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manual_async_fn: take input lifetimes into account

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The anonymous future returned from an `async fn` captures all input
lifetimes. This was not being taken into account.

See https://github.com/rust-lang/rfcs/blob/master/text/2394-async_await.md#lifetime-capture-in-the-anonymous-future
This commit is contained in:
Eduardo Broto 2020-08-03 00:36:28 +02:00
parent 2e0f8b6cc6
commit e336fe80d2
6 changed files with 146 additions and 40 deletions
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63
clippy_lints/src/manual_async_fn.rs
View file

@ -4,8 +4,8 @@ use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::intravisit::FnKind;
use rustc_hir::{
AsyncGeneratorKind, Block, Body, Expr, ExprKind, FnDecl, FnRetTy, GeneratorKind, GenericBound, HirId, IsAsync,
ItemKind, TraitRef, Ty, TyKind, TypeBindingKind,
AsyncGeneratorKind, Block, Body, Expr, ExprKind, FnDecl, FnRetTy, GeneratorKind, GenericArg, GenericBound, HirId,
IsAsync, ItemKind, LifetimeName, TraitRef, Ty, TyKind, TypeBindingKind,
};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
@ -27,8 +27,6 @@ declare_clippy_lint! {
/// ```
/// Use instead:
/// ```rust
/// use std::future::Future;
///
/// async fn foo() -> i32 { 42 }
/// ```
pub MANUAL_ASYNC_FN,
@ -53,8 +51,9 @@ impl<'tcx> LateLintPass<'tcx> for ManualAsyncFn {
if let IsAsync::NotAsync = header.asyncness;
// Check that this function returns `impl Future`
if let FnRetTy::Return(ret_ty) = decl.output;
if let Some(trait_ref) = future_trait_ref(cx, ret_ty);
if let Some((trait_ref, output_lifetimes)) = future_trait_ref(cx, ret_ty);
if let Some(output) = future_output_ty(trait_ref);
if captures_all_lifetimes(decl.inputs, &output_lifetimes);
// Check that the body of the function consists of one async block
if let ExprKind::Block(block, _) = body.value.kind;
if block.stmts.is_empty();
@ -97,16 +96,35 @@ impl<'tcx> LateLintPass<'tcx> for ManualAsyncFn {
}
}
fn future_trait_ref<'tcx>(cx: &LateContext<'tcx>, ty: &'tcx Ty<'tcx>) -> Option<&'tcx TraitRef<'tcx>> {
fn future_trait_ref<'tcx>(
cx: &LateContext<'tcx>,
ty: &'tcx Ty<'tcx>,
) -> Option<(&'tcx TraitRef<'tcx>, Vec<LifetimeName>)> {
if_chain! {
if let TyKind::OpaqueDef(item_id, _) = ty.kind;
if let TyKind::OpaqueDef(item_id, bounds) = ty.kind;
let item = cx.tcx.hir().item(item_id.id);
if let ItemKind::OpaqueTy(opaque) = &item.kind;
if opaque.bounds.len() == 1;
if let GenericBound::Trait(poly, _) = &opaque.bounds[0];
if poly.trait_ref.trait_def_id() == cx.tcx.lang_items().future_trait();
if let Some(trait_ref) = opaque.bounds.iter().find_map(|bound| {
if let GenericBound::Trait(poly, _) = bound {
Some(&poly.trait_ref)
} else {
None
}
});
if trait_ref.trait_def_id() == cx.tcx.lang_items().future_trait();
then {
return Some(&poly.trait_ref);
let output_lifetimes = bounds
.iter()
.filter_map(|bound| {
if let GenericArg::Lifetime(lt) = bound {
Some(lt.name)
} else {
None
}
})
.collect();
return Some((trait_ref, output_lifetimes));
}
}
@ -129,6 +147,29 @@ fn future_output_ty<'tcx>(trait_ref: &'tcx TraitRef<'tcx>) -> Option<&'tcx Ty<'t
None
}
fn captures_all_lifetimes(inputs: &[Ty<'_>], output_lifetimes: &[LifetimeName]) -> bool {
let input_lifetimes: Vec<LifetimeName> = inputs
.iter()
.filter_map(|ty| {
if let TyKind::Rptr(lt, _) = ty.kind {
Some(lt.name)
} else {
None
}
})
.collect();
// The lint should trigger in one of these cases:
// - There are no input lifetimes
// - There's only one output lifetime bound using `+ '_`
// - All input lifetimes are explicitly bound to the output
input_lifetimes.is_empty()
|| (output_lifetimes.len() == 1 && matches!(output_lifetimes[0], LifetimeName::Underscore))
|| input_lifetimes
.iter()
.all(|in_lt| output_lifetimes.iter().any(|out_lt| in_lt == out_lt))
}
fn desugared_async_block<'tcx>(cx: &LateContext<'tcx>, block: &'tcx Block<'tcx>) -> Option<&'tcx Body<'tcx>> {
if_chain! {
if let Some(block_expr) = block.expr;