Since fileset/revset/template expressions are specified as command-line
arguments, it's sometimes convenient to use single quotes instead of double
quotes. Various scripting languages parse single-quoted strings in various ways,
but I choose the TOML rule because it's simple and practically useful. TOML is
our config language, so copying the TOML syntax would be less surprising than
borrowing it from another language.
https://github.com/toml-lang/toml/issues/188
While I like strict parsing, it's not uncommon that we have to deal with file
names containing spaces, and doubly-quoted strings such as '"Foo Bar"' look
ugly. So, this patch adds an exception that accepts top-level bare strings.
This parsing rule is specific to command arguments, and won't be enabled when
loading fileset aliases.
Since fileset is primarily used in CLI, it's better to avoid inner quoting if
possible. For example, ".." would have to be quoted in the original grammar
derived from the revset.
This patch also adds a stricter version of an identifier rule. If we add a
symbol alias, it will follow the "strict_identifier" rule.
The fileset grammar is basically a stripped-down version of the revset grammar,
with a few adjustments:
* extract function call to "function" rule (like templater)
* inline "symbol" rule (because "identifier" and "string" should be treated
differently at the early parsing stage.)
The parser will have a separate name resolution stage. This will help to do
alias substitution properly. I'll probably rewrite the revset parser in the
same way. It will also help if we want to embed fileset expression in file()
revset.
