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, 3 insertions, 47 deletions

diff --git a/gdb/symtab.c b/gdb/symtab.c
index 996d521..bb98619 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -4725,29 +4725,8 @@ completion_list_add_name (completion_tracker &tracker,
      of matches.  Note that the name is moved to freshly malloc'd space.  */
 
   {
-    char *newobj;
-
-    if (word == text)
-      {
-	newobj = (char *) xmalloc (strlen (symname) + 5);
-	strcpy (newobj, symname);
-      }
-    else if (word > text)
-      {
-	/* Return some portion of symname.  */
-	newobj = (char *) xmalloc (strlen (symname) + 5);
-	strcpy (newobj, symname + (word - text));
-      }
-    else
-      {
-	/* Return some of SYM_TEXT plus symname.  */
-	newobj = (char *) xmalloc (strlen (symname) + (text - word) + 5);
-	strncpy (newobj, word, text - word);
-	newobj[text - word] = '\0';
-	strcat (newobj, symname);
-      }
-
-    gdb::unique_xmalloc_ptr<char> completion (newobj);
+    gdb::unique_xmalloc_ptr<char> completion
+      = make_completion_match_str (symname, text, word);
 
     /* Here we pass the match-for-lcd object to add_completion.  Some
        languages match the user text against substrings of symbol
@@ -5322,30 +5301,7 @@ static void
 add_filename_to_list (const char *fname, const char *text, const char *word,
 		      completion_list *list)
 {
-  char *newobj;
-  size_t fnlen = strlen (fname);
-
-  if (word == text)
-    {
-      /* Return exactly fname.  */
-      newobj = (char *) xmalloc (fnlen + 5);
-      strcpy (newobj, fname);
-    }
-  else if (word > text)
-    {
-      /* Return some portion of fname.  */
-      newobj = (char *) xmalloc (fnlen + 5);
-      strcpy (newobj, fname + (word - text));
-    }
-  else
-    {
-      /* Return some of TEXT plus fname.  */
-      newobj = (char *) xmalloc (fnlen + (text - word) + 5);
-      strncpy (newobj, word, text - word);
-      newobj[text - word] = '\0';
-      strcat (newobj, fname);
-    }
-  list->emplace_back (newobj);
+  list->emplace_back (make_completion_match_str (fname, text, word));
 }
 
 static int