teach diff machinery about --ignore-space-at-eol

`git diff --ignore-space-at-eol` will ignore whitespace at the
line ends.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff.c

@@ -2038,6 +2038,8 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 		options->xdl_opts |= XDF_IGNORE_WHITESPACE;
 	else if (!strcmp(arg, "-b") || !strcmp(arg, "--ignore-space-change"))
 		options->xdl_opts |= XDF_IGNORE_WHITESPACE_CHANGE;
+	else if (!strcmp(arg, "--ignore-space-at-eol"))
+		options->xdl_opts |= XDF_IGNORE_WHITESPACE_AT_EOL;
 	else if (!strcmp(arg, "--color-words"))
 		options->color_diff = options->color_diff_words = 1;
 	else if (!strcmp(arg, "--no-renames"))

xdiff/xdiff.h

@@ -31,7 +31,8 @@ extern "C" {
 #define XDF_NEED_MINIMAL (1 << 1)
 #define XDF_IGNORE_WHITESPACE (1 << 2)
 #define XDF_IGNORE_WHITESPACE_CHANGE (1 << 3)
-#define XDF_WHITESPACE_FLAGS (XDF_IGNORE_WHITESPACE | XDF_IGNORE_WHITESPACE_CHANGE)
+#define XDF_IGNORE_WHITESPACE_AT_EOL (1 << 4)
+#define XDF_WHITESPACE_FLAGS (XDF_IGNORE_WHITESPACE | XDF_IGNORE_WHITESPACE_CHANGE | XDF_IGNORE_WHITESPACE_AT_EOL)
 
 #define XDL_PATCH_NORMAL '-'
 #define XDL_PATCH_REVERSE '+'

xdiff/xutils.c

@@ -215,6 +215,21 @@ int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags)
 				return 0;
 		}
 		return (i1 >= s1 && i2 >= s2);
+	} else if (flags & XDF_IGNORE_WHITESPACE_AT_EOL) {
+		for (i1 = i2 = 0; i1 < s1 && i2 < s2; ) {
+			if (l1[i1] != l2[i2]) {
+				while (i1 < s1 && isspace(l1[i1]))
+					i1++;
+				while (i2 < s2 && isspace(l2[i2]))
+					i2++;
+				if (i1 < s1 || i2 < s2)
+					return 0;
+				return 1;
+			}
+			i1++;
+			i2++;
+		}
+		return i1 >= s1 && i2 >= s2;
 	} else
 		return s1 == s2 && !memcmp(l1, l2, s1);
 
@@ -227,6 +242,7 @@ unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
 
 	for (; ptr < top && *ptr != '\n'; ptr++) {
 		if (isspace(*ptr) && (flags & XDF_WHITESPACE_FLAGS)) {
+			const char *ptr2 = ptr;
 			while (ptr + 1 < top && isspace(ptr[1])
 					&& ptr[1] != '\n')
 				ptr++;
@@ -235,6 +251,14 @@ unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
 				ha += (ha << 5);
 				ha ^= (unsigned long) ' ';
 			}
+			if (flags & XDF_IGNORE_WHITESPACE_AT_EOL
+					&& ptr[1] != '\n') {
+				while (ptr2 != ptr + 1) {
+					ha += (ha << 5);
+					ha ^= (unsigned long) *ptr2;
+					ptr2++;
+				}
+			}
 			continue;
 		}
 		ha += (ha << 5);