Add RFC for disablable assertions

active/0000-assert.md

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+- Start Date: 2014-04-18
+- RFC PR #: (leave this empty)
+- Rust Issue #: (leave this empty)
+
+# Summary
+
+Asserts are too expensive for release builds and mess up inlining. There must be a way to turn them off. I propose macros `debug_assert!` and `assert!`. For test cases, `assert!` should be used.
+
+# Motivation
+
+Asserts are too expensive in release builds.
+
+# Detailed design
+
+There should be two macros, `debug_assert!(EXPR)` and `assert!(EXPR)`. In debug builds (without `--cfg ndebug`), `debug_assert!()` is the same as `assert!()`. In release builds (with `--cfg ndebug`), `debug_assert!()` compiles away to nothing. The definition of `assert!()` is `if (!EXPR) { fail!("assertion failed ({}, {}): {}", file!(), line!(), stringify!(expr) }`
+
+# Alternatives
+
+Other designs that have been considered are using `debug_assert!` in test cases and not providing `assert!`, but this doesn't work with separate compilation.
+
+The impact of not doing this is that `assert!` will be expensive, prompting people will write their own local `debug_assert!` macros, duplicating functionality that should have been in the standard library.
+
+# Unresolved questions
+
+None.