-Wwrite-strings: Constify word break character arrays

-Wwrite-strings flags several cases of missing casts around
initializations like:

   static char *gdb_completer_command_word_break_characters =
    " \t\n!@#$%^&*()+=|~`}{[]\"';:?/>.<,";

Obviously these could/should be const.  However, while at it, there's
no need for these variables to be pointers instead of arrays.  They
are never changed to point to anything else.

Unfortunately, readline's rl_completer_word_break_characters is
"char *", not "const char *".  So we always need a cast somewhere.  The
approach taken here is to add a new
set_rl_completer_word_break_characters function that becomes the only
place that writes to rl_completer_word_break_characters, and thus the
single place that needs the cast.

gdb/ChangeLog:
2017-04-05  Pedro Alves  <palves@redhat.com>

	* ada-lang.c (ada_completer_word_break_characters): Now a const
	array.
	(ada_get_gdb_completer_word_break_characters): Constify.
	* completer.c (gdb_completer_command_word_break_characters)
	(gdb_completer_file_name_break_characters)
	(gdb_completer_quote_characters): Now const arrays.
	(get_gdb_completer_quote_characters): Constify.
	(set_rl_completer_word_break_characters): New function.
	(set_gdb_completion_word_break_characters)
	(complete_line_internal): Use it.
	* completer.h (get_gdb_completer_quote_characters): Constify.
	(set_rl_completer_word_break_characters): Declare.
	* f-lang.c (f_word_break_characters): Constify.
	* language.c (default_word_break_characters): Constify.
	* language.h (language_defn::la_word_break_characters): Constify.
	(default_word_break_characters): Constify.
	* top.c (init_main): Use set_rl_completer_word_break_characters.

8 files changed, 69 insertions, 34 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index f021968..bc9fa4f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,25 @@
 2017-04-05  Pedro Alves  <palves@redhat.com>
 
+	* ada-lang.c (ada_completer_word_break_characters): Now a const
+	array.
+	(ada_get_gdb_completer_word_break_characters): Constify.
+	* completer.c (gdb_completer_command_word_break_characters)
+	(gdb_completer_file_name_break_characters)
+	(gdb_completer_quote_characters): Now const arrays.
+	(get_gdb_completer_quote_characters): Constify.
+	(set_rl_completer_word_break_characters): New function.
+	(set_gdb_completion_word_break_characters)
+	(complete_line_internal): Use it.
+	* completer.h (get_gdb_completer_quote_characters): Constify.
+	(set_rl_completer_word_break_characters): Declare.
+	* f-lang.c (f_word_break_characters): Constify.
+	* language.c (default_word_break_characters): Constify.
+	* language.h (language_defn::la_word_break_characters): Constify.
+	(default_word_break_characters): Constify.
+	* top.c (init_main): Use set_rl_completer_word_break_characters.
+
+2017-04-05  Pedro Alves  <palves@redhat.com>
+
 	* aix-thread.c (aix_thread_pid_to_str)
 	(aix_thread_extra_thread_info): Constify.
 	* bsd-kvm.c (bsd_kvm_pid_to_str): Constify.
diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 9b91e0c..7be135e 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -315,9 +315,7 @@ static void ada_free_symbol_cache (struct ada_symbol_cache *sym_cache);
 /* Maximum-sized dynamic type.  */
 static unsigned int varsize_limit;
 
-/* FIXME: brobecker/2003-09-17: No longer a const because it is
-   returned by a function that does not return a const char *.  */
-static char *ada_completer_word_break_characters =
+static const char ada_completer_word_break_characters[] =
 #ifdef VMS
   " \t\n!@#%^&*()+=|~`}{[]\";:?/,-";
 #else
@@ -558,7 +556,7 @@ add_angle_brackets (const char *str)
   return result;
 }
 
-static char *
+static const char *
 ada_get_gdb_completer_word_break_characters (void)
 {
   return ada_completer_word_break_characters;
diff --git a/gdb/completer.c b/gdb/completer.c
index 45adc62..9183e2a 100644
--- a/gdb/completer.c
+++ b/gdb/completer.c
@@ -84,29 +84,30 @@ char *line_completion_function (const char *text, int matches,
    readline library sees one in any of the current completion strings,
    it thinks that the string needs to be quoted and automatically
    supplies a leading quote.  */
-static char *gdb_completer_command_word_break_characters =
+static const char gdb_completer_command_word_break_characters[] =
 " \t\n!@#$%^&*()+=|~`}{[]\"';:?/>.<,";
 
 /* When completing on file names, we remove from the list of word
    break characters any characters that are commonly used in file
    names, such as '-', '+', '~', etc.  Otherwise, readline displays
    incorrect completion candidates.  */
-#ifdef HAVE_DOS_BASED_FILE_SYSTEM
 /* MS-DOS and MS-Windows use colon as part of the drive spec, and most
    programs support @foo style response files.  */
-static char *gdb_completer_file_name_break_characters = " \t\n*|\"';?><@";
+static const char gdb_completer_file_name_break_characters[] =
+#ifdef HAVE_DOS_BASED_FILE_SYSTEM
+  " \t\n*|\"';?><@";
 #else
-static char *gdb_completer_file_name_break_characters = " \t\n*|\"';:?><";
+  " \t\n*|\"';:?><";
 #endif
 
 /* Characters that can be used to quote completion strings.  Note that
    we can't include '"' because the gdb C parser treats such quoted
    sequences as strings.  */
-static char *gdb_completer_quote_characters = "'";
+static const char gdb_completer_quote_characters[] = "'";
 
 /* Accessor for some completer data that may interest other files.  */
 
-char *
+const char *
 get_gdb_completer_quote_characters (void)
 {
   return gdb_completer_quote_characters;
@@ -652,16 +653,26 @@ expression_completer (struct cmd_list_element *ignore,
 /* See definition in completer.h.  */
 
 void
+set_rl_completer_word_break_characters (const char *break_chars)
+{
+  rl_completer_word_break_characters = (char *) break_chars;
+}
+
+/* See definition in completer.h.  */
+
+void
 set_gdb_completion_word_break_characters (completer_ftype *fn)
 {
+  const char *break_chars;
+
   /* So far we are only interested in differentiating filename
      completers from everything else.  */
   if (fn == filename_completer)
-    rl_completer_word_break_characters
-      = gdb_completer_file_name_break_characters;
+    break_chars = gdb_completer_file_name_break_characters;
   else
-    rl_completer_word_break_characters
-      = gdb_completer_command_word_break_characters;
+    break_chars = gdb_completer_command_word_break_characters;
+
+  set_rl_completer_word_break_characters (break_chars);
 }
 
 /* Here are some useful test cases for completion.  FIXME: These
@@ -743,8 +754,8 @@ complete_line_internal (const char *text,
      then we will switch to the special word break set for command
      strings, which leaves out the '-' character used in some
      commands.  */
-  rl_completer_word_break_characters =
-    current_language->la_word_break_characters();
+  set_rl_completer_word_break_characters
+    (current_language->la_word_break_characters());
 
   /* Decide whether to complete on a list of gdb commands or on
      symbols.  */
@@ -821,8 +832,8 @@ complete_line_internal (const char *text,
 	    }
 	  /* Ensure that readline does the right thing with respect to
 	     inserting quotes.  */
-	  rl_completer_word_break_characters =
-	    gdb_completer_command_word_break_characters;
+	  set_rl_completer_word_break_characters
+	    (gdb_completer_command_word_break_characters);
 	}
     }
   else
@@ -848,8 +859,8 @@ complete_line_internal (const char *text,
 
 		  /* Ensure that readline does the right thing
 		     with respect to inserting quotes.  */
-		  rl_completer_word_break_characters =
-		    gdb_completer_command_word_break_characters;
+		  set_rl_completer_word_break_characters
+		    (gdb_completer_command_word_break_characters);
 		}
 	      else if (reason == handle_help)
 		list = NULL;
@@ -857,8 +868,8 @@ complete_line_internal (const char *text,
 		{
 		  if (reason != handle_brkchars)
 		    list = complete_on_enum (c->enums, p, word);
-		  rl_completer_word_break_characters =
-		    gdb_completer_command_word_break_characters;
+		  set_rl_completer_word_break_characters
+		    (gdb_completer_command_word_break_characters);
 		}
 	      else
 		{
@@ -879,8 +890,8 @@ complete_line_internal (const char *text,
 			     && strchr (gdb_completer_file_name_break_characters, p[-1]) == NULL;
 			   p--)
 			;
-		      rl_completer_word_break_characters =
-			gdb_completer_file_name_break_characters;
+		      set_rl_completer_word_break_characters
+			(gdb_completer_file_name_break_characters);
 		    }
 		  if (reason == handle_brkchars
 		      && c->completer_handle_brkchars != NULL)
@@ -913,8 +924,8 @@ complete_line_internal (const char *text,
 
 	      /* Ensure that readline does the right thing
 		 with respect to inserting quotes.  */
-	      rl_completer_word_break_characters =
-		gdb_completer_command_word_break_characters;
+	      set_rl_completer_word_break_characters
+		(gdb_completer_command_word_break_characters);
 	    }
 	}
       else if (reason == handle_help)
@@ -947,8 +958,8 @@ complete_line_internal (const char *text,
 				    p[-1]) == NULL;
 		       p--)
 		    ;
-		  rl_completer_word_break_characters =
-		    gdb_completer_file_name_break_characters;
+		  set_rl_completer_word_break_characters
+		    (gdb_completer_file_name_break_characters);
 		}
 	      if (reason == handle_brkchars
 		  && c->completer_handle_brkchars != NULL)
diff --git a/gdb/completer.h b/gdb/completer.h
index 416b313..2aa1987 100644
--- a/gdb/completer.h
+++ b/gdb/completer.h
@@ -99,10 +99,16 @@ extern VEC (char_ptr) *reg_or_group_completer (struct cmd_list_element *,
 extern VEC (char_ptr) *reggroup_completer (struct cmd_list_element *,
 					   const char *, const char *);
 
-extern char *get_gdb_completer_quote_characters (void);
+extern const char *get_gdb_completer_quote_characters (void);
 
 extern char *gdb_completion_word_break_characters (void);
 
+/* Set the word break characters array to BREAK_CHARS.  This function
+   is useful as const-correct alternative to direct assignment to
+   rl_completer_word_break_characters, which is "char *",
+   not "const char *".  */
+extern void set_rl_completer_word_break_characters (const char *break_chars);
+
 /* Set the word break characters array to the corresponding set of
    chars, based on FN.  This function is useful for cases when the
    completer doesn't know the type of the completion until some
diff --git a/gdb/f-lang.c b/gdb/f-lang.c
index 8aba5ef..3c30d75 100644
--- a/gdb/f-lang.c
+++ b/gdb/f-lang.c
@@ -203,7 +203,7 @@ f_language_arch_info (struct gdbarch *gdbarch,
 
 /* Remove the modules separator :: from the default break list.  */
 
-static char *
+static const char *
 f_word_break_characters (void)
 {
   static char *retval;
diff --git a/gdb/language.c b/gdb/language.c
index 119c07e..f1fc220 100644
--- a/gdb/language.c
+++ b/gdb/language.c
@@ -698,7 +698,7 @@ default_pass_by_reference (struct type *type)
    delimiting words.  This is a reasonable default value that
    most languages should be able to use.  */
 
-char *
+const char *
 default_word_break_characters (void)
 {
   return " \t\n!@#$%^&*()+=|~`}{[]\"';:?/>.<,-";
diff --git a/gdb/language.h b/gdb/language.h
index 3d21e4e..96080ac 100644
--- a/gdb/language.h
+++ b/gdb/language.h
@@ -321,7 +321,7 @@ struct language_defn
     char string_lower_bound;
 
     /* The list of characters forming word boundaries.  */
-    char *(*la_word_break_characters) (void);
+    const char *(*la_word_break_characters) (void);
 
     /* Should return a vector of all symbols which are possible
        completions for TEXT.  WORD is the entire command on which the
@@ -583,7 +583,7 @@ extern char *language_class_name_from_physname (const struct language_defn *,
 					        const char *physname);
 
 /* Splitting strings into words.  */
-extern char *default_word_break_characters (void);
+extern const char *default_word_break_characters (void);
 
 /* Print the index of an array element using the C99 syntax.  */
 extern void default_print_array_index (struct value *index_value,
diff --git a/gdb/top.c b/gdb/top.c
index 295b680..4a22be1 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -2022,7 +2022,7 @@ init_main (void)
   /* Setup important stuff for command line editing.  */
   rl_completion_word_break_hook = gdb_completion_word_break_characters;
   rl_completion_entry_function = readline_line_completion_function;
-  rl_completer_word_break_characters = default_word_break_characters ();
+  set_rl_completer_word_break_characters (default_word_break_characters ());
   rl_completer_quote_characters = get_gdb_completer_quote_characters ();
   rl_completion_display_matches_hook = cli_display_match_list;
   rl_readline_name = "gdb";