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

templater: try to read %include in mapfiles from resources The "show" style is an example of a style that uses an "%include" statement in its definition. This patch makes `hg log --style show` work. This takes the number of failing tests with PyOxidizer from 72 to 62. Differential Revision: https://phab.mercurial-scm.org/D8896