clippy_lints/src/consts.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10
  11 #![allow(clippy::float_cmp)]
  12
  13 use crate::rustc::lint::LateContext;
  14 use crate::rustc::{span_bug, bug};
  15 use crate::rustc::hir::def::Def;
  16 use crate::rustc::hir::*;
  17 use crate::rustc::ty::{self, Ty, TyCtxt, Instance};
  18 use crate::rustc::ty::subst::{Subst, Substs};
  19 use std::cmp::Ordering::{self, Equal};
  20 use std::cmp::PartialOrd;
  21 use std::convert::TryInto;
  22 use std::hash::{Hash, Hasher};
  23 use std::mem;
  24 use std::rc::Rc;
  25 use crate::syntax::ast::{FloatTy, LitKind};
  26 use crate::syntax::ptr::P;
  27 use crate::utils::{sext, unsext, clip};
  28
  29 /// A `LitKind`-like enum to fold constant `Expr`s into.
  30 #[derive(Debug, Clone)]
  31 pub enum Constant {
  32     /// a String "abc"
  33     Str(String),
  34     /// a Binary String b"abc"
  35     Binary(Rc<Vec<u8>>),
  36     /// a single char 'a'
  37     Char(char),
  38     /// an integer's bit representation
  39     Int(u128),
  40     /// an f32
  41     F32(f32),
  42     /// an f64
  43     F64(f64),
  44     /// true or false
  45     Bool(bool),
  46     /// an array of constants
  47     Vec(Vec<Constant>),
  48     /// also an array, but with only one constant, repeated N times
  49     Repeat(Box<Constant>, u64),
  50     /// a tuple of constants
  51     Tuple(Vec<Constant>),
  52 }
  53
  54 impl PartialEq for Constant {
  55     fn eq(&self, other: &Self) -> bool {
  56         match (self, other) {
  57             (&Constant::Str(ref ls), &Constant::Str(ref rs)) => ls == rs,
  58             (&Constant::Binary(ref l), &Constant::Binary(ref r)) => l == r,
  59             (&Constant::Char(l), &Constant::Char(r)) => l == r,
  60             (&Constant::Int(l), &Constant::Int(r)) => l == r,
  61             (&Constant::F64(l), &Constant::F64(r)) => {
  62                 // we want `Fw32 == FwAny` and `FwAny == Fw64`, by transitivity we must have
  63                 // `Fw32 == Fw64` so don’t compare them
  64                 // mem::transmute is required to catch non-matching 0.0, -0.0, and NaNs
  65                 unsafe { mem::transmute::<f64, u64>(l) == mem::transmute::<f64, u64>(r) }
  66             },
  67             (&Constant::F32(l), &Constant::F32(r)) => {
  68                 // we want `Fw32 == FwAny` and `FwAny == Fw64`, by transitivity we must have
  69                 // `Fw32 == Fw64` so don’t compare them
  70                 // mem::transmute is required to catch non-matching 0.0, -0.0, and NaNs
  71                 unsafe { mem::transmute::<f64, u64>(f64::from(l)) == mem::transmute::<f64, u64>(f64::from(r)) }
  72             },
  73             (&Constant::Bool(l), &Constant::Bool(r)) => l == r,
  74             (&Constant::Vec(ref l), &Constant::Vec(ref r)) | (&Constant::Tuple(ref l), &Constant::Tuple(ref r)) => l == r,
  75             (&Constant::Repeat(ref lv, ref ls), &Constant::Repeat(ref rv, ref rs)) => ls == rs && lv == rv,
  76             _ => false, // TODO: Are there inter-type equalities?
  77         }
  78     }
  79 }
  80
  81 impl Hash for Constant {
  82     fn hash<H>(&self, state: &mut H)
  83     where
  84         H: Hasher,
  85     {
  86         match *self {
  87             Constant::Str(ref s) => {
  88                 s.hash(state);
  89             },
  90             Constant::Binary(ref b) => {
  91                 b.hash(state);
  92             },
  93             Constant::Char(c) => {
  94                 c.hash(state);
  95             },
  96             Constant::Int(i) => {
  97                 i.hash(state);
  98             },
  99             Constant::F32(f) => {
 100                 unsafe { mem::transmute::<f64, u64>(f64::from(f)) }.hash(state);
 101             },
 102             Constant::F64(f) => {
 103                 unsafe { mem::transmute::<f64, u64>(f) }.hash(state);
 104             },
 105             Constant::Bool(b) => {
 106                 b.hash(state);
 107             },
 108             Constant::Vec(ref v) | Constant::Tuple(ref v) => {
 109                 v.hash(state);
 110             },
 111             Constant::Repeat(ref c, l) => {
 112                 c.hash(state);
 113                 l.hash(state);
 114             },
 115         }
 116     }
 117 }
 118
 119 impl Constant {
 120     pub fn partial_cmp(tcx: TyCtxt<'_, '_, '_>, cmp_type: &ty::TyKind<'_>, left: &Self, right: &Self) -> Option<Ordering> {
 121         match (left, right) {
 122             (&Constant::Str(ref ls), &Constant::Str(ref rs)) => Some(ls.cmp(rs)),
 123             (&Constant::Char(ref l), &Constant::Char(ref r)) => Some(l.cmp(r)),
 124             (&Constant::Int(l), &Constant::Int(r)) => {
 125                 if let ty::Int(int_ty) = *cmp_type {
 126                     Some(sext(tcx, l, int_ty).cmp(&sext(tcx, r, int_ty)))
 127                 } else {
 128                     Some(l.cmp(&r))
 129                 }
 130             },
 131             (&Constant::F64(l), &Constant::F64(r)) => l.partial_cmp(&r),
 132             (&Constant::F32(l), &Constant::F32(r)) => l.partial_cmp(&r),
 133             (&Constant::Bool(ref l), &Constant::Bool(ref r)) => Some(l.cmp(r)),
 134             (&Constant::Tuple(ref l), &Constant::Tuple(ref r)) | (&Constant::Vec(ref l), &Constant::Vec(ref r)) => l
 135                 .iter()
 136                 .zip(r.iter())
 137                 .map(|(li, ri)| Self::partial_cmp(tcx, cmp_type, li, ri))
 138                 .find(|r| r.map_or(true, |o| o != Ordering::Equal))
 139                 .unwrap_or_else(|| Some(l.len().cmp(&r.len()))),
 140             (&Constant::Repeat(ref lv, ref ls), &Constant::Repeat(ref rv, ref rs)) => {
 141                 match Self::partial_cmp(tcx, cmp_type, lv, rv) {
 142                     Some(Equal) => Some(ls.cmp(rs)),
 143                     x => x,
 144                 }
 145             },
 146             _ => None, // TODO: Are there any useful inter-type orderings?
 147         }
 148     }
 149 }
 150
 151 /// parse a `LitKind` to a `Constant`
 152 pub fn lit_to_constant<'tcx>(lit: &LitKind, ty: Ty<'tcx>) -> Constant {
 153     use crate::syntax::ast::*;
 154
 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(Rc::clone(s)),
 159         LitKind::Char(c) => Constant::Char(c),
 160         LitKind::Int(n, _) => Constant::Int(n),
 161         LitKind::Float(ref is, _) |
 162         LitKind::FloatUnsuffixed(ref is) => match ty.sty {
 163             ty::Float(FloatTy::F32) => Constant::F32(is.as_str().parse().unwrap()),
 164             ty::Float(FloatTy::F64) => Constant::F64(is.as_str().parse().unwrap()),
 165             _ => bug!(),
 166         },
 167         LitKind::Bool(b) => Constant::Bool(b),
 168     }
 169 }
 170
 171 pub fn constant<'c, 'cc>(lcx: &LateContext<'c, 'cc>, tables: &'c ty::TypeckTables<'cc>, e: &Expr) -> Option<(Constant, bool)> {
 172     let mut cx = ConstEvalLateContext {
 173         tcx: lcx.tcx,
 174         tables,
 175         param_env: lcx.param_env,
 176         needed_resolution: false,
 177         substs: lcx.tcx.intern_substs(&[]),
 178     };
 179     cx.expr(e).map(|cst| (cst, cx.needed_resolution))
 180 }
 181
 182 pub fn constant_simple<'c, 'cc>(lcx: &LateContext<'c, 'cc>, tables: &'c ty::TypeckTables<'cc>, e: &Expr) -> Option<Constant> {
 183     constant(lcx, tables, e).and_then(|(cst, res)| if res { None } else { Some(cst) })
 184 }
 185
 186 /// Creates a `ConstEvalLateContext` from the given `LateContext` and `TypeckTables`
 187 pub fn constant_context<'c, 'cc>(lcx: &LateContext<'c, 'cc>, tables: &'c ty::TypeckTables<'cc>) -> ConstEvalLateContext<'c, 'cc> {
 188     ConstEvalLateContext {
 189         tcx: lcx.tcx,
 190         tables,
 191         param_env: lcx.param_env,
 192         needed_resolution: false,
 193         substs: lcx.tcx.intern_substs(&[]),
 194     }
 195 }
 196
 197 pub struct ConstEvalLateContext<'a, 'tcx: 'a> {
 198     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 199     tables: &'a ty::TypeckTables<'tcx>,
 200     param_env: ty::ParamEnv<'tcx>,
 201     needed_resolution: bool,
 202     substs: &'tcx Substs<'tcx>,
 203 }
 204
 205 impl<'c, 'cc> ConstEvalLateContext<'c, 'cc> {
 206     /// simple constant folding: Insert an expression, get a constant or none.
 207     pub fn expr(&mut self, e: &Expr) -> Option<Constant> {
 208         match e.node {
 209             ExprKind::Path(ref qpath) => self.fetch_path(qpath, e.hir_id),
 210             ExprKind::Block(ref block, _) => self.block(block),
 211             ExprKind::If(ref cond, ref then, ref otherwise) => self.ifthenelse(cond, then, otherwise),
 212             ExprKind::Lit(ref lit) => Some(lit_to_constant(&lit.node, self.tables.expr_ty(e))),
 213             ExprKind::Array(ref vec) => self.multi(vec).map(Constant::Vec),
 214             ExprKind::Tup(ref tup) => self.multi(tup).map(Constant::Tuple),
 215             ExprKind::Repeat(ref value, _) => {
 216                 let n = match self.tables.expr_ty(e).sty {
 217                     ty::Array(_, n) => n.assert_usize(self.tcx).expect("array length"),
 218                     _ => span_bug!(e.span, "typeck error"),
 219                 };
 220                 self.expr(value).map(|v| Constant::Repeat(Box::new(v), n))
 221             },
 222             ExprKind::Unary(op, ref operand) => self.expr(operand).and_then(|o| match op {
 223                 UnNot => self.constant_not(&o, self.tables.expr_ty(e)),
 224                 UnNeg => self.constant_negate(&o, self.tables.expr_ty(e)),
 225                 UnDeref => Some(o),
 226             }),
 227             ExprKind::Binary(op, ref left, ref right) => self.binop(op, left, right),
 228             // TODO: add other expressions
 229             _ => None,
 230         }
 231     }
 232
 233     #[allow(clippy::cast_possible_wrap)]
 234     fn constant_not(&self, o: &Constant, ty: ty::Ty<'_>) -> Option<Constant> {
 235         use self::Constant::*;
 236         match *o {
 237             Bool(b) => Some(Bool(!b)),
 238             Int(value) => {
 239                 let value = !value;
 240                 match ty.sty {
 241                     ty::Int(ity) => Some(Int(unsext(self.tcx, value as i128, ity))),
 242                     ty::Uint(ity) => Some(Int(clip(self.tcx, value, ity))),
 243                     _ => None,
 244                 }
 245             },
 246             _ => None,
 247         }
 248     }
 249
 250     fn constant_negate(&self, o: &Constant, ty: ty::Ty<'_>) -> Option<Constant> {
 251         use self::Constant::*;
 252         match *o {
 253             Int(value) => {
 254                 let ity = match ty.sty {
 255                     ty::Int(ity) => ity,
 256                     _ => return None,
 257                 };
 258                 // sign extend
 259                 let value = sext(self.tcx, value, ity);
 260                 let value = value.checked_neg()?;
 261                 // clear unused bits
 262                 Some(Int(unsext(self.tcx, value, ity)))
 263             },
 264             F32(f) => Some(F32(-f)),
 265             F64(f) => Some(F64(-f)),
 266             _ => None,
 267         }
 268     }
 269
 270     /// create `Some(Vec![..])` of all constants, unless there is any
 271     /// non-constant part
 272     fn multi(&mut self, vec: &[Expr]) -> Option<Vec<Constant>> {
 273         vec.iter()
 274             .map(|elem| self.expr(elem))
 275             .collect::<Option<_>>()
 276     }
 277
 278     /// lookup a possibly constant expression from a ExprKind::Path
 279     fn fetch_path(&mut self, qpath: &QPath, id: HirId) -> Option<Constant> {
 280         use crate::rustc::mir::interpret::GlobalId;
 281
 282         let def = self.tables.qpath_def(qpath, id);
 283         match def {
 284             Def::Const(def_id) | Def::AssociatedConst(def_id) => {
 285                 let substs = self.tables.node_substs(id);
 286                 let substs = if self.substs.is_empty() {
 287                     substs
 288                 } else {
 289                     substs.subst(self.tcx, self.substs)
 290                 };
 291                 let instance = Instance::resolve(self.tcx, self.param_env, def_id, substs)?;
 292                 let gid = GlobalId {
 293                     instance,
 294                     promoted: None,
 295                 };
 296
 297                 let result = self.tcx.const_eval(self.param_env.and(gid)).ok()?;
 298                 let ret = miri_to_const(self.tcx, result);
 299                 if ret.is_some() {
 300                     self.needed_resolution = true;
 301                 }
 302                 return ret;
 303             },
 304             _ => {},
 305         }
 306         None
 307     }
 308
 309     /// A block can only yield a constant if it only has one constant expression
 310     fn block(&mut self, block: &Block) -> Option<Constant> {
 311         if block.stmts.is_empty() {
 312             block.expr.as_ref().and_then(|b| self.expr(b))
 313         } else {
 314             None
 315         }
 316     }
 317
 318     fn ifthenelse(&mut self, cond: &Expr, then: &P<Expr>, otherwise: &Option<P<Expr>>) -> Option<Constant> {
 319         if let Some(Constant::Bool(b)) = self.expr(cond) {
 320             if b {
 321                 self.expr(&**then)
 322             } else {
 323                 otherwise.as_ref().and_then(|expr| self.expr(expr))
 324             }
 325         } else {
 326             None
 327         }
 328     }
 329
 330     fn binop(&mut self, op: BinOp, left: &Expr, right: &Expr) -> Option<Constant> {
 331         let l = self.expr(left)?;
 332         let r = self.expr(right);
 333         match (l, r) {
 334             (Constant::Int(l), Some(Constant::Int(r))) => {
 335                 match self.tables.expr_ty(left).sty {
 336                     ty::Int(ity) => {
 337                         let l = sext(self.tcx, l, ity);
 338                         let r = sext(self.tcx, r, ity);
 339                         let zext = |n: i128| Constant::Int(unsext(self.tcx, n, ity));
 340                         match op.node {
 341                             BinOpKind::Add => l.checked_add(r).map(zext),
 342                             BinOpKind::Sub => l.checked_sub(r).map(zext),
 343                             BinOpKind::Mul => l.checked_mul(r).map(zext),
 344                             BinOpKind::Div if r != 0 => l.checked_div(r).map(zext),
 345                             BinOpKind::Rem if r != 0 => l.checked_rem(r).map(zext),
 346                             BinOpKind::Shr => l.checked_shr(
 347                                     r.try_into().expect("invalid shift")
 348                                 ).map(zext),
 349                             BinOpKind::Shl => l.checked_shl(
 350                                     r.try_into().expect("invalid shift")
 351                                 ).map(zext),
 352                             BinOpKind::BitXor => Some(zext(l ^ r)),
 353                             BinOpKind::BitOr => Some(zext(l | r)),
 354                             BinOpKind::BitAnd => Some(zext(l & r)),
 355                             BinOpKind::Eq => Some(Constant::Bool(l == r)),
 356                             BinOpKind::Ne => Some(Constant::Bool(l != r)),
 357                             BinOpKind::Lt => Some(Constant::Bool(l < r)),
 358                             BinOpKind::Le => Some(Constant::Bool(l <= r)),
 359                             BinOpKind::Ge => Some(Constant::Bool(l >= r)),
 360                             BinOpKind::Gt => Some(Constant::Bool(l > r)),
 361                             _ => None,
 362                         }
 363                     }
 364                     ty::Uint(_) => {
 365                         match op.node {
 366                             BinOpKind::Add => l.checked_add(r).map(Constant::Int),
 367                             BinOpKind::Sub => l.checked_sub(r).map(Constant::Int),
 368                             BinOpKind::Mul => l.checked_mul(r).map(Constant::Int),
 369                             BinOpKind::Div => l.checked_div(r).map(Constant::Int),
 370                             BinOpKind::Rem => l.checked_rem(r).map(Constant::Int),
 371                             BinOpKind::Shr => l.checked_shr(
 372                                     r.try_into().expect("shift too large")
 373                                 ).map(Constant::Int),
 374                             BinOpKind::Shl => l.checked_shl(
 375                                     r.try_into().expect("shift too large")
 376                                 ).map(Constant::Int),
 377                             BinOpKind::BitXor => Some(Constant::Int(l ^ r)),
 378                             BinOpKind::BitOr => Some(Constant::Int(l | r)),
 379                             BinOpKind::BitAnd => Some(Constant::Int(l & r)),
 380                             BinOpKind::Eq => Some(Constant::Bool(l == r)),
 381                             BinOpKind::Ne => Some(Constant::Bool(l != r)),
 382                             BinOpKind::Lt => Some(Constant::Bool(l < r)),
 383                             BinOpKind::Le => Some(Constant::Bool(l <= r)),
 384                             BinOpKind::Ge => Some(Constant::Bool(l >= r)),
 385                             BinOpKind::Gt => Some(Constant::Bool(l > r)),
 386                             _ => None,
 387                         }
 388                     },
 389                     _ => None,
 390                 }
 391             },
 392             (Constant::F32(l), Some(Constant::F32(r))) => match op.node {
 393                 BinOpKind::Add => Some(Constant::F32(l + r)),
 394                 BinOpKind::Sub => Some(Constant::F32(l - r)),
 395                 BinOpKind::Mul => Some(Constant::F32(l * r)),
 396                 BinOpKind::Div => Some(Constant::F32(l / r)),
 397                 BinOpKind::Rem => Some(Constant::F32(l % r)),
 398                 BinOpKind::Eq => Some(Constant::Bool(l == r)),
 399                 BinOpKind::Ne => Some(Constant::Bool(l != r)),
 400                 BinOpKind::Lt => Some(Constant::Bool(l < r)),
 401                 BinOpKind::Le => Some(Constant::Bool(l <= r)),
 402                 BinOpKind::Ge => Some(Constant::Bool(l >= r)),
 403                 BinOpKind::Gt => Some(Constant::Bool(l > r)),
 404                 _ => None,
 405             },
 406             (Constant::F64(l), Some(Constant::F64(r))) => match op.node {
 407                 BinOpKind::Add => Some(Constant::F64(l + r)),
 408                 BinOpKind::Sub => Some(Constant::F64(l - r)),
 409                 BinOpKind::Mul => Some(Constant::F64(l * r)),
 410                 BinOpKind::Div => Some(Constant::F64(l / r)),
 411                 BinOpKind::Rem => Some(Constant::F64(l % r)),
 412                 BinOpKind::Eq => Some(Constant::Bool(l == r)),
 413                 BinOpKind::Ne => Some(Constant::Bool(l != r)),
 414                 BinOpKind::Lt => Some(Constant::Bool(l < r)),
 415                 BinOpKind::Le => Some(Constant::Bool(l <= r)),
 416                 BinOpKind::Ge => Some(Constant::Bool(l >= r)),
 417                 BinOpKind::Gt => Some(Constant::Bool(l > r)),
 418                 _ => None,
 419             },
 420             (l, r) => match (op.node, l, r) {
 421                 (BinOpKind::And, Constant::Bool(false), _) => Some(Constant::Bool(false)),
 422                 (BinOpKind::Or, Constant::Bool(true), _) => Some(Constant::Bool(true)),
 423                 (BinOpKind::And, Constant::Bool(true), Some(r)) | (BinOpKind::Or, Constant::Bool(false), Some(r)) => Some(r),
 424                 (BinOpKind::BitXor, Constant::Bool(l), Some(Constant::Bool(r))) => Some(Constant::Bool(l ^ r)),
 425                 (BinOpKind::BitAnd, Constant::Bool(l), Some(Constant::Bool(r))) => Some(Constant::Bool(l & r)),
 426                 (BinOpKind::BitOr, Constant::Bool(l), Some(Constant::Bool(r))) => Some(Constant::Bool(l | r)),
 427                 _ => None,
 428             },
 429         }
 430     }
 431 }
 432
 433 pub fn miri_to_const<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, result: &ty::Const<'tcx>) -> Option<Constant> {
 434     use crate::rustc::mir::interpret::{Scalar, ConstValue};
 435     match result.val {
 436         ConstValue::Scalar(Scalar::Bits{ bits: b, ..}) => match result.ty.sty {
 437             ty::Bool => Some(Constant::Bool(b == 1)),
 438             ty::Uint(_) | ty::Int(_) => Some(Constant::Int(b)),
 439             ty::Float(FloatTy::F32) => Some(Constant::F32(f32::from_bits(
 440                 b.try_into().expect("invalid f32 bit representation")
 441             ))),
 442             ty::Float(FloatTy::F64) => Some(Constant::F64(f64::from_bits(
 443                 b.try_into().expect("invalid f64 bit representation")
 444             ))),
 445             // FIXME: implement other conversion
 446             _ => None,
 447         },
 448         ConstValue::ScalarPair(Scalar::Ptr(ptr),
 449                                 Scalar::Bits { bits: n, .. }) => match result.ty.sty {
 450             ty::Ref(_, tam, _) => match tam.sty {
 451                 ty::Str => {
 452                     let alloc = tcx
 453                         .alloc_map
 454                         .lock()
 455                         .unwrap_memory(ptr.alloc_id);
 456                     let offset = ptr.offset.bytes().try_into().expect("too-large pointer offset");
 457                     let n = n as usize;
 458                     String::from_utf8(alloc.bytes[offset..(offset + n)].to_owned()).ok().map(Constant::Str)
 459                 },
 460                 _ => None,
 461             },
 462             _ => None,
 463         }
 464         // FIXME: implement other conversions
 465         _ => None,
 466     }
 467 }