clippy_lints/src/consts.rs

   1 #![allow(clippy::float_cmp)]
   2
   3 use crate::utils::{clip, get_def_path, sext, unsext};
   4 use if_chain::if_chain;
   5 use rustc::hir::def::Def;
   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::ptr::P;
  19 use syntax_pos::symbol::{LocalInternedString, Symbol};
  20
  21 /// A `LitKind`-like enum to fold constant `Expr`s into.
  22 #[derive(Debug, Clone)]
  23 pub enum Constant {
  24     /// A `String` (e.g., "abc").
  25     Str(String),
  26     /// A binary string (e.g., `b"abc"`).
  27     Binary(Lrc<Vec<u8>>),
  28     /// A single `char` (e.g., `'a'`).
  29     Char(char),
  30     /// An integer's bit representation.
  31     Int(u128),
  32     /// An `f32`.
  33     F32(f32),
  34     /// An `f64`.
  35     F64(f64),
  36     /// `true` or `false`.
  37     Bool(bool),
  38     /// An array of constants.
  39     Vec(Vec<Constant>),
  40     /// Also an array, but with only one constant, repeated N times.
  41     Repeat(Box<Constant>, u64),
  42     /// A tuple of constants.
  43     Tuple(Vec<Constant>),
  44     /// A raw pointer.
  45     RawPtr(u128),
  46     /// A literal with syntax error.
  47     Err(Symbol),
  48 }
  49
  50 impl PartialEq for Constant {
  51     fn eq(&self, other: &Self) -> bool {
  52         match (self, other) {
  53             (&Constant::Str(ref ls), &Constant::Str(ref rs)) => ls == rs,
  54             (&Constant::Binary(ref l), &Constant::Binary(ref r)) => l == r,
  55             (&Constant::Char(l), &Constant::Char(r)) => l == r,
  56             (&Constant::Int(l), &Constant::Int(r)) => l == r,
  57             (&Constant::F64(l), &Constant::F64(r)) => {
  58                 // We want `Fw32 == FwAny` and `FwAny == Fw64`, and by transitivity we must have
  59                 // `Fw32 == Fw64`, so don’t compare them.
  60                 // `to_bits` is required to catch non-matching 0.0, -0.0, and NaNs.
  61                 l.to_bits() == r.to_bits()
  62             },
  63             (&Constant::F32(l), &Constant::F32(r)) => {
  64                 // We want `Fw32 == FwAny` and `FwAny == Fw64`, and by transitivity we must have
  65                 // `Fw32 == Fw64`, so don’t compare them.
  66                 // `to_bits` is required to catch non-matching 0.0, -0.0, and NaNs.
  67                 f64::from(l).to_bits() == f64::from(r).to_bits()
  68             },
  69             (&Constant::Bool(l), &Constant::Bool(r)) => l == r,
  70             (&Constant::Vec(ref l), &Constant::Vec(ref r)) | (&Constant::Tuple(ref l), &Constant::Tuple(ref r)) => {
  71                 l == r
  72             },
  73             (&Constant::Repeat(ref lv, ref ls), &Constant::Repeat(ref rv, ref rs)) => ls == rs && lv == rv,
  74             // TODO: are there inter-type equalities?
  75             _ => false,
  76         }
  77     }
  78 }
  79
  80 impl Hash for Constant {
  81     fn hash<H>(&self, state: &mut H)
  82     where
  83         H: Hasher,
  84     {
  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         tcx: lcx.tcx,
 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: &LateContext<'c, 'cc>,
 203     tables: &'c ty::TypeckTables<'cc>,
 204 ) -> ConstEvalLateContext<'c, 'cc> {
 205     ConstEvalLateContext {
 206         tcx: lcx.tcx,
 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     tcx: TyCtxt<'a, 'tcx, '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         match e.node {
 226             ExprKind::Path(ref qpath) => self.fetch_path(qpath, e.hir_id),
 227             ExprKind::Block(ref block, _) => self.block(block),
 228             ExprKind::If(ref cond, ref then, ref otherwise) => self.ifthenelse(cond, then, otherwise),
 229             ExprKind::Lit(ref lit) => Some(lit_to_constant(&lit.node, self.tables.expr_ty(e))),
 230             ExprKind::Array(ref vec) => self.multi(vec).map(Constant::Vec),
 231             ExprKind::Tup(ref tup) => self.multi(tup).map(Constant::Tuple),
 232             ExprKind::Repeat(ref value, _) => {
 233                 let n = match self.tables.expr_ty(e).sty {
 234                     ty::Array(_, n) => n.assert_usize(self.tcx).expect("array length"),
 235                     _ => span_bug!(e.span, "typeck error"),
 236                 };
 237                 self.expr(value).map(|v| Constant::Repeat(Box::new(v), n))
 238             },
 239             ExprKind::Unary(op, ref operand) => self.expr(operand).and_then(|o| match op {
 240                 UnNot => self.constant_not(&o, self.tables.expr_ty(e)),
 241                 UnNeg => self.constant_negate(&o, self.tables.expr_ty(e)),
 242                 UnDeref => Some(o),
 243             }),
 244             ExprKind::Binary(op, ref left, ref right) => self.binop(op, left, right),
 245             ExprKind::Call(ref callee, ref args) => {
 246                 // We only handle a few const functions for now.
 247                 if_chain! {
 248                     if args.is_empty();
 249                     if let ExprKind::Path(qpath) = &callee.node;
 250                     let def = self.tables.qpath_def(qpath, callee.hir_id);
 251                     if let Some(def_id) = def.opt_def_id();
 252                     let def_path = get_def_path(self.tcx, def_id)
 253                         .iter()
 254                         .map(LocalInternedString::get)
 255                         .collect::<Vec<_>>();
 256                     if let &["core", "num", impl_ty, "max_value"] = &def_path[..];
 257                     then {
 258                        let value = match impl_ty {
 259                            "<impl i8>" => i8::max_value() as u128,
 260                            "<impl i16>" => i16::max_value() as u128,
 261                            "<impl i32>" => i32::max_value() as u128,
 262                            "<impl i64>" => i64::max_value() as u128,
 263                            "<impl i128>" => i128::max_value() as u128,
 264                            _ => return None,
 265                        };
 266                        Some(Constant::Int(value))
 267                     }
 268                     else {
 269                         None
 270                     }
 271                 }
 272             },
 273             // TODO: add other expressions.
 274             _ => None,
 275         }
 276     }
 277
 278     #[allow(clippy::cast_possible_wrap)]
 279     fn constant_not(&self, o: &Constant, ty: Ty<'_>) -> Option<Constant> {
 280         use self::Constant::*;
 281         match *o {
 282             Bool(b) => Some(Bool(!b)),
 283             Int(value) => {
 284                 let value = !value;
 285                 match ty.sty {
 286                     ty::Int(ity) => Some(Int(unsext(self.tcx, value as i128, ity))),
 287                     ty::Uint(ity) => Some(Int(clip(self.tcx, value, ity))),
 288                     _ => None,
 289                 }
 290             },
 291             _ => None,
 292         }
 293     }
 294
 295     fn constant_negate(&self, o: &Constant, ty: Ty<'_>) -> Option<Constant> {
 296         use self::Constant::*;
 297         match *o {
 298             Int(value) => {
 299                 let ity = match ty.sty {
 300                     ty::Int(ity) => ity,
 301                     _ => return None,
 302                 };
 303                 // sign extend
 304                 let value = sext(self.tcx, value, ity);
 305                 let value = value.checked_neg()?;
 306                 // clear unused bits
 307                 Some(Int(unsext(self.tcx, value, ity)))
 308             },
 309             F32(f) => Some(F32(-f)),
 310             F64(f) => Some(F64(-f)),
 311             _ => None,
 312         }
 313     }
 314
 315     /// Create `Some(Vec![..])` of all constants, unless there is any
 316     /// non-constant part.
 317     fn multi(&mut self, vec: &[Expr]) -> Option<Vec<Constant>> {
 318         vec.iter().map(|elem| self.expr(elem)).collect::<Option<_>>()
 319     }
 320
 321     /// Lookup a possibly constant expression from a ExprKind::Path.
 322     fn fetch_path(&mut self, qpath: &QPath, id: HirId) -> Option<Constant> {
 323         use rustc::mir::interpret::GlobalId;
 324
 325         let def = self.tables.qpath_def(qpath, id);
 326         match def {
 327             Def::Const(def_id) | Def::AssociatedConst(def_id) => {
 328                 let substs = self.tables.node_substs(id);
 329                 let substs = if self.substs.is_empty() {
 330                     substs
 331                 } else {
 332                     substs.subst(self.tcx, self.substs)
 333                 };
 334                 let instance = Instance::resolve(self.tcx, self.param_env, def_id, substs)?;
 335                 let gid = GlobalId {
 336                     instance,
 337                     promoted: None,
 338                 };
 339
 340                 let result = self.tcx.const_eval(self.param_env.and(gid)).ok()?;
 341                 let ret = miri_to_const(self.tcx, &result);
 342                 if ret.is_some() {
 343                     self.needed_resolution = true;
 344                 }
 345                 ret
 346             },
 347             // FIXME: cover all useable cases.
 348             _ => None,
 349         }
 350     }
 351
 352     /// A block can only yield a constant if it only has one constant expression.
 353     fn block(&mut self, block: &Block) -> Option<Constant> {
 354         if block.stmts.is_empty() {
 355             block.expr.as_ref().and_then(|b| self.expr(b))
 356         } else {
 357             None
 358         }
 359     }
 360
 361     fn ifthenelse(&mut self, cond: &Expr, then: &P<Expr>, otherwise: &Option<P<Expr>>) -> Option<Constant> {
 362         if let Some(Constant::Bool(b)) = self.expr(cond) {
 363             if b {
 364                 self.expr(&**then)
 365             } else {
 366                 otherwise.as_ref().and_then(|expr| self.expr(expr))
 367             }
 368         } else {
 369             None
 370         }
 371     }
 372
 373     fn binop(&mut self, op: BinOp, left: &Expr, right: &Expr) -> Option<Constant> {
 374         let l = self.expr(left)?;
 375         let r = self.expr(right);
 376         match (l, r) {
 377             (Constant::Int(l), Some(Constant::Int(r))) => match self.tables.expr_ty(left).sty {
 378                 ty::Int(ity) => {
 379                     let l = sext(self.tcx, l, ity);
 380                     let r = sext(self.tcx, r, ity);
 381                     let zext = |n: i128| Constant::Int(unsext(self.tcx, n, ity));
 382                     match op.node {
 383                         BinOpKind::Add => l.checked_add(r).map(zext),
 384                         BinOpKind::Sub => l.checked_sub(r).map(zext),
 385                         BinOpKind::Mul => l.checked_mul(r).map(zext),
 386                         BinOpKind::Div if r != 0 => l.checked_div(r).map(zext),
 387                         BinOpKind::Rem if r != 0 => l.checked_rem(r).map(zext),
 388                         BinOpKind::Shr => l.checked_shr(r.try_into().expect("invalid shift")).map(zext),
 389                         BinOpKind::Shl => l.checked_shl(r.try_into().expect("invalid shift")).map(zext),
 390                         BinOpKind::BitXor => Some(zext(l ^ r)),
 391                         BinOpKind::BitOr => Some(zext(l | r)),
 392                         BinOpKind::BitAnd => Some(zext(l & r)),
 393                         BinOpKind::Eq => Some(Constant::Bool(l == r)),
 394                         BinOpKind::Ne => Some(Constant::Bool(l != r)),
 395                         BinOpKind::Lt => Some(Constant::Bool(l < r)),
 396                         BinOpKind::Le => Some(Constant::Bool(l <= r)),
 397                         BinOpKind::Ge => Some(Constant::Bool(l >= r)),
 398                         BinOpKind::Gt => Some(Constant::Bool(l > r)),
 399                         _ => None,
 400                     }
 401                 },
 402                 ty::Uint(_) => match op.node {
 403                     BinOpKind::Add => l.checked_add(r).map(Constant::Int),
 404                     BinOpKind::Sub => l.checked_sub(r).map(Constant::Int),
 405                     BinOpKind::Mul => l.checked_mul(r).map(Constant::Int),
 406                     BinOpKind::Div => l.checked_div(r).map(Constant::Int),
 407                     BinOpKind::Rem => l.checked_rem(r).map(Constant::Int),
 408                     BinOpKind::Shr => l.checked_shr(r.try_into().expect("shift too large")).map(Constant::Int),
 409                     BinOpKind::Shl => l.checked_shl(r.try_into().expect("shift too large")).map(Constant::Int),
 410                     BinOpKind::BitXor => Some(Constant::Int(l ^ r)),
 411                     BinOpKind::BitOr => Some(Constant::Int(l | r)),
 412                     BinOpKind::BitAnd => Some(Constant::Int(l & r)),
 413                     BinOpKind::Eq => Some(Constant::Bool(l == r)),
 414                     BinOpKind::Ne => Some(Constant::Bool(l != r)),
 415                     BinOpKind::Lt => Some(Constant::Bool(l < r)),
 416                     BinOpKind::Le => Some(Constant::Bool(l <= r)),
 417                     BinOpKind::Ge => Some(Constant::Bool(l >= r)),
 418                     BinOpKind::Gt => Some(Constant::Bool(l > r)),
 419                     _ => None,
 420                 },
 421                 _ => None,
 422             },
 423             (Constant::F32(l), Some(Constant::F32(r))) => match op.node {
 424                 BinOpKind::Add => Some(Constant::F32(l + r)),
 425                 BinOpKind::Sub => Some(Constant::F32(l - r)),
 426                 BinOpKind::Mul => Some(Constant::F32(l * r)),
 427                 BinOpKind::Div => Some(Constant::F32(l / r)),
 428                 BinOpKind::Rem => Some(Constant::F32(l % r)),
 429                 BinOpKind::Eq => Some(Constant::Bool(l == r)),
 430                 BinOpKind::Ne => Some(Constant::Bool(l != r)),
 431                 BinOpKind::Lt => Some(Constant::Bool(l < r)),
 432                 BinOpKind::Le => Some(Constant::Bool(l <= r)),
 433                 BinOpKind::Ge => Some(Constant::Bool(l >= r)),
 434                 BinOpKind::Gt => Some(Constant::Bool(l > r)),
 435                 _ => None,
 436             },
 437             (Constant::F64(l), Some(Constant::F64(r))) => match op.node {
 438                 BinOpKind::Add => Some(Constant::F64(l + r)),
 439                 BinOpKind::Sub => Some(Constant::F64(l - r)),
 440                 BinOpKind::Mul => Some(Constant::F64(l * r)),
 441                 BinOpKind::Div => Some(Constant::F64(l / r)),
 442                 BinOpKind::Rem => Some(Constant::F64(l % r)),
 443                 BinOpKind::Eq => Some(Constant::Bool(l == r)),
 444                 BinOpKind::Ne => Some(Constant::Bool(l != r)),
 445                 BinOpKind::Lt => Some(Constant::Bool(l < r)),
 446                 BinOpKind::Le => Some(Constant::Bool(l <= r)),
 447                 BinOpKind::Ge => Some(Constant::Bool(l >= r)),
 448                 BinOpKind::Gt => Some(Constant::Bool(l > r)),
 449                 _ => None,
 450             },
 451             (l, r) => match (op.node, l, r) {
 452                 (BinOpKind::And, Constant::Bool(false), _) => Some(Constant::Bool(false)),
 453                 (BinOpKind::Or, Constant::Bool(true), _) => Some(Constant::Bool(true)),
 454                 (BinOpKind::And, Constant::Bool(true), Some(r)) | (BinOpKind::Or, Constant::Bool(false), Some(r)) => {
 455                     Some(r)
 456                 },
 457                 (BinOpKind::BitXor, Constant::Bool(l), Some(Constant::Bool(r))) => Some(Constant::Bool(l ^ r)),
 458                 (BinOpKind::BitAnd, Constant::Bool(l), Some(Constant::Bool(r))) => Some(Constant::Bool(l & r)),
 459                 (BinOpKind::BitOr, Constant::Bool(l), Some(Constant::Bool(r))) => Some(Constant::Bool(l | r)),
 460                 _ => None,
 461             },
 462         }
 463     }
 464 }
 465
 466 pub fn miri_to_const<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, result: &ty::Const<'tcx>) -> Option<Constant> {
 467     use rustc::mir::interpret::{ConstValue, Scalar};
 468     match result.val {
 469         ConstValue::Scalar(Scalar::Bits { bits: b, .. }) => match result.ty.sty {
 470             ty::Bool => Some(Constant::Bool(b == 1)),
 471             ty::Uint(_) | ty::Int(_) => Some(Constant::Int(b)),
 472             ty::Float(FloatTy::F32) => Some(Constant::F32(f32::from_bits(
 473                 b.try_into().expect("invalid f32 bit representation"),
 474             ))),
 475             ty::Float(FloatTy::F64) => Some(Constant::F64(f64::from_bits(
 476                 b.try_into().expect("invalid f64 bit representation"),
 477             ))),
 478             ty::RawPtr(type_and_mut) => {
 479                 if let ty::Uint(_) = type_and_mut.ty.sty {
 480                     return Some(Constant::RawPtr(b));
 481                 }
 482                 None
 483             },
 484             // FIXME: implement other conversions.
 485             _ => None,
 486         },
 487         ConstValue::Slice(Scalar::Ptr(ptr), n) => match result.ty.sty {
 488             ty::Ref(_, tam, _) => match tam.sty {
 489                 ty::Str => {
 490                     let alloc = tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
 491                     let offset = ptr.offset.bytes().try_into().expect("too-large pointer offset");
 492                     let n = usize::try_from(n).unwrap();
 493                     String::from_utf8(alloc.bytes[offset..(offset + n)].to_owned())
 494                         .ok()
 495                         .map(Constant::Str)
 496                 },
 497                 _ => None,
 498             },
 499             _ => None,
 500         },
 501         // FIXME: implement other conversions.
 502         _ => None,
 503     }
 504 }