Add a CAUTION message to --debug=FILTER for trailing whitespace.

NEWS.md

@@ -138,6 +138,9 @@
 
  - More ASM optimizations from Shark64.
 
+ - Using `--debug=FILTER` now outputs a caution message if a filter rule
+   has trailing whitespace.
+
  - Transformed rrsync into a python script with improvements:
    - Security has been beefed up.
    - The known rsync options were updated to include recent additions.

exclude.c

@@ -152,13 +152,17 @@ static void add_rule(filter_rule_list *listp, const char *pat, unsigned int pat_
 {
 	const char *cp;
 	unsigned int pre_len, suf_len, slash_cnt = 0;
+	char *mention_rule_suffix;
 
-	if (DEBUG_GTE(FILTER, 2)) {
-		rprintf(FINFO, "[%s] add_rule(%s%.*s%s)%s\n",
+	if (DEBUG_GTE(FILTER, 1) && pat_len && (pat[pat_len-1] == ' ' || pat[pat_len-1] == '\t'))
+		mention_rule_suffix = " -- CAUTION: trailing whitespace!";
+	else
+		mention_rule_suffix = DEBUG_GTE(FILTER, 2) ? "" : NULL;
+	if (mention_rule_suffix) {
+		rprintf(FINFO, "[%s] add_rule(%s%.*s%s)%s%s\n",
 			who_am_i(), get_rule_prefix(rule, pat, 0, NULL),
-			(int)pat_len, pat,
-			(rule->rflags & FILTRULE_DIRECTORY) ? "/" : "",
-			listp->debug_type);
+			(int)pat_len, pat, (rule->rflags & FILTRULE_DIRECTORY) ? "/" : "",
+			listp->debug_type, mention_rule_suffix);
 	}
 
 	/* These flags also indicate that we're reading a list that

rsync.1.md

@@ -3723,6 +3723,14 @@ first matching pattern is acted on: if it is an exclude pattern, then that file
 is skipped; if it is an include pattern then that filename is not skipped; if
 no matching pattern is found, then the filename is not skipped.
 
+Aside: because the interactions of filter rules can be complex, it is useful to
+use the `--debug=FILTER` option if things aren't working they way you expect.
+The level-1 output (the default if no level number is specified) mentions the
+filter rule that is first matched by each file in the transfer.  It also warns
+if a filter rule has trailing whitespace.  The level-2 output mentions a lot
+more filter events, including the definition of each rule and the handling of
+per-directory filter files.
+
 Rsync builds an ordered list of filter rules as specified on the command-line.
 Filter rules have the following syntax: