rust-clippy/clippy_lints/src/consts.rs
2021-01-07 18:54:12 -03:00

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#![allow(clippy::float_cmp)]
use crate::utils::{clip, sext, unsext};
use if_chain::if_chain;
use rustc_ast::ast::{FloatTy, LitFloatType, LitKind};
use rustc_data_structures::sync::Lrc;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::{BinOp, BinOpKind, Block, Expr, ExprKind, HirId, QPath, UnOp};
use rustc_lint::LateContext;
use rustc_middle::mir::interpret::Scalar;
use rustc_middle::ty::subst::{Subst, SubstsRef};
use rustc_middle::ty::{self, ScalarInt, Ty, TyCtxt};
use rustc_middle::{bug, span_bug};
use rustc_span::symbol::Symbol;
use std::cmp::Ordering::{self, Equal};
use std::convert::TryInto;
use std::hash::{Hash, Hasher};
/// A `LitKind`-like enum to fold constant `Expr`s into.
#[derive(Debug, Clone)]
pub enum Constant {
/// A `String` (e.g., "abc").
Str(String),
/// A binary string (e.g., `b"abc"`).
Binary(Lrc<[u8]>),
/// A single `char` (e.g., `'a'`).
Char(char),
/// An integer's bit representation.
Int(u128),
/// An `f32`.
F32(f32),
/// An `f64`.
F64(f64),
/// `true` or `false`.
Bool(bool),
/// An array of constants.
Vec(Vec<Constant>),
/// Also an array, but with only one constant, repeated N times.
Repeat(Box<Constant>, u64),
/// A tuple of constants.
Tuple(Vec<Constant>),
/// A raw pointer.
RawPtr(u128),
/// A reference
Ref(Box<Constant>),
/// A literal with syntax error.
Err(Symbol),
}
impl PartialEq for Constant {
fn eq(&self, other: &Self) -> bool {
match (self, other) {
(&Self::Str(ref ls), &Self::Str(ref rs)) => ls == rs,
(&Self::Binary(ref l), &Self::Binary(ref r)) => l == r,
(&Self::Char(l), &Self::Char(r)) => l == r,
(&Self::Int(l), &Self::Int(r)) => l == r,
(&Self::F64(l), &Self::F64(r)) => {
// We want `Fw32 == FwAny` and `FwAny == Fw64`, and by transitivity we must have
// `Fw32 == Fw64`, so dont compare them.
// `to_bits` is required to catch non-matching 0.0, -0.0, and NaNs.
l.to_bits() == r.to_bits()
},
(&Self::F32(l), &Self::F32(r)) => {
// We want `Fw32 == FwAny` and `FwAny == Fw64`, and by transitivity we must have
// `Fw32 == Fw64`, so dont compare them.
// `to_bits` is required to catch non-matching 0.0, -0.0, and NaNs.
f64::from(l).to_bits() == f64::from(r).to_bits()
},
(&Self::Bool(l), &Self::Bool(r)) => l == r,
(&Self::Vec(ref l), &Self::Vec(ref r)) | (&Self::Tuple(ref l), &Self::Tuple(ref r)) => l == r,
(&Self::Repeat(ref lv, ref ls), &Self::Repeat(ref rv, ref rs)) => ls == rs && lv == rv,
(&Self::Ref(ref lb), &Self::Ref(ref rb)) => *lb == *rb,
// TODO: are there inter-type equalities?
_ => false,
}
}
}
impl Hash for Constant {
fn hash<H>(&self, state: &mut H)
where
H: Hasher,
{
std::mem::discriminant(self).hash(state);
match *self {
Self::Str(ref s) => {
s.hash(state);
},
Self::Binary(ref b) => {
b.hash(state);
},
Self::Char(c) => {
c.hash(state);
},
Self::Int(i) => {
i.hash(state);
},
Self::F32(f) => {
f64::from(f).to_bits().hash(state);
},
Self::F64(f) => {
f.to_bits().hash(state);
},
Self::Bool(b) => {
b.hash(state);
},
Self::Vec(ref v) | Self::Tuple(ref v) => {
v.hash(state);
},
Self::Repeat(ref c, l) => {
c.hash(state);
l.hash(state);
},
Self::RawPtr(u) => {
u.hash(state);
},
Self::Ref(ref r) => {
r.hash(state);
},
Self::Err(ref s) => {
s.hash(state);
},
}
}
}
impl Constant {
pub fn partial_cmp(tcx: TyCtxt<'_>, cmp_type: Ty<'_>, left: &Self, right: &Self) -> Option<Ordering> {
match (left, right) {
(&Self::Str(ref ls), &Self::Str(ref rs)) => Some(ls.cmp(rs)),
(&Self::Char(ref l), &Self::Char(ref r)) => Some(l.cmp(r)),
(&Self::Int(l), &Self::Int(r)) => {
if let ty::Int(int_ty) = *cmp_type.kind() {
Some(sext(tcx, l, int_ty).cmp(&sext(tcx, r, int_ty)))
} else {
Some(l.cmp(&r))
}
},
(&Self::F64(l), &Self::F64(r)) => l.partial_cmp(&r),
(&Self::F32(l), &Self::F32(r)) => l.partial_cmp(&r),
(&Self::Bool(ref l), &Self::Bool(ref r)) => Some(l.cmp(r)),
(&Self::Tuple(ref l), &Self::Tuple(ref r)) | (&Self::Vec(ref l), &Self::Vec(ref r)) => l
.iter()
.zip(r.iter())
.map(|(li, ri)| Self::partial_cmp(tcx, cmp_type, li, ri))
.find(|r| r.map_or(true, |o| o != Ordering::Equal))
.unwrap_or_else(|| Some(l.len().cmp(&r.len()))),
(&Self::Repeat(ref lv, ref ls), &Self::Repeat(ref rv, ref rs)) => {
match Self::partial_cmp(tcx, cmp_type, lv, rv) {
Some(Equal) => Some(ls.cmp(rs)),
x => x,
}
},
(&Self::Ref(ref lb), &Self::Ref(ref rb)) => Self::partial_cmp(tcx, cmp_type, lb, rb),
// TODO: are there any useful inter-type orderings?
_ => None,
}
}
}
/// Parses a `LitKind` to a `Constant`.
pub fn lit_to_constant(lit: &LitKind, ty: Option<Ty<'_>>) -> Constant {
match *lit {
LitKind::Str(ref is, _) => Constant::Str(is.to_string()),
LitKind::Byte(b) => Constant::Int(u128::from(b)),
LitKind::ByteStr(ref s) => Constant::Binary(Lrc::clone(s)),
LitKind::Char(c) => Constant::Char(c),
LitKind::Int(n, _) => Constant::Int(n),
LitKind::Float(ref is, LitFloatType::Suffixed(fty)) => match fty {
FloatTy::F32 => Constant::F32(is.as_str().parse().unwrap()),
FloatTy::F64 => Constant::F64(is.as_str().parse().unwrap()),
},
LitKind::Float(ref is, LitFloatType::Unsuffixed) => match ty.expect("type of float is known").kind() {
ty::Float(FloatTy::F32) => Constant::F32(is.as_str().parse().unwrap()),
ty::Float(FloatTy::F64) => Constant::F64(is.as_str().parse().unwrap()),
_ => bug!(),
},
LitKind::Bool(b) => Constant::Bool(b),
LitKind::Err(s) => Constant::Err(s),
}
}
pub fn constant<'tcx>(
lcx: &LateContext<'tcx>,
typeck_results: &ty::TypeckResults<'tcx>,
e: &Expr<'_>,
) -> Option<(Constant, bool)> {
let mut cx = ConstEvalLateContext {
lcx,
typeck_results,
param_env: lcx.param_env,
needed_resolution: false,
substs: lcx.tcx.intern_substs(&[]),
};
cx.expr(e).map(|cst| (cst, cx.needed_resolution))
}
pub fn constant_simple<'tcx>(
lcx: &LateContext<'tcx>,
typeck_results: &ty::TypeckResults<'tcx>,
e: &Expr<'_>,
) -> Option<Constant> {
constant(lcx, typeck_results, e).and_then(|(cst, res)| if res { None } else { Some(cst) })
}
/// Creates a `ConstEvalLateContext` from the given `LateContext` and `TypeckResults`.
pub fn constant_context<'a, 'tcx>(
lcx: &'a LateContext<'tcx>,
typeck_results: &'a ty::TypeckResults<'tcx>,
) -> ConstEvalLateContext<'a, 'tcx> {
ConstEvalLateContext {
lcx,
typeck_results,
param_env: lcx.param_env,
needed_resolution: false,
substs: lcx.tcx.intern_substs(&[]),
}
}
pub struct ConstEvalLateContext<'a, 'tcx> {
lcx: &'a LateContext<'tcx>,
typeck_results: &'a ty::TypeckResults<'tcx>,
param_env: ty::ParamEnv<'tcx>,
needed_resolution: bool,
substs: SubstsRef<'tcx>,
}
impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> {
/// Simple constant folding: Insert an expression, get a constant or none.
pub fn expr(&mut self, e: &Expr<'_>) -> Option<Constant> {
match e.kind {
ExprKind::Path(ref qpath) => self.fetch_path(qpath, e.hir_id, self.typeck_results.expr_ty(e)),
ExprKind::Block(ref block, _) => self.block(block),
ExprKind::Lit(ref lit) => Some(lit_to_constant(&lit.node, self.typeck_results.expr_ty_opt(e))),
ExprKind::Array(ref vec) => self.multi(vec).map(Constant::Vec),
ExprKind::Tup(ref tup) => self.multi(tup).map(Constant::Tuple),
ExprKind::Repeat(ref value, _) => {
let n = match self.typeck_results.expr_ty(e).kind() {
ty::Array(_, n) => n.try_eval_usize(self.lcx.tcx, self.lcx.param_env)?,
_ => span_bug!(e.span, "typeck error"),
};
self.expr(value).map(|v| Constant::Repeat(Box::new(v), n))
},
ExprKind::Unary(op, ref operand) => self.expr(operand).and_then(|o| match op {
UnOp::UnNot => self.constant_not(&o, self.typeck_results.expr_ty(e)),
UnOp::UnNeg => self.constant_negate(&o, self.typeck_results.expr_ty(e)),
UnOp::UnDeref => Some(if let Constant::Ref(r) = o { *r } else { o }),
}),
ExprKind::If(ref cond, ref then, ref otherwise) => self.ifthenelse(cond, then, *otherwise),
ExprKind::Binary(op, ref left, ref right) => self.binop(op, left, right),
ExprKind::Call(ref callee, ref args) => {
// We only handle a few const functions for now.
if_chain! {
if args.is_empty();
if let ExprKind::Path(qpath) = &callee.kind;
let res = self.typeck_results.qpath_res(qpath, callee.hir_id);
if let Some(def_id) = res.opt_def_id();
let def_path: Vec<_> = self.lcx.get_def_path(def_id).into_iter().map(Symbol::as_str).collect();
let def_path: Vec<&str> = def_path.iter().take(4).map(|s| &**s).collect();
if let ["core", "num", int_impl, "max_value"] = *def_path;
then {
let value = match int_impl {
"<impl i8>" => i8::MAX as u128,
"<impl i16>" => i16::MAX as u128,
"<impl i32>" => i32::MAX as u128,
"<impl i64>" => i64::MAX as u128,
"<impl i128>" => i128::MAX as u128,
_ => return None,
};
Some(Constant::Int(value))
}
else {
None
}
}
},
ExprKind::Index(ref arr, ref index) => self.index(arr, index),
ExprKind::AddrOf(_, _, ref inner) => self.expr(inner).map(|r| Constant::Ref(Box::new(r))),
// TODO: add other expressions.
_ => None,
}
}
#[allow(clippy::cast_possible_wrap)]
fn constant_not(&self, o: &Constant, ty: Ty<'_>) -> Option<Constant> {
use self::Constant::{Bool, Int};
match *o {
Bool(b) => Some(Bool(!b)),
Int(value) => {
let value = !value;
match *ty.kind() {
ty::Int(ity) => Some(Int(unsext(self.lcx.tcx, value as i128, ity))),
ty::Uint(ity) => Some(Int(clip(self.lcx.tcx, value, ity))),
_ => None,
}
},
_ => None,
}
}
fn constant_negate(&self, o: &Constant, ty: Ty<'_>) -> Option<Constant> {
use self::Constant::{Int, F32, F64};
match *o {
Int(value) => {
let ity = match *ty.kind() {
ty::Int(ity) => ity,
_ => return None,
};
// sign extend
let value = sext(self.lcx.tcx, value, ity);
let value = value.checked_neg()?;
// clear unused bits
Some(Int(unsext(self.lcx.tcx, value, ity)))
},
F32(f) => Some(F32(-f)),
F64(f) => Some(F64(-f)),
_ => None,
}
}
/// Create `Some(Vec![..])` of all constants, unless there is any
/// non-constant part.
fn multi(&mut self, vec: &[Expr<'_>]) -> Option<Vec<Constant>> {
vec.iter().map(|elem| self.expr(elem)).collect::<Option<_>>()
}
/// Lookup a possibly constant expression from a `ExprKind::Path`.
fn fetch_path(&mut self, qpath: &QPath<'_>, id: HirId, ty: Ty<'tcx>) -> Option<Constant> {
let res = self.typeck_results.qpath_res(qpath, id);
match res {
Res::Def(DefKind::Const | DefKind::AssocConst, def_id) => {
let substs = self.typeck_results.node_substs(id);
let substs = if self.substs.is_empty() {
substs
} else {
substs.subst(self.lcx.tcx, self.substs)
};
let result = self
.lcx
.tcx
.const_eval_resolve(
self.param_env,
ty::WithOptConstParam::unknown(def_id),
substs,
None,
None,
)
.ok()
.map(|val| rustc_middle::ty::Const::from_value(self.lcx.tcx, val, ty))?;
let result = miri_to_const(&result);
if result.is_some() {
self.needed_resolution = true;
}
result
},
// FIXME: cover all usable cases.
_ => None,
}
}
fn index(&mut self, lhs: &'_ Expr<'_>, index: &'_ Expr<'_>) -> Option<Constant> {
let lhs = self.expr(lhs);
let index = self.expr(index);
match (lhs, index) {
(Some(Constant::Vec(vec)), Some(Constant::Int(index))) => match vec.get(index as usize) {
Some(Constant::F32(x)) => Some(Constant::F32(*x)),
Some(Constant::F64(x)) => Some(Constant::F64(*x)),
_ => None,
},
(Some(Constant::Vec(vec)), _) => {
if !vec.is_empty() && vec.iter().all(|x| *x == vec[0]) {
match vec.get(0) {
Some(Constant::F32(x)) => Some(Constant::F32(*x)),
Some(Constant::F64(x)) => Some(Constant::F64(*x)),
_ => None,
}
} else {
None
}
},
_ => None,
}
}
/// A block can only yield a constant if it only has one constant expression.
fn block(&mut self, block: &Block<'_>) -> Option<Constant> {
if block.stmts.is_empty() {
block.expr.as_ref().and_then(|b| self.expr(b))
} else {
None
}
}
fn ifthenelse(&mut self, cond: &Expr<'_>, then: &Expr<'_>, otherwise: Option<&Expr<'_>>) -> Option<Constant> {
if let Some(Constant::Bool(b)) = self.expr(cond) {
if b {
self.expr(&*then)
} else {
otherwise.as_ref().and_then(|expr| self.expr(expr))
}
} else {
None
}
}
fn binop(&mut self, op: BinOp, left: &Expr<'_>, right: &Expr<'_>) -> Option<Constant> {
let l = self.expr(left)?;
let r = self.expr(right);
match (l, r) {
(Constant::Int(l), Some(Constant::Int(r))) => match *self.typeck_results.expr_ty_opt(left)?.kind() {
ty::Int(ity) => {
let l = sext(self.lcx.tcx, l, ity);
let r = sext(self.lcx.tcx, r, ity);
let zext = |n: i128| Constant::Int(unsext(self.lcx.tcx, n, ity));
match op.node {
BinOpKind::Add => l.checked_add(r).map(zext),
BinOpKind::Sub => l.checked_sub(r).map(zext),
BinOpKind::Mul => l.checked_mul(r).map(zext),
BinOpKind::Div if r != 0 => l.checked_div(r).map(zext),
BinOpKind::Rem if r != 0 => l.checked_rem(r).map(zext),
BinOpKind::Shr => l.checked_shr(r.try_into().expect("invalid shift")).map(zext),
BinOpKind::Shl => l.checked_shl(r.try_into().expect("invalid shift")).map(zext),
BinOpKind::BitXor => Some(zext(l ^ r)),
BinOpKind::BitOr => Some(zext(l | r)),
BinOpKind::BitAnd => Some(zext(l & r)),
BinOpKind::Eq => Some(Constant::Bool(l == r)),
BinOpKind::Ne => Some(Constant::Bool(l != r)),
BinOpKind::Lt => Some(Constant::Bool(l < r)),
BinOpKind::Le => Some(Constant::Bool(l <= r)),
BinOpKind::Ge => Some(Constant::Bool(l >= r)),
BinOpKind::Gt => Some(Constant::Bool(l > r)),
_ => None,
}
},
ty::Uint(_) => match op.node {
BinOpKind::Add => l.checked_add(r).map(Constant::Int),
BinOpKind::Sub => l.checked_sub(r).map(Constant::Int),
BinOpKind::Mul => l.checked_mul(r).map(Constant::Int),
BinOpKind::Div => l.checked_div(r).map(Constant::Int),
BinOpKind::Rem => l.checked_rem(r).map(Constant::Int),
BinOpKind::Shr => l.checked_shr(r.try_into().expect("shift too large")).map(Constant::Int),
BinOpKind::Shl => l.checked_shl(r.try_into().expect("shift too large")).map(Constant::Int),
BinOpKind::BitXor => Some(Constant::Int(l ^ r)),
BinOpKind::BitOr => Some(Constant::Int(l | r)),
BinOpKind::BitAnd => Some(Constant::Int(l & r)),
BinOpKind::Eq => Some(Constant::Bool(l == r)),
BinOpKind::Ne => Some(Constant::Bool(l != r)),
BinOpKind::Lt => Some(Constant::Bool(l < r)),
BinOpKind::Le => Some(Constant::Bool(l <= r)),
BinOpKind::Ge => Some(Constant::Bool(l >= r)),
BinOpKind::Gt => Some(Constant::Bool(l > r)),
_ => None,
},
_ => None,
},
(Constant::F32(l), Some(Constant::F32(r))) => match op.node {
BinOpKind::Add => Some(Constant::F32(l + r)),
BinOpKind::Sub => Some(Constant::F32(l - r)),
BinOpKind::Mul => Some(Constant::F32(l * r)),
BinOpKind::Div => Some(Constant::F32(l / r)),
BinOpKind::Rem => Some(Constant::F32(l % r)),
BinOpKind::Eq => Some(Constant::Bool(l == r)),
BinOpKind::Ne => Some(Constant::Bool(l != r)),
BinOpKind::Lt => Some(Constant::Bool(l < r)),
BinOpKind::Le => Some(Constant::Bool(l <= r)),
BinOpKind::Ge => Some(Constant::Bool(l >= r)),
BinOpKind::Gt => Some(Constant::Bool(l > r)),
_ => None,
},
(Constant::F64(l), Some(Constant::F64(r))) => match op.node {
BinOpKind::Add => Some(Constant::F64(l + r)),
BinOpKind::Sub => Some(Constant::F64(l - r)),
BinOpKind::Mul => Some(Constant::F64(l * r)),
BinOpKind::Div => Some(Constant::F64(l / r)),
BinOpKind::Rem => Some(Constant::F64(l % r)),
BinOpKind::Eq => Some(Constant::Bool(l == r)),
BinOpKind::Ne => Some(Constant::Bool(l != r)),
BinOpKind::Lt => Some(Constant::Bool(l < r)),
BinOpKind::Le => Some(Constant::Bool(l <= r)),
BinOpKind::Ge => Some(Constant::Bool(l >= r)),
BinOpKind::Gt => Some(Constant::Bool(l > r)),
_ => None,
},
(l, r) => match (op.node, l, r) {
(BinOpKind::And, Constant::Bool(false), _) => Some(Constant::Bool(false)),
(BinOpKind::Or, Constant::Bool(true), _) => Some(Constant::Bool(true)),
(BinOpKind::And, Constant::Bool(true), Some(r)) | (BinOpKind::Or, Constant::Bool(false), Some(r)) => {
Some(r)
},
(BinOpKind::BitXor, Constant::Bool(l), Some(Constant::Bool(r))) => Some(Constant::Bool(l ^ r)),
(BinOpKind::BitAnd, Constant::Bool(l), Some(Constant::Bool(r))) => Some(Constant::Bool(l & r)),
(BinOpKind::BitOr, Constant::Bool(l), Some(Constant::Bool(r))) => Some(Constant::Bool(l | r)),
_ => None,
},
}
}
}
pub fn miri_to_const(result: &ty::Const<'_>) -> Option<Constant> {
use rustc_middle::mir::interpret::ConstValue;
match result.val {
ty::ConstKind::Value(ConstValue::Scalar(Scalar::Int(int))) => {
match result.ty.kind() {
ty::Bool => Some(Constant::Bool(int == ScalarInt::TRUE)),
ty::Uint(_) | ty::Int(_) => Some(Constant::Int(int.assert_bits(int.size()))),
ty::Float(FloatTy::F32) => Some(Constant::F32(f32::from_bits(
int.try_into().expect("invalid f32 bit representation"),
))),
ty::Float(FloatTy::F64) => Some(Constant::F64(f64::from_bits(
int.try_into().expect("invalid f64 bit representation"),
))),
ty::RawPtr(type_and_mut) => {
if let ty::Uint(_) = type_and_mut.ty.kind() {
return Some(Constant::RawPtr(int.assert_bits(int.size())));
}
None
},
// FIXME: implement other conversions.
_ => None,
}
},
ty::ConstKind::Value(ConstValue::Slice { data, start, end }) => match result.ty.kind() {
ty::Ref(_, tam, _) => match tam.kind() {
ty::Str => String::from_utf8(
data.inspect_with_uninit_and_ptr_outside_interpreter(start..end)
.to_owned(),
)
.ok()
.map(Constant::Str),
_ => None,
},
_ => None,
},
ty::ConstKind::Value(ConstValue::ByRef { alloc, offset: _ }) => match result.ty.kind() {
ty::Array(sub_type, len) => match sub_type.kind() {
ty::Float(FloatTy::F32) => match miri_to_const(len) {
Some(Constant::Int(len)) => alloc
.inspect_with_uninit_and_ptr_outside_interpreter(0..(4 * len as usize))
.to_owned()
.chunks(4)
.map(|chunk| {
Some(Constant::F32(f32::from_le_bytes(
chunk.try_into().expect("this shouldn't happen"),
)))
})
.collect::<Option<Vec<Constant>>>()
.map(Constant::Vec),
_ => None,
},
ty::Float(FloatTy::F64) => match miri_to_const(len) {
Some(Constant::Int(len)) => alloc
.inspect_with_uninit_and_ptr_outside_interpreter(0..(8 * len as usize))
.to_owned()
.chunks(8)
.map(|chunk| {
Some(Constant::F64(f64::from_le_bytes(
chunk.try_into().expect("this shouldn't happen"),
)))
})
.collect::<Option<Vec<Constant>>>()
.map(Constant::Vec),
_ => None,
},
// FIXME: implement other array type conversions.
_ => None,
},
_ => None,
},
// FIXME: implement other conversions.
_ => None,
}
}