Remove #[static_assert]

This was always a weird feature, and isn't being used in the compiler.
Static assertions should be done better than this.

Fixes #13951
Fixes #23008
Fixes #6676

This is behind a feature gate, but that's still a

[breaking-change]

Author: steveklabnik

src/doc/reference.md

@@ -1872,8 +1872,6 @@ macro scope.
 - `simd` - on certain tuple structs, derive the arithmetic operators, which
   lower to the target's SIMD instructions, if any; the `simd` feature gate
   is necessary to use this attribute.
-- `static_assert` - on statics whose type is `bool`, terminates compilation
-  with an error if it is not initialized to `true`.
 - `unsafe_destructor` - allow implementations of the "drop" language item
   where the type it is implemented for does not implement the "send" language
   item; the `unsafe_destructor` feature gate is needed to use this attribute
@@ -2231,12 +2229,6 @@ The currently implemented features of the reference compiler are:
                  crate. Stability markers are also attributes: `#[stable]`,
                  `#[unstable]`, and `#[deprecated]` are the three levels.
 
-* `static_assert` - The `#[static_assert]` functionality is experimental and
-                    unstable. The attribute can be attached to a `static` of
-                    type `bool` and the compiler will error if the `bool` is
-                    `false` at compile time. This version of this functionality
-                    is unintuitive and suboptimal.
-
 * `start` - Allows use of the `#[start]` attribute, which changes the entry point
             into a Rust program. This capability, especially the signature for the
             annotated function, is subject to change.

src/librustc_trans/trans/base.rs

@@ -2025,28 +2025,6 @@ pub fn trans_item(ccx: &CrateContext, item: &ast::Item) {
 
           let g = consts::trans_static(ccx, m, item.id);
           update_linkage(ccx, g, Some(item.id), OriginalTranslation);
-
-          // Do static_assert checking. It can't really be done much earlier
-          // because we need to get the value of the bool out of LLVM
-          if attr::contains_name(&item.attrs, "static_assert") {
-              if !ty::type_is_bool(ty::expr_ty(ccx.tcx(), expr)) {
-                  ccx.sess().span_fatal(expr.span,
-                                        "can only have static_assert on a static \
-                                         with type `bool`");
-              }
-              if m == ast::MutMutable {
-                  ccx.sess().span_fatal(expr.span,
-                                        "cannot have static_assert on a mutable \
-                                         static");
-              }
-
-              let v = ccx.static_values().borrow().get(&item.id).unwrap().clone();
-              unsafe {
-                  if !(llvm::LLVMConstIntGetZExtValue(v) != 0) {
-                      ccx.sess().span_fatal(expr.span, "static assertion failed");
-                  }
-              }
-          }
       },
       ast::ItemForeignMod(ref foreign_mod) => {
         foreign::trans_foreign_mod(ccx, foreign_mod);

src/libsyntax/feature_gate.rs

@@ -141,9 +141,6 @@ const KNOWN_FEATURES: &'static [(&'static str, &'static str, Status)] = &[
     // Allows the use of rustc_* attributes; RFC 572
     ("rustc_attrs", "1.0.0", Active),
 
-    // Allows the use of `static_assert`
-    ("static_assert", "1.0.0", Active),
-
     // Allows the use of #[allow_internal_unstable]. This is an
     // attribute on macro_rules! and can't use the attribute handling
     // below (it has to be checked before expansion possibly makes
@@ -265,8 +262,6 @@ pub const KNOWN_ATTRIBUTES: &'static [(&'static str, AttributeType)] = &[
     ("no_mangle", Whitelisted),
     ("no_stack_check", Whitelisted),
     ("packed", Whitelisted),
-    ("static_assert", Gated("static_assert",
-                            "`#[static_assert]` is an experimental feature, and has a poor API")),
     ("no_debug", Whitelisted),
     ("omit_gdb_pretty_printer_section", Whitelisted),
     ("unsafe_no_drop_flag", Gated("unsafe_no_drop_flag",