assert_type_match/
flags.rs

1use syn::parse::{Parse, ParseStream};
2use syn::spanned::Spanned;
3use syn::token::Token;
4use syn::{LitBool, Token};
5
6/// An optional boolean flag, returned by [`ParseFlag::parse_flag`].
7pub(crate) type Flag = Option<LitBool>;
8
9/// Extension trait for smartly parsing a boolean flag from a [`ParseStream`].
10pub(crate) trait ParseFlag {
11    /// Parse the next token(s) in the stream as a [`LitBool`].
12    ///
13    /// Accepts either:
14    /// - An instance of `T`
15    /// - An instance of `T` followed by an equals sign and a boolean literal
16    ///
17    /// For example, both `foo` and `foo = true` will evaluate to `true`.
18    /// Whereas, `foo = false` will evaluate to `false`.
19    fn parse_flag<T: Parse + Spanned>(&self) -> syn::Result<Flag>;
20}
21
22impl<'a> ParseFlag for ParseStream<'a> {
23    fn parse_flag<T: Parse + Spanned>(&self) -> syn::Result<Flag> {
24        let keyword = self.parse::<T>()?;
25        if self.peek(Token![=]) {
26            self.parse::<Token![=]>()?;
27            Ok(Some(self.parse::<LitBool>()?))
28        } else {
29            Ok(Some(LitBool::new(true, keyword.span())))
30        }
31    }
32}
33
34/// Converts an optional boolean flag into a `bool`.
35pub(crate) fn flag_to_bool(flag: &Flag) -> bool {
36    flag.as_ref().map(LitBool::value).unwrap_or_default()
37}
38
39/// Attempts to merge two optional boolean flags.
40pub(crate) fn merge_flags<T: Token>(base: Flag, other: Flag) -> syn::Result<Flag> {
41    match (base, other) {
42        (Some(a), Some(b)) if a.value == b.value => Ok(Some(a)),
43        (Some(a), None) => Ok(Some(a)),
44        (None, Some(b)) => Ok(Some(b)),
45        (None, None) => Ok(None),
46        (Some(_), Some(b)) => Err(syn::Error::new_spanned(
47            b,
48            format_args!("conflicting `{}` arguments", T::display()),
49        )),
50    }
51}
assert_type_match/flags.rs

assert_type_match/
flags.rs
