Auto merge of #30587 - oli-obk:eager_const_eval2, r=nikomatsakis

typestrong const integers

~~It would be great if someone could run crater on this PR, as this has a high danger of breaking valid code~~ Crater ran. Good to go.

----

So this PR does a few things:

1. ~~const eval array values when const evaluating an array expression~~
2. ~~const eval repeat value when const evaluating a repeat expression~~
3. ~~const eval all struct and tuple fields when evaluating a struct/tuple expression~~
4. remove the `ConstVal::Int` and `ConstVal::Uint` variants and replace them with a single enum (`ConstInt`) which has variants for all integral types
  * `usize`/`isize` are also enums with variants for 32 and 64 bit. At creation and various usage steps there are assertions in place checking if the target bitwidth matches with the chosen enum variant
5. enum discriminants (`ty::Disr`) are now `ConstInt`
6. trans has its own `Disr` type now (newtype around `u64`)

This obviously can't be done without breaking changes (the ones that are noticable in stable)
We could probably write lints that find those situations and error on it for a cycle or two. But then again, those situations are rare and really bugs imo anyway:

```rust
let v10 = 10 as i8;
let v4 = 4 as isize;
assert_eq!(v10 << v4 as usize, 160 as i8);
 ```

stops compiling because 160 is not a valid i8

```rust
struct S<T, S> {
    a: T,
    b: u8,
    c: S
}
let s = S { a: 0xff_ff_ff_ffu32, b: 1, c: 0xaa_aa_aa_aa as i32 };
```

stops compiling because `0xaa_aa_aa_aa` is not a valid i32

----

cc @eddyb @pnkfelix

related: rust-lang/rfcs#1071

Author: bors

mk/crates.mk

@@ -53,7 +53,7 @@ TARGET_CRATES := libc std term \
                  getopts collections test rand \
                  core alloc \
                  rustc_unicode rustc_bitflags \
-		 alloc_system alloc_jemalloc
+		 alloc_system alloc_jemalloc rustc_const_eval
 RUSTC_CRATES := rustc rustc_typeck rustc_mir rustc_borrowck rustc_resolve rustc_driver \
                 rustc_trans rustc_back rustc_llvm rustc_privacy rustc_lint \
                 rustc_data_structures rustc_front rustc_platform_intrinsics \
@@ -91,8 +91,11 @@ DEPS_test := std getopts term native:rust_test_helpers
 DEPS_syntax := std term serialize log arena libc rustc_bitflags rustc_unicode
 DEPS_syntax_ext := syntax fmt_macros
 
+DEPS_rustc_const_eval := std syntax
+
 DEPS_rustc := syntax fmt_macros flate arena serialize getopts rbml rustc_front\
-              log graphviz rustc_llvm rustc_back rustc_data_structures
+              log graphviz rustc_llvm rustc_back rustc_data_structures\
+		  	  rustc_const_eval
 DEPS_rustc_back := std syntax rustc_llvm rustc_front flate log libc
 DEPS_rustc_borrowck := rustc rustc_front log graphviz syntax
 DEPS_rustc_data_structures := std log serialize
@@ -103,16 +106,17 @@ DEPS_rustc_driver := arena flate getopts graphviz libc rustc rustc_back rustc_bo
 DEPS_rustc_front := std syntax log serialize
 DEPS_rustc_lint := rustc log syntax
 DEPS_rustc_llvm := native:rustllvm libc std rustc_bitflags
-DEPS_rustc_metadata := rustc rustc_front syntax rbml
+DEPS_rustc_metadata := rustc rustc_front syntax rbml rustc_const_eval
 DEPS_rustc_passes := syntax rustc core rustc_front
-DEPS_rustc_mir := rustc rustc_front syntax
+DEPS_rustc_mir := rustc rustc_front syntax rustc_const_eval
 DEPS_rustc_resolve := arena rustc rustc_front log syntax
 DEPS_rustc_platform_intrinsics := rustc rustc_llvm
 DEPS_rustc_plugin := rustc rustc_metadata syntax rustc_mir
 DEPS_rustc_privacy := rustc rustc_front log syntax
 DEPS_rustc_trans := arena flate getopts graphviz libc rustc rustc_back rustc_mir \
-                    log syntax serialize rustc_llvm rustc_front rustc_platform_intrinsics
-DEPS_rustc_typeck := rustc syntax rustc_front rustc_platform_intrinsics
+                    log syntax serialize rustc_llvm rustc_front rustc_platform_intrinsics \
+					rustc_const_eval
+DEPS_rustc_typeck := rustc syntax rustc_front rustc_platform_intrinsics rustc_const_eval
 
 DEPS_rustdoc := rustc rustc_driver native:hoedown serialize getopts \
                 test rustc_lint rustc_front

src/librustc/Cargo.toml

@@ -18,6 +18,7 @@ log = { path = "../liblog" }
 rbml = { path = "../librbml" }
 rustc_back = { path = "../librustc_back" }
 rustc_bitflags = { path = "../librustc_bitflags" }
+rustc_const_eval = { path = "../librustc_const_eval" }
 rustc_data_structures = { path = "../librustc_data_structures" }
 rustc_front = { path = "../librustc_front" }
 rustc_llvm = { path = "../librustc_llvm" }

src/librustc/lib.rs

@@ -55,6 +55,7 @@ extern crate rustc_front;
 extern crate rustc_data_structures;
 extern crate serialize;
 extern crate collections;
+extern crate rustc_const_eval;
 #[macro_use] extern crate log;
 #[macro_use] extern crate syntax;
 #[macro_use] #[no_link] extern crate rustc_bitflags;

src/librustc/middle/check_match.rs

@@ -476,7 +476,7 @@ impl<'a, 'tcx> Folder for StaticInliner<'a, 'tcx> {
                     Some(Def::AssociatedConst(did)) |
                     Some(Def::Const(did)) => match lookup_const_by_id(self.tcx, did,
                                                                     Some(pat.id), None) {
-                        Some(const_expr) => {
+                        Some((const_expr, _const_ty)) => {
                             const_expr_to_pat(self.tcx, const_expr, pat.span).map(|new_pat| {
 
                                 if let Some(ref mut renaming_map) = self.renaming_map {