Creating HTML diffs with vim gets very slow when the files
become larger and there are very large blocks that differ.
To speed this up, the individual differing blocks are
shrunk when they are longer than a configured number of lines.
The information about the blocks is obtained by first calling
'diff', which is extremely fast even on large files.

Closes: #764140

Helmut Grohne authored Jan 09, 2015 and Jérémy Bobbio committed Jan 09, 2015

Let's not call guess_mime_type for every comparator available. Doing it once
should be enough.

Using magic and doing smart comparisons is slower than comparing bytes
directly. Let's assume most files will actually be identical and start
comparing small files directly. If they match, we can skip the smart
bits entirely.

This lead to drastic run time improvements when comparing source tarballs
with many small files (e.g. linux-source).

Closes: #773573

Even when we fallback to binary comparison.

We actually want to use the path given by the caller. We now properly
display the path of a file when it is in an archive.

D'oh!

No changes required.

Closes: #764470

Seems I did not properly read the warning in subprocess documentation:
“Do not use stdout=PIPE or stderr=PIPE with this function as that can deadlock
based on the child process output volume”.

And indeed, we had a deadlock on files with very long lines. So let's switch
to use Popen and communicate().

Closes: #764131, #764420

Some jar files contained no apparant differences in plain `zipinfo`,
but showed some in `zipinfo -v`. The former is more readable, so still try
to get some result with it first.

Thanks to Hans-Christoph Steiner.