Factor out final completion match string building

We have several places doing essentially the same thing; factor them
out to a central place.  Some of the places overallocate for no good
reason, or use strcat unnecessarily.  The centralized version is more
precise and to the point.

(I considered making the gdb::unique_xmalloc_ptr overload version of
make_completer_match_str try to realloc (not xrealloc) probably
avoiding an allocation in most cases, but that'd be probably overdoing
it, and also, now that I'm writing this I thought I'd try to see how
could we ever get to filename_completer with "text != word", but I
couldn't figure it out.  Running the testsuite with 'gdb_assert (text
== word);' never tripped on the assertion either.  So post gdb 8.1,
I'll probably propose a patch to simplify filename_completer a bit,
and the gdb::unique_xmalloc_str overload can be removed then.)

gdb/ChangeLog:
2017-12-13  Pedro Alves  <palves@redhat.com>

	* cli/cli-decode.c (complete_on_cmdlist, complete_on_enum): Use
	make_completion_match_str.
	* completer.c: Use gdb::unique_xmalloc_ptr and
	make_completion_match_str.
	(make_completion_match_str_1): New.
	(make_completion_match_str(const char *, const char *,
	const char *)): New.
	(make_completion_match_str(gdb::unique_xmalloc_ptr<char> &&,
	const char *, const char *)): New.
	* completer.h (make_completion_match_str(const char *,
	const char *, const char *)): New.
	(make_completion_match_str(gdb::unique_xmalloc_ptr<char> &&,
	const char *, const char *)): New.
	* interps.c (interpreter_completer): Use make_completion_match_str.
	* symtab.c (completion_list_add_name, add_filename_to_list): Use
	make_completion_match_str.

1 files changed, 15 insertions, 0 deletions

diff --git a/gdb/completer.h b/gdb/completer.h
index 9ce70bf..73c0f4c 100644
--- a/gdb/completer.h
+++ b/gdb/completer.h
@@ -482,6 +482,21 @@ private:
   bool m_lowest_common_denominator_unique = false;
 };
 
+/* Return a string to hand off to readline as a completion match
+   candidate, potentially composed of parts of MATCH_NAME and of
+   TEXT/WORD.  For a description of TEXT/WORD see completer_ftype.  */
+
+extern gdb::unique_xmalloc_ptr<char>
+  make_completion_match_str (const char *match_name,
+			     const char *text, const char *word);
+
+/* Like above, but takes ownership of MATCH_NAME (i.e., can
+   reuse/return it).  */
+
+extern gdb::unique_xmalloc_ptr<char>
+  make_completion_match_str (gdb::unique_xmalloc_ptr<char> &&match_name,
+			     const char *text, const char *word);
+
 extern void gdb_display_match_list (char **matches, int len, int max,
 				    const struct match_list_displayer *);