templater: deduplicate iterator of overlay mappings

templater: complain about invalid application of '%' operator (BC) Before, '{x % y % z ...}' was silently evaluated as '{x % y}'. We no longer need this hack since the web template bugs was fixed by earlier patches. At this point, the error message may contain '<generator *>', which will be fixed later.

hgweb: fix type of {nav} keyword when linerange filter is active Spotted by making '%' operator check the operand type more strictly. Before, "{nav}" would be evaluated to a lazy "" (empty string) and {"" % x} would yield one empty string.

hgweb: fix {diff} expansion in JSON template The same sort of bug as the previous patch. In this case, I decided to fix the JSON template since we aren't ready to fix the {diff} keyword without BC. I'll rework it later.

hgweb: fix summary {tags} and {shortlog} to not forcibly expand template The same sort of bug as the previous patch. In this case, JSON template was wrong.

hgweb: fix search {entries} to not return results of template expansion "{entries%changelogentry}" in raw/search.tmpl was utterly wrong because "{entries}" here was a generator yielding results of template expansion. That's why we have a weird hack in runmap(), which I'm going to get rid of. https://www.mercurial-scm.org/repo/hg/file/4.5.2/mercurial/templater.py#l469 We have two choices: a) drop "%changelogentry" from raw/search.tmpl b) fix "{entries}" to yield mappings I take (b) because that's what the other log-like "{entries}" do. The "entries" keyword is wrapped by mappinggenerator so "{entries}" without "%searchentry" still works.

templater: add class representing a nested mappings The mappinggenerator class is necessary to fix hgweb bugs without BC. The mappinglist is for nested formatter items. They are similar, so factored out the base class. The mappinglist could be implemented by using the mappinggenerator, but we'll probably need a direct access to the raw list, so they are implemented as separate classes. Note that tovalue() isn't conforming to the spec yet in that it may return a list of dicts containing unprintable resources. This problem will be fixed later. Tests will be added by subsequent patches.

templater: add function that expands internal literal templates This will be used when rendering nested formatter items with the default template, e.g. fm.nested('parents', tmpl='{rev}:{node|formatnode}', sep=' ') ^^^^^^^^^^^^^^^^^^^^^^^ the default item template

bookmarks: use isrevsymbol() for detecting collision with existing symbol Differential Revision: https://phab.mercurial-scm.org/D3167

debugwhyunstable: add support for revsets Differential Revision: https://phab.mercurial-scm.org/D3166