Overhaul cast semantics and make them follow RFC401

This should hopefully fix all cast-related ICEs once and for all.

I managed to make diagnostics hate me and give me spurious "decoder error"
 - removing $build/tmp/extended-errors seems to fix it.

Author: Ariel Ben-Yehuda

src/librustc/diagnostics.rs

@@ -801,7 +801,6 @@ struct Foo<T: 'static> {
 
 register_diagnostics! {
     E0011,
-    E0012,
     E0014,
     E0016,
     E0017,

src/librustc/lib.rs

@@ -92,6 +92,7 @@ pub mod back {
 pub mod middle {
     pub mod astconv_util;
     pub mod astencode;
+    pub mod cast;
     pub mod cfg;
     pub mod check_const;
     pub mod check_static_recursion;

src/librustc/metadata/common.rs

@@ -148,6 +148,7 @@ enum_from_u32! {
         tag_table_capture_modes = 0x67,
         tag_table_object_cast_map = 0x68,
         tag_table_const_qualif = 0x69,
+        tag_table_cast_kinds = 0x6a,
     }
 }
 

src/librustc/middle/astencode.rs

@@ -23,6 +23,7 @@ use metadata::tydecode;
 use metadata::tydecode::{DefIdSource, NominalType, TypeWithId, TypeParameter};
 use metadata::tydecode::{RegionParameter, ClosureSource};
 use metadata::tyencode;
+use middle::cast;
 use middle::check_const::ConstQualif;
 use middle::mem_categorization::Typer;
 use middle::privacy::{AllPublic, LastMod};
@@ -688,6 +689,10 @@ pub fn encode_closure_kind(ebml_w: &mut Encoder, kind: ty::ClosureKind) {
     kind.encode(ebml_w).unwrap();
 }
 
+pub fn encode_cast_kind(ebml_w: &mut Encoder, kind: cast::CastKind) {
+    kind.encode(ebml_w).unwrap();
+}
+
 pub trait vtable_decoder_helpers<'tcx> {
     fn read_vec_per_param_space<T, F>(&mut self, f: F) -> VecPerParamSpace<T> where
         F: FnMut(&mut Self) -> T;
@@ -1248,6 +1253,13 @@ fn encode_side_tables_for_id(ecx: &e::EncodeContext,
         })
     }
 
+    if let Some(cast_kind) = tcx.cast_kinds.borrow().get(&id) {
+        rbml_w.tag(c::tag_table_cast_kinds, |rbml_w| {
+            rbml_w.id(id);
+            encode_cast_kind(rbml_w, *cast_kind)
+        })
+    }
+
     for &qualif in tcx.const_qualif_map.borrow().get(&id).iter() {
         rbml_w.tag(c::tag_table_const_qualif, |rbml_w| {
             rbml_w.id(id);
@@ -1289,6 +1301,8 @@ trait rbml_decoder_decoder_helpers<'tcx> {
                            -> subst::Substs<'tcx>;
     fn read_auto_adjustment<'a, 'b>(&mut self, dcx: &DecodeContext<'a, 'b, 'tcx>)
                                     -> ty::AutoAdjustment<'tcx>;
+    fn read_cast_kind<'a, 'b>(&mut self, dcx: &DecodeContext<'a, 'b, 'tcx>)
+                                 -> cast::CastKind;
     fn read_closure_kind<'a, 'b>(&mut self, dcx: &DecodeContext<'a, 'b, 'tcx>)
                                  -> ty::ClosureKind;
     fn read_closure_ty<'a, 'b>(&mut self, dcx: &DecodeContext<'a, 'b, 'tcx>)
@@ -1641,6 +1655,12 @@ impl<'a, 'tcx> rbml_decoder_decoder_helpers<'tcx> for reader::Decoder<'a> {
         }).unwrap()
     }
 
+    fn read_cast_kind<'b, 'c>(&mut self, _dcx: &DecodeContext<'b, 'c, 'tcx>)
+                              -> cast::CastKind
+    {
+        Decodable::decode(self).unwrap()
+    }
+
     fn read_closure_kind<'b, 'c>(&mut self, _dcx: &DecodeContext<'b, 'c, 'tcx>)
                                  -> ty::ClosureKind
     {
@@ -1801,6 +1821,11 @@ fn decode_side_tables(dcx: &DecodeContext,
                         dcx.tcx.closure_kinds.borrow_mut().insert(ast_util::local_def(id),
                                                                   closure_kind);
                     }
+                    c::tag_table_cast_kinds => {
+                        let cast_kind =
+                            val_dsr.read_cast_kind(dcx);
+                        dcx.tcx.cast_kinds.borrow_mut().insert(id, cast_kind);
+                    }
                     c::tag_table_const_qualif => {
                         let qualif: ConstQualif = Decodable::decode(val_dsr).unwrap();
                         dcx.tcx.const_qualif_map.borrow_mut().insert(id, qualif);

src/librustc/middle/cast.rs

@@ -0,0 +1,71 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Helpers for handling cast expressions, used in both
+// typeck and trans.
+
+use middle::ty::{self, Ty};
+
+use syntax::ast;
+
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum IntTy {
+    U(ast::UintTy),
+    I,
+    CEnum,
+    Bool,
+    Char
+}
+
+// Valid types for the result of a non-coercion cast
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum CastTy<'tcx> {
+    Int(IntTy),
+    Float,
+    FPtr,
+    Ptr(&'tcx ty::mt<'tcx>),
+    RPtr(&'tcx ty::mt<'tcx>),
+}
+
+/// Cast Kind. See RFC 401 (or librustc_typeck/check/cast.rs)
+#[derive(Copy, Clone, Debug, RustcEncodable, RustcDecodable)]
+pub enum CastKind {
+    CoercionCast,
+    PtrPtrCast,
+    PtrAddrCast,
+    AddrPtrCast,
+    NumericCast,
+    EnumCast,
+    PrimIntCast,
+    U8CharCast,
+    ArrayPtrCast,
+    FPtrPtrCast,
+    FPtrAddrCast
+}
+
+impl<'tcx> CastTy<'tcx> {
+    pub fn recognize(tcx: &ty::ctxt<'tcx>, t: Ty<'tcx>)
+                     -> Option<CastTy<'tcx>> {
+        match t.sty {
+            ty::ty_bool => Some(CastTy::Int(IntTy::Bool)),
+            ty::ty_char => Some(CastTy::Int(IntTy::Char)),
+            ty::ty_int(_) => Some(CastTy::Int(IntTy::I)),
+            ty::ty_uint(u) => Some(CastTy::Int(IntTy::U(u))),
+            ty::ty_float(_) => Some(CastTy::Float),
+            ty::ty_enum(..) if ty::type_is_c_like_enum(
+                tcx, t) => Some(CastTy::Int(IntTy::CEnum)),
+            ty::ty_ptr(ref mt) => Some(CastTy::Ptr(mt)),
+            ty::ty_rptr(_, ref mt) => Some(CastTy::RPtr(mt)),
+            ty::ty_bare_fn(..) => Some(CastTy::FPtr),
+            _ => None,
+        }
+    }
+}

src/librustc/middle/check_const.rs

@@ -24,6 +24,7 @@
 // - It's not possible to take the address of a static item with unsafe interior. This is enforced
 // by borrowck::gather_loans
 
+use middle::cast::{CastKind};
 use middle::const_eval;
 use middle::def;
 use middle::expr_use_visitor as euv;
@@ -32,11 +33,10 @@ use middle::mem_categorization as mc;
 use middle::traits;
 use middle::ty::{self, Ty};
 use util::nodemap::NodeMap;
-use util::ppaux;
+use util::ppaux::Repr;
 
 use syntax::ast;
 use syntax::codemap::Span;
-use syntax::print::pprust;
 use syntax::visit::{self, Visitor};
 
 use std::collections::hash_map::Entry;
@@ -197,7 +197,7 @@ impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
 
 impl<'a, 'tcx, 'v> Visitor<'v> for CheckCrateVisitor<'a, 'tcx> {
     fn visit_item(&mut self, i: &ast::Item) {
-        debug!("visit_item(item={})", pprust::item_to_string(i));
+        debug!("visit_item(item={})", i.repr(self.tcx));
         match i.node {
             ast::ItemStatic(_, ast::MutImmutable, ref expr) => {
                 self.check_static_type(&**expr);
@@ -440,26 +440,17 @@ fn check_expr<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>,
             }
         }
         ast::ExprCast(ref from, _) => {
-            let toty = ty::expr_ty(v.tcx, e);
-            let fromty = ty::expr_ty(v.tcx, &**from);
-            let is_legal_cast =
-                ty::type_is_numeric(toty) ||
-                ty::type_is_unsafe_ptr(toty) ||
-                (ty::type_is_bare_fn(toty) && ty::type_is_bare_fn_item(fromty));
-            if !is_legal_cast {
-                v.add_qualif(ConstQualif::NOT_CONST);
-                if v.mode != Mode::Var {
-                    span_err!(v.tcx.sess, e.span, E0012,
-                              "can not cast to `{}` in {}s",
-                              ppaux::ty_to_string(v.tcx, toty), v.msg());
-                }
-            }
-            if ty::type_is_unsafe_ptr(fromty) && ty::type_is_numeric(toty) {
-                v.add_qualif(ConstQualif::NOT_CONST);
-                if v.mode != Mode::Var {
-                    span_err!(v.tcx.sess, e.span, E0018,
-                              "can not cast a pointer to an integer in {}s", v.msg());
+            debug!("Checking const cast(id={})", from.id);
+            match v.tcx.cast_kinds.borrow().get(&from.id) {
+                None => v.tcx.sess.span_bug(e.span, "no kind for cast"),
+                Some(&CastKind::PtrAddrCast) | Some(&CastKind::FPtrAddrCast) => {
+                    v.add_qualif(ConstQualif::NOT_CONST);
+                    if v.mode != Mode::Var {
+                        span_err!(v.tcx.sess, e.span, E0018,
+                                  "can not cast a pointer to an integer in {}s", v.msg());
+                    }
                 }
+                _ => {}
             }
         }
         ast::ExprPath(..) => {

src/librustc/middle/const_eval.rs

@@ -992,7 +992,7 @@ fn cast_const<'tcx>(tcx: &ty::ctxt<'tcx>, val: const_val, ty: Ty) -> CastResult
     macro_rules! convert_val {
         ($intermediate_ty:ty, $const_type:ident, $target_ty:ty) => {
             match val {
-                const_bool(b) => Ok($const_type(b as $intermediate_ty as $target_ty)),
+                const_bool(b) => Ok($const_type(b as u64 as $intermediate_ty as $target_ty)),
                 const_uint(u) => Ok($const_type(u as $intermediate_ty as $target_ty)),
                 const_int(i) => Ok($const_type(i as $intermediate_ty as $target_ty)),
                 const_float(f) => Ok($const_type(f as $intermediate_ty as $target_ty)),

src/librustc/middle/ty.rs

@@ -41,6 +41,7 @@ use session::Session;
 use lint;
 use metadata::csearch;
 use middle;
+use middle::cast;
 use middle::check_const;
 use middle::const_eval;
 use middle::def::{self, DefMap, ExportMap};
@@ -288,15 +289,6 @@ pub struct field_ty {
     pub origin: ast::DefId,  // The DefId of the struct in which the field is declared.
 }
 
-// Contains information needed to resolve types and (in the future) look up
-// the types of AST nodes.
-#[derive(Copy, Clone, PartialEq, Eq, Hash)]
-pub struct creader_cache_key {
-    pub cnum: CrateNum,
-    pub pos: usize,
-    pub len: usize
-}
-
 #[derive(Clone, PartialEq, RustcDecodable, RustcEncodable)]
 pub struct ItemVariances {
     pub types: VecPerParamSpace<Variance>,
@@ -562,6 +554,15 @@ pub enum vtable_origin<'tcx> {
 // expr to the associated trait ref.
 pub type ObjectCastMap<'tcx> = RefCell<NodeMap<ty::PolyTraitRef<'tcx>>>;
 
+// Contains information needed to resolve types and (in the future) look up
+// the types of AST nodes.
+#[derive(Copy, Clone, PartialEq, Eq, Hash)]
+pub struct creader_cache_key {
+    pub cnum: CrateNum,
+    pub pos: usize,
+    pub len: usize
+}
+
 /// A restriction that certain types must be the same size. The use of
 /// `transmute` gives rise to these restrictions. These generally
 /// cannot be checked until trans; therefore, each call to `transmute`
@@ -827,6 +828,10 @@ pub struct ctxt<'tcx> {
 
     /// Caches CoerceUnsized kinds for impls on custom types.
     pub custom_coerce_unsized_kinds: RefCell<DefIdMap<CustomCoerceUnsized>>,
+
+    /// Maps a cast expression to its kind. This is keyed on the
+    /// *from* expression of the cast, not the cast itself.
+    pub cast_kinds: RefCell<NodeMap<cast::CastKind>>,
 }
 
 impl<'tcx> ctxt<'tcx> {
@@ -2819,6 +2824,7 @@ pub fn mk_ctxt<'tcx>(s: Session,
         type_impls_sized_cache: RefCell::new(HashMap::new()),
         const_qualif_map: RefCell::new(NodeMap()),
         custom_coerce_unsized_kinds: RefCell::new(DefIdMap()),
+        cast_kinds: RefCell::new(NodeMap()),
    }
 }
 

src/librustc_trans/trans/consts.rs

@@ -29,6 +29,7 @@ use trans::declare;
 use trans::monomorphize;
 use trans::type_::Type;
 use trans::type_of;
+use middle::cast::{CastTy,IntTy};
 use middle::subst::Substs;
 use middle::ty::{self, Ty};
 use util::ppaux::{Repr, ty_to_string};
@@ -616,53 +617,62 @@ fn const_expr_unadjusted<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
               }
           }
           ast::ExprCast(ref base, _) => {
-            let llty = type_of::type_of(cx, ety);
-            let (v, basety) = const_expr(cx, &**base, param_substs);
-            if expr::cast_is_noop(basety, ety) {
+            let t_1 = ety;
+            let llty = type_of::type_of(cx, t_1);
+            let (v, t_e) = const_expr(cx, &**base, param_substs);
+            debug!("trans_const_cast({} as {})", t_e.repr(cx.tcx()), t_1.repr(cx.tcx()));
+            if expr::cast_is_noop(cx.tcx(), base, t_e, t_1) {
                 return v;
             }
-            match (expr::cast_type_kind(cx.tcx(), basety),
-                   expr::cast_type_kind(cx.tcx(), ety)) {
-
-              (expr::cast_integral, expr::cast_integral) => {
-                let s = ty::type_is_signed(basety) as Bool;
+            if type_is_fat_ptr(cx.tcx(), t_e) {
+                // Fat pointer casts.
+                let t_1_inner = ty::deref(t_1, true).expect("cast to non-pointer").ty;
+                let ptr_ty = type_of::in_memory_type_of(cx, t_1_inner).ptr_to();
+                let addr = ptrcast(const_get_elt(cx, v, &[abi::FAT_PTR_ADDR as u32]),
+                                   ptr_ty);
+                if type_is_fat_ptr(cx.tcx(), t_1) {
+                    let info = const_get_elt(cx, v, &[abi::FAT_PTR_EXTRA as u32]);
+                    return C_struct(cx, &[addr, info], false)
+                } else {
+                    return addr;
+                }
+            }
+            match (CastTy::recognize(cx.tcx(), t_e).expect("bad input type for cast"),
+                   CastTy::recognize(cx.tcx(), t_1).expect("bad output type for cast")) {
+              (CastTy::Int(IntTy::CEnum), CastTy::Int(_)) => {
+                let repr = adt::represent_type(cx, t_e);
+                let discr = adt::const_get_discrim(cx, &*repr, v);
+                let iv = C_integral(cx.int_type(), discr, false);
+                let s = adt::is_discr_signed(&*repr) as Bool;
+                llvm::LLVMConstIntCast(iv, llty.to_ref(), s)
+              }
+              (CastTy::Int(_), CastTy::Int(_)) => {
+                let s = ty::type_is_signed(t_e) as Bool;
                 llvm::LLVMConstIntCast(v, llty.to_ref(), s)
               }
-              (expr::cast_integral, expr::cast_float) => {
-                if ty::type_is_signed(basety) {
+              (CastTy::Int(_), CastTy::Float) => {
+                if ty::type_is_signed(t_e) {
                     llvm::LLVMConstSIToFP(v, llty.to_ref())
                 } else {
                     llvm::LLVMConstUIToFP(v, llty.to_ref())
                 }
               }
-              (expr::cast_float, expr::cast_float) => {
+              (CastTy::Float, CastTy::Float) => {
                 llvm::LLVMConstFPCast(v, llty.to_ref())
               }
-              (expr::cast_float, expr::cast_integral) => {
-                if ty::type_is_signed(ety) { llvm::LLVMConstFPToSI(v, llty.to_ref()) }
+              (CastTy::Float, CastTy::Int(_)) => {
+                if ty::type_is_signed(t_1) { llvm::LLVMConstFPToSI(v, llty.to_ref()) }
                 else { llvm::LLVMConstFPToUI(v, llty.to_ref()) }
               }
-              (expr::cast_enum, expr::cast_integral) => {
-                let repr = adt::represent_type(cx, basety);
-                let discr = adt::const_get_discrim(cx, &*repr, v);
-                let iv = C_integral(cx.int_type(), discr, false);
-                let ety_cast = expr::cast_type_kind(cx.tcx(), ety);
-                match ety_cast {
-                    expr::cast_integral => {
-                        let s = ty::type_is_signed(ety) as Bool;
-                        llvm::LLVMConstIntCast(iv, llty.to_ref(), s)
-                    }
-                    _ => cx.sess().bug("enum cast destination is not \
-                                        integral")
-                }
-              }
-              (expr::cast_pointer, expr::cast_pointer) => {
+              (CastTy::Ptr(_), CastTy::Ptr(_)) | (CastTy::FPtr, CastTy::Ptr(_))
+                    | (CastTy::RPtr(_), CastTy::Ptr(_)) => {
                 ptrcast(v, llty)
               }
-              (expr::cast_integral, expr::cast_pointer) => {
+              (CastTy::FPtr, CastTy::FPtr) => ptrcast(v, llty), // isn't this a coercion?
+              (CastTy::Int(_), CastTy::Ptr(_)) => {
                 llvm::LLVMConstIntToPtr(v, llty.to_ref())
               }
-              (expr::cast_pointer, expr::cast_integral) => {
+              (CastTy::Ptr(_), CastTy::Int(_)) | (CastTy::FPtr, CastTy::Int(_)) => {
                 llvm::LLVMConstPtrToInt(v, llty.to_ref())
               }
               _ => {