponding filename_completer_handle_brkchars function which
provides gdb_completer_file_name_break_characters as the word break
characters to readline, and also sets rl_completer_quote_characters.
As such, I would expect readline to be able to correctly find the
start of the completion word.

There is one change which I've needed to make as a consequence of
removing the above code, and I think this is a bug fix.

In complete_line_internal_normal_command we initialised temporary
variable P to the CMD_ARGS; this is the complete text after the
command name.  Meanwhile, complete_line_internal_normal_command also
accepts an argument WORD, which is the completion word that readline
found for us.

In the code I removed P was updated, it was first set to WORD, and
then moved backwards to the "new" start of the completion word.

But notice, the default for P is the complete command argument text,
and only if we are performing filename completion do we modify P to be
the completion word.

We then passed P through to the actual commands completion function.

If we are doing anything other than filename completion then the value
of P passed is the complete argument text.

If we are doing filename completion then the value of P passed is the
completion word.

Thus in filename_completer we get two arguments TEXT and WORD, the
TEXT argument gets the value of P which is the "new" completion word,
while WORD is the completion word that readline calculated.

However, after I removed the special case in
complete_line_internal_normal_command, the temporary P is removed, we
now always pass through the complete argument text where P was
previous used.

As such, filename_completer now receives TEXT as the complete argument
text, and WORD as the readline calculated completion word.

Previously in filename_completer we actually tried to generate
completions based on TEXT, which due to the special case, was the
completion word.  But after my change this is no longer the case.  So
I've updated filename_completer to generate completions based on WORD,
the readline calculated completion word.

If I'm correct, then I don't expect to see any user visible changes
after this commit.
---
 gdb/completer.c | 25 ++++---------------------
 1 file changed, 4 insertions(+), 21 deletions(-)

diff --git a/gdb/completer.c b/gdb/completer.c
index 9c89aa43810..b78946d66dd 100644
--- a/gdb/completer.c
+++ b/gdb/completer.c
@@ -210,7 +210,7 @@ filename_completer (struct cmd_list_element *ignore,
   while (1)
     {
       gdb::unique_xmalloc_ptr<char> p_rl
-	(rl_filename_completion_function (text, subsequent_name));
+	(rl_filename_completion_function (word, subsequent_name));
       if (p_rl == NULL)
 	break;
       /* We need to set subsequent_name to a non-zero value before the
@@ -239,7 +239,7 @@ filename_completer (struct cmd_list_element *ignore,
 	}
 
       tracker.add_completion
-	(make_completion_match_str (std::move (p_rl), text, word));
+	(make_completion_match_str (std::move (p_rl), word, word));
     }
 }
 
@@ -1193,23 +1193,6 @@ complete_line_internal_normal_command (completion_tracker &tracker,
 				       complete_line_internal_reason reason,
 				       struct cmd_list_element *c)
 {
-  const char *p = cmd_args;
-
-  if (c->completer == filename_completer)
-    {
-      /* Many commands which want to complete on file names accept
-	 several file names, as in "run foo bar >>baz".  So we don't
-	 want to complete the entire text after the command, just the
-	 last word.  To this end, we need to find the beginning of the
-	 file name by starting at `word' and going backwards.  */
-      for (p = word;
-	   p > command
-	     && strchr (gdb_completer_file_name_break_characters,
-			p[-1]) == NULL;
-	   p--)
-	;
-    }
-
   if (reason == handle_brkchars)
     {
       completer_handle_brkchars_ftype *brkchars_fn;
@@ -1223,11 +1206,11 @@ complete_line_internal_normal_command (completion_tracker &tracker,
 	       (c->completer));
 	}
 
-      brkchars_fn (c, tracker, p, word);
+      brkchars_fn (c, tracker, cmd_args, word);
     }
 
   if (reason != handle_brkchars && c->completer != NULL)
-    (*c->completer) (c, tracker, p, word);
+    (*c->completer) (c, tracker, cmd_args, word);
 }
 
 /* Internal function used to handle completions.
-- 
2.25.4