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https://github.com/rust-lang/rust-clippy
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Threadlocal_initializer_can_be_made_const will not trigger for unreachable initializers
This commit introduces a check to ensure that the lint won't trigger when the initializer is unreachable, such as: ``` thread_local! { static STATE: Cell<usize> = panic!(); } ``` This is achieved by looking at the unpeeled initializer expression and ensuring that the parent macro is not `panic!()`, `todo!()`, `unreachable!()`, `unimplemented!()`. fixes #12637 changelog: [`threadlocal_initializer_can_be_made_const`] will no longer trigger on `unreachable` macros.
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3 changed files with 95 additions and 7 deletions
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@ -1,13 +1,14 @@
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use clippy_config::msrvs::{self, Msrv};
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use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::macros::macro_backtrace;
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use clippy_utils::qualify_min_const_fn::is_min_const_fn;
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use clippy_utils::source::snippet;
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use clippy_utils::{fn_has_unsatisfiable_preds, peel_blocks};
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use rustc_errors::Applicability;
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use rustc_hir::{intravisit, ExprKind};
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use rustc_hir::{intravisit, Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::impl_lint_pass;
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use rustc_span::sym::thread_local_macro;
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use rustc_span::sym::{self, thread_local_macro};
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declare_clippy_lint! {
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/// ### What it does
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@ -69,6 +70,26 @@ fn is_thread_local_initializer(
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)
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}
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fn is_unreachable(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
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if let Some(macro_call) = macro_backtrace(expr.span).next()
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&& let Some(diag_name) = cx.tcx.get_diagnostic_name(macro_call.def_id)
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{
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return (matches!(
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diag_name,
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sym::core_panic_macro
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| sym::std_panic_macro
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| sym::core_panic_2015_macro
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| sym::std_panic_2015_macro
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| sym::core_panic_2021_macro
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) && !cx.tcx.hir().is_inside_const_context(expr.hir_id))
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|| matches!(
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diag_name,
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sym::unimplemented_macro | sym::todo_macro | sym::unreachable_macro | sym::unreachable_2015_macro
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);
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}
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false
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}
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#[inline]
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fn initializer_can_be_made_const(cx: &LateContext<'_>, defid: rustc_span::def_id::DefId, msrv: &Msrv) -> bool {
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// Building MIR for `fn`s with unsatisfiable preds results in ICE.
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@ -102,12 +123,17 @@ impl<'tcx> LateLintPass<'tcx> for ThreadLocalInitializerCanBeMadeConst {
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// for details on this issue, see:
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// https://github.com/rust-lang/rust-clippy/pull/12276
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&& !cx.tcx.is_const_fn(defid)
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&& initializer_can_be_made_const(cx, defid, &self.msrv)
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// we know that the function is const-qualifiable, so now
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// we need only to get the initializer expression to span-lint it.
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&& let ExprKind::Block(block, _) = body.value.kind
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&& let Some(unpeeled) = block.expr
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&& let ret_expr = peel_blocks(unpeeled)
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// A common pattern around threadlocal! is to make the value unreachable
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// to force an initialization before usage
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// https://github.com/rust-lang/rust-clippy/issues/12637
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// we ensure that this is reachable before we check in mir
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&& !is_unreachable(cx, ret_expr)
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&& initializer_can_be_made_const(cx, defid, &self.msrv)
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// we know that the function is const-qualifiable, so now
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// we need only to get the initializer expression to span-lint it.
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&& let initializer_snippet = snippet(cx, ret_expr.span, "thread_local! { ... }")
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&& initializer_snippet != "thread_local! { ... }"
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{
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@ -1,6 +1,6 @@
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#![warn(clippy::thread_local_initializer_can_be_made_const)]
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use std::cell::RefCell;
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use std::cell::{Cell, RefCell};
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fn main() {
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// lint and suggest const
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@ -36,6 +36,37 @@ fn main() {
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}
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}
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fn issue_12637() {
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/// The set methods on LocalKey<Cell<T>> and LocalKey<RefCell<T>> are
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/// guaranteed to bypass the thread_local's initialization expression.
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/// See rust-lang/rust#92122. Thus, = panic!() is a useful idiom for
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/// forcing the use of set on each thread before it accesses the thread local in any other
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/// manner.
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thread_local! {
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static STATE_12637_PANIC: Cell<usize> = panic!();
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}
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STATE_12637_PANIC.set(9);
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println!("{}", STATE_12637_PANIC.get());
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thread_local! {
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static STATE_12637_TODO: Cell<usize> = todo!();
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}
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STATE_12637_TODO.set(9);
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println!("{}", STATE_12637_TODO.get());
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thread_local! {
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static STATE_12637_UNIMPLEMENTED: Cell<usize> = unimplemented!();
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}
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STATE_12637_UNIMPLEMENTED.set(9);
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println!("{}", STATE_12637_UNIMPLEMENTED.get());
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thread_local! {
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static STATE_12637_UNREACHABLE: Cell<usize> = unreachable!();
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}
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STATE_12637_UNREACHABLE.set(9);
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println!("{}", STATE_12637_UNREACHABLE.get());
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}
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#[clippy::msrv = "1.58"]
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fn f() {
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thread_local! {
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@ -1,6 +1,6 @@
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#![warn(clippy::thread_local_initializer_can_be_made_const)]
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use std::cell::RefCell;
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use std::cell::{Cell, RefCell};
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fn main() {
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// lint and suggest const
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@ -36,6 +36,37 @@ fn main() {
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}
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}
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fn issue_12637() {
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/// The set methods on LocalKey<Cell<T>> and LocalKey<RefCell<T>> are
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/// guaranteed to bypass the thread_local's initialization expression.
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/// See rust-lang/rust#92122. Thus, = panic!() is a useful idiom for
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/// forcing the use of set on each thread before it accesses the thread local in any other
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/// manner.
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thread_local! {
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static STATE_12637_PANIC: Cell<usize> = panic!();
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}
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STATE_12637_PANIC.set(9);
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println!("{}", STATE_12637_PANIC.get());
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thread_local! {
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static STATE_12637_TODO: Cell<usize> = todo!();
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}
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STATE_12637_TODO.set(9);
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println!("{}", STATE_12637_TODO.get());
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thread_local! {
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static STATE_12637_UNIMPLEMENTED: Cell<usize> = unimplemented!();
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}
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STATE_12637_UNIMPLEMENTED.set(9);
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println!("{}", STATE_12637_UNIMPLEMENTED.get());
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thread_local! {
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static STATE_12637_UNREACHABLE: Cell<usize> = unreachable!();
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}
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STATE_12637_UNREACHABLE.set(9);
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println!("{}", STATE_12637_UNREACHABLE.get());
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}
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#[clippy::msrv = "1.58"]
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fn f() {
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thread_local! {
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