tracking issue for rustc parser changes

[calebcartwright]

Looks like there's going to be some changes in the rustc parser that will involve the removal of parts of the parser interface that rustfmt uses today (default_submod_path and I'd guess submod_path_from_attr too).

rust-lang/rust#68135 (comment)

Note that methods like default_submod_path are going to be removed from the parser when we fix #64197, so making those public will likely be short-lived. (cc petrochenkov)

Not sure what the changes will entail, but opening this to help keep track of the pending upstream changes in the parser.

Places in rustfmt that'll probably be impacted by those upstream changes:

rustfmt/rustfmt-core/rustfmt-lib/src/syntux/session.rs

Lines 140 to 152 in cc56957

	pub(crate) fn default_submod_path(
	&self,
	id: ast::Ident,
	relative: Option<ast::Ident>,
	dir_path: &Path,
	) -> syntax::parse::parser::ModulePath {
	syntax::parse::parser::Parser::default_submod_path(
	id,
	relative,
	dir_path,
	self.parse_sess.source_map(),
	)
	}

rustfmt/rustfmt-core/rustfmt-lib/src/modules.rs

Lines 258 to 261 in cc56957

	match self
	.parse_sess
	.default_submod_path(mod_name, relative, &self.directory.path)
	.result

rustfmt/rustfmt-core/rustfmt-lib/src/syntux/parser.rs

Lines 133 to 135 in cc56957

	pub(crate) fn submod_path_from_attr(attrs: &[ast::Attribute], path: &Path) -> Option<PathBuf> {
	syntax::parse::parser::Parser::submod_path_from_attr(attrs, path)
	}

rustfmt/rustfmt-core/rustfmt-lib/src/modules.rs

Lines 244 to 249 in cc56957

	if let Some(path) = Parser::submod_path_from_attr(attrs, &self.directory.path) {
	return Ok(SubModKind::External(
	path,
	DirectoryOwnership::Owned { relative: None },
	));
	}