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