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.
A formatted error is not a string containing ANSI escape sequences because 1.
the output may be differently colored inside "hint", 2. the caller might not
be accessible to ui.new_formatter().
Highlighting "{n}: " will help to follow error sources containing multi-line
messages. I'm going to make revset/template alias errors be formatted as plain
error chain.
The lowercase "warning: " is unified to "Warning: " as it is the jj's
convention afaik.
The _default() suffix could be dropped from these methods, but it's probably
better to break the existing codebase for the moment. Otherwise, the caller
might do writeln!(ui.warning(), "Warning: ..").
The existing .hint() method is renamed to .hint_no_heading() to clarify that
it's not the default choice to print a hint. I'll add .hint_default() later,
which will be the shorthand for .hint_with_heading("Hint: ").
This helps to implement CommandError::add_hint(). The inner errors could be
embedded in the enum as before, but they're mostly of the same type. And I think
it's okay to use downcast_ref() to deal with the clap::Error special case.
I'm going to reorganize CommandError as (kind, err, hints) tuple so that we
can add_hint() to the constructed error object.
Some config error messages are slightly adjusted because the inner error is
now printed in separate line.
This should address both use cases:
1. If from_relative_path() is directly called, the error says ".." shouldn't
be included in the (normalized) relative path.
2. If parse_fs_path() is used, the error message contains paths relative to
cwd. #3216
