Bug#848049: diffoscope: Add detection of order-only differences in plain text formats

[Daniel Shahaf]

Маша Глухова wrote on Sat, Dec 24, 2016 at 18:14:16 +0000:
> +def order_only_difference(unified_diff):
> +    diff_lines = unified_diff.splitlines()
> +    added_lines = [line[1:] for line in diff_lines if line.startswith('+')]
> +    removed_lines = [line[1:] for line in diff_lines if line.startswith('-')]
> +    # Faster check: does number of lines match?
> +    if len(added_lines) != len(removed_lines):
> +        return False
> +    # Counter stores line and number of its occurrences.
> +    return sorted(added_lines) == sorted(removed_lines)

What happens if one of the files has a trailing newline and one does
not?  Strictly speaking, that's not an "ordering only difference", but
this function doesn't seem to handle this case.

Example:

% diff -u <(echo foo) <(printf foo) 
--- /proc/self/fd/11	2016-12-24 20:24:22.064115616 +0000
+++ /proc/self/fd/12	2016-12-24 20:24:22.064115616 +0000
@@ -1 +1 @@
-foo
+foo
\ No newline at end of file

Cheers,

Daniel