I'm going to reorganize "single"/"default_single" revset functions in a way
that resolve_single_rev_with_hint_about_all_prefix() is inlined.
evaluate_revset_to_single_commit() could be a private method of
WorkspaceCommandHelper, but I want to minimize the code that has to be hosted
there.
Many callers of resolve_revset() and evaluate_revset() will be migrated to
this wrapper. "single" and "default_single" APIs won't be replaced because
they require more contexts to construct error messages.
id_prefix_context() now uses bare revset::parse() to avoid dependency cycle.
Because the CLI error handler now prints error sources in multi-line format,
it doesn't make much sense to render Revset/TemplateParseError differently.
This patch also fixes the source() of the SyntaxError kind. It should be
self.pest_error.source() (= None), not self.pest_error.
It's inconsistent that some warnings have headings and some don't, and it seems
the choice is arbitrary. Let's unify the style. There are two exceptions:
1. continued line following labeled message,
2. "unrecognized response" followed by prompt.
AST substitution is technically closer to parsing, but the parsed expression
can be modified further by caller. So I think it's better to do optimize() in
later pass.
revset_util::parse() is inlined.
I just wanted to remove CommandError from parse_immutable_expression(), which
will be called from the templater, but the new error message looks also better.
Some of them will be called directly from the commit templater which shouldn't
know WorkspaceCommandHelper. All parameters are passed as function arguments
instead of having a nicer wrapper struct. That's because some resources (e.g.
repo and id prefix context) are also used for different purposes, and it seemed
uneasy to introduce high-level abstraction satisfying all the use cases.
