Possible bug in bzr diff

[Aaron Bentley]

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Goffredo Baroncelli wrote:
> Hi all,
> 
> during the develop of the command "bzr patch", I found what I think a bug in 
> the 'bzr diff' command.
> 
> If a file is changed _AND_ is moved or an entry of its path is renamed, 
> the diff is wrong:
> The output of the diff command should be  
> 	--- a/dir/file
> instead
> 	--- a/new-dir/file
> 
> The patch attached should solve the problem. A test case is added

I agree that the above is wrong, but I'm not certain your fix is right.
   Diff cannot detect renames.  So it emits a file move as a
delete/create pair.

e.g.
$ diff -rNu a b
diff -rNu a/bar b/bar
- --- a/bar       1969-12-31 19:00:00.000000000 -0500
+++ b/bar       2006-03-21 15:34:06.000000000 -0500
@@ -0,0 +1 @@
+Foo
diff -rNu a/foo b/foo
- --- a/foo       2006-03-21 15:33:45.000000000 -0500
+++ b/foo       1969-12-31 19:00:00.000000000 -0500
@@ -1 +0,0 @@
- -Foo

If you apply this patch to a, you get b.

But if you apply a rename patch, patch doesn't honour the rename.

Here is an example patch:
diff -rNu a/bar b/bar
- --- a/bar       2006-03-21 15:37:08.000000000 -0500
+++ b/baz       2006-03-21 15:38:30.000000000 -0500
@@ -1 +1 @@
- -Foo
+Foop

Applying it does not rename the file to baz, it only changes the content.

Since the primary target of bzr diff is the standard patch command, I
think we should emulate the standard diff's rename-insensitive behavour.

That means that every file that is renamed or modified should be
compared to its filename's content in the other tree.

Note that I say its *filename*'s content; it is possible that, in the
other tree, a file with a different file ID has that filename, so it
would appear to be modification of the other file ID's content.

Aaron
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