gdb: extend completion of quoted filenames to work in brkchars phase

Up to this point filename completion for possibly quoted filenames has
always been handled during the second (non-brkchars) phase of
completion.  This works fine for commands that only want to complete
on a single filename argument.

In a later commit though I need to perform completion of a quoted
filename argument during the first (brkchars) phase of completion.
This will allow me to add a custom completer that completes both
command options and arguments for a command (remove-symbol-file) that
takes a possibly quoted filename argument.

This commit doesn't add the remove-symbol-file completer, this commit
is just about putting support for that in place.

To achieve this I've added the new function
advance_to_filename_maybe_quoted_complete_word_point, which is unused
in this commit.  I've then had to extend some other functions in order
to extract the quoting state during the brkchars phase.

As this commit doesn't use the new functionality, the important thing
at this point is that I've not regressed the existing filename
completion (or any of the other completion).  The next commit in this
series will make use of the new functionality, and will include
tests.

There should be no user visible changes after this commit.

2 files changed, 91 insertions, 15 deletions

diff --git a/gdb/completer.c b/gdb/completer.c
index b80649c..e8f5e7b 100644
--- a/gdb/completer.c
+++ b/gdb/completer.c
@@ -730,13 +730,23 @@ gdb_rl_find_completion_word (struct gdb_rl_completion_word_info *info,
 
 /* Find the completion word point for TEXT, emulating the algorithm
    readline uses to find the word point, using WORD_BREAK_CHARACTERS
-   as word break characters.  */
+   as word break characters.
+
+   The output argument *FOUND_ANY_QUOTING is set to true if the completion
+   word found either has an opening quote, or contains backslash escaping
+   within it.  Otherwise *FOUND_ANY_QUOTING is set to false.
+
+   The output argument *QC is set to the opening quote character for the
+   completion word that is found, or to the null character if there is no
+   opening quote.  */
 
 static const char *
 advance_to_completion_word (completion_tracker &tracker,
 			    const char *word_break_characters,
 			    const char *quote_characters,
-			    const char *text)
+			    const char *text,
+			    bool *found_any_quoting,
+			    int *qc)
 {
   gdb_rl_completion_word_info info;
 
@@ -746,7 +756,8 @@ advance_to_completion_word (completion_tracker &tracker,
 
   int delimiter;
   const char *start
-    = gdb_rl_find_completion_word (&info, nullptr, &delimiter, nullptr, text);
+    = gdb_rl_find_completion_word (&info, qc, &delimiter, found_any_quoting,
+				   text);
 
   tracker.advance_custom_word_point_by (start - text);
 
@@ -767,18 +778,54 @@ advance_to_expression_complete_word_point (completion_tracker &tracker,
 {
   const char *brk_chars = current_language->word_break_characters ();
   const char *quote_chars = gdb_completer_expression_quote_characters;
-  return advance_to_completion_word (tracker, brk_chars, quote_chars, text);
+  return advance_to_completion_word (tracker, brk_chars, quote_chars,
+				     text, nullptr, nullptr);
 }
 
 /* See completer.h.  */
 
 const char *
-advance_to_deprecated_filename_complete_word_point
+advance_to_filename_maybe_quoted_complete_word_point
   (completion_tracker &tracker, const char *text)
 {
+  const char *brk_chars = gdb_completer_file_name_break_characters;
+  const char *quote_chars = gdb_completer_file_name_quote_characters;
+  rl_char_is_quoted_p = gdb_completer_file_name_char_is_quoted;
+  bool found_any_quoting = false;
+  int qc;
+  const char *result
+    = advance_to_completion_word (tracker, brk_chars, quote_chars,
+				  text, &found_any_quoting, &qc);
+  rl_completion_found_quote = found_any_quoting ? 1 : 0;
+  if (qc != '\0')
+    {
+      tracker.set_quote_char (qc);
+      /* If we're completing for readline (not the 'complete' command) then
+	 we want readline to correctly detect the opening quote.  The set
+	 of quote characters will have been set during the brkchars phase,
+	 so now we move the word point back by one (so it's pointing at
+	 the quote character) and now readline will correctly spot the
+	 opening quote.  For the 'complete' command setting the quote
+	 character in the tracker is enough, so there's no need to move
+	 the word point back here.  */
+      if (tracker.from_readline ())
+	tracker.advance_custom_word_point_by (-1);
+    }
+  return result;
+}
+
+/* See completer.h.  */
+
+const char *
+advance_to_deprecated_filename_complete_word_point (completion_tracker &tracker,
+						    const char *text)
+{
   const char *brk_chars = gdb_completer_path_break_characters;
   const char *quote_chars = nullptr;
-  return advance_to_completion_word (tracker, brk_chars, quote_chars, text);
+  rl_filename_quoting_desired = 0;
+
+  return advance_to_completion_word (tracker, brk_chars, quote_chars,
+				     text, nullptr, nullptr);
 }
 
 /* See completer.h.  */
@@ -2283,7 +2330,21 @@ gdb_completion_word_break_characters_throw ()
 
       gdb_custom_word_point_brkchars[0] = rl_line_buffer[rl_point];
       rl_completer_word_break_characters = gdb_custom_word_point_brkchars;
-      rl_completer_quote_characters = NULL;
+
+      /* When performing filename completion we have two options, unquoted
+	 filename completion, in which case the quote characters will have
+	 already been set to nullptr, or quoted filename completion in
+	 which case the quote characters will be set to a string of
+	 characters.  In this second case we need readline to perform the
+	 check for a quoted string so that it sets its internal notion of
+	 the quote character correctly, this allows readline to correctly
+	 add the trailing quote (if necessary) after completing a
+	 filename.
+
+	 For non-filename completion we manually add a trailing quote if
+	 needed, so we clear the quote characters set here.  */
+      if (!rl_filename_completion_desired)
+	rl_completer_quote_characters = NULL;
 
       /* Clear this too, so that if we're completing a quoted string,
 	 readline doesn't consider the quote character a delimiter.
@@ -2330,7 +2391,12 @@ gdb_completion_word_break_characters () noexcept
    handle_brkchars phase (using TRACKER) to figure out the right work break
    characters for the command in TEXT.  QUOTE_CHAR, if non-null, is set to
    the opening quote character if we found an unclosed quoted substring,
-   '\0' otherwise.  */
+   '\0' otherwise.
+
+   The argument *FOUND_ANY_QUOTING is set to true if the completion word is
+   either surrounded by quotes, or contains any backslash escapes, but is
+   only set if TRACKER.use_custom_word_point() is false, otherwise
+   *FOUND_ANY_QUOTING is just set to false.  */
 
 static const char *
 completion_find_completion_word (completion_tracker &tracker, const char *text,
@@ -2344,13 +2410,12 @@ completion_find_completion_word (completion_tracker &tracker, const char *text,
     {
       gdb_assert (tracker.custom_word_point () > 0);
       *quote_char = tracker.quote_char ();
-      /* This isn't really correct, we're ignoring the case where we found
-	 a backslash escaping a character.  However, this isn't an issue
-	 right now as we only rely on *FOUND_ANY_QUOTING being set when
-	 performing filename completion, which doesn't go through this
-	 path.  */
+      /* If use_custom_word_point is set then the completions have already
+	 been calculated, in which case we don't need to have this flag
+	 set correctly, which is lucky as we don't currently have any way
+	 to know if the completion word included any backslash escapes.  */
       if (found_any_quoting != nullptr)
-	*found_any_quoting = *quote_char != '\0';
+	*found_any_quoting = false;
       return text + tracker.custom_word_point ();
     }
 
@@ -2527,7 +2592,10 @@ completion_tracker::build_completion_result (const char *text,
     {
       bool completion_suppress_append;
 
-      if (from_readline ())
+      /* For filename completion we rely on readline to append the closing
+	 quote.  While for other types of completion we append the closing
+	 quote here.  */
+      if (from_readline () && !rl_filename_completion_desired)
 	{
 	  /* We don't rely on readline appending the quote char as
 	     delimiter as then readline wouldn't append the ' ' after the
diff --git a/gdb/completer.h b/gdb/completer.h
index c18bd16..44eafc4 100644
--- a/gdb/completer.h
+++ b/gdb/completer.h
@@ -618,6 +618,14 @@ const char *advance_to_expression_complete_word_point
 extern const char *advance_to_deprecated_filename_complete_word_point
   (completion_tracker &tracker, const char *text);
 
+/* Assuming TEXT is a filename, find the completion word point for TEXT,
+   emulating the algorithm readline uses to find the word point.  The
+   filenames that are located by this function assume that filenames
+   can be quoted, this function should be paired with
+   filename_maybe_quoted_completer.  */
+extern const char *advance_to_filename_maybe_quoted_complete_word_point
+  (completion_tracker &tracker, const char *text);
+
 extern void noop_completer (struct cmd_list_element *,
 			    completion_tracker &tracker,
 			    const char *, const char *);