Re: How to use my own diff tool ?

On Sun, Sep 9, 2018 at 3:49 PM Thomas B <thomas.burg@gmail.com> wrote:
>
> Hello
>
> I am struggling at comparing xml file (vim -d file1.xml file2.xml). Usual GNU diff does not produce useful data. So I am looking to use my custom and structure aware diff tool with vim. Because viewing difference is still a concern and vim allow to do that.
>
> So I follow the manual notes and put following lines in my .vimrc:
>
> set diffexpr=MyDiff()
>
> function MyDiff()
> silent execute '!my_custom_diff '. v:fname_in . ' ' . v:fname_new . ' > ' .v:fname_out
> endfunction
>
> But all my trial finish by "E97: Cannot create diffs" message. While my_custom_diff in standalone produce an output compatible to what GNU diff can produce...
> I end up to search this message in the vim source code and found that vim prior to run the diff on user's files is performing a sanity check of the diff command with pattern: "line1\n" compare to "line2\n" (source code comment refer to "quick test")
> My custom tool is unable to produce the expected result since it must run exclusively on xml file.
>
> I did not found any way to bypass this "quick test". Is there a way ?
> Is my use case valid ? I mean the usage of a diff tool not correctly answering to the "quick test" procedure ?
>
> Thanks for your help and comment.
> Thomas

Maybe you could "cheat" and adjust your custom tool to fall back on
/usr/bin/diff (or wherever GNU diff is found) until or unless you get
a line beginning in <?xml followed by a space?

Also, make sure that your custom tool produces "old-style" diff output
as laid out at ":help diff-diffexpr" and in particular NOT a context
or unified diff.

Best regards,
Tony.

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