grep: restore pre-9ef10437bb88 behavior, enable wdir search by tweakdefaults Unfortunately, python-hglib relies on the original grep behavior and is documented as such. Even though we agreed to introduce the BC, we shouldn't break existing libraries. So this patch flips the default again and move the new default to ui.tweakdefaults. We could instead use HGPLAIN to turn this flag off, but that would be rather confusing as the old/new behaviors are quite different. Differential Revision: https://phab.mercurial-scm.org/D3919

grep: add config knob to enable/disable the default wdir search This allows us to conditionally enable the new behavior to unbreak python-hglib. See the next patch. The config option is undocumented since the --all-files is still experimental and isn't fully implemented. It can be moved to [experimental] if that's preferred. Differential Revision: https://phab.mercurial-scm.org/D3918

grep: search working directory files by default if --all-files is specified The default was -rtip:0 before, but "--all-files -rtip:0" would be the most useless combination, and it isn't supported yet. Let's change the default to something useful. This isn't flagged as BC since --all-files isn't released. Differential Revision: https://phab.mercurial-scm.org/D3917

grep: reject --diff --all-files This combination doesn't make any sense since --diff is the flag to search change history, whereas --all-files is to include unmodified contents. Differential Revision: https://phab.mercurial-scm.org/D3916

grep: rename --allfiles to --all-files This matches the config name to be added. Note that we don't have to keep the old flag since it isn't released yet. Differential Revision: https://phab.mercurial-scm.org/D3915

debugdeltachain: protect against 0 readsize If you don't read any data, read density should be 1.