Macro parse_by_kind

macro_rules! parse_by_kind {
    (
        $self:ident,
        $expr_id:expr,
        $expr_name:pat,
        $expected:literal,
        $(
            @call($name:ident, $args:ident) => $call_expr:expr,
        )*
        $(
            @variant($adt:ident, $variant:ident) => $variant_expr:expr,
        )*
        $(
            $pat:pat $(if $guard:expr)? => $expr:expr,
        )*
    ) => { ... };
}

Helper macro for parsing custom MIR.

Example usage looks something like:

parse_by_kind!(
    self, // : &ParseCtxt
    expr_id, // what you're matching against
    "assignment", // the thing you're trying to parse
    @call("mir_assign", args) => { args[0] }, // match invocations of the `mir_assign` special function
    ExprKind::Assign { lhs, .. } => { lhs }, // match thir assignment expressions
    // no need for fallthrough case - reasonable error is automatically generated
)