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};
/// ```
/// Use instead:
/// ```rust
- /// use std::future::Future;
- ///
/// async fn foo() -> i32 { 42 }
/// ```
pub MANUAL_ASYNC_FN,
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();
}
}
-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));
}
}
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;
...
error: this function can be simplified using the `async fn` syntax
- --> $DIR/manual_async_fn.rs:54:5
+ --> $DIR/manual_async_fn.rs:73:1
|
-LL | fn meth_fut(&self) -> impl Future<Output = i32> {
- | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | fn elided(_: &i32) -> impl Future<Output = i32> + '_ {
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
help: make the function `async` and return the output of the future directly
|
-LL | async fn meth_fut(&self) -> i32 {
- | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | async fn elided(_: &i32) -> i32 {
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: move the body of the async block to the enclosing function
|
-LL | fn meth_fut(&self) -> impl Future<Output = i32> { 42 }
- | ^^^^^^
+LL | fn elided(_: &i32) -> impl Future<Output = i32> + '_ { 42 }
+ | ^^^^^^
error: this function can be simplified using the `async fn` syntax
- --> $DIR/manual_async_fn.rs:58:5
+ --> $DIR/manual_async_fn.rs:82:1
|
-LL | fn empty_fut(&self) -> impl Future<Output = ()> {
- | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | fn explicit<'a, 'b>(_: &'a i32, _: &'b i32) -> impl Future<Output = i32> + 'a + 'b {
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
-help: make the function `async` and remove the return type
+help: make the function `async` and return the output of the future directly
|
-LL | async fn empty_fut(&self) {
- | ^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | async fn explicit<'a, 'b>(_: &'a i32, _: &'b i32) -> i32 {
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: move the body of the async block to the enclosing function
|
-LL | fn empty_fut(&self) -> impl Future<Output = ()> {}
- | ^^
+LL | fn explicit<'a, 'b>(_: &'a i32, _: &'b i32) -> impl Future<Output = i32> + 'a + 'b { 42 }
+ | ^^^^^^
error: aborting due to 6 previous errors