diff: introduce diff.<driver>.binary

The "diff" gitattribute is somewhat overloaded right now. It
can say one of three things:

  1. this file is definitely binary, or definitely not
     (i.e., diff or !diff)
  2. this file should use an external diff engine (i.e.,
     diff=foo, diff.foo.command = custom-script)
  3. this file should use particular funcname patterns
     (i.e., diff=foo, diff.foo.(x?)funcname = some-regex)

Most of the time, there is no conflict between these uses,
since using one implies that the other is irrelevant (e.g.,
an external diff engine will decide for itself whether the
file is binary).

However, there is at least one conflicting situation: there
is no way to say "use the regular rules to determine whether
this file is binary, but if we do diff it textually, use
this funcname pattern." That is, currently setting diff=foo
indicates that the file is definitely text.

This patch introduces a "binary" config option for a diff
driver, so that one can explicitly set diff.foo.binary. We
default this value to "don't know". That is, setting a diff
attribute to "foo" and using "diff.foo.funcname" will have
no effect on the binaryness of a file. To get the current
behavior, one can set diff.foo.binary to true.

This patch also has one additional advantage: it cleans up
the interface to the userdiff code a bit. Before, calling
code had to know more about whether attributes were false,
true, or unset to determine binaryness. Now that binaryness
is a property of a driver, we can represent these situations
just by passing back a driver struct.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/diffcore.h b/diffcore.h
index 8ae35785fd..713cca785c 100644
--- a/diffcore.h
+++ b/diffcore.h
@@ -22,6 +22,8 @@
 
 #define MINIMUM_BREAK_SIZE     400 /* do not break a file smaller than this */
 
+struct userdiff_driver;
+
 struct diff_filespec {
 	unsigned char sha1[20];
 	char *path;
@@ -40,8 +42,10 @@ struct diff_filespec {
 #define DIFF_FILE_VALID(spec) (((spec)->mode) != 0)
 	unsigned should_free : 1; /* data should be free()'ed */
 	unsigned should_munmap : 1; /* data should be munmap()'ed */
-	unsigned checked_attr : 1;
-	unsigned is_binary : 1; /* data should be considered "binary" */
+
+	struct userdiff_driver *driver;
+	/* data should be considered "binary"; -1 means "don't know yet" */
+	int is_binary;
 };
 
 extern struct diff_filespec *alloc_filespec(const char *);