1//! Helper module for exporting the `pattern_type` macro
2
3/// Creates a pattern type.
4/// ```ignore (cannot test this from within core yet)
5/// type Positive = std::pat::pattern_type!(i32 is 1..);
6/// ```
7#[macro_export]
8#[rustc_builtin_macro(pattern_type)]
9#[unstable(feature = "pattern_type_macro", issue = "123646")]
10macro_rules! pattern_type {
11 ($($arg:tt)*) => {
12 /* compiler built-in */
13 };
14}
15
16/// A trait implemented for integer types and `char`.
17/// Useful in the future for generic pattern types, but
18/// used right now to simplify ast lowering of pattern type ranges.
19#[unstable(feature = "pattern_type_range_trait", issue = "123646")]
20#[rustc_const_unstable(feature = "pattern_type_range_trait", issue = "123646")]
21#[const_trait]
22#[diagnostic::on_unimplemented(
23 message = "`{Self}` is not a valid base type for range patterns",
24 label = "only integer types and `char` are supported"
25)]
26pub trait RangePattern {
27 /// Trait version of the inherent `MIN` assoc const.
28 #[lang = "RangeMin"]
29 const MIN: Self;
30
31 /// Trait version of the inherent `MIN` assoc const.
32 #[lang = "RangeMax"]
33 const MAX: Self;
34
35 /// A compile-time helper to subtract 1 for exclusive ranges.
36 #[lang = "RangeSub"]
37 #[track_caller]
38 fn sub_one(self) -> Self;
39}
40
41macro_rules! impl_range_pat {
42 ($($ty:ty,)*) => {
43 $(
44 #[rustc_const_unstable(feature = "pattern_type_range_trait", issue = "123646")]
45 impl const RangePattern for $ty {
46 const MIN: $ty = <$ty>::MIN;
47 const MAX: $ty = <$ty>::MAX;
48 fn sub_one(self) -> Self {
49 match self.checked_sub(1) {
50 Some(val) => val,
51 None => panic!("exclusive range end at minimum value of type")
52 }
53 }
54 }
55 )*
56 }
57}
58
59impl_range_pat! {
60 i8, i16, i32, i64, i128, isize,
61 u8, u16, u32, u64, u128, usize,
62}
63
64#[rustc_const_unstable(feature = "pattern_type_range_trait", issue = "123646")]
65impl const RangePattern for char {
66 const MIN: Self = char::MIN;
67
68 const MAX: Self = char::MAX;
69
70 fn sub_one(self) -> Self {
71 match char::from_u32(self as u32 - 1) {
72 None => panic!("exclusive range to start of valid chars"),
73 Some(val: char) => val,
74 }
75 }
76}
77