351 lines
12 KiB
Rust
351 lines
12 KiB
Rust
use clippy_utils::diagnostics::{span_lint, span_lint_and_note};
|
|
use clippy_utils::{get_parent_expr, path_to_local, path_to_local_id};
|
|
use if_chain::if_chain;
|
|
use rustc_hir::intravisit::{walk_expr, Visitor};
|
|
use rustc_hir::{BinOpKind, Block, Expr, ExprKind, Guard, HirId, Local, Node, Stmt, StmtKind};
|
|
use rustc_lint::{LateContext, LateLintPass};
|
|
use rustc_middle::ty;
|
|
use rustc_session::{declare_lint_pass, declare_tool_lint};
|
|
|
|
declare_clippy_lint! {
|
|
/// ### What it does
|
|
/// Checks for a read and a write to the same variable where
|
|
/// whether the read occurs before or after the write depends on the evaluation
|
|
/// order of sub-expressions.
|
|
///
|
|
/// ### Why is this bad?
|
|
/// It is often confusing to read. As described [here](https://doc.rust-lang.org/reference/expressions.html?highlight=subexpression#evaluation-order-of-operands),
|
|
/// the operands of these expressions are evaluated before applying the effects of the expression.
|
|
///
|
|
/// ### Known problems
|
|
/// Code which intentionally depends on the evaluation
|
|
/// order, or which is correct for any evaluation order.
|
|
///
|
|
/// ### Example
|
|
/// ```rust
|
|
/// let mut x = 0;
|
|
///
|
|
/// let a = {
|
|
/// x = 1;
|
|
/// 1
|
|
/// } + x;
|
|
/// // Unclear whether a is 1 or 2.
|
|
/// ```
|
|
///
|
|
/// Use instead:
|
|
/// ```rust
|
|
/// # let mut x = 0;
|
|
/// let tmp = {
|
|
/// x = 1;
|
|
/// 1
|
|
/// };
|
|
/// let a = tmp + x;
|
|
/// ```
|
|
#[clippy::version = "pre 1.29.0"]
|
|
pub MIXED_READ_WRITE_IN_EXPRESSION,
|
|
restriction,
|
|
"whether a variable read occurs before a write depends on sub-expression evaluation order"
|
|
}
|
|
|
|
declare_clippy_lint! {
|
|
/// ### What it does
|
|
/// Checks for diverging calls that are not match arms or
|
|
/// statements.
|
|
///
|
|
/// ### Why is this bad?
|
|
/// It is often confusing to read. In addition, the
|
|
/// sub-expression evaluation order for Rust is not well documented.
|
|
///
|
|
/// ### Known problems
|
|
/// Someone might want to use `some_bool || panic!()` as a
|
|
/// shorthand.
|
|
///
|
|
/// ### Example
|
|
/// ```rust,no_run
|
|
/// # fn b() -> bool { true }
|
|
/// # fn c() -> bool { true }
|
|
/// let a = b() || panic!() || c();
|
|
/// // `c()` is dead, `panic!()` is only called if `b()` returns `false`
|
|
/// let x = (a, b, c, panic!());
|
|
/// // can simply be replaced by `panic!()`
|
|
/// ```
|
|
#[clippy::version = "pre 1.29.0"]
|
|
pub DIVERGING_SUB_EXPRESSION,
|
|
complexity,
|
|
"whether an expression contains a diverging sub expression"
|
|
}
|
|
|
|
declare_lint_pass!(EvalOrderDependence => [MIXED_READ_WRITE_IN_EXPRESSION, DIVERGING_SUB_EXPRESSION]);
|
|
|
|
impl<'tcx> LateLintPass<'tcx> for EvalOrderDependence {
|
|
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
|
|
// Find a write to a local variable.
|
|
let var = if_chain! {
|
|
if let ExprKind::Assign(lhs, ..) | ExprKind::AssignOp(_, lhs, _) = expr.kind;
|
|
if let Some(var) = path_to_local(lhs);
|
|
if expr.span.desugaring_kind().is_none();
|
|
then { var } else { return; }
|
|
};
|
|
let mut visitor = ReadVisitor {
|
|
cx,
|
|
var,
|
|
write_expr: expr,
|
|
last_expr: expr,
|
|
};
|
|
check_for_unsequenced_reads(&mut visitor);
|
|
}
|
|
fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
|
|
match stmt.kind {
|
|
StmtKind::Local(local) => {
|
|
if let Local { init: Some(e), .. } = local {
|
|
DivergenceVisitor { cx }.visit_expr(e);
|
|
}
|
|
},
|
|
StmtKind::Expr(e) | StmtKind::Semi(e) => DivergenceVisitor { cx }.maybe_walk_expr(e),
|
|
StmtKind::Item(..) => {},
|
|
}
|
|
}
|
|
}
|
|
|
|
struct DivergenceVisitor<'a, 'tcx> {
|
|
cx: &'a LateContext<'tcx>,
|
|
}
|
|
|
|
impl<'a, 'tcx> DivergenceVisitor<'a, 'tcx> {
|
|
fn maybe_walk_expr(&mut self, e: &'tcx Expr<'_>) {
|
|
match e.kind {
|
|
ExprKind::Closure { .. } => {},
|
|
ExprKind::Match(e, arms, _) => {
|
|
self.visit_expr(e);
|
|
for arm in arms {
|
|
if let Some(Guard::If(if_expr)) = arm.guard {
|
|
self.visit_expr(if_expr);
|
|
}
|
|
// make sure top level arm expressions aren't linted
|
|
self.maybe_walk_expr(arm.body);
|
|
}
|
|
},
|
|
_ => walk_expr(self, e),
|
|
}
|
|
}
|
|
fn report_diverging_sub_expr(&mut self, e: &Expr<'_>) {
|
|
span_lint(self.cx, DIVERGING_SUB_EXPRESSION, e.span, "sub-expression diverges");
|
|
}
|
|
}
|
|
|
|
impl<'a, 'tcx> Visitor<'tcx> for DivergenceVisitor<'a, 'tcx> {
|
|
fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
|
|
match e.kind {
|
|
ExprKind::Continue(_) | ExprKind::Break(_, _) | ExprKind::Ret(_) => self.report_diverging_sub_expr(e),
|
|
ExprKind::Call(func, _) => {
|
|
let typ = self.cx.typeck_results().expr_ty(func);
|
|
match typ.kind() {
|
|
ty::FnDef(..) | ty::FnPtr(_) => {
|
|
let sig = typ.fn_sig(self.cx.tcx);
|
|
if self.cx.tcx.erase_late_bound_regions(sig).output().kind() == &ty::Never {
|
|
self.report_diverging_sub_expr(e);
|
|
}
|
|
},
|
|
_ => {},
|
|
}
|
|
},
|
|
ExprKind::MethodCall(..) => {
|
|
let borrowed_table = self.cx.typeck_results();
|
|
if borrowed_table.expr_ty(e).is_never() {
|
|
self.report_diverging_sub_expr(e);
|
|
}
|
|
},
|
|
_ => {
|
|
// do not lint expressions referencing objects of type `!`, as that required a
|
|
// diverging expression
|
|
// to begin with
|
|
},
|
|
}
|
|
self.maybe_walk_expr(e);
|
|
}
|
|
fn visit_block(&mut self, _: &'tcx Block<'_>) {
|
|
// don't continue over blocks, LateLintPass already does that
|
|
}
|
|
}
|
|
|
|
/// Walks up the AST from the given write expression (`vis.write_expr`) looking
|
|
/// for reads to the same variable that are unsequenced relative to the write.
|
|
///
|
|
/// This means reads for which there is a common ancestor between the read and
|
|
/// the write such that
|
|
///
|
|
/// * evaluating the ancestor necessarily evaluates both the read and the write (for example, `&x`
|
|
/// and `|| x = 1` don't necessarily evaluate `x`), and
|
|
///
|
|
/// * which one is evaluated first depends on the order of sub-expression evaluation. Blocks, `if`s,
|
|
/// loops, `match`es, and the short-circuiting logical operators are considered to have a defined
|
|
/// evaluation order.
|
|
///
|
|
/// When such a read is found, the lint is triggered.
|
|
fn check_for_unsequenced_reads(vis: &mut ReadVisitor<'_, '_>) {
|
|
let map = &vis.cx.tcx.hir();
|
|
let mut cur_id = vis.write_expr.hir_id;
|
|
loop {
|
|
let parent_id = map.get_parent_node(cur_id);
|
|
if parent_id == cur_id {
|
|
break;
|
|
}
|
|
let parent_node = match map.find(parent_id) {
|
|
Some(parent) => parent,
|
|
None => break,
|
|
};
|
|
|
|
let stop_early = match parent_node {
|
|
Node::Expr(expr) => check_expr(vis, expr),
|
|
Node::Stmt(stmt) => check_stmt(vis, stmt),
|
|
Node::Item(_) => {
|
|
// We reached the top of the function, stop.
|
|
break;
|
|
},
|
|
_ => StopEarly::KeepGoing,
|
|
};
|
|
match stop_early {
|
|
StopEarly::Stop => break,
|
|
StopEarly::KeepGoing => {},
|
|
}
|
|
|
|
cur_id = parent_id;
|
|
}
|
|
}
|
|
|
|
/// Whether to stop early for the loop in `check_for_unsequenced_reads`. (If
|
|
/// `check_expr` weren't an independent function, this would be unnecessary and
|
|
/// we could just use `break`).
|
|
enum StopEarly {
|
|
KeepGoing,
|
|
Stop,
|
|
}
|
|
|
|
fn check_expr<'a, 'tcx>(vis: &mut ReadVisitor<'a, 'tcx>, expr: &'tcx Expr<'_>) -> StopEarly {
|
|
if expr.hir_id == vis.last_expr.hir_id {
|
|
return StopEarly::KeepGoing;
|
|
}
|
|
|
|
match expr.kind {
|
|
ExprKind::Array(_)
|
|
| ExprKind::Tup(_)
|
|
| ExprKind::MethodCall(..)
|
|
| ExprKind::Call(_, _)
|
|
| ExprKind::Assign(..)
|
|
| ExprKind::Index(_, _)
|
|
| ExprKind::Repeat(_, _)
|
|
| ExprKind::Struct(_, _, _) => {
|
|
walk_expr(vis, expr);
|
|
},
|
|
ExprKind::Binary(op, _, _) | ExprKind::AssignOp(op, _, _) => {
|
|
if op.node == BinOpKind::And || op.node == BinOpKind::Or {
|
|
// x && y and x || y always evaluate x first, so these are
|
|
// strictly sequenced.
|
|
} else {
|
|
walk_expr(vis, expr);
|
|
}
|
|
},
|
|
ExprKind::Closure { .. } => {
|
|
// Either
|
|
//
|
|
// * `var` is defined in the closure body, in which case we've reached the top of the enclosing
|
|
// function and can stop, or
|
|
//
|
|
// * `var` is captured by the closure, in which case, because evaluating a closure does not evaluate
|
|
// its body, we don't necessarily have a write, so we need to stop to avoid generating false
|
|
// positives.
|
|
//
|
|
// This is also the only place we need to stop early (grrr).
|
|
return StopEarly::Stop;
|
|
},
|
|
// All other expressions either have only one child or strictly
|
|
// sequence the evaluation order of their sub-expressions.
|
|
_ => {},
|
|
}
|
|
|
|
vis.last_expr = expr;
|
|
|
|
StopEarly::KeepGoing
|
|
}
|
|
|
|
fn check_stmt<'a, 'tcx>(vis: &mut ReadVisitor<'a, 'tcx>, stmt: &'tcx Stmt<'_>) -> StopEarly {
|
|
match stmt.kind {
|
|
StmtKind::Expr(expr) | StmtKind::Semi(expr) => check_expr(vis, expr),
|
|
// If the declaration is of a local variable, check its initializer
|
|
// expression if it has one. Otherwise, keep going.
|
|
StmtKind::Local(local) => local
|
|
.init
|
|
.as_ref()
|
|
.map_or(StopEarly::KeepGoing, |expr| check_expr(vis, expr)),
|
|
StmtKind::Item(..) => StopEarly::KeepGoing,
|
|
}
|
|
}
|
|
|
|
/// A visitor that looks for reads from a variable.
|
|
struct ReadVisitor<'a, 'tcx> {
|
|
cx: &'a LateContext<'tcx>,
|
|
/// The ID of the variable we're looking for.
|
|
var: HirId,
|
|
/// The expressions where the write to the variable occurred (for reporting
|
|
/// in the lint).
|
|
write_expr: &'tcx Expr<'tcx>,
|
|
/// The last (highest in the AST) expression we've checked, so we know not
|
|
/// to recheck it.
|
|
last_expr: &'tcx Expr<'tcx>,
|
|
}
|
|
|
|
impl<'a, 'tcx> Visitor<'tcx> for ReadVisitor<'a, 'tcx> {
|
|
fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
|
|
if expr.hir_id == self.last_expr.hir_id {
|
|
return;
|
|
}
|
|
|
|
if path_to_local_id(expr, self.var) {
|
|
// Check that this is a read, not a write.
|
|
if !is_in_assignment_position(self.cx, expr) {
|
|
span_lint_and_note(
|
|
self.cx,
|
|
MIXED_READ_WRITE_IN_EXPRESSION,
|
|
expr.span,
|
|
&format!("unsequenced read of `{}`", self.cx.tcx.hir().name(self.var)),
|
|
Some(self.write_expr.span),
|
|
"whether read occurs before this write depends on evaluation order",
|
|
);
|
|
}
|
|
}
|
|
match expr.kind {
|
|
// We're about to descend a closure. Since we don't know when (or
|
|
// if) the closure will be evaluated, any reads in it might not
|
|
// occur here (or ever). Like above, bail to avoid false positives.
|
|
ExprKind::Closure{..} |
|
|
|
|
// We want to avoid a false positive when a variable name occurs
|
|
// only to have its address taken, so we stop here. Technically,
|
|
// this misses some weird cases, eg.
|
|
//
|
|
// ```rust
|
|
// let mut x = 0;
|
|
// let a = foo(&{x = 1; x}, x);
|
|
// ```
|
|
//
|
|
// TODO: fix this
|
|
ExprKind::AddrOf(_, _, _) => {
|
|
return;
|
|
}
|
|
_ => {}
|
|
}
|
|
|
|
walk_expr(self, expr);
|
|
}
|
|
}
|
|
|
|
/// Returns `true` if `expr` is the LHS of an assignment, like `expr = ...`.
|
|
fn is_in_assignment_position(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
|
|
if let Some(parent) = get_parent_expr(cx, expr) {
|
|
if let ExprKind::Assign(lhs, ..) = parent.kind {
|
|
return lhs.hir_id == expr.hir_id;
|
|
}
|
|
}
|
|
false
|
|
}
|