diff: correct binary testing logic This seems to be more correct given the table drawn in the previous patch. Namely, "losedatafn" and "opts.git" are removed, "not opts.text" is added. - losedatafn: diff output (binary) should not be affected by "losedatafn" - opts.git: binary testing is helpful for detecting a fast path in the next path. the fast path can also be used if opts.git is False - opts.text: if it's set, we should treat the content as non-binary

diff: draw a table about binary diff behaviors The table should make it easier to reason about future changes.

diff: use fctx.size() to test empty fctx.size() could have a fast path that does not require loading content.

diff: use fctx.isbinary() to test binary The end goal is to avoid calling fctx.data() when unnecessary. For example, if diff.nobinary=1 and files are binary, the expected behavior is to print "Binary file has changed". That could avoid reading fctx.data() sometimes. This is mainly to enable an external LFS extension to skip expensive binary file loading sometimes (read: most of the time with diff.nobinary=1 and diff.text=0), without any behavior changes to mercurial (i.e. whether a file is LFS or not does not change any behavior, LFS could be 100% transparent to users).

pycompat: extract helper to raise exception with traceback It uses "raise excobj, None, tb" form which I think is simpler and more useful than "raise exctype, args, tb".

largefiles: make sure debugstate command is populated before wrapping Copied the hack from 869d660b8669, which seemed the simplest workaround. Perhaps debugcommands.py should have its own commands table.

check-code: ignore re-exports of os.environ in encoding.py These are valid uses of os.environ.

check-code: exclude demandimport.py and policy.py from Python 3 checks These modules can't depend on pycompat.py, which means we have to write Py3 hacks in them.

check-code: rewrite py3 exclusion pattern with negative lookahead I want to add more patterns, but negative lookbehind requires patterns of the same length so not useful.

cleanup: remove useless re-raises of KeyboardInterrupt KeyboardInterrupt is no longer a subclass of Exception since Python 2.5. https://docs.python.org/2/whatsnew/2.5.html#pep-352-exceptions-as-new-style-classes