Auto merge of #48813 - sinkuu:build_in_assert_macro, r=alexcrichton

Make `assert` a built-in procedural macro

Makes `assert` macro a built-in one without touching its functionality. This is a prerequisite for RFC 2011 (#44838).

2 files changed, 56 insertions, 1 deletions

diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index cd9484de85a..70a1f82c9a1 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -355,8 +355,9 @@ use prelude::v1::*;
 // We want to re-export a few macros from core but libcore has already been
 // imported by the compiler (via our #[no_std] attribute) In this case we just
 // add a new crate name so we can attach the re-exports to it.
-#[macro_reexport(assert, assert_eq, assert_ne, debug_assert, debug_assert_eq,
+#[macro_reexport(assert_eq, assert_ne, debug_assert, debug_assert_eq,
                  debug_assert_ne, unreachable, unimplemented, write, writeln, try)]
+#[cfg_attr(stage0, macro_reexport(assert))]
 extern crate core as __core;
 
 #[macro_use]
diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs
index b804cf7cd90..000f9713615 100644
--- a/src/libstd/macros.rs
+++ b/src/libstd/macros.rs
@@ -719,6 +719,60 @@ pub mod builtin {
         ($file:expr) => ({ /* compiler built-in */ });
         ($file:expr,) => ({ /* compiler built-in */ });
     }
+
+    /// Ensure that a boolean expression is `true` at runtime.
+    ///
+    /// This will invoke the [`panic!`] macro if the provided expression cannot be
+    /// evaluated to `true` at runtime.
+    ///
+    /// # Uses
+    ///
+    /// Assertions are always checked in both debug and release builds, and cannot
+    /// be disabled. See [`debug_assert!`] for assertions that are not enabled in
+    /// release builds by default.
+    ///
+    /// Unsafe code relies on `assert!` to enforce run-time invariants that, if
+    /// violated could lead to unsafety.
+    ///
+    /// Other use-cases of `assert!` include [testing] and enforcing run-time
+    /// invariants in safe code (whose violation cannot result in unsafety).
+    ///
+    /// # Custom Messages
+    ///
+    /// This macro has a second form, where a custom panic message can
+    /// be provided with or without arguments for formatting.  See [`std::fmt`]
+    /// for syntax for this form.
+    ///
+    /// [`panic!`]: macro.panic.html
+    /// [`debug_assert!`]: macro.debug_assert.html
+    /// [testing]: ../book/second-edition/ch11-01-writing-tests.html#checking-results-with-the-assert-macro
+    /// [`std::fmt`]: ../std/fmt/index.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// // the panic message for these assertions is the stringified value of the
+    /// // expression given.
+    /// assert!(true);
+    ///
+    /// fn some_computation() -> bool { true } // a very simple function
+    ///
+    /// assert!(some_computation());
+    ///
+    /// // assert with a custom message
+    /// let x = true;
+    /// assert!(x, "x wasn't true!");
+    ///
+    /// let a = 3; let b = 27;
+    /// assert!(a + b == 30, "a = {}, b = {}", a, b);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[macro_export]
+    macro_rules! assert {
+        ($cond:expr) => ({ /* compiler built-in */ });
+        ($cond:expr,) => ({ /* compiler built-in */ });
+        ($cond:expr, $($arg:tt)+) => ({ /* compiler built-in */ });
+    }
 }
 
 /// A macro for defining #[cfg] if-else statements.