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diff --git a/assertions/src/lib.rs b/assertions/src/lib.rs
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+// Copyright 2018 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+//! Macros that assert properties of code at compile time.
+//!
+//! A static assertion is particularly appropriate when unsafe code relies on
+//! two types to have the same size, or on some type to have a particular size.
+
+#[doc(hidden)]
+pub mod mechanism;
+
+// Re-export so that these types appear with a more concise name in error
+// messages.
+#[doc(hidden)]
+pub use mechanism::*;
+
+/// Macro that fails to compile if a given const expression is not true.
+///
+/// # Example
+///
+/// ```rust
+/// extern crate assertions;
+/// use assertions::const_assert;
+///
+/// fn main() {
+///     const_assert!(std::mem::size_of::<String>() == 24);
+/// }
+/// ```
+///
+/// # Example that fails to compile
+///
+/// ```rust,compile_fail
+/// extern crate assertions;
+/// use assertions::const_assert;
+///
+/// fn main() {
+///     // fails to compile:
+///     const_assert!(std::mem::size_of::<String>() == 8);
+/// }
+/// ```
+#[macro_export]
+macro_rules! const_assert {
+    ($e:expr) => {
+        let _: $crate::Assert<[(); $e as bool as usize]>;
+    };
+}