mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-23 11:33:19 +00:00
160 lines
5.8 KiB
Rust
160 lines
5.8 KiB
Rust
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use crate::utils::paths::FUTURE_FROM_GENERATOR;
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use crate::utils::{match_function_call, snippet_block, snippet_opt, span_lint_and_then};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir::intravisit::FnKind;
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use rustc_hir::{
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AsyncGeneratorKind, Block, Body, Expr, ExprKind, FnDecl, FnRetTy, GeneratorKind, GenericBound, HirId, IsAsync,
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ItemKind, TraitRef, Ty, TyKind, TypeBindingKind,
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};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::Span;
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declare_clippy_lint! {
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/// **What it does:** It checks for manual implementations of `async` functions.
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///
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/// **Why is this bad?** It's more idiomatic to use the dedicated syntax.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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///
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/// ```rust
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/// use std::future::Future;
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///
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/// fn foo() -> impl Future<Output = i32> { async { 42 } }
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/// ```
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/// Use instead:
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/// ```rust
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/// use std::future::Future;
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///
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/// async fn foo() -> i32 { 42 }
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/// ```
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pub MANUAL_ASYNC_FN,
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style,
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"manual implementations of `async` functions can be simplified using the dedicated syntax"
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}
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declare_lint_pass!(ManualAsyncFn => [MANUAL_ASYNC_FN]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ManualAsyncFn {
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fn check_fn(
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&mut self,
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cx: &LateContext<'a, 'tcx>,
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kind: FnKind<'tcx>,
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decl: &'tcx FnDecl<'_>,
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body: &'tcx Body<'_>,
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span: Span,
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_: HirId,
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) {
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if_chain! {
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if let Some(header) = kind.header();
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if let IsAsync::NotAsync = header.asyncness;
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// Check that this function returns `impl Future`
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if let FnRetTy::Return(ret_ty) = decl.output;
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if let Some(trait_ref) = future_trait_ref(cx, ret_ty);
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if let Some(output) = future_output_ty(trait_ref);
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// Check that the body of the function consists of one async block
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if let ExprKind::Block(block, _) = body.value.kind;
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if block.stmts.is_empty();
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if let Some(closure_body) = desugared_async_block(cx, block);
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then {
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let header_span = span.with_hi(ret_ty.span.hi());
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span_lint_and_then(
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cx,
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MANUAL_ASYNC_FN,
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header_span,
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"this function can be simplified using the `async fn` syntax",
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|diag| {
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if_chain! {
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if let Some(header_snip) = snippet_opt(cx, header_span);
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if let Some(ret_pos) = header_snip.rfind("->");
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if let Some((ret_sugg, ret_snip)) = suggested_ret(cx, output);
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then {
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let help = format!("make the function `async` and {}", ret_sugg);
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diag.span_suggestion(
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header_span,
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&help,
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format!("async {}{}", &header_snip[..ret_pos], ret_snip),
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Applicability::MachineApplicable
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);
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let body_snip = snippet_block(cx, closure_body.value.span, "..", Some(block.span));
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diag.span_suggestion(
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block.span,
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"move the body of the async block to the enclosing function",
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body_snip.to_string(),
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Applicability::MachineApplicable
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);
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}
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}
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},
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);
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}
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}
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}
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}
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fn future_trait_ref<'tcx>(cx: &LateContext<'_, 'tcx>, ty: &'tcx Ty<'tcx>) -> Option<&'tcx TraitRef<'tcx>> {
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if_chain! {
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if let TyKind::Def(item_id, _) = ty.kind;
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let item = cx.tcx.hir().item(item_id.id);
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if let ItemKind::OpaqueTy(opaque) = &item.kind;
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if opaque.bounds.len() == 1;
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if let GenericBound::Trait(poly, _) = &opaque.bounds[0];
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if poly.trait_ref.trait_def_id() == cx.tcx.lang_items().future_trait();
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then {
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return Some(&poly.trait_ref);
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}
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}
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None
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}
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fn future_output_ty<'tcx>(trait_ref: &'tcx TraitRef<'tcx>) -> Option<&'tcx Ty<'tcx>> {
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if_chain! {
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if let Some(segment) = trait_ref.path.segments.last();
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if let Some(args) = segment.args;
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if args.bindings.len() == 1;
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let binding = &args.bindings[0];
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if binding.ident.as_str() == "Output";
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if let TypeBindingKind::Equality{ty: output} = binding.kind;
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then {
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return Some(output)
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}
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}
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None
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}
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fn desugared_async_block<'tcx>(cx: &LateContext<'_, 'tcx>, block: &'tcx Block<'tcx>) -> Option<&'tcx Body<'tcx>> {
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if_chain! {
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if let Some(block_expr) = block.expr;
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if let Some(args) = match_function_call(cx, block_expr, &FUTURE_FROM_GENERATOR);
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if args.len() == 1;
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if let Expr{kind: ExprKind::Closure(_, _, body_id, ..), ..} = args[0];
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let closure_body = cx.tcx.hir().body(body_id);
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if let Some(GeneratorKind::Async(AsyncGeneratorKind::Block)) = closure_body.generator_kind;
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then {
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return Some(closure_body);
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}
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}
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None
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}
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fn suggested_ret(cx: &LateContext<'_, '_>, output: &Ty<'_>) -> Option<(&'static str, String)> {
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match output.kind {
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TyKind::Tup(tys) if tys.is_empty() => {
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let sugg = "remove the return type";
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Some((sugg, "".into()))
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},
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_ => {
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let sugg = "return the output of the future directly";
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snippet_opt(cx, output.span).map(|snip| (sugg, format!("-> {}", snip)))
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},
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}
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}
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