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_ast::ast::{FloatTy, LitFloatType, LitKind};
   9 use rustc_data_structures::sync::Lrc;
  10 use rustc_hir::def::{DefKind, Res};
  11 use rustc_hir::{BinOp, BinOpKind, Block, Expr, ExprKind, HirId, QPath, UnOp};
  12 use rustc_lint::LateContext;
  13 use rustc_span::symbol::Symbol;
  14 use std::cmp::Ordering::{self, Equal};
  15 use std::convert::TryInto;
  16 use std::hash::{Hash, Hasher};
  17
  18 /// A `LitKind`-like enum to fold constant `Expr`s into.
  19 #[derive(Debug, Clone)]
  20 pub enum Constant {
  21     /// A `String` (e.g., "abc").
  22     Str(String),
  23     /// A binary string (e.g., `b"abc"`).
  24     Binary(Lrc<Vec<u8>>),
  25     /// A single `char` (e.g., `'a'`).
  26     Char(char),
  27     /// An integer's bit representation.
  28     Int(u128),
  29     /// An `f32`.
  30     F32(f32),
  31     /// An `f64`.
  32     F64(f64),
  33     /// `true` or `false`.
  34     Bool(bool),
  35     /// An array of constants.
  36     Vec(Vec<Constant>),
  37     /// Also an array, but with only one constant, repeated N times.
  38     Repeat(Box<Constant>, u64),
  39     /// A tuple of constants.
  40     Tuple(Vec<Constant>),
  41     /// A raw pointer.
  42     RawPtr(u128),
  43     /// A literal with syntax error.
  44     Err(Symbol),
  45 }
  46
  47 impl PartialEq for Constant {
  48     fn eq(&self, other: &Self) -> bool {
  49         match (self, other) {
  50             (&Self::Str(ref ls), &Self::Str(ref rs)) => ls == rs,
  51             (&Self::Binary(ref l), &Self::Binary(ref r)) => l == r,
  52             (&Self::Char(l), &Self::Char(r)) => l == r,
  53             (&Self::Int(l), &Self::Int(r)) => l == r,
  54             (&Self::F64(l), &Self::F64(r)) => {
  55                 // We want `Fw32 == FwAny` and `FwAny == Fw64`, and by transitivity we must have
  56                 // `Fw32 == Fw64`, so don’t compare them.
  57                 // `to_bits` is required to catch non-matching 0.0, -0.0, and NaNs.
  58                 l.to_bits() == r.to_bits()
  59             },
  60             (&Self::F32(l), &Self::F32(r)) => {
  61                 // We want `Fw32 == FwAny` and `FwAny == Fw64`, and by transitivity we must have
  62                 // `Fw32 == Fw64`, so don’t compare them.
  63                 // `to_bits` is required to catch non-matching 0.0, -0.0, and NaNs.
  64                 f64::from(l).to_bits() == f64::from(r).to_bits()
  65             },
  66             (&Self::Bool(l), &Self::Bool(r)) => l == r,
  67             (&Self::Vec(ref l), &Self::Vec(ref r)) | (&Self::Tuple(ref l), &Self::Tuple(ref r)) => l == r,
  68             (&Self::Repeat(ref lv, ref ls), &Self::Repeat(ref rv, ref rs)) => ls == rs && lv == rv,
  69             // TODO: are there inter-type equalities?
  70             _ => false,
  71         }
  72     }
  73 }
  74
  75 impl Hash for Constant {
  76     fn hash<H>(&self, state: &mut H)
  77     where
  78         H: Hasher,
  79     {
  80         std::mem::discriminant(self).hash(state);
  81         match *self {
  82             Self::Str(ref s) => {
  83                 s.hash(state);
  84             },
  85             Self::Binary(ref b) => {
  86                 b.hash(state);
  87             },
  88             Self::Char(c) => {
  89                 c.hash(state);
  90             },
  91             Self::Int(i) => {
  92                 i.hash(state);
  93             },
  94             Self::F32(f) => {
  95                 f64::from(f).to_bits().hash(state);
  96             },
  97             Self::F64(f) => {
  98                 f.to_bits().hash(state);
  99             },
 100             Self::Bool(b) => {
 101                 b.hash(state);
 102             },
 103             Self::Vec(ref v) | Self::Tuple(ref v) => {
 104                 v.hash(state);
 105             },
 106             Self::Repeat(ref c, l) => {
 107                 c.hash(state);
 108                 l.hash(state);
 109             },
 110             Self::RawPtr(u) => {
 111                 u.hash(state);
 112             },
 113             Self::Err(ref s) => {
 114                 s.hash(state);
 115             },
 116         }
 117     }
 118 }
 119
 120 impl Constant {
 121     pub fn partial_cmp(tcx: TyCtxt<'_>, cmp_type: Ty<'_>, left: &Self, right: &Self) -> Option<Ordering> {
 122         match (left, right) {
 123             (&Self::Str(ref ls), &Self::Str(ref rs)) => Some(ls.cmp(rs)),
 124             (&Self::Char(ref l), &Self::Char(ref r)) => Some(l.cmp(r)),
 125             (&Self::Int(l), &Self::Int(r)) => {
 126                 if let ty::Int(int_ty) = cmp_type.kind {
 127                     Some(sext(tcx, l, int_ty).cmp(&sext(tcx, r, int_ty)))
 128                 } else {
 129                     Some(l.cmp(&r))
 130                 }
 131             },
 132             (&Self::F64(l), &Self::F64(r)) => l.partial_cmp(&r),
 133             (&Self::F32(l), &Self::F32(r)) => l.partial_cmp(&r),
 134             (&Self::Bool(ref l), &Self::Bool(ref r)) => Some(l.cmp(r)),
 135             (&Self::Tuple(ref l), &Self::Tuple(ref r)) | (&Self::Vec(ref l), &Self::Vec(ref r)) => l
 136                 .iter()
 137                 .zip(r.iter())
 138                 .map(|(li, ri)| Self::partial_cmp(tcx, cmp_type, li, ri))
 139                 .find(|r| r.map_or(true, |o| o != Ordering::Equal))
 140                 .unwrap_or_else(|| Some(l.len().cmp(&r.len()))),
 141             (&Self::Repeat(ref lv, ref ls), &Self::Repeat(ref rv, ref rs)) => {
 142                 match Self::partial_cmp(tcx, cmp_type, lv, rv) {
 143                     Some(Equal) => Some(ls.cmp(rs)),
 144                     x => x,
 145                 }
 146             },
 147             // TODO: are there any useful inter-type orderings?
 148             _ => None,
 149         }
 150     }
 151 }
 152
 153 /// Parses a `LitKind` to a `Constant`.
 154 pub fn lit_to_constant(lit: &LitKind, ty: Option<Ty<'_>>) -> Constant {
 155     match *lit {
 156         LitKind::Str(ref is, _) => Constant::Str(is.to_string()),
 157         LitKind::Byte(b) => Constant::Int(u128::from(b)),
 158         LitKind::ByteStr(ref s) => Constant::Binary(Lrc::clone(s)),
 159         LitKind::Char(c) => Constant::Char(c),
 160         LitKind::Int(n, _) => Constant::Int(n),
 161         LitKind::Float(ref is, LitFloatType::Suffixed(fty)) => match fty {
 162             FloatTy::F32 => Constant::F32(is.as_str().parse().unwrap()),
 163             FloatTy::F64 => Constant::F64(is.as_str().parse().unwrap()),
 164         },
 165         LitKind::Float(ref is, LitFloatType::Unsuffixed) => match ty.expect("type of float is known").kind {
 166             ty::Float(FloatTy::F32) => Constant::F32(is.as_str().parse().unwrap()),
 167             ty::Float(FloatTy::F64) => Constant::F64(is.as_str().parse().unwrap()),
 168             _ => bug!(),
 169         },
 170         LitKind::Bool(b) => Constant::Bool(b),
 171         LitKind::Err(s) => Constant::Err(s),
 172     }
 173 }
 174
 175 pub fn constant<'c, 'cc>(
 176     lcx: &LateContext<'c, 'cc>,
 177     tables: &'c ty::TypeckTables<'cc>,
 178     e: &Expr<'_>,
 179 ) -> Option<(Constant, bool)> {
 180     let mut cx = ConstEvalLateContext {
 181         lcx,
 182         tables,
 183         param_env: lcx.param_env,
 184         needed_resolution: false,
 185         substs: lcx.tcx.intern_substs(&[]),
 186     };
 187     cx.expr(e).map(|cst| (cst, cx.needed_resolution))
 188 }
 189
 190 pub fn constant_simple<'c, 'cc>(
 191     lcx: &LateContext<'c, 'cc>,
 192     tables: &'c ty::TypeckTables<'cc>,
 193     e: &Expr<'_>,
 194 ) -> Option<Constant> {
 195     constant(lcx, tables, e).and_then(|(cst, res)| if res { None } else { Some(cst) })
 196 }
 197
 198 /// Creates a `ConstEvalLateContext` from the given `LateContext` and `TypeckTables`.
 199 pub fn constant_context<'c, 'cc>(
 200     lcx: &'c LateContext<'c, 'cc>,
 201     tables: &'c ty::TypeckTables<'cc>,
 202 ) -> ConstEvalLateContext<'c, 'cc> {
 203     ConstEvalLateContext {
 204         lcx,
 205         tables,
 206         param_env: lcx.param_env,
 207         needed_resolution: false,
 208         substs: lcx.tcx.intern_substs(&[]),
 209     }
 210 }
 211
 212 pub struct ConstEvalLateContext<'a, 'tcx> {
 213     lcx: &'a LateContext<'a, 'tcx>,
 214     tables: &'a ty::TypeckTables<'tcx>,
 215     param_env: ty::ParamEnv<'tcx>,
 216     needed_resolution: bool,
 217     substs: SubstsRef<'tcx>,
 218 }
 219
 220 impl<'c, 'cc> ConstEvalLateContext<'c, 'cc> {
 221     /// Simple constant folding: Insert an expression, get a constant or none.
 222     pub fn expr(&mut self, e: &Expr<'_>) -> Option<Constant> {
 223         if let Some((ref cond, ref then, otherwise)) = higher::if_block(&e) {
 224             return self.ifthenelse(cond, then, otherwise);
 225         }
 226         match e.kind {
 227             ExprKind::Path(ref qpath) => self.fetch_path(qpath, e.hir_id, self.tables.expr_ty(e)),
 228             ExprKind::Block(ref block, _) => self.block(block),
 229             ExprKind::Lit(ref lit) => Some(lit_to_constant(&lit.node, self.tables.expr_ty_opt(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).kind {
 234                     ty::Array(_, n) => {
 235                         if let Some(n) = n.try_eval_usize(self.lcx.tcx, self.lcx.param_env) {
 236                             n
 237                         } else {
 238                             return None;
 239                         }
 240                     },
 241                     _ => span_bug!(e.span, "typeck error"),
 242                 };
 243                 self.expr(value).map(|v| Constant::Repeat(Box::new(v), n))
 244             },
 245             ExprKind::Unary(op, ref operand) => self.expr(operand).and_then(|o| match op {
 246                 UnOp::UnNot => self.constant_not(&o, self.tables.expr_ty(e)),
 247                 UnOp::UnNeg => self.constant_negate(&o, self.tables.expr_ty(e)),
 248                 UnOp::UnDeref => Some(o),
 249             }),
 250             ExprKind::Binary(op, ref left, ref right) => self.binop(op, left, right),
 251             ExprKind::Call(ref callee, ref args) => {
 252                 // We only handle a few const functions for now.
 253                 if_chain! {
 254                     if args.is_empty();
 255                     if let ExprKind::Path(qpath) = &callee.kind;
 256                     let res = self.tables.qpath_res(qpath, callee.hir_id);
 257                     if let Some(def_id) = res.opt_def_id();
 258                     let def_path: Vec<_> = self.lcx.get_def_path(def_id).into_iter().map(Symbol::as_str).collect();
 259                     let def_path: Vec<&str> = def_path.iter().take(4).map(|s| &**s).collect();
 260                     if let ["core", "num", int_impl, "max_value"] = *def_path;
 261                     then {
 262                        let value = match int_impl {
 263                            "<impl i8>" => i8::max_value() as u128,
 264                            "<impl i16>" => i16::max_value() as u128,
 265                            "<impl i32>" => i32::max_value() as u128,
 266                            "<impl i64>" => i64::max_value() as u128,
 267                            "<impl i128>" => i128::max_value() as u128,
 268                            _ => return None,
 269                        };
 270                        Some(Constant::Int(value))
 271                     }
 272                     else {
 273                         None
 274                     }
 275                 }
 276             },
 277             // TODO: add other expressions.
 278             _ => None,
 279         }
 280     }
 281
 282     #[allow(clippy::cast_possible_wrap)]
 283     fn constant_not(&self, o: &Constant, ty: Ty<'_>) -> Option<Constant> {
 284         use self::Constant::{Bool, Int};
 285         match *o {
 286             Bool(b) => Some(Bool(!b)),
 287             Int(value) => {
 288                 let value = !value;
 289                 match ty.kind {
 290                     ty::Int(ity) => Some(Int(unsext(self.lcx.tcx, value as i128, ity))),
 291                     ty::Uint(ity) => Some(Int(clip(self.lcx.tcx, value, ity))),
 292                     _ => None,
 293                 }
 294             },
 295             _ => None,
 296         }
 297     }
 298
 299     fn constant_negate(&self, o: &Constant, ty: Ty<'_>) -> Option<Constant> {
 300         use self::Constant::{Int, F32, F64};
 301         match *o {
 302             Int(value) => {
 303                 let ity = match ty.kind {
 304                     ty::Int(ity) => ity,
 305                     _ => return None,
 306                 };
 307                 // sign extend
 308                 let value = sext(self.lcx.tcx, value, ity);
 309                 let value = value.checked_neg()?;
 310                 // clear unused bits
 311                 Some(Int(unsext(self.lcx.tcx, value, ity)))
 312             },
 313             F32(f) => Some(F32(-f)),
 314             F64(f) => Some(F64(-f)),
 315             _ => None,
 316         }
 317     }
 318
 319     /// Create `Some(Vec![..])` of all constants, unless there is any
 320     /// non-constant part.
 321     fn multi(&mut self, vec: &[Expr<'_>]) -> Option<Vec<Constant>> {
 322         vec.iter().map(|elem| self.expr(elem)).collect::<Option<_>>()
 323     }
 324
 325     /// Lookup a possibly constant expression from a `ExprKind::Path`.
 326     fn fetch_path(&mut self, qpath: &QPath<'_>, id: HirId, ty: Ty<'cc>) -> Option<Constant> {
 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
 337                 let result = self
 338                     .lcx
 339                     .tcx
 340                     .const_eval_resolve(self.param_env, def_id, substs, None, None)
 341                     .ok()
 342                     .map(|val| rustc::ty::Const::from_value(self.lcx.tcx, val, ty))?;
 343                 let result = miri_to_const(&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).kind {
 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(result: &ty::Const<'_>) -> Option<Constant> {
 469     use rustc::mir::interpret::{ConstValue, Scalar};
 470     match result.val {
 471         ty::ConstKind::Value(ConstValue::Scalar(Scalar::Raw { data: d, .. })) => match result.ty.kind {
 472             ty::Bool => Some(Constant::Bool(d == 1)),
 473             ty::Uint(_) | ty::Int(_) => Some(Constant::Int(d)),
 474             ty::Float(FloatTy::F32) => Some(Constant::F32(f32::from_bits(
 475                 d.try_into().expect("invalid f32 bit representation"),
 476             ))),
 477             ty::Float(FloatTy::F64) => Some(Constant::F64(f64::from_bits(
 478                 d.try_into().expect("invalid f64 bit representation"),
 479             ))),
 480             ty::RawPtr(type_and_mut) => {
 481                 if let ty::Uint(_) = type_and_mut.ty.kind {
 482                     return Some(Constant::RawPtr(d));
 483                 }
 484                 None
 485             },
 486             // FIXME: implement other conversions.
 487             _ => None,
 488         },
 489         ty::ConstKind::Value(ConstValue::Slice { data, start, end }) => match result.ty.kind {
 490             ty::Ref(_, tam, _) => match tam.kind {
 491                 ty::Str => String::from_utf8(
 492                     data.inspect_with_undef_and_ptr_outside_interpreter(start..end)
 493                         .to_owned(),
 494                 )
 495                 .ok()
 496                 .map(Constant::Str),
 497                 _ => None,
 498             },
 499             _ => None,
 500         },
 501         // FIXME: implement other conversions.
 502         _ => None,
 503     }
 504 }