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