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|
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::match_function_call_with_def_id;
use clippy_utils::source::{position_before_rarrow, snippet_block, snippet_opt};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::intravisit::FnKind;
use rustc_hir::{
AsyncGeneratorKind, Block, Body, Closure, Expr, ExprKind, FnDecl, FnRetTy, GeneratorKind, GenericArg, GenericBound,
ItemKind, LifetimeName, Term, TraitRef, Ty, TyKind, TypeBindingKind,
};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::def_id::LocalDefId;
use rustc_span::{sym, Span};
declare_clippy_lint! {
/// ### What it does
/// It checks for manual implementations of `async` functions.
///
/// ### Why is this bad?
/// It's more idiomatic to use the dedicated syntax.
///
/// ### Example
/// ```rust
/// use std::future::Future;
///
/// fn foo() -> impl Future<Output = i32> { async { 42 } }
/// ```
/// Use instead:
/// ```rust
/// async fn foo() -> i32 { 42 }
/// ```
#[clippy::version = "1.45.0"]
pub MANUAL_ASYNC_FN,
style,
"manual implementations of `async` functions can be simplified using the dedicated syntax"
}
declare_lint_pass!(ManualAsyncFn => [MANUAL_ASYNC_FN]);
impl<'tcx> LateLintPass<'tcx> for ManualAsyncFn {
fn check_fn(
&mut self,
cx: &LateContext<'tcx>,
kind: FnKind<'tcx>,
decl: &'tcx FnDecl<'_>,
body: &'tcx Body<'_>,
span: Span,
_: LocalDefId,
) {
if_chain! {
if let Some(header) = kind.header();
if !header.asyncness.is_async();
// Check that this function returns `impl Future`
if let FnRetTy::Return(ret_ty) = decl.output;
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();
if let Some(closure_body) = desugared_async_block(cx, block);
then {
let header_span = span.with_hi(ret_ty.span.hi());
span_lint_and_then(
cx,
MANUAL_ASYNC_FN,
header_span,
"this function can be simplified using the `async fn` syntax",
|diag| {
if_chain! {
if let Some(header_snip) = snippet_opt(cx, header_span);
if let Some(ret_pos) = position_before_rarrow(&header_snip);
if let Some((ret_sugg, ret_snip)) = suggested_ret(cx, output);
then {
let help = format!("make the function `async` and {ret_sugg}");
diag.span_suggestion(
header_span,
help,
format!("async {}{ret_snip}", &header_snip[..ret_pos]),
Applicability::MachineApplicable
);
let body_snip = snippet_block(cx, closure_body.value.span, "..", Some(block.span));
diag.span_suggestion(
block.span,
"move the body of the async block to the enclosing function",
body_snip,
Applicability::MachineApplicable
);
}
}
},
);
}
}
}
}
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, bounds, false) = ty.kind;
let item = cx.tcx.hir().item(item_id);
if let ItemKind::OpaqueTy(opaque) = &item.kind;
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 {
let output_lifetimes = bounds
.iter()
.filter_map(|bound| {
if let GenericArg::Lifetime(lt) = bound {
Some(lt.res)
} else {
None
}
})
.collect();
return Some((trait_ref, output_lifetimes));
}
}
None
}
fn future_output_ty<'tcx>(trait_ref: &'tcx TraitRef<'tcx>) -> Option<&'tcx Ty<'tcx>> {
if_chain! {
if let Some(segment) = trait_ref.path.segments.last();
if let Some(args) = segment.args;
if args.bindings.len() == 1;
let binding = &args.bindings[0];
if binding.ident.name == sym::Output;
if let TypeBindingKind::Equality { term: Term::Ty(output) } = binding.kind;
then {
return Some(output);
}
}
None
}
fn captures_all_lifetimes(inputs: &[Ty<'_>], output_lifetimes: &[LifetimeName]) -> bool {
let input_lifetimes: Vec<LifetimeName> = inputs
.iter()
.filter_map(|ty| {
if let TyKind::Ref(lt, _) = ty.kind {
Some(lt.res)
} 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::Infer))
|| 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;
if let Some(args) = cx
.tcx
.lang_items()
.identity_future_fn()
.and_then(|def_id| match_function_call_with_def_id(cx, block_expr, def_id));
if args.len() == 1;
if let Expr {
kind: ExprKind::Closure(&Closure { body, .. }),
..
} = args[0];
let closure_body = cx.tcx.hir().body(body);
if closure_body.generator_kind == Some(GeneratorKind::Async(AsyncGeneratorKind::Block));
then {
return Some(closure_body);
}
}
None
}
fn suggested_ret(cx: &LateContext<'_>, output: &Ty<'_>) -> Option<(&'static str, String)> {
match output.kind {
TyKind::Tup(tys) if tys.is_empty() => {
let sugg = "remove the return type";
Some((sugg, String::new()))
},
_ => {
let sugg = "return the output of the future directly";
snippet_opt(cx, output.span).map(|snip| (sugg, format!(" -> {snip}")))
},
}
}
|
