xdiff-interface.c: strip newline (and cr) from line before pattern matching

POSIX doth sayeth:

   "In the regular expression processing described in IEEE Std 1003.1-2001,
    the <newline> is regarded as an ordinary character and both a period and
    a non-matching list can match one. ... Those utilities (like grep) that
    do not allow <newline>s to match are responsible for eliminating any
    <newline> from strings before matching against the RE."

Thus far git has not been removing the trailing newline from strings matched
against regular expression patterns. This has the effect that (quoting
Jonathan del Strother) "... a line containing just 'FUNCNAME' (terminated by
a newline) will be matched by the pattern '^(FUNCNAME.$)' but not
'^(FUNCNAME$)'", and more simply not '^FUNCNAME$'.

Signed-off-by: Brandon Casey <[email protected]>
Signed-off-by: Shawn O. Pearce <[email protected]>

Author: drafnel

t/t4018-diff-funcname.sh

@@ -69,7 +69,7 @@ test_expect_success 'last regexp must not be negated' '
 	grep "fatal: Last expression must not be negated:"
 '
 
-test_expect_failure 'pattern which matches to end of line' '
+test_expect_success 'pattern which matches to end of line' '
 	git config diff.java.funcname "Beer$" &&
 	git diff --no-index Beer.java Beer-correct.java |
 	grep "^@@.*@@ Beer"

xdiff-interface.c

@@ -179,11 +179,21 @@ struct ff_regs {
 static long ff_regexp(const char *line, long len,
 		char *buffer, long buffer_size, void *priv)
 {
-	char *line_buffer = xstrndup(line, len); /* make NUL terminated */
+	char *line_buffer;
 	struct ff_regs *regs = priv;
 	regmatch_t pmatch[2];
 	int result = 0, i;
 
+	/* Exclude terminating newline (and cr) from matching */
+	if (len > 0 && line[len-1] == '\n') {
+		if (len > 1 && line[len-2] == '\r')
+			len -= 2;
+		else
+			len--;
+	}
+
+	line_buffer = xstrndup(line, len); /* make NUL terminated */
+
 	for (i = 0; i < regs->nr; i++) {
 		struct ff_reg *reg = regs->array + i;
 		if (reg->negate ^ !!regexec(&reg->re,