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Auto merge of #8666 - Jarcho:while_let_loop_7913, r=dswij

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Don't lint `while_let_loop` when significant drop order would change

fixes #7226
fixes #7913
fixes #5717

For #5717 it may not stay fully fixed. This is only completely fixed right now due to all the allowed drop impls have `#[may_dangle]` on their drop impls. This may get changed in the future based on how significant drops are determined, but the example listed with `RefCell` shouldn't break.

changelog: Don't lint `while_let_loop` when the order of significant drops would change
This commit is contained in:
bors 2022-06-30 04:04:08 +00:00
commit 88591ba239
4 changed files with 209 additions and 142 deletions
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110
clippy_lints/src/loops/while_let_loop.rs
View File

@ -2,71 +2,60 @@
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::higher;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::ty::needs_ordered_drop;
use clippy_utils::visitors::any_temporaries_need_ordered_drop;
use rustc_errors::Applicability;
use rustc_hir::{Block, Expr, ExprKind, MatchSource, Pat, StmtKind};
use rustc_lint::{LateContext, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_hir::{Block, Expr, ExprKind, Local, MatchSource, Pat, StmtKind};
use rustc_lint::LateContext;
pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, loop_block: &'tcx Block<'_>) {
// extract the expression from the first statement (if any) in a block
let inner_stmt_expr = extract_expr_from_first_stmt(loop_block);
// or extract the first expression (if any) from the block
if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(loop_block)) {
if let Some(higher::IfLet {
let_pat,
let_expr,
if_else: Some(if_else),
..
}) = higher::IfLet::hir(cx, inner)
{
if is_simple_break_expr(if_else) {
could_be_while_let(cx, expr, let_pat, let_expr);
let (init, has_trailing_exprs) = match (loop_block.stmts, loop_block.expr) {
([stmt, stmts @ ..], expr) => {
if let StmtKind::Local(&Local { init: Some(e), .. }) | StmtKind::Semi(e) | StmtKind::Expr(e) = stmt.kind {
(e, !stmts.is_empty() || expr.is_some())
} else {
return;
}
}
if let ExprKind::Match(matchexpr, arms, MatchSource::Normal) = inner.kind {
if arms.len() == 2
&& arms[0].guard.is_none()
&& arms[1].guard.is_none()
&& is_simple_break_expr(arms[1].body)
{
could_be_while_let(cx, expr, arms[0].pat, matchexpr);
}
}
}
}
/// If a block begins with a statement (possibly a `let` binding) and has an
/// expression, return it.
fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
if let Some(first_stmt) = block.stmts.get(0) {
if let StmtKind::Local(local) = first_stmt.kind {
return local.init;
}
}
None
}
/// If a block begins with an expression (with or without semicolon), return it.
fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
match block.expr {
Some(expr) if block.stmts.is_empty() => Some(expr),
None if !block.stmts.is_empty() => match block.stmts[0].kind {
StmtKind::Expr(expr) | StmtKind::Semi(expr) => Some(expr),
StmtKind::Local(..) | StmtKind::Item(..) => None,
},
_ => None,
([], Some(e)) => (e, false),
_ => return,
};
if let Some(if_let) = higher::IfLet::hir(cx, init)
&& let Some(else_expr) = if_let.if_else
&& is_simple_break_expr(else_expr)
{
could_be_while_let(cx, expr, if_let.let_pat, if_let.let_expr, has_trailing_exprs);
} else if let ExprKind::Match(scrutinee, [arm1, arm2], MatchSource::Normal) = init.kind
&& arm1.guard.is_none()
&& arm2.guard.is_none()
&& is_simple_break_expr(arm2.body)
{
could_be_while_let(cx, expr, arm1.pat, scrutinee, has_trailing_exprs);
}
}
/// Returns `true` if expr contains a single break expr without destination label
/// and
/// passed expression. The expression may be within a block.
fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
match expr.kind {
ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
ExprKind::Block(b, _) => extract_first_expr(b).map_or(false, is_simple_break_expr),
_ => false,
/// Returns `true` if expr contains a single break expression without a label or eub-expression.
fn is_simple_break_expr(e: &Expr<'_>) -> bool {
matches!(peel_blocks(e).kind, ExprKind::Break(dest, None) if dest.label.is_none())
}
/// Removes any blocks containing only a single expression.
fn peel_blocks<'tcx>(e: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
if let ExprKind::Block(b, _) = e.kind {
match (b.stmts, b.expr) {
([s], None) => {
if let StmtKind::Expr(e) | StmtKind::Semi(e) = s.kind {
peel_blocks(e)
} else {
e
}
},
([], Some(e)) => peel_blocks(e),
_ => e,
}
} else {
e
}
}
@ -75,8 +64,13 @@ fn could_be_while_let<'tcx>(
expr: &'tcx Expr<'_>,
let_pat: &'tcx Pat<'_>,
let_expr: &'tcx Expr<'_>,
has_trailing_exprs: bool,
) {
if in_external_macro(cx.sess(), expr.span) {
if has_trailing_exprs
&& (needs_ordered_drop(cx, cx.typeck_results().expr_ty(let_expr))
|| any_temporaries_need_ordered_drop(cx, let_expr))
{
// Switching to a `while let` loop will extend the lifetime of some values.
return;
}

84
clippy_lints/src/matches/redundant_pattern_match.rs
View File

@ -3,16 +3,13 @@
use clippy_utils::source::snippet;
use clippy_utils::sugg::Sugg;
use clippy_utils::ty::needs_ordered_drop;
use clippy_utils::{higher, match_def_path};
use clippy_utils::{is_lang_ctor, is_trait_method, paths};
use clippy_utils::visitors::any_temporaries_need_ordered_drop;
use clippy_utils::{higher, is_lang_ctor, is_trait_method, match_def_path, paths};
use if_chain::if_chain;
use rustc_ast::ast::LitKind;
use rustc_errors::Applicability;
use rustc_hir::LangItem::{OptionNone, PollPending};
use rustc_hir::{
intravisit::{walk_expr, Visitor},
Arm, Block, Expr, ExprKind, Node, Pat, PatKind, QPath, UnOp,
};
use rustc_hir::{Arm, Expr, ExprKind, Node, Pat, PatKind, QPath, UnOp};
use rustc_lint::LateContext;
use rustc_middle::ty::{self, subst::GenericArgKind, DefIdTree, Ty};
use rustc_span::sym;
@ -47,79 +44,6 @@ fn try_get_generic_ty(ty: Ty<'_>, index: usize) -> Option<Ty<'_>> {
}
}
// Checks if there are any temporaries created in the given expression for which drop order
// matters.
fn temporaries_need_ordered_drop<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
struct V<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
res: bool,
}
impl<'a, 'tcx> Visitor<'tcx> for V<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
match expr.kind {
// Taking the reference of a value leaves a temporary
// e.g. In `&String::new()` the string is a temporary value.
// Remaining fields are temporary values
// e.g. In `(String::new(), 0).1` the string is a temporary value.
ExprKind::AddrOf(_, _, expr) | ExprKind::Field(expr, _) => {
if !matches!(expr.kind, ExprKind::Path(_)) {
if needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(expr)) {
self.res = true;
} else {
self.visit_expr(expr);
}
}
},
// the base type is always taken by reference.
// e.g. In `(vec![0])[0]` the vector is a temporary value.
ExprKind::Index(base, index) => {
if !matches!(base.kind, ExprKind::Path(_)) {
if needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(base)) {
self.res = true;
} else {
self.visit_expr(base);
}
}
self.visit_expr(index);
},
// Method calls can take self by reference.
// e.g. In `String::new().len()` the string is a temporary value.
ExprKind::MethodCall(_, [self_arg, args @ ..], _) => {
if !matches!(self_arg.kind, ExprKind::Path(_)) {
let self_by_ref = self
.cx
.typeck_results()
.type_dependent_def_id(expr.hir_id)
.map_or(false, |id| self.cx.tcx.fn_sig(id).skip_binder().inputs()[0].is_ref());
if self_by_ref && needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(self_arg)) {
self.res = true;
} else {
self.visit_expr(self_arg);
}
}
args.iter().for_each(|arg| self.visit_expr(arg));
},
// Either explicitly drops values, or changes control flow.
ExprKind::DropTemps(_)
| ExprKind::Ret(_)
| ExprKind::Break(..)
| ExprKind::Yield(..)
| ExprKind::Block(Block { expr: None, .. }, _)
| ExprKind::Loop(..) => (),
// Only consider the final expression.
ExprKind::Block(Block { expr: Some(expr), .. }, _) => self.visit_expr(expr),
_ => walk_expr(self, expr),
}
}
}
let mut v = V { cx, res: false };
v.visit_expr(expr);
v.res
}
fn find_sugg_for_if_let<'tcx>(
cx: &LateContext<'tcx>,
expr: &'tcx Expr<'_>,
@ -191,7 +115,7 @@ fn find_sugg_for_if_let<'tcx>(
// scrutinee would be, so they have to be considered as well.
// e.g. in `if let Some(x) = foo.lock().unwrap().baz.as_ref() { .. }` the lock will be held
// for the duration if body.
let needs_drop = needs_ordered_drop(cx, check_ty) || temporaries_need_ordered_drop(cx, let_expr);
let needs_drop = needs_ordered_drop(cx, check_ty) || any_temporaries_need_ordered_drop(cx, let_expr);
// check that `while_let_on_iterator` lint does not trigger
if_chain! {

131
clippy_utils/src/visitors.rs
View File

@ -1,16 +1,18 @@
use crate::ty::needs_ordered_drop;
use crate::{get_enclosing_block, path_to_local_id};
use core::ops::ControlFlow;
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def::{CtorKind, DefKind, Res};
use rustc_hir::intravisit::{self, walk_block, walk_expr, Visitor};
use rustc_hir::{
Arm, Block, BlockCheckMode, Body, BodyId, Expr, ExprKind, HirId, ItemId, ItemKind, Stmt, UnOp, UnsafeSource,
Unsafety,
Arm, Block, BlockCheckMode, Body, BodyId, Expr, ExprKind, HirId, ItemId, ItemKind, Let, QPath, Stmt, UnOp,
UnsafeSource, Unsafety,
};
use rustc_lint::LateContext;
use rustc_middle::hir::map::Map;
use rustc_middle::hir::nested_filter;
use rustc_middle::ty;
use rustc_middle::ty::adjustment::Adjust;
use rustc_middle::ty::{self, Ty, TypeckResults};
/// Convenience method for creating a `Visitor` with just `visit_expr` overridden and nested
/// bodies (i.e. closures) are visited.
@ -494,3 +496,124 @@ fn visit_expr(&mut self, e: &'tcx Expr<'tcx>) {
ControlFlow::Continue(())
}
}
// Calls the given function for every unconsumed temporary created by the expression. Note the
// function is only guaranteed to be called for types which need to be dropped, but it may be called
// for other types.
pub fn for_each_unconsumed_temporary<'tcx, B>(
cx: &LateContext<'tcx>,
e: &'tcx Expr<'tcx>,
mut f: impl FnMut(Ty<'tcx>) -> ControlFlow<B>,
) -> ControlFlow<B> {
// Todo: Handle partially consumed values.
fn helper<'tcx, B>(
typeck: &'tcx TypeckResults<'tcx>,
consume: bool,
e: &'tcx Expr<'tcx>,
f: &mut impl FnMut(Ty<'tcx>) -> ControlFlow<B>,
) -> ControlFlow<B> {
if !consume
|| matches!(
typeck.expr_adjustments(e),
[adjust, ..] if matches!(adjust.kind, Adjust::Borrow(_) | Adjust::Deref(_))
)
{
match e.kind {
ExprKind::Path(QPath::Resolved(None, p))
if matches!(p.res, Res::Def(DefKind::Ctor(_, CtorKind::Const), _)) =>
{
f(typeck.expr_ty(e))?;
},
ExprKind::Path(_)
| ExprKind::Unary(UnOp::Deref, _)
| ExprKind::Index(..)
| ExprKind::Field(..)
| ExprKind::AddrOf(..) => (),
_ => f(typeck.expr_ty(e))?,
}
}
match e.kind {
ExprKind::AddrOf(_, _, e)
| ExprKind::Field(e, _)
| ExprKind::Unary(UnOp::Deref, e)
| ExprKind::Match(e, ..)
| ExprKind::Let(&Let { init: e, .. }) => {
helper(typeck, false, e, f)?;
},
ExprKind::Block(&Block { expr: Some(e), .. }, _)
| ExprKind::Box(e)
| ExprKind::Cast(e, _)
| ExprKind::Unary(_, e) => {
helper(typeck, true, e, f)?;
},
ExprKind::Call(callee, args) => {
helper(typeck, true, callee, f)?;
for arg in args {
helper(typeck, true, arg, f)?;
}
},
ExprKind::MethodCall(_, args, _) | ExprKind::Tup(args) | ExprKind::Array(args) => {
for arg in args {
helper(typeck, true, arg, f)?;
}
},
ExprKind::Index(borrowed, consumed)
| ExprKind::Assign(borrowed, consumed, _)
| ExprKind::AssignOp(_, borrowed, consumed) => {
helper(typeck, false, borrowed, f)?;
helper(typeck, true, consumed, f)?;
},
ExprKind::Binary(_, lhs, rhs) => {
helper(typeck, true, lhs, f)?;
helper(typeck, true, rhs, f)?;
},
ExprKind::Struct(_, fields, default) => {
for field in fields {
helper(typeck, true, field.expr, f)?;
}
if let Some(default) = default {
helper(typeck, false, default, f)?;
}
},
ExprKind::If(cond, then, else_expr) => {
helper(typeck, true, cond, f)?;
helper(typeck, true, then, f)?;
if let Some(else_expr) = else_expr {
helper(typeck, true, else_expr, f)?;
}
},
ExprKind::Type(e, _) => {
helper(typeck, consume, e, f)?;
},
// Either drops temporaries, jumps out of the current expression, or has no sub expression.
ExprKind::DropTemps(_)
| ExprKind::Ret(_)
| ExprKind::Break(..)
| ExprKind::Yield(..)
| ExprKind::Block(..)
| ExprKind::Loop(..)
| ExprKind::Repeat(..)
| ExprKind::Lit(_)
| ExprKind::ConstBlock(_)
| ExprKind::Closure { .. }
| ExprKind::Path(_)
| ExprKind::Continue(_)
| ExprKind::InlineAsm(_)
| ExprKind::Err => (),
}
ControlFlow::Continue(())
}
helper(cx.typeck_results(), true, e, &mut f)
}
pub fn any_temporaries_need_ordered_drop<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>) -> bool {
for_each_unconsumed_temporary(cx, e, |ty| {
if needs_ordered_drop(cx, ty) {
ControlFlow::Break(())
} else {
ControlFlow::Continue(())
}
})
.is_break()
}

26
tests/ui/while_let_loop.rs
View File

@ -117,3 +117,29 @@ fn issue1948() {
}
};
}
fn issue_7913(m: &std::sync::Mutex<Vec<u32>>) {
// Don't lint. The lock shouldn't be held while printing.
loop {
let x = if let Some(x) = m.lock().unwrap().pop() {
x
} else {
break;
};
println!("{}", x);
}
}
fn issue_5715(mut m: core::cell::RefCell<Option<u32>>) {
// Don't lint. The temporary from `borrow_mut` must be dropped before overwriting the `RefCell`.
loop {
let x = if let &mut Some(x) = &mut *m.borrow_mut() {
x
} else {
break;
};
m = core::cell::RefCell::new(Some(x + 1));
}
}