Introduce the diff option '--patience'

This commit teaches Git to produce diff output using the patience diff
algorithm with the diff option '--patience'.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/diff-options.txt

@@ -40,6 +40,9 @@ endif::git-format-patch[]
 --patch-with-raw::
 	Synonym for "-p --raw".
 
+--patience:
+	Generate a diff using the "patience diff" algorithm.
+
 --stat[=width[,name-width]]::
 	Generate a diffstat.  You can override the default
 	output width for 80-column terminal by "--stat=width".

Makefile

@@ -1287,7 +1287,7 @@ $(LIB_FILE): $(LIB_OBJS)
 	$(QUIET_AR)$(RM) $@ && $(AR) rcs $@ $(LIB_OBJS)
 
 XDIFF_OBJS=xdiff/xdiffi.o xdiff/xprepare.o xdiff/xutils.o xdiff/xemit.o \
-	xdiff/xmerge.o
+	xdiff/xmerge.o xdiff/xpatience.o
 $(XDIFF_OBJS): xdiff/xinclude.h xdiff/xmacros.h xdiff/xdiff.h xdiff/xtypes.h \
 	xdiff/xutils.h xdiff/xprepare.h xdiff/xdiffi.h xdiff/xemit.h
 

diff.c

@@ -2471,6 +2471,8 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 		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, "--patience"))
+		options->xdl_opts |= XDF_PATIENCE_DIFF;
 
 	/* flags options */
 	else if (!strcmp(arg, "--binary")) {

t/t4033-diff-patience.sh

@@ -0,0 +1,168 @@
+#!/bin/sh
+
+test_description='patience diff algorithm'
+
+. ./test-lib.sh
+
+cat >file1 <<\EOF
+#include <stdio.h>
+
+// Frobs foo heartily
+int frobnitz(int foo)
+{
+    int i;
+    for(i = 0; i < 10; i++)
+    {
+        printf("Your answer is: ");
+        printf("%d\n", foo);
+    }
+}
+
+int fact(int n)
+{
+    if(n > 1)
+    {
+        return fact(n-1) * n;
+    }
+    return 1;
+}
+
+int main(int argc, char **argv)
+{
+    frobnitz(fact(10));
+}
+EOF
+
+cat >file2 <<\EOF
+#include <stdio.h>
+
+int fib(int n)
+{
+    if(n > 2)
+    {
+        return fib(n-1) + fib(n-2);
+    }
+    return 1;
+}
+
+// Frobs foo heartily
+int frobnitz(int foo)
+{
+    int i;
+    for(i = 0; i < 10; i++)
+    {
+        printf("%d\n", foo);
+    }
+}
+
+int main(int argc, char **argv)
+{
+    frobnitz(fib(10));
+}
+EOF
+
+cat >expect <<\EOF
+diff --git a/file1 b/file2
+index 6faa5a3..e3af329 100644
+--- a/file1
++++ b/file2
+@@ -1,26 +1,25 @@
+ #include <stdio.h>
+ 
++int fib(int n)
++{
++    if(n > 2)
++    {
++        return fib(n-1) + fib(n-2);
++    }
++    return 1;
++}
++
+ // Frobs foo heartily
+ int frobnitz(int foo)
+ {
+     int i;
+     for(i = 0; i < 10; i++)
+     {
+-        printf("Your answer is: ");
+         printf("%d\n", foo);
+     }
+ }
+ 
+-int fact(int n)
+-{
+-    if(n > 1)
+-    {
+-        return fact(n-1) * n;
+-    }
+-    return 1;
+-}
+-
+ int main(int argc, char **argv)
+ {
+-    frobnitz(fact(10));
++    frobnitz(fib(10));
+ }
+EOF
+
+test_expect_success 'patience diff' '
+
+	test_must_fail git diff --no-index --patience file1 file2 > output &&
+	test_cmp expect output
+
+'
+
+test_expect_success 'patience diff output is valid' '
+
+	mv file2 expect &&
+	git apply < output &&
+	test_cmp expect file2
+
+'
+
+cat >uniq1 <<\EOF
+1
+2
+3
+4
+5
+6
+EOF
+
+cat >uniq2 <<\EOF
+a
+b
+c
+d
+e
+f
+EOF
+
+cat >expect <<\EOF
+diff --git a/uniq1 b/uniq2
+index b414108..0fdf397 100644
+--- a/uniq1
++++ b/uniq2
+@@ -1,6 +1,6 @@
+-1
+-2
+-3
+-4
+-5
+-6
++a
++b
++c
++d
++e
++f
+EOF
+
+test_expect_success 'completely different files' '
+
+	test_must_fail git diff --no-index --patience uniq1 uniq2 > output &&
+	test_cmp expect output
+
+'
+
+test_done