"complete" command and completion word break characters

The linespec/locations/completer testcase added later in the series
tests every completion with both TAB completion and the "complete"
command.  This exposed problems in the "complete" command, around
determining the completion word point.

First, the complete command has a too-simple approximation of what
readline's TAB-completion code does to find the completion word point.
Unfortunately, readline doesn't expose the functionality it uses
internally, so to fix this this patch copies over the relevant code,
and adjusts it a bit to better fit the use cases we need it for.
(Specifically, our version avoids relying on the
rl_word_break_characters, etc. globals, and instead takes those as
arguments.)

A following patch will want to use this function for TAB-completion
too, but the "complete" command was a good excuse to split this to a
separate patch.

Then, notice how the complete_command does not call into the completer
for the command being completed to determine the right set of word
break characters.  It always uses the default set.  That is fixed by
having the "complete" command call into complete_line_internal for a
full handle_brkchars phase, just TAB-completion.

gdb/ChangeLog:
2017-07-17  Pedro Alves  <palves@redhat.com>

	* cli/cli-cmds.c (complete_command): Use a completion tracker
	along with completion_find_completion_word for handle_brkchars
	phase.
	* completer.c (RL_QF_SINGLE_QUOTE, RL_QF_DOUBLE_QUOTE)
	(RL_QF_BACKSLASH, RL_QF_OTHER_QUOTE): New.
	(struct gdb_rl_completion_word_info): New.
	(gdb_rl_find_completion_word): New.
	(completion_find_completion_word): New.
	* completer.h (completion_find_completion_word): Declare.

1 files changed, 173 insertions, 0 deletions

diff --git a/gdb/completer.c b/gdb/completer.c
index 85e6d88..196610d 100644
--- a/gdb/completer.c
+++ b/gdb/completer.c
@@ -212,6 +212,160 @@ filename_completer_handle_brkchars (struct cmd_list_element *ignore,
     (gdb_completer_file_name_break_characters);
 }
 
+/* Possible values for the found_quote flags word used by the completion
+   functions.  It says what kind of (shell-like) quoting we found anywhere
+   in the line. */
+#define RL_QF_SINGLE_QUOTE      0x01
+#define RL_QF_DOUBLE_QUOTE      0x02
+#define RL_QF_BACKSLASH         0x04
+#define RL_QF_OTHER_QUOTE       0x08
+
+/* Find the bounds of the current word for completion purposes, and
+   return a pointer to the end of the word.  This mimics (and is a
+   modified version of) readline's _rl_find_completion_word internal
+   function.
+
+   This function skips quoted substrings (characters between matched
+   pairs of characters in rl_completer_quote_characters).  We try to
+   find an unclosed quoted substring on which to do matching.  If one
+   is not found, we use the word break characters to find the
+   boundaries of the current word.  QC, if non-null, is set to the
+   opening quote character if we found an unclosed quoted substring,
+   '\0' otherwise.  DP, if non-null, is set to the value of the
+   delimiter character that caused a word break.  */
+
+struct gdb_rl_completion_word_info
+{
+  const char *word_break_characters;
+  const char *quote_characters;
+  const char *basic_quote_characters;
+};
+
+static const char *
+gdb_rl_find_completion_word (struct gdb_rl_completion_word_info *info,
+			     int *qc, int *dp,
+			     const char *line_buffer)
+{
+  int scan, end, found_quote, delimiter, pass_next, isbrk;
+  char quote_char;
+  const char *brkchars;
+  int point = strlen (line_buffer);
+
+  /* The algorithm below does '--point'.  Avoid buffer underflow with
+     the empty string.  */
+  if (point == 0)
+    {
+      if (qc != NULL)
+	*qc = '\0';
+      if (dp != NULL)
+	*dp = '\0';
+      return line_buffer;
+    }
+
+  end = point;
+  found_quote = delimiter = 0;
+  quote_char = '\0';
+
+  brkchars = info->word_break_characters;
+
+  if (info->quote_characters != NULL)
+    {
+      /* We have a list of characters which can be used in pairs to
+	 quote substrings for the completer.  Try to find the start of
+	 an unclosed quoted substring.  */
+      /* FOUND_QUOTE is set so we know what kind of quotes we
+	 found.  */
+      for (scan = pass_next = 0;
+	   scan < end;
+	   scan++)
+	{
+	  if (pass_next)
+	    {
+	      pass_next = 0;
+	      continue;
+	    }
+
+	  /* Shell-like semantics for single quotes -- don't allow
+	     backslash to quote anything in single quotes, especially
+	     not the closing quote.  If you don't like this, take out
+	     the check on the value of quote_char.  */
+	  if (quote_char != '\'' && line_buffer[scan] == '\\')
+	    {
+	      pass_next = 1;
+	      found_quote |= RL_QF_BACKSLASH;
+	      continue;
+	    }
+
+	  if (quote_char != '\0')
+	    {
+	      /* Ignore everything until the matching close quote
+		 char.  */
+	      if (line_buffer[scan] == quote_char)
+		{
+		  /* Found matching close.  Abandon this
+		     substring.  */
+		  quote_char = '\0';
+		  point = end;
+		}
+	    }
+	  else if (strchr (info->quote_characters, line_buffer[scan]))
+	    {
+	      /* Found start of a quoted substring.  */
+	      quote_char = line_buffer[scan];
+	      point = scan + 1;
+	      /* Shell-like quoting conventions.  */
+	      if (quote_char == '\'')
+		found_quote |= RL_QF_SINGLE_QUOTE;
+	      else if (quote_char == '"')
+		found_quote |= RL_QF_DOUBLE_QUOTE;
+	      else
+		found_quote |= RL_QF_OTHER_QUOTE;
+	    }
+	}
+    }
+
+  if (point == end && quote_char == '\0')
+    {
+      /* We didn't find an unclosed quoted substring upon which to do
+	 completion, so use the word break characters to find the
+	 substring on which to complete.  */
+      while (--point)
+	{
+	  scan = line_buffer[point];
+
+	  if (strchr (brkchars, scan) != 0)
+	    break;
+	}
+    }
+
+  /* If we are at an unquoted word break, then advance past it.  */
+  scan = line_buffer[point];
+
+  if (scan)
+    {
+      isbrk = strchr (brkchars, scan) != 0;
+
+      if (isbrk)
+	{
+	  /* If the character that caused the word break was a quoting
+	     character, then remember it as the delimiter.  */
+	  if (info->basic_quote_characters
+	      && strchr (info->basic_quote_characters, scan)
+	      && (end - point) > 1)
+	    delimiter = scan;
+
+	  point++;
+	}
+    }
+
+  if (qc != NULL)
+    *qc = quote_char;
+  if (dp != NULL)
+    *dp = delimiter;
+
+  return line_buffer + point;
+}
+
 /* Complete on linespecs, which might be of two possible forms:
 
        file:line
@@ -1306,6 +1460,25 @@ gdb_completion_word_break_characters ()
 
 /* See completer.h.  */
 
+const char *
+completion_find_completion_word (completion_tracker &tracker, const char *text,
+				 int *quote_char)
+{
+  size_t point = strlen (text);
+
+  complete_line_internal (tracker, NULL, text, point, handle_brkchars);
+
+  gdb_rl_completion_word_info info;
+
+  info.word_break_characters = rl_completer_word_break_characters;
+  info.quote_characters = gdb_completer_quote_characters;
+  info.basic_quote_characters = rl_basic_quote_characters;
+
+  return gdb_rl_find_completion_word (&info, quote_char, NULL, text);
+}
+
+/* See completer.h.  */
+
 void
 completion_tracker::recompute_lowest_common_denominator (const char *new_match)
 {