This makes the summary line more informative. Even though it just duplicates
the message printed later, I think it's easier to follow.
This patch also adjusts some RevsetParseError messages because it seemed
redundant to repeat "revset function", "argument", etc.
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
