clippy_lints/src/consts.rs

   1 #![allow(clippy::float_cmp)]
   2
   3 use crate::utils::{clip, higher, sext, unsext};
   4 use if_chain::if_chain;
   5 use rustc::hir::def::{DefKind, Res};
   6 use rustc::hir::*;
   7 use rustc::lint::LateContext;
   8 use rustc::ty::subst::{Subst, SubstsRef};
   9 use rustc::ty::{self, Instance, Ty, TyCtxt};
  10 use rustc::{bug, span_bug};
  11 use rustc_data_structures::sync::Lrc;
  12 use std::cmp::Ordering::{self, Equal};
  13 use std::cmp::PartialOrd;
  14 use std::convert::TryFrom;
  15 use std::convert::TryInto;
  16 use std::hash::{Hash, Hasher};
  17 use syntax::ast::{FloatTy, LitKind};
  18 use syntax_pos::symbol::{LocalInternedString, Symbol};
  19
  20 /// A `LitKind`-like enum to fold constant `Expr`s into.
  21 #[derive(Debug, Clone)]
  22 pub enum Constant {
  23     /// A `String` (e.g., "abc").
  24     Str(String),
  25     /// A binary string (e.g., `b"abc"`).
  26     Binary(Lrc<Vec<u8>>),
  27     /// A single `char` (e.g., `'a'`).
  28     Char(char),
  29     /// An integer's bit representation.
  30     Int(u128),
  31     /// An `f32`.
  32     F32(f32),
  33     /// An `f64`.
  34     F64(f64),
  35     /// `true` or `false`.
  36     Bool(bool),
  37     /// An array of constants.
  38     Vec(Vec<Constant>),
  39     /// Also an array, but with only one constant, repeated N times.
  40     Repeat(Box<Constant>, u64),
  41     /// A tuple of constants.
  42     Tuple(Vec<Constant>),
  43     /// A raw pointer.
  44     RawPtr(u128),
  45     /// A literal with syntax error.
  46     Err(Symbol),
  47 }
  48
  49 impl PartialEq for Constant {
  50     fn eq(&self, other: &Self) -> bool {
  51         match (self, other) {
  52             (&Constant::Str(ref ls), &Constant::Str(ref rs)) => ls == rs,
  53             (&Constant::Binary(ref l), &Constant::Binary(ref r)) => l == r,
  54             (&Constant::Char(l), &Constant::Char(r)) => l == r,
  55             (&Constant::Int(l), &Constant::Int(r)) => l == r,
  56             (&Constant::F64(l), &Constant::F64(r)) => {
  57                 // We want `Fw32 == FwAny` and `FwAny == Fw64`, and by transitivity we must have
  58                 // `Fw32 == Fw64`, so don’t compare them.
  59                 // `to_bits` is required to catch non-matching 0.0, -0.0, and NaNs.
  60                 l.to_bits() == r.to_bits()
  61             },
  62             (&Constant::F32(l), &Constant::F32(r)) => {
  63                 // We want `Fw32 == FwAny` and `FwAny == Fw64`, and by transitivity we must have
  64                 // `Fw32 == Fw64`, so don’t compare them.
  65                 // `to_bits` is required to catch non-matching 0.0, -0.0, and NaNs.
  66                 f64::from(l).to_bits() == f64::from(r).to_bits()
  67             },
  68             (&Constant::Bool(l), &Constant::Bool(r)) => l == r,
  69             (&Constant::Vec(ref l), &Constant::Vec(ref r)) | (&Constant::Tuple(ref l), &Constant::Tuple(ref r)) => {
  70                 l == r
  71             },
  72             (&Constant::Repeat(ref lv, ref ls), &Constant::Repeat(ref rv, ref rs)) => ls == rs && lv == rv,
  73             // TODO: are there inter-type equalities?
  74             _ => false,
  75         }
  76     }
  77 }
  78
  79 impl Hash for Constant {
  80     fn hash<H>(&self, state: &mut H)
  81     where
  82         H: Hasher,
  83     {
  84         std::mem::discriminant(self).hash(state);
  85         match *self {
  86             Constant::Str(ref s) => {
  87                 s.hash(state);
  88             },
  89             Constant::Binary(ref b) => {
  90                 b.hash(state);
  91             },
  92             Constant::Char(c) => {
  93                 c.hash(state);
  94             },
  95             Constant::Int(i) => {
  96                 i.hash(state);
  97             },
  98             Constant::F32(f) => {
  99                 f64::from(f).to_bits().hash(state);
 100             },
 101             Constant::F64(f) => {
 102                 f.to_bits().hash(state);
 103             },
 104             Constant::Bool(b) => {
 105                 b.hash(state);
 106             },
 107             Constant::Vec(ref v) | Constant::Tuple(ref v) => {
 108                 v.hash(state);
 109             },
 110             Constant::Repeat(ref c, l) => {
 111                 c.hash(state);
 112                 l.hash(state);
 113             },
 114             Constant::RawPtr(u) => {
 115                 u.hash(state);
 116             },
 117             Constant::Err(ref s) => {
 118                 s.hash(state);
 119             },
 120         }
 121     }
 122 }
 123
 124 impl Constant {
 125     pub fn partial_cmp(tcx: TyCtxt<'_, '_, '_>, cmp_type: Ty<'_>, left: &Self, right: &Self) -> Option<Ordering> {
 126         match (left, right) {
 127             (&Constant::Str(ref ls), &Constant::Str(ref rs)) => Some(ls.cmp(rs)),
 128             (&Constant::Char(ref l), &Constant::Char(ref r)) => Some(l.cmp(r)),
 129             (&Constant::Int(l), &Constant::Int(r)) => {
 130                 if let ty::Int(int_ty) = cmp_type.sty {
 131                     Some(sext(tcx, l, int_ty).cmp(&sext(tcx, r, int_ty)))
 132                 } else {
 133                     Some(l.cmp(&r))
 134                 }
 135             },
 136             (&Constant::F64(l), &Constant::F64(r)) => l.partial_cmp(&r),
 137             (&Constant::F32(l), &Constant::F32(r)) => l.partial_cmp(&r),
 138             (&Constant::Bool(ref l), &Constant::Bool(ref r)) => Some(l.cmp(r)),
 139             (&Constant::Tuple(ref l), &Constant::Tuple(ref r)) | (&Constant::Vec(ref l), &Constant::Vec(ref r)) => l
 140                 .iter()
 141                 .zip(r.iter())
 142                 .map(|(li, ri)| Self::partial_cmp(tcx, cmp_type, li, ri))
 143                 .find(|r| r.map_or(true, |o| o != Ordering::Equal))
 144                 .unwrap_or_else(|| Some(l.len().cmp(&r.len()))),
 145             (&Constant::Repeat(ref lv, ref ls), &Constant::Repeat(ref rv, ref rs)) => {
 146                 match Self::partial_cmp(tcx, cmp_type, lv, rv) {
 147                     Some(Equal) => Some(ls.cmp(rs)),
 148                     x => x,
 149                 }
 150             },
 151             // TODO: are there any useful inter-type orderings?
 152             _ => None,
 153         }
 154     }
 155 }
 156
 157 /// Parses a `LitKind` to a `Constant`.
 158 pub fn lit_to_constant<'tcx>(lit: &LitKind, ty: Ty<'tcx>) -> Constant {
 159     use syntax::ast::*;
 160
 161     match *lit {
 162         LitKind::Str(ref is, _) => Constant::Str(is.to_string()),
 163         LitKind::Byte(b) => Constant::Int(u128::from(b)),
 164         LitKind::ByteStr(ref s) => Constant::Binary(Lrc::clone(s)),
 165         LitKind::Char(c) => Constant::Char(c),
 166         LitKind::Int(n, _) => Constant::Int(n),
 167         LitKind::Float(ref is, _) | LitKind::FloatUnsuffixed(ref is) => match ty.sty {
 168             ty::Float(FloatTy::F32) => Constant::F32(is.as_str().parse().unwrap()),
 169             ty::Float(FloatTy::F64) => Constant::F64(is.as_str().parse().unwrap()),
 170             _ => bug!(),
 171         },
 172         LitKind::Bool(b) => Constant::Bool(b),
 173         LitKind::Err(s) => Constant::Err(s),
 174     }
 175 }
 176
 177 pub fn constant<'c, 'cc>(
 178     lcx: &LateContext<'c, 'cc>,
 179     tables: &'c ty::TypeckTables<'cc>,
 180     e: &Expr,
 181 ) -> Option<(Constant, bool)> {
 182     let mut cx = ConstEvalLateContext {
 183         lcx,
 184         tables,
 185         param_env: lcx.param_env,
 186         needed_resolution: false,
 187         substs: lcx.tcx.intern_substs(&[]),
 188     };
 189     cx.expr(e).map(|cst| (cst, cx.needed_resolution))
 190 }
 191
 192 pub fn constant_simple<'c, 'cc>(
 193     lcx: &LateContext<'c, 'cc>,
 194     tables: &'c ty::TypeckTables<'cc>,
 195     e: &Expr,
 196 ) -> Option<Constant> {
 197     constant(lcx, tables, e).and_then(|(cst, res)| if res { None } else { Some(cst) })
 198 }
 199
 200 /// Creates a `ConstEvalLateContext` from the given `LateContext` and `TypeckTables`.
 201 pub fn constant_context<'c, 'cc>(
 202     lcx: &'c LateContext<'c, 'cc>,
 203     tables: &'c ty::TypeckTables<'cc>,
 204 ) -> ConstEvalLateContext<'c, 'cc> {
 205     ConstEvalLateContext {
 206         lcx,
 207         tables,
 208         param_env: lcx.param_env,
 209         needed_resolution: false,
 210         substs: lcx.tcx.intern_substs(&[]),
 211     }
 212 }
 213
 214 pub struct ConstEvalLateContext<'a, 'tcx: 'a> {
 215     lcx: &'a LateContext<'a, 'tcx>,
 216     tables: &'a ty::TypeckTables<'tcx>,
 217     param_env: ty::ParamEnv<'tcx>,
 218     needed_resolution: bool,
 219     substs: SubstsRef<'tcx>,
 220 }
 221
 222 impl<'c, 'cc> ConstEvalLateContext<'c, 'cc> {
 223     /// Simple constant folding: Insert an expression, get a constant or none.
 224     pub fn expr(&mut self, e: &Expr) -> Option<Constant> {
 225         if let Some((ref cond, ref then, otherwise)) = higher::if_block(&e) {
 226             return self.ifthenelse(cond, then, otherwise);
 227         }
 228         match e.node {
 229             ExprKind::Path(ref qpath) => self.fetch_path(qpath, e.hir_id),
 230             ExprKind::Block(ref block, _) => self.block(block),
 231             ExprKind::Lit(ref lit) => Some(lit_to_constant(&lit.node, self.tables.expr_ty(e))),
 232             ExprKind::Array(ref vec) => self.multi(vec).map(Constant::Vec),
 233             ExprKind::Tup(ref tup) => self.multi(tup).map(Constant::Tuple),
 234             ExprKind::Repeat(ref value, _) => {
 235                 let n = match self.tables.expr_ty(e).sty {
 236                     ty::Array(_, n) => n.assert_usize(self.lcx.tcx).expect("array length"),
 237                     _ => span_bug!(e.span, "typeck error"),
 238                 };
 239                 self.expr(value).map(|v| Constant::Repeat(Box::new(v), n))
 240             },
 241             ExprKind::Unary(op, ref operand) => self.expr(operand).and_then(|o| match op {
 242                 UnNot => self.constant_not(&o, self.tables.expr_ty(e)),
 243                 UnNeg => self.constant_negate(&o, self.tables.expr_ty(e)),
 244                 UnDeref => Some(o),
 245             }),
 246             ExprKind::Binary(op, ref left, ref right) => self.binop(op, left, right),
 247             ExprKind::Call(ref callee, ref args) => {
 248                 // We only handle a few const functions for now.
 249                 if_chain! {
 250                     if args.is_empty();
 251                     if let ExprKind::Path(qpath) = &callee.node;
 252                     let res = self.tables.qpath_res(qpath, callee.hir_id);
 253                     if let Some(def_id) = res.opt_def_id();
 254                     let def_path = self.lcx.get_def_path(def_id)
 255                         .iter()
 256                         .map(LocalInternedString::get)
 257                         .collect::<Vec<_>>();
 258                     if let &["core", "num", impl_ty, "max_value"] = &def_path[..];
 259                     then {
 260                        let value = match impl_ty {
 261                            "<impl i8>" => i8::max_value() as u128,
 262                            "<impl i16>" => i16::max_value() as u128,
 263                            "<impl i32>" => i32::max_value() as u128,
 264                            "<impl i64>" => i64::max_value() as u128,
 265                            "<impl i128>" => i128::max_value() as u128,
 266                            _ => return None,
 267                        };
 268                        Some(Constant::Int(value))
 269                     }
 270                     else {
 271                         None
 272                     }
 273                 }
 274             },
 275             // TODO: add other expressions.
 276             _ => None,
 277         }
 278     }
 279
 280     #[allow(clippy::cast_possible_wrap)]
 281     fn constant_not(&self, o: &Constant, ty: Ty<'_>) -> Option<Constant> {
 282         use self::Constant::*;
 283         match *o {
 284             Bool(b) => Some(Bool(!b)),
 285             Int(value) => {
 286                 let value = !value;
 287                 match ty.sty {
 288                     ty::Int(ity) => Some(Int(unsext(self.lcx.tcx, value as i128, ity))),
 289                     ty::Uint(ity) => Some(Int(clip(self.lcx.tcx, value, ity))),
 290                     _ => None,
 291                 }
 292             },
 293             _ => None,
 294         }
 295     }
 296
 297     fn constant_negate(&self, o: &Constant, ty: Ty<'_>) -> Option<Constant> {
 298         use self::Constant::*;
 299         match *o {
 300             Int(value) => {
 301                 let ity = match ty.sty {
 302                     ty::Int(ity) => ity,
 303                     _ => return None,
 304                 };
 305                 // sign extend
 306                 let value = sext(self.lcx.tcx, value, ity);
 307                 let value = value.checked_neg()?;
 308                 // clear unused bits
 309                 Some(Int(unsext(self.lcx.tcx, value, ity)))
 310             },
 311             F32(f) => Some(F32(-f)),
 312             F64(f) => Some(F64(-f)),
 313             _ => None,
 314         }
 315     }
 316
 317     /// Create `Some(Vec![..])` of all constants, unless there is any
 318     /// non-constant part.
 319     fn multi(&mut self, vec: &[Expr]) -> Option<Vec<Constant>> {
 320         vec.iter().map(|elem| self.expr(elem)).collect::<Option<_>>()
 321     }
 322
 323     /// Lookup a possibly constant expression from a ExprKind::Path.
 324     fn fetch_path(&mut self, qpath: &QPath, id: HirId) -> Option<Constant> {
 325         use rustc::mir::interpret::GlobalId;
 326
 327         let res = self.tables.qpath_res(qpath, id);
 328         match res {
 329             Res::Def(DefKind::Const, def_id) | Res::Def(DefKind::AssocConst, def_id) => {
 330                 let substs = self.tables.node_substs(id);
 331                 let substs = if self.substs.is_empty() {
 332                     substs
 333                 } else {
 334                     substs.subst(self.lcx.tcx, self.substs)
 335                 };
 336                 let instance = Instance::resolve(self.lcx.tcx, self.param_env, def_id, substs)?;
 337                 let gid = GlobalId {
 338                     instance,
 339                     promoted: None,
 340                 };
 341
 342                 let result = self.lcx.tcx.const_eval(self.param_env.and(gid)).ok()?;
 343                 let result = miri_to_const(self.lcx.tcx, &result);
 344                 if result.is_some() {
 345                     self.needed_resolution = true;
 346                 }
 347                 result
 348             },
 349             // FIXME: cover all usable cases.
 350             _ => None,
 351         }
 352     }
 353
 354     /// A block can only yield a constant if it only has one constant expression.
 355     fn block(&mut self, block: &Block) -> Option<Constant> {
 356         if block.stmts.is_empty() {
 357             block.expr.as_ref().and_then(|b| self.expr(b))
 358         } else {
 359             None
 360         }
 361     }
 362
 363     fn ifthenelse(&mut self, cond: &Expr, then: &Expr, otherwise: Option<&Expr>) -> Option<Constant> {
 364         if let Some(Constant::Bool(b)) = self.expr(cond) {
 365             if b {
 366                 self.expr(&*then)
 367             } else {
 368                 otherwise.as_ref().and_then(|expr| self.expr(expr))
 369             }
 370         } else {
 371             None
 372         }
 373     }
 374
 375     fn binop(&mut self, op: BinOp, left: &Expr, right: &Expr) -> Option<Constant> {
 376         let l = self.expr(left)?;
 377         let r = self.expr(right);
 378         match (l, r) {
 379             (Constant::Int(l), Some(Constant::Int(r))) => match self.tables.expr_ty(left).sty {
 380                 ty::Int(ity) => {
 381                     let l = sext(self.lcx.tcx, l, ity);
 382                     let r = sext(self.lcx.tcx, r, ity);
 383                     let zext = |n: i128| Constant::Int(unsext(self.lcx.tcx, n, ity));
 384                     match op.node {
 385                         BinOpKind::Add => l.checked_add(r).map(zext),
 386                         BinOpKind::Sub => l.checked_sub(r).map(zext),
 387                         BinOpKind::Mul => l.checked_mul(r).map(zext),
 388                         BinOpKind::Div if r != 0 => l.checked_div(r).map(zext),
 389                         BinOpKind::Rem if r != 0 => l.checked_rem(r).map(zext),
 390                         BinOpKind::Shr => l.checked_shr(r.try_into().expect("invalid shift")).map(zext),
 391                         BinOpKind::Shl => l.checked_shl(r.try_into().expect("invalid shift")).map(zext),
 392                         BinOpKind::BitXor => Some(zext(l ^ r)),
 393                         BinOpKind::BitOr => Some(zext(l | r)),
 394                         BinOpKind::BitAnd => Some(zext(l & r)),
 395                         BinOpKind::Eq => Some(Constant::Bool(l == r)),
 396                         BinOpKind::Ne => Some(Constant::Bool(l != r)),
 397                         BinOpKind::Lt => Some(Constant::Bool(l < r)),
 398                         BinOpKind::Le => Some(Constant::Bool(l <= r)),
 399                         BinOpKind::Ge => Some(Constant::Bool(l >= r)),
 400                         BinOpKind::Gt => Some(Constant::Bool(l > r)),
 401                         _ => None,
 402                     }
 403                 },
 404                 ty::Uint(_) => match op.node {
 405                     BinOpKind::Add => l.checked_add(r).map(Constant::Int),
 406                     BinOpKind::Sub => l.checked_sub(r).map(Constant::Int),
 407                     BinOpKind::Mul => l.checked_mul(r).map(Constant::Int),
 408                     BinOpKind::Div => l.checked_div(r).map(Constant::Int),
 409                     BinOpKind::Rem => l.checked_rem(r).map(Constant::Int),
 410                     BinOpKind::Shr => l.checked_shr(r.try_into().expect("shift too large")).map(Constant::Int),
 411                     BinOpKind::Shl => l.checked_shl(r.try_into().expect("shift too large")).map(Constant::Int),
 412                     BinOpKind::BitXor => Some(Constant::Int(l ^ r)),
 413                     BinOpKind::BitOr => Some(Constant::Int(l | r)),
 414                     BinOpKind::BitAnd => Some(Constant::Int(l & r)),
 415                     BinOpKind::Eq => Some(Constant::Bool(l == r)),
 416                     BinOpKind::Ne => Some(Constant::Bool(l != r)),
 417                     BinOpKind::Lt => Some(Constant::Bool(l < r)),
 418                     BinOpKind::Le => Some(Constant::Bool(l <= r)),
 419                     BinOpKind::Ge => Some(Constant::Bool(l >= r)),
 420                     BinOpKind::Gt => Some(Constant::Bool(l > r)),
 421                     _ => None,
 422                 },
 423                 _ => None,
 424             },
 425             (Constant::F32(l), Some(Constant::F32(r))) => match op.node {
 426                 BinOpKind::Add => Some(Constant::F32(l + r)),
 427                 BinOpKind::Sub => Some(Constant::F32(l - r)),
 428                 BinOpKind::Mul => Some(Constant::F32(l * r)),
 429                 BinOpKind::Div => Some(Constant::F32(l / r)),
 430                 BinOpKind::Rem => Some(Constant::F32(l % r)),
 431                 BinOpKind::Eq => Some(Constant::Bool(l == r)),
 432                 BinOpKind::Ne => Some(Constant::Bool(l != r)),
 433                 BinOpKind::Lt => Some(Constant::Bool(l < r)),
 434                 BinOpKind::Le => Some(Constant::Bool(l <= r)),
 435                 BinOpKind::Ge => Some(Constant::Bool(l >= r)),
 436                 BinOpKind::Gt => Some(Constant::Bool(l > r)),
 437                 _ => None,
 438             },
 439             (Constant::F64(l), Some(Constant::F64(r))) => match op.node {
 440                 BinOpKind::Add => Some(Constant::F64(l + r)),
 441                 BinOpKind::Sub => Some(Constant::F64(l - r)),
 442                 BinOpKind::Mul => Some(Constant::F64(l * r)),
 443                 BinOpKind::Div => Some(Constant::F64(l / r)),
 444                 BinOpKind::Rem => Some(Constant::F64(l % r)),
 445                 BinOpKind::Eq => Some(Constant::Bool(l == r)),
 446                 BinOpKind::Ne => Some(Constant::Bool(l != r)),
 447                 BinOpKind::Lt => Some(Constant::Bool(l < r)),
 448                 BinOpKind::Le => Some(Constant::Bool(l <= r)),
 449                 BinOpKind::Ge => Some(Constant::Bool(l >= r)),
 450                 BinOpKind::Gt => Some(Constant::Bool(l > r)),
 451                 _ => None,
 452             },
 453             (l, r) => match (op.node, l, r) {
 454                 (BinOpKind::And, Constant::Bool(false), _) => Some(Constant::Bool(false)),
 455                 (BinOpKind::Or, Constant::Bool(true), _) => Some(Constant::Bool(true)),
 456                 (BinOpKind::And, Constant::Bool(true), Some(r)) | (BinOpKind::Or, Constant::Bool(false), Some(r)) => {
 457                     Some(r)
 458                 },
 459                 (BinOpKind::BitXor, Constant::Bool(l), Some(Constant::Bool(r))) => Some(Constant::Bool(l ^ r)),
 460                 (BinOpKind::BitAnd, Constant::Bool(l), Some(Constant::Bool(r))) => Some(Constant::Bool(l & r)),
 461                 (BinOpKind::BitOr, Constant::Bool(l), Some(Constant::Bool(r))) => Some(Constant::Bool(l | r)),
 462                 _ => None,
 463             },
 464         }
 465     }
 466 }
 467
 468 pub fn miri_to_const<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, result: &ty::Const<'tcx>) -> Option<Constant> {
 469     use rustc::mir::interpret::{ConstValue, Scalar};
 470     match result.val {
 471         ConstValue::Scalar(Scalar::Bits { bits: b, .. }) => match result.ty.sty {
 472             ty::Bool => Some(Constant::Bool(b == 1)),
 473             ty::Uint(_) | ty::Int(_) => Some(Constant::Int(b)),
 474             ty::Float(FloatTy::F32) => Some(Constant::F32(f32::from_bits(
 475                 b.try_into().expect("invalid f32 bit representation"),
 476             ))),
 477             ty::Float(FloatTy::F64) => Some(Constant::F64(f64::from_bits(
 478                 b.try_into().expect("invalid f64 bit representation"),
 479             ))),
 480             ty::RawPtr(type_and_mut) => {
 481                 if let ty::Uint(_) = type_and_mut.ty.sty {
 482                     return Some(Constant::RawPtr(b));
 483                 }
 484                 None
 485             },
 486             // FIXME: implement other conversions.
 487             _ => None,
 488         },
 489         ConstValue::Slice(Scalar::Ptr(ptr), n) => match result.ty.sty {
 490             ty::Ref(_, tam, _) => match tam.sty {
 491                 ty::Str => {
 492                     let alloc = tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
 493                     let offset = ptr.offset.bytes().try_into().expect("too-large pointer offset");
 494                     let n = usize::try_from(n).unwrap();
 495                     String::from_utf8(alloc.bytes[offset..(offset + n)].to_owned())
 496                         .ok()
 497                         .map(Constant::Str)
 498                 },
 499                 _ => None,
 500             },
 501             _ => None,
 502         },
 503         // FIXME: implement other conversions.
 504         _ => None,
 505     }
 506 }