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Support if-let-guard in matches! and assert_matches! #152832

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Support if-let-guard in matches! and assert_matches! #152832

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31 changes: 31 additions & 0 deletions library/core/src/macros/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -192,6 +192,30 @@ pub macro assert_matches {
}
}
},
($left:expr, $(|)? $( $pattern:pat_param )|+ $( if let $($let_guards: tt)+ )? $(,)?) => {
match $left {
$( $pattern )|+ $( if let $($let_guards)+ )? => {}
ref left_val => {
$crate::panicking::assert_matches_failed(
left_val,
$crate::stringify!($($pattern)|+ $(if let $($let_guards)+)?),
$crate::option::Option::None
);
}
}
},
($left:expr, $(|)? $( $pattern:pat_param )|+ $( if let $($let_guards: tt)+ )?, $($arg:tt)+) => {
match $left {
$( $pattern )|+ $( if let $($let_guards)+ )? => {}
ref left_val => {
$crate::panicking::assert_matches_failed(
left_val,
$crate::stringify!($($pattern)|+ $(if let $($let_guards)+)?),
$crate::option::Option::Some($crate::format_args!($($arg)+))
);
}
}
},
}

/// Selects code at compile-time based on `cfg` predicates.
Expand Down Expand Up @@ -435,6 +459,13 @@ macro_rules! matches {
_ => false
}
};
($expression:expr, $pattern:pat $(if let $($let_guards:tt)+)? $(,)?) => {
#[allow(non_exhaustive_omitted_patterns)]
match $expression {
$pattern $(if let $($let_guards)+)? => true,
_ => false
}
};
}

/// Unwraps a result or propagates its error.
Expand Down
10 changes: 10 additions & 0 deletions library/coretests/tests/macros.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,16 @@ fn matches_leading_pipe() {
matches!(1, | 1 | 2 | 3);
}

#[test]
fn matches_if_let_guard() {
use std::assert_matches;

assert!(
matches!(Some(Some(2_i32)), Some(inner) if let Some(value) = inner && value.pow(2) == 4)
);
assert_matches!(Some(Some(2_i32)), Some(inner) if let Some(value) = inner && value.pow(2) == 4);
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@theemathas theemathas Feb 19, 2026

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Needs another test for assert_matches!() with a panic message.

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@SpriteOvO SpriteOvO Feb 19, 2026

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Oh, so looks like we can't simply use $(tt)+ to catch if-let guards because it also catches the comma and panic message.

Does this mean we have to start implementing it as a compiler built-in macro? Especially since we already have 4 arms here.

}

#[test]
fn cfg_select_basic() {
cfg_select! {
Expand Down
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