commitctx: return a richer object from _prepare_files Instead of returning a lot of different list, we introduce a rich object that hold all the file related information. The unique object help with data consistency and simply functions arguments and return. In the rest of this series we will increase usage of this object to simplify more code.

templater: teach template loader to use open_template() function The template loader can apparently load templates from relative paths, so I needed to add that support to `open_template()`. This takes the number of failing tests with PyOxidizer from 54 to 34. Differential Revision: https://phab.mercurial-scm.org/D8907

templater: restructure open_template() a little to prepare for relative paths I found that it was easier to add support for relative paths after this restructuring. It also made it easier to explain each case with a code comment (which I did). Differential Revision: https://phab.mercurial-scm.org/D8906

templater: add exception-raising version of open_template() I'm about to add another caller of `open_template()` (in the template loader). That caller will want to get exceptions instead of `(None, None)` if the template doesn't exist. This patch therefore changes `open_template()` to raise exceptions and adds a new `try_open_template()` that returns the `(None, None)` value. Differential Revision: https://phab.mercurial-scm.org/D8905

templater: replace Py3-only exception types by super-types available in Py2 As noted by @indygreg, `test-check-pyflakes.t` started failing on Py2 after my recent D8894, because that introduced catching of the Py3-only types `ModuleNotFoundError` and `FileNotFoundError`. Let's switch to less precise types that are also available in Py2. Differential Revision: https://phab.mercurial-scm.org/D8902

hgweb: enable reading styles from resources in frozen binaries All we need to do to read styles from resources is to pass the file-like object we get from `open_template()` on to `frommapfile()`. This takes the number of failing tests with PyOxidizer from 62 to 54. Differential Revision: https://phab.mercurial-scm.org/D8901

hgweb: rely on open_template()'s fallback to using templatedir() Differential Revision: https://phab.mercurial-scm.org/D8900

hgweb: open mapfile using templater.open_template() This will help us read templates from resources in frozen binaries. Differential Revision: https://phab.mercurial-scm.org/D8899

hgweb: simplify a constant-length list by converting to literal tuple The call to `.append()` has been unnecessary since d3dbdca92458 (hgweb: don't choke when an inexistent style is requested (issue1901), 2009-11-12). Differential Revision: https://phab.mercurial-scm.org/D8898

hgweb: remove some accesses to private member uimod._unset Differential Revision: https://phab.mercurial-scm.org/D8897