src/librustc_typeck/check/op.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Code related to processing overloaded binary and unary operators.
  12
  13 use super::{
  14     check_expr,
  15     check_expr_coercable_to_type,
  16     check_expr_with_lvalue_pref,
  17     demand,
  18     method,
  19     FnCtxt,
  20     PreferMutLvalue,
  21     structurally_resolved_type,
  22 };
  23 use middle::traits;
  24 use middle::ty::{self, Ty};
  25 use syntax::ast;
  26 use syntax::ast_util;
  27 use syntax::parse::token;
  28 use util::ppaux::{Repr, UserString};
  29
  30 /// Check a `a <op>= b`
  31 pub fn check_binop_assign<'a,'tcx>(fcx: &FnCtxt<'a,'tcx>,
  32                                    expr: &'tcx ast::Expr,
  33                                    op: ast::BinOp,
  34                                    lhs_expr: &'tcx ast::Expr,
  35                                    rhs_expr: &'tcx ast::Expr)
  36 {
  37     let tcx = fcx.ccx.tcx;
  38
  39     check_expr_with_lvalue_pref(fcx, lhs_expr, PreferMutLvalue);
  40     check_expr(fcx, rhs_expr);
  41
  42     let lhs_ty = structurally_resolved_type(fcx, lhs_expr.span, fcx.expr_ty(lhs_expr));
  43     let rhs_ty = structurally_resolved_type(fcx, rhs_expr.span, fcx.expr_ty(rhs_expr));
  44
  45     if is_builtin_binop(fcx.tcx(), lhs_ty, rhs_ty, op) {
  46         enforce_builtin_binop_types(fcx, lhs_expr, lhs_ty, rhs_expr, rhs_ty, op);
  47         fcx.write_nil(expr.id);
  48     } else {
  49         // error types are considered "builtin"
  50         assert!(!ty::type_is_error(lhs_ty) || !ty::type_is_error(rhs_ty));
  51         span_err!(tcx.sess, lhs_expr.span, E0368,
  52                   "binary assignment operation `{}=` cannot be applied to types `{}` and `{}`",
  53                   ast_util::binop_to_string(op.node),
  54                   lhs_ty.user_string(fcx.tcx()),
  55                   rhs_ty.user_string(fcx.tcx()));
  56         fcx.write_error(expr.id);
  57     }
  58
  59     let tcx = fcx.tcx();
  60     if !ty::expr_is_lval(tcx, lhs_expr) {
  61         span_err!(tcx.sess, lhs_expr.span, E0067, "illegal left-hand side expression");
  62     }
  63
  64     fcx.require_expr_have_sized_type(lhs_expr, traits::AssignmentLhsSized);
  65 }
  66
  67 /// Check a potentially overloaded binary operator.
  68 pub fn check_binop<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
  69                              expr: &'tcx ast::Expr,
  70                              op: ast::BinOp,
  71                              lhs_expr: &'tcx ast::Expr,
  72                              rhs_expr: &'tcx ast::Expr)
  73 {
  74     let tcx = fcx.ccx.tcx;
  75
  76     debug!("check_binop(expr.id={}, expr={}, op={:?}, lhs_expr={}, rhs_expr={})",
  77            expr.id,
  78            expr.repr(tcx),
  79            op,
  80            lhs_expr.repr(tcx),
  81            rhs_expr.repr(tcx));
  82
  83     check_expr(fcx, lhs_expr);
  84     let lhs_ty = fcx.resolve_type_vars_if_possible(fcx.expr_ty(lhs_expr));
  85
  86     // Annoyingly, SIMD ops don't fit into the PartialEq/PartialOrd
  87     // traits, because their return type is not bool. Perhaps this
  88     // should change, but for now if LHS is SIMD we go down a
  89     // different path that bypassess all traits.
  90     if ty::type_is_simd(fcx.tcx(), lhs_ty) {
  91         check_expr_coercable_to_type(fcx, rhs_expr, lhs_ty);
  92         let rhs_ty = fcx.resolve_type_vars_if_possible(fcx.expr_ty(lhs_expr));
  93         let return_ty = enforce_builtin_binop_types(fcx, lhs_expr, lhs_ty, rhs_expr, rhs_ty, op);
  94         fcx.write_ty(expr.id, return_ty);
  95         return;
  96     }
  97
  98     match BinOpCategory::from(op) {
  99         BinOpCategory::Shortcircuit => {
 100             // && and || are a simple case.
 101             demand::suptype(fcx, lhs_expr.span, ty::mk_bool(tcx), lhs_ty);
 102             check_expr_coercable_to_type(fcx, rhs_expr, ty::mk_bool(tcx));
 103             fcx.write_ty(expr.id, ty::mk_bool(tcx));
 104         }
 105         _ => {
 106             // Otherwise, we always treat operators as if they are
 107             // overloaded. This is the way to be most flexible w/r/t
 108             // types that get inferred.
 109             let (rhs_ty, return_ty) =
 110                 check_overloaded_binop(fcx, expr, lhs_expr, lhs_ty, rhs_expr, op);
 111
 112             // Supply type inference hints if relevant. Probably these
 113             // hints should be enforced during select as part of the
 114             // `consider_unification_despite_ambiguity` routine, but this
 115             // more convenient for now.
 116             //
 117             // The basic idea is to help type inference by taking
 118             // advantage of things we know about how the impls for
 119             // scalar types are arranged. This is important in a
 120             // scenario like `1_u32 << 2`, because it lets us quickly
 121             // deduce that the result type should be `u32`, even
 122             // though we don't know yet what type 2 has and hence
 123             // can't pin this down to a specific impl.
 124             let rhs_ty = fcx.resolve_type_vars_if_possible(rhs_ty);
 125             if
 126                 !ty::type_is_ty_var(lhs_ty) &&
 127                 !ty::type_is_ty_var(rhs_ty) &&
 128                 is_builtin_binop(fcx.tcx(), lhs_ty, rhs_ty, op)
 129             {
 130                 let builtin_return_ty =
 131                     enforce_builtin_binop_types(fcx, lhs_expr, lhs_ty, rhs_expr, rhs_ty, op);
 132                 demand::suptype(fcx, expr.span, builtin_return_ty, return_ty);
 133             }
 134
 135             fcx.write_ty(expr.id, return_ty);
 136         }
 137     }
 138 }
 139
 140 fn enforce_builtin_binop_types<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 141                                          lhs_expr: &'tcx ast::Expr,
 142                                          lhs_ty: Ty<'tcx>,
 143                                          rhs_expr: &'tcx ast::Expr,
 144                                          rhs_ty: Ty<'tcx>,
 145                                          op: ast::BinOp)
 146                                          -> Ty<'tcx>
 147 {
 148     debug_assert!(is_builtin_binop(fcx.tcx(), lhs_ty, rhs_ty, op));
 149
 150     let tcx = fcx.tcx();
 151     match BinOpCategory::from(op) {
 152         BinOpCategory::Shortcircuit => {
 153             demand::suptype(fcx, lhs_expr.span, ty::mk_bool(tcx), lhs_ty);
 154             demand::suptype(fcx, rhs_expr.span, ty::mk_bool(tcx), rhs_ty);
 155             ty::mk_bool(tcx)
 156         }
 157
 158         BinOpCategory::Shift => {
 159             // For integers, the shift amount can be of any integral
 160             // type. For simd, the type must match exactly.
 161             if ty::type_is_simd(tcx, lhs_ty) {
 162                 demand::suptype(fcx, rhs_expr.span, lhs_ty, rhs_ty);
 163             }
 164
 165             // result type is same as LHS always
 166             lhs_ty
 167         }
 168
 169         BinOpCategory::Math |
 170         BinOpCategory::Bitwise => {
 171             // both LHS and RHS and result will have the same type
 172             demand::suptype(fcx, rhs_expr.span, lhs_ty, rhs_ty);
 173             lhs_ty
 174         }
 175
 176         BinOpCategory::Comparison => {
 177             // both LHS and RHS and result will have the same type
 178             demand::suptype(fcx, rhs_expr.span, lhs_ty, rhs_ty);
 179
 180             // if this is simd, result is same as lhs, else bool
 181             if ty::type_is_simd(tcx, lhs_ty) {
 182                 let unit_ty = ty::simd_type(tcx, lhs_ty);
 183                 debug!("enforce_builtin_binop_types: lhs_ty={} unit_ty={}",
 184                        lhs_ty.repr(tcx),
 185                        unit_ty.repr(tcx));
 186                 if !ty::type_is_integral(unit_ty) {
 187                     tcx.sess.span_err(
 188                         lhs_expr.span,
 189                         &format!("binary comparison operation `{}` not supported \
 190                                   for floating point SIMD vector `{}`",
 191                                  ast_util::binop_to_string(op.node),
 192                                  lhs_ty.user_string(tcx)));
 193                     tcx.types.err
 194                 } else {
 195                     lhs_ty
 196                 }
 197             } else {
 198                 ty::mk_bool(tcx)
 199             }
 200         }
 201     }
 202 }
 203
 204 fn check_overloaded_binop<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 205                                     expr: &'tcx ast::Expr,
 206                                     lhs_expr: &'tcx ast::Expr,
 207                                     lhs_ty: Ty<'tcx>,
 208                                     rhs_expr: &'tcx ast::Expr,
 209                                     op: ast::BinOp)
 210                                     -> (Ty<'tcx>, Ty<'tcx>)
 211 {
 212     debug!("check_overloaded_binop(expr.id={}, lhs_ty={})",
 213            expr.id,
 214            lhs_ty.repr(fcx.tcx()));
 215
 216     let (name, trait_def_id) = name_and_trait_def_id(fcx, op);
 217
 218     // NB: As we have not yet type-checked the RHS, we don't have the
 219     // type at hand. Make a variable to represent it. The whole reason
 220     // for this indirection is so that, below, we can check the expr
 221     // using this variable as the expected type, which sometimes lets
 222     // us do better coercions than we would be able to do otherwise,
 223     // particularly for things like `String + &String`.
 224     let rhs_ty_var = fcx.infcx().next_ty_var();
 225
 226     let return_ty = match lookup_op_method(fcx, expr, lhs_ty, vec![rhs_ty_var],
 227                                            token::intern(name), trait_def_id,
 228                                            lhs_expr) {
 229         Ok(return_ty) => return_ty,
 230         Err(()) => {
 231             // error types are considered "builtin"
 232             if !ty::type_is_error(lhs_ty) {
 233                 span_err!(fcx.tcx().sess, lhs_expr.span, E0369,
 234                           "binary operation `{}` cannot be applied to type `{}`",
 235                           ast_util::binop_to_string(op.node),
 236                           lhs_ty.user_string(fcx.tcx()));
 237             }
 238             fcx.tcx().types.err
 239         }
 240     };
 241
 242     // see `NB` above
 243     check_expr_coercable_to_type(fcx, rhs_expr, rhs_ty_var);
 244
 245     (rhs_ty_var, return_ty)
 246 }
 247
 248 pub fn check_user_unop<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 249                                  op_str: &str,
 250                                  mname: &str,
 251                                  trait_did: Option<ast::DefId>,
 252                                  ex: &'tcx ast::Expr,
 253                                  operand_expr: &'tcx ast::Expr,
 254                                  operand_ty: Ty<'tcx>,
 255                                  op: ast::UnOp)
 256                                  -> Ty<'tcx>
 257 {
 258     assert!(ast_util::is_by_value_unop(op));
 259     match lookup_op_method(fcx, ex, operand_ty, vec![],
 260                            token::intern(mname), trait_did,
 261                            operand_expr) {
 262         Ok(t) => t,
 263         Err(()) => {
 264             fcx.type_error_message(ex.span, |actual| {
 265                 format!("cannot apply unary operator `{}` to type `{}`",
 266                         op_str, actual)
 267             }, operand_ty, None);
 268             fcx.tcx().types.err
 269         }
 270     }
 271 }
 272
 273 fn name_and_trait_def_id(fcx: &FnCtxt, op: ast::BinOp) -> (&'static str, Option<ast::DefId>) {
 274     let lang = &fcx.tcx().lang_items;
 275     match op.node {
 276         ast::BiAdd => ("add", lang.add_trait()),
 277         ast::BiSub => ("sub", lang.sub_trait()),
 278         ast::BiMul => ("mul", lang.mul_trait()),
 279         ast::BiDiv => ("div", lang.div_trait()),
 280         ast::BiRem => ("rem", lang.rem_trait()),
 281         ast::BiBitXor => ("bitxor", lang.bitxor_trait()),
 282         ast::BiBitAnd => ("bitand", lang.bitand_trait()),
 283         ast::BiBitOr => ("bitor", lang.bitor_trait()),
 284         ast::BiShl => ("shl", lang.shl_trait()),
 285         ast::BiShr => ("shr", lang.shr_trait()),
 286         ast::BiLt => ("lt", lang.ord_trait()),
 287         ast::BiLe => ("le", lang.ord_trait()),
 288         ast::BiGe => ("ge", lang.ord_trait()),
 289         ast::BiGt => ("gt", lang.ord_trait()),
 290         ast::BiEq => ("eq", lang.eq_trait()),
 291         ast::BiNe => ("ne", lang.eq_trait()),
 292         ast::BiAnd | ast::BiOr => {
 293             fcx.tcx().sess.span_bug(op.span, "&& and || are not overloadable")
 294         }
 295     }
 296 }
 297
 298 fn lookup_op_method<'a, 'tcx>(fcx: &'a FnCtxt<'a, 'tcx>,
 299                               expr: &'tcx ast::Expr,
 300                               lhs_ty: Ty<'tcx>,
 301                               other_tys: Vec<Ty<'tcx>>,
 302                               opname: ast::Name,
 303                               trait_did: Option<ast::DefId>,
 304                               lhs_expr: &'a ast::Expr)
 305                               -> Result<Ty<'tcx>,()>
 306 {
 307     debug!("lookup_op_method(expr={}, lhs_ty={}, opname={:?}, trait_did={}, lhs_expr={})",
 308            expr.repr(fcx.tcx()),
 309            lhs_ty.repr(fcx.tcx()),
 310            opname,
 311            trait_did.repr(fcx.tcx()),
 312            lhs_expr.repr(fcx.tcx()));
 313
 314     let method = match trait_did {
 315         Some(trait_did) => {
 316             method::lookup_in_trait_adjusted(fcx,
 317                                              expr.span,
 318                                              Some(lhs_expr),
 319                                              opname,
 320                                              trait_did,
 321                                              0,
 322                                              false,
 323                                              lhs_ty,
 324                                              Some(other_tys))
 325         }
 326         None => None
 327     };
 328
 329     match method {
 330         Some(method) => {
 331             let method_ty = method.ty;
 332
 333             // HACK(eddyb) Fully qualified path to work around a resolve bug.
 334             let method_call = ::middle::ty::MethodCall::expr(expr.id);
 335             fcx.inh.method_map.borrow_mut().insert(method_call, method);
 336
 337             // extract return type for method; all late bound regions
 338             // should have been instantiated by now
 339             let ret_ty = ty::ty_fn_ret(method_ty);
 340             Ok(ty::no_late_bound_regions(fcx.tcx(), &ret_ty).unwrap().unwrap())
 341         }
 342         None => {
 343             Err(())
 344         }
 345     }
 346 }
 347
 348 // Binary operator categories. These categories summarize the behavior
 349 // with respect to the builtin operationrs supported.
 350 enum BinOpCategory {
 351     /// &&, || -- cannot be overridden
 352     Shortcircuit,
 353
 354     /// <<, >> -- when shifting a single integer, rhs can be any
 355     /// integer type. For simd, types must match.
 356     Shift,
 357
 358     /// +, -, etc -- takes equal types, produces same type as input,
 359     /// applicable to ints/floats/simd
 360     Math,
 361
 362     /// &, |, ^ -- takes equal types, produces same type as input,
 363     /// applicable to ints/floats/simd/bool
 364     Bitwise,
 365
 366     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 367     /// which produce the input type
 368     Comparison,
 369 }
 370
 371 impl BinOpCategory {
 372     fn from(op: ast::BinOp) -> BinOpCategory {
 373         match op.node {
 374             ast::BiShl | ast::BiShr =>
 375                 BinOpCategory::Shift,
 376
 377             ast::BiAdd |
 378             ast::BiSub |
 379             ast::BiMul |
 380             ast::BiDiv |
 381             ast::BiRem =>
 382                 BinOpCategory::Math,
 383
 384             ast::BiBitXor |
 385             ast::BiBitAnd |
 386             ast::BiBitOr =>
 387                 BinOpCategory::Bitwise,
 388
 389             ast::BiEq |
 390             ast::BiNe |
 391             ast::BiLt |
 392             ast::BiLe |
 393             ast::BiGe |
 394             ast::BiGt =>
 395                 BinOpCategory::Comparison,
 396
 397             ast::BiAnd |
 398             ast::BiOr =>
 399                 BinOpCategory::Shortcircuit,
 400         }
 401     }
 402 }
 403
 404 /// Returns true if this is a built-in arithmetic operation (e.g. u32
 405 /// + u32, i16x4 == i16x4) and false if these types would have to be
 406 /// overloaded to be legal. There are two reasons that we distinguish
 407 /// builtin operations from overloaded ones (vs trying to drive
 408 /// everything uniformly through the trait system and intrinsics or
 409 /// something like that):
 410 ///
 411 /// 1. Builtin operations can trivially be evaluated in constants.
 412 /// 2. For comparison operators applied to SIMD types the result is
 413 ///    not of type `bool`. For example, `i16x4==i16x4` yields a
 414 ///    type like `i16x4`. This means that the overloaded trait
 415 ///    `PartialEq` is not applicable.
 416 ///
 417 /// Reason #2 is the killer. I tried for a while to always use
 418 /// overloaded logic and just check the types in constants/trans after
 419 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 420 fn is_builtin_binop<'tcx>(cx: &ty::ctxt<'tcx>,
 421                           lhs: Ty<'tcx>,
 422                           rhs: Ty<'tcx>,
 423                           op: ast::BinOp)
 424                           -> bool
 425 {
 426     match BinOpCategory::from(op) {
 427         BinOpCategory::Shortcircuit => {
 428             true
 429         }
 430
 431         BinOpCategory::Shift => {
 432             ty::type_is_error(lhs) || ty::type_is_error(rhs) ||
 433                 ty::type_is_integral(lhs) && ty::type_is_integral(rhs) ||
 434                 ty::type_is_simd(cx, lhs) && ty::type_is_simd(cx, rhs)
 435         }
 436
 437         BinOpCategory::Math => {
 438             ty::type_is_error(lhs) || ty::type_is_error(rhs) ||
 439                 ty::type_is_integral(lhs) && ty::type_is_integral(rhs) ||
 440                 ty::type_is_floating_point(lhs) && ty::type_is_floating_point(rhs) ||
 441                 ty::type_is_simd(cx, lhs) && ty::type_is_simd(cx, rhs)
 442         }
 443
 444         BinOpCategory::Bitwise => {
 445             ty::type_is_error(lhs) || ty::type_is_error(rhs) ||
 446                 ty::type_is_integral(lhs) && ty::type_is_integral(rhs) ||
 447                 ty::type_is_floating_point(lhs) && ty::type_is_floating_point(rhs) ||
 448                 ty::type_is_simd(cx, lhs) && ty::type_is_simd(cx, rhs) ||
 449                 ty::type_is_bool(lhs) && ty::type_is_bool(rhs)
 450         }
 451
 452         BinOpCategory::Comparison => {
 453             ty::type_is_error(lhs) || ty::type_is_error(rhs) ||
 454                 ty::type_is_scalar(lhs) && ty::type_is_scalar(rhs) ||
 455                 ty::type_is_simd(cx, lhs) && ty::type_is_simd(cx, rhs)
 456         }
 457     }
 458 }
 459