lightningd: configvar style fixes

1) We can't simply cast away const to manipulate a string, the compiler can assume
   we don't.  The type must be made non-const.
2) cisspace() is nicer to use than isspace() (no cast required!)
3) Simply place a NUL terminator instead of using memmove to set it.
4) Use cast_const to add const to char **, where necessary.
5) Add Changelog line, for CHANGELOG.md

Changelog-Fixed: Config: whitespace at the end of (most) options is now ignored, not complained about.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/configvar.c

@@ -31,7 +31,7 @@ const struct opt_table *configvar_unparsed(struct configvar *cv)
 		ot = opt_find_short(cv->configline[0]);
 		cv->optarg = NULL;
 	} else {
-		ot = opt_find_long(cv->configline, &cv->optarg);
+		ot = opt_find_long(cv->configline, cast_const2(const char **, &cv->optarg));
 	}
 	if (!ot)
 		return NULL;
@@ -51,18 +51,13 @@ const struct opt_table *configvar_unparsed(struct configvar *cv)
 	return ot;
 }
 
-static void trim_whitespace(const char *s)
+static void trim_whitespace(char *s)
 {
 	size_t len = strlen(s);
 
-	/* Cast away const to allow modifications */
-	char *mutable_s = (char *)s;
-
-	while (len > 0 && isspace((unsigned char)mutable_s[len - 1]))
+	while (len > 0 && cisspace(s[len - 1]))
 		len--;
-
-	/* Move null terminator to the end of the trimmed string */
-	memmove(mutable_s + len, mutable_s + strlen(s), 1);
+	s[len] = '\0';
 }
 
 const char *configvar_parse(struct configvar *cv,

common/configvar.h

@@ -35,13 +35,13 @@ struct configvar {
 	/* Where did we get this from? */
 	enum configvar_src src;
 	/* Never NULL, the whole line */
-	const char *configline;
+	char *configline;
 
 	/* These are filled in by configvar_parse */
 	/* The variable name (without any =) */
 	const char *optvar;
 	/* NULL for no-arg options, otherwise points after =. */
-	const char *optarg;
+	char *optarg;
 	/* Was this overridden by a following option? */
 	bool overridden;
 };

lightningd/options.c

@@ -1887,9 +1887,9 @@ void handle_early_opts(struct lightningd *ld, int argc, char *argv[])
 }
 
 /* Free *str, set *str to copy with `cln` prepended */
-static void prefix_cln(const char **str STEALS)
+static void prefix_cln(char **str STEALS)
 {
-	const char *newstr = tal_fmt(tal_parent(*str), "cln%s", *str);
+	char *newstr = tal_fmt(tal_parent(*str), "cln%s", *str);
 	tal_free(*str);
 	*str = newstr;
 }
@@ -1910,7 +1910,7 @@ static void fixup_clnrest_options(struct lightningd *ld)
 		    && !strstarts(cv->configline, "rest-certs="))
 			continue;
 		/* Did some (plugin) claim it? */
-		if (opt_find_long(cv->configline, &cv->optarg))
+		if (opt_find_long(cv->configline, cast_const2(const char **, &cv->optarg)))
 			continue;
 		if (!opt_deprecated_ok(ld,
 				       tal_strndup(tmpctx, cv->configline,