move const_panic/assert macros into core::panic module (since they are just internal helpers)

Author: RalfJung

library/core/src/char/methods.rs

@@ -1,7 +1,7 @@
 //! impl char {}
 
 use super::*;
-use crate::macros::const_panic;
+use crate::panic::const_panic;
 use crate::slice;
 use crate::str::from_utf8_unchecked_mut;
 use crate::unicode::printable::is_printable;

library/core/src/ffi/c_str.rs

@@ -413,7 +413,7 @@ impl CStr {
     #[rustc_allow_const_fn_unstable(const_eval_select)]
     pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
         const_eval_select!(
-            (bytes: &[u8]) -> &CStr:
+            @capture { bytes: &[u8] } -> &CStr:
             if const {
                 // Saturating so that an empty slice panics in the assert with a good
                 // message, not here due to underflow.
@@ -429,7 +429,7 @@ impl CStr {
 
                 // SAFETY: See runtime cast comment below.
                 unsafe { &*(bytes as *const [u8] as *const CStr) }
-            } else #[inline] {
+            } else {
                 // Chance at catching some UB at runtime with debug builds.
                 debug_assert!(!bytes.is_empty() && bytes[bytes.len() - 1] == 0);
 
@@ -735,7 +735,7 @@ impl AsRef<CStr> for CStr {
 #[rustc_allow_const_fn_unstable(const_eval_select)]
 const unsafe fn strlen(ptr: *const c_char) -> usize {
     const_eval_select!(
-        (s: *const c_char = ptr) -> usize:
+        @capture { s: *const c_char = ptr } -> usize:
         if const {
             let mut len = 0;
 
@@ -745,7 +745,7 @@ const unsafe fn strlen(ptr: *const c_char) -> usize {
             }
 
             len
-        } else #[inline] {
+        } else {
             extern "C" {
                 /// Provided by libc or compiler_builtins.
                 fn strlen(s: *const c_char) -> usize;

library/core/src/intrinsics.rs

@@ -2791,31 +2791,36 @@ where
 /// A macro to make it easier to invoke const_eval_select. Use as follows:
 /// ```rust,ignore (just a macro example)
 /// const_eval_select!(
-///     #[inline]
-///     (arg1: i32 = some_expr, arg2: T = other_expr) -> U:
-///     if const {
+///     @capture { arg1: i32 = some_expr, arg2: T = other_expr } -> U:
+///     if const #[attributes_for_const_arm] {
 ///         // Compile-time code goes here.
-///     } else {
+///     } else #[attributes_for_runtime_arm] {
 ///         // Run-time code goes here.
 ///     }
 /// )
 /// ```
+/// The `@capture` block declares which surrounding variables / expressions can be
+/// used inside the `if const`.
+/// Note that the two arms of this `if` really each become their own function, which is why the
+/// macro supports setting attributes for those functions. The runtime function is always
+/// markes as `#[inline]`.
+///
+/// See [`const_eval_select()`] for the rules and requirements around that intrinsic.
 pub(crate) macro const_eval_select {
     (
+        @capture { $($arg:ident : $ty:ty = $val:expr),* $(,)? } $( -> $ret:ty )? :
         $(#[$attr:meta])*
-        ($($arg:ident : $ty:ty = $val:expr),* $(,)?) $( -> $ret:ty )?:
         if const
             $(#[$compiletime_attr:meta])* $compiletime:block
         else
             $(#[$runtime_attr:meta])* $runtime:block
     ) => {{
-        $(#[$attr])*
         $(#[$runtime_attr])*
+        #[inline]
         fn runtime($($arg: $ty),*) $( -> $ret )? {
             $runtime
         }
 
-        $(#[$attr])*
         $(#[$compiletime_attr])*
         const fn compiletime($($arg: $ty),*) $( -> $ret )? {
             // Don't warn if one of the arguments is unused.
@@ -2829,16 +2834,14 @@ pub(crate) macro const_eval_select {
     // We support leaving away the `val` expressions for *all* arguments
     // (but not for *some* arguments, that's too tricky).
     (
-        $(#[$attr:meta])*
-        ($($arg:ident : $ty:ty),* $(,)?) -> $ret:ty:
+        @capture { $($arg:ident : $ty:ty),* $(,)? } $( -> $ret:ty )? :
         if const
             $(#[$compiletime_attr:meta])* $compiletime:block
         else
             $(#[$runtime_attr:meta])* $runtime:block
     ) => {
         $crate::intrinsics::const_eval_select!(
-            $(#[$attr])*
-            ($($arg : $ty = $arg),*) -> $ret:
+            @capture { $($arg : $ty = $arg),* } $(-> $ret)? :
             if const
                 $(#[$compiletime_attr])* $compiletime
             else
@@ -3794,7 +3797,7 @@ pub(crate) const fn miri_promise_symbolic_alignment(ptr: *const (), align: usize
     }
 
     const_eval_select!(
-        (ptr: *const (), align: usize):
+        @capture { ptr: *const (), align: usize}:
         if const {
             // Do nothing.
         } else {

library/core/src/macros/mod.rs

@@ -12,51 +12,6 @@ macro_rules! panic {
     };
 }
 
-/// Helper macro for panicking in a `const fn`.
-/// Invoke as:
-/// ```rust,ignore (just an example)
-/// core::macros::const_panic!("boring message", "flavored message {a} {b:?}", a: u32 = foo.len(), b: Something = bar);
-/// ```
-/// where the first message will be printed in const-eval,
-/// and the second message will be printed at runtime.
-// All uses of this macro are FIXME(const-hack).
-#[unstable(feature = "panic_internals", issue = "none")]
-#[doc(hidden)]
-pub macro const_panic {
-    ($const_msg:literal, $runtime_msg:literal, $($arg:ident : $ty:ty = $val:expr),* $(,)?) => {{
-        // Wrap call to `const_eval_select` in a function so that we can
-        // add the `rustc_allow_const_fn_unstable`. This is okay to do
-        // because both variants will panic, just with different messages.
-        #[rustc_allow_const_fn_unstable(const_eval_select)]
-        #[inline(always)]
-        #[track_caller]
-        #[cfg_attr(bootstrap, rustc_const_stable(feature = "const_panic", since = "CURRENT_RUSTC_VERSION"))]
-        const fn do_panic($($arg: $ty),*) -> ! {
-            $crate::intrinsics::const_eval_select!(
-                #[inline]
-                #[track_caller]
-                ($($arg: $ty),*) -> !:
-                if const {
-                    $crate::panic!($const_msg)
-                } else {
-                    $crate::panic!($runtime_msg)
-                }
-            )
-        }
-
-        do_panic($($val),*)
-    }},
-    // We support leaving away the `val` expressions for *all* arguments
-    // (but not for *some* arguments, that's too tricky).
-    ($const_msg:literal, $runtime_msg:literal, $($arg:ident : $ty:ty),* $(,)?) => {
-        $crate::macros::const_panic!(
-            $const_msg,
-            $runtime_msg,
-            $($arg: $ty = $arg),*
-        )
-    },
-}
-
 /// Asserts that two expressions are equal to each other (using [`PartialEq`]).
 ///
 /// Assertions are always checked in both debug and release builds, and cannot
@@ -241,19 +196,6 @@ pub macro assert_matches {
     },
 }
 
-/// A version of `assert` that prints a non-formatting message in const contexts.
-///
-/// See [`const_panic!`].
-#[unstable(feature = "panic_internals", issue = "none")]
-#[doc(hidden)]
-pub macro const_assert {
-    ($condition: expr, $const_msg:literal, $runtime_msg:literal, $($arg:tt)*) => {{
-        if !$crate::intrinsics::likely($condition) {
-            $crate::macros::const_panic!($const_msg, $runtime_msg, $($arg)*)
-        }
-    }}
-}
-
 /// A macro for defining `#[cfg]` match-like statements.
 ///
 /// It is similar to the `if/elif` C preprocessor macro by allowing definition of a cascade of

library/core/src/num/f128.rs

@@ -14,9 +14,9 @@
 use crate::convert::FloatToInt;
 #[cfg(not(test))]
 use crate::intrinsics;
-use crate::macros::const_assert;
 use crate::mem;
 use crate::num::FpCategory;
+use crate::panic::const_assert;
 
 /// Basic mathematical constants.
 #[unstable(feature = "f128", issue = "116909")]

library/core/src/num/f16.rs

@@ -14,9 +14,9 @@
 use crate::convert::FloatToInt;
 #[cfg(not(test))]
 use crate::intrinsics;
-use crate::macros::const_assert;
 use crate::mem;
 use crate::num::FpCategory;
+use crate::panic::const_assert;
 
 /// Basic mathematical constants.
 #[unstable(feature = "f16", issue = "116909")]

library/core/src/num/f32.rs

@@ -14,9 +14,9 @@
 use crate::convert::FloatToInt;
 #[cfg(not(test))]
 use crate::intrinsics;
-use crate::macros::const_assert;
 use crate::mem;
 use crate::num::FpCategory;
+use crate::panic::const_assert;
 
 /// The radix or base of the internal representation of `f32`.
 /// Use [`f32::RADIX`] instead.

library/core/src/num/f64.rs

@@ -14,9 +14,9 @@
 use crate::convert::FloatToInt;
 #[cfg(not(test))]
 use crate::intrinsics;
-use crate::macros::const_assert;
 use crate::mem;
 use crate::num::FpCategory;
+use crate::panic::const_assert;
 
 /// The radix or base of the internal representation of `f64`.
 /// Use [`f64::RADIX`] instead.

library/core/src/num/mod.rs

@@ -2,7 +2,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use crate::macros::const_panic;
+use crate::panic::const_panic;
 use crate::str::FromStr;
 use crate::ub_checks::assert_unsafe_precondition;
 use crate::{ascii, intrinsics, mem};

library/core/src/panic.rs

@@ -189,3 +189,59 @@ pub unsafe trait PanicPayload: crate::fmt::Display {
         None
     }
 }
+
+/// Helper macro for panicking in a `const fn`.
+/// Invoke as:
+/// ```rust,ignore (just an example)
+/// core::macros::const_panic!("boring message", "flavored message {a} {b:?}", a: u32 = foo.len(), b: Something = bar);
+/// ```
+/// where the first message will be printed in const-eval,
+/// and the second message will be printed at runtime.
+// All uses of this macro are FIXME(const-hack).
+#[unstable(feature = "panic_internals", issue = "none")]
+#[doc(hidden)]
+pub macro const_panic {
+    ($const_msg:literal, $runtime_msg:literal, $($arg:ident : $ty:ty = $val:expr),* $(,)?) => {{
+        // Wrap call to `const_eval_select` in a function so that we can
+        // add the `rustc_allow_const_fn_unstable`. This is okay to do
+        // because both variants will panic, just with different messages.
+        #[rustc_allow_const_fn_unstable(const_eval_select)]
+        #[inline(always)]
+        #[track_caller]
+        #[cfg_attr(bootstrap, rustc_const_stable(feature = "const_panic", since = "CURRENT_RUSTC_VERSION"))]
+        const fn do_panic($($arg: $ty),*) -> ! {
+            $crate::intrinsics::const_eval_select!(
+                @capture { $($arg: $ty),* } -> !:
+                if const #[track_caller] {
+                    $crate::panic!($const_msg)
+                } else #[track_caller] {
+                    $crate::panic!($runtime_msg)
+                }
+            )
+        }
+
+        do_panic($($val),*)
+    }},
+    // We support leaving away the `val` expressions for *all* arguments
+    // (but not for *some* arguments, that's too tricky).
+    ($const_msg:literal, $runtime_msg:literal, $($arg:ident : $ty:ty),* $(,)?) => {
+        $crate::panic::const_panic!(
+            $const_msg,
+            $runtime_msg,
+            $($arg: $ty = $arg),*
+        )
+    },
+}
+
+/// A version of `assert` that prints a non-formatting message in const contexts.
+///
+/// See [`const_panic!`].
+#[unstable(feature = "panic_internals", issue = "none")]
+#[doc(hidden)]
+pub macro const_assert {
+    ($condition: expr, $const_msg:literal, $runtime_msg:literal, $($arg:tt)*) => {{
+        if !$crate::intrinsics::likely($condition) {
+            $crate::panic::const_panic!($const_msg, $runtime_msg, $($arg)*)
+        }
+    }}
+}

library/core/src/panicking.rs

@@ -29,6 +29,7 @@
 )]
 
 use crate::fmt;
+use crate::intrinsics::const_eval_select;
 use crate::panic::{Location, PanicInfo};
 
 #[cfg(feature = "panic_immediate_abort")]
@@ -89,40 +90,35 @@ pub const fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
 #[cfg_attr(not(bootstrap), rustc_const_stable_indirect)] // must follow stable const rules since it is exposed to stable
 #[rustc_allow_const_fn_unstable(const_eval_select)]
 pub const fn panic_nounwind_fmt(fmt: fmt::Arguments<'_>, force_no_backtrace: bool) -> ! {
-    #[inline] // this should always be inlined into `panic_nounwind_fmt`
-    #[track_caller]
-    fn runtime(fmt: fmt::Arguments<'_>, force_no_backtrace: bool) -> ! {
-        if cfg!(feature = "panic_immediate_abort") {
-            super::intrinsics::abort()
+    const_eval_select!(
+        @capture { fmt: fmt::Arguments<'_>, force_no_backtrace: bool } -> !:
+        if const #[track_caller] {
+            // We don't unwind anyway at compile-time so we can call the regular `panic_fmt`.
+            panic_fmt(fmt)
+        } else #[track_caller] {
+            if cfg!(feature = "panic_immediate_abort") {
+                super::intrinsics::abort()
+            }
+
+            // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
+            // that gets resolved to the `#[panic_handler]` function.
+            extern "Rust" {
+                #[lang = "panic_impl"]
+                fn panic_impl(pi: &PanicInfo<'_>) -> !;
+            }
+
+            // PanicInfo with the `can_unwind` flag set to false forces an abort.
+            let pi = PanicInfo::new(
+                &fmt,
+                Location::caller(),
+                /* can_unwind */ false,
+                force_no_backtrace,
+            );
+
+            // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
+            unsafe { panic_impl(&pi) }
         }
-
-        // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
-        // that gets resolved to the `#[panic_handler]` function.
-        extern "Rust" {
-            #[lang = "panic_impl"]
-            fn panic_impl(pi: &PanicInfo<'_>) -> !;
-        }
-
-        // PanicInfo with the `can_unwind` flag set to false forces an abort.
-        let pi = PanicInfo::new(
-            &fmt,
-            Location::caller(),
-            /* can_unwind */ false,
-            force_no_backtrace,
-        );
-
-        // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
-        unsafe { panic_impl(&pi) }
-    }
-
-    #[inline]
-    #[track_caller]
-    const fn comptime(fmt: fmt::Arguments<'_>, _force_no_backtrace: bool) -> ! {
-        // We don't unwind anyway at compile-time so we can call the regular `panic_fmt`.
-        panic_fmt(fmt);
-    }
-
-    super::intrinsics::const_eval_select((fmt, force_no_backtrace), comptime, runtime);
+    )
 }
 
 // Next we define a bunch of higher-level wrappers that all bottom out in the two core functions