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| 1 | +use crate::utils::paths::FUTURE_FROM_GENERATOR; |
| 2 | +use crate::utils::{match_function_call, snippet_block, snippet_opt, span_lint_and_then}; |
| 3 | +use if_chain::if_chain; |
| 4 | +use rustc_errors::Applicability; |
| 5 | +use rustc_hir::intravisit::FnKind; |
| 6 | +use rustc_hir::{ |
| 7 | + AsyncGeneratorKind, Block, Body, Expr, ExprKind, FnDecl, FnRetTy, GeneratorKind, GenericBound, HirId, IsAsync, |
| 8 | + ItemKind, TraitRef, Ty, TyKind, TypeBindingKind, |
| 9 | +}; |
| 10 | +use rustc_lint::{LateContext, LateLintPass}; |
| 11 | +use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| 12 | +use rustc_span::Span; |
| 13 | + |
| 14 | +declare_clippy_lint! { |
| 15 | + /// **What it does:** It checks for manual implementations of `async` functions. |
| 16 | + /// |
| 17 | + /// **Why is this bad?** It's more idiomatic to use the dedicated syntax. |
| 18 | + /// |
| 19 | + /// **Known problems:** None. |
| 20 | + /// |
| 21 | + /// **Example:** |
| 22 | + /// |
| 23 | + /// ```rust |
| 24 | + /// use std::future::Future; |
| 25 | + /// |
| 26 | + /// fn foo() -> impl Future<Output = i32> { async { 42 } } |
| 27 | + /// ``` |
| 28 | + /// Use instead: |
| 29 | + /// ```rust |
| 30 | + /// use std::future::Future; |
| 31 | + /// |
| 32 | + /// async fn foo() -> i32 { 42 } |
| 33 | + /// ``` |
| 34 | + pub MANUAL_ASYNC_FN, |
| 35 | + style, |
| 36 | + "manual implementations of `async` functions can be simplified using the dedicated syntax" |
| 37 | +} |
| 38 | + |
| 39 | +declare_lint_pass!(ManualAsyncFn => [MANUAL_ASYNC_FN]); |
| 40 | + |
| 41 | +impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ManualAsyncFn { |
| 42 | + fn check_fn( |
| 43 | + &mut self, |
| 44 | + cx: &LateContext<'a, 'tcx>, |
| 45 | + kind: FnKind<'tcx>, |
| 46 | + decl: &'tcx FnDecl<'_>, |
| 47 | + body: &'tcx Body<'_>, |
| 48 | + span: Span, |
| 49 | + _: HirId, |
| 50 | + ) { |
| 51 | + if_chain! { |
| 52 | + if let Some(header) = kind.header(); |
| 53 | + if let IsAsync::NotAsync = header.asyncness; |
| 54 | + // Check that this function returns `impl Future` |
| 55 | + if let FnRetTy::Return(ret_ty) = decl.output; |
| 56 | + if let Some(trait_ref) = future_trait_ref(cx, ret_ty); |
| 57 | + if let Some(output) = future_output_ty(trait_ref); |
| 58 | + // Check that the body of the function consists of one async block |
| 59 | + if let ExprKind::Block(block, _) = body.value.kind; |
| 60 | + if block.stmts.is_empty(); |
| 61 | + if let Some(closure_body) = desugared_async_block(cx, block); |
| 62 | + then { |
| 63 | + let header_span = span.with_hi(ret_ty.span.hi()); |
| 64 | + |
| 65 | + span_lint_and_then( |
| 66 | + cx, |
| 67 | + MANUAL_ASYNC_FN, |
| 68 | + header_span, |
| 69 | + "this function can be simplified using the `async fn` syntax", |
| 70 | + |diag| { |
| 71 | + if_chain! { |
| 72 | + if let Some(header_snip) = snippet_opt(cx, header_span); |
| 73 | + if let Some(ret_pos) = header_snip.rfind("->"); |
| 74 | + if let Some((ret_sugg, ret_snip)) = suggested_ret(cx, output); |
| 75 | + then { |
| 76 | + let help = format!("make the function `async` and {}", ret_sugg); |
| 77 | + diag.span_suggestion( |
| 78 | + header_span, |
| 79 | + &help, |
| 80 | + format!("async {}{}", &header_snip[..ret_pos], ret_snip), |
| 81 | + Applicability::MachineApplicable |
| 82 | + ); |
| 83 | + |
| 84 | + let body_snip = snippet_block(cx, closure_body.value.span, "..", Some(block.span)); |
| 85 | + diag.span_suggestion( |
| 86 | + block.span, |
| 87 | + "move the body of the async block to the enclosing function", |
| 88 | + body_snip.to_string(), |
| 89 | + Applicability::MachineApplicable |
| 90 | + ); |
| 91 | + } |
| 92 | + } |
| 93 | + }, |
| 94 | + ); |
| 95 | + } |
| 96 | + } |
| 97 | + } |
| 98 | +} |
| 99 | + |
| 100 | +fn future_trait_ref<'tcx>(cx: &LateContext<'_, 'tcx>, ty: &'tcx Ty<'tcx>) -> Option<&'tcx TraitRef<'tcx>> { |
| 101 | + if_chain! { |
| 102 | + if let TyKind::Def(item_id, _) = ty.kind; |
| 103 | + let item = cx.tcx.hir().item(item_id.id); |
| 104 | + if let ItemKind::OpaqueTy(opaque) = &item.kind; |
| 105 | + if opaque.bounds.len() == 1; |
| 106 | + if let GenericBound::Trait(poly, _) = &opaque.bounds[0]; |
| 107 | + if poly.trait_ref.trait_def_id() == cx.tcx.lang_items().future_trait(); |
| 108 | + then { |
| 109 | + return Some(&poly.trait_ref); |
| 110 | + } |
| 111 | + } |
| 112 | + |
| 113 | + None |
| 114 | +} |
| 115 | + |
| 116 | +fn future_output_ty<'tcx>(trait_ref: &'tcx TraitRef<'tcx>) -> Option<&'tcx Ty<'tcx>> { |
| 117 | + if_chain! { |
| 118 | + if let Some(segment) = trait_ref.path.segments.last(); |
| 119 | + if let Some(args) = segment.args; |
| 120 | + if args.bindings.len() == 1; |
| 121 | + let binding = &args.bindings[0]; |
| 122 | + if binding.ident.as_str() == "Output"; |
| 123 | + if let TypeBindingKind::Equality{ty: output} = binding.kind; |
| 124 | + then { |
| 125 | + return Some(output) |
| 126 | + } |
| 127 | + } |
| 128 | + |
| 129 | + None |
| 130 | +} |
| 131 | + |
| 132 | +fn desugared_async_block<'tcx>(cx: &LateContext<'_, 'tcx>, block: &'tcx Block<'tcx>) -> Option<&'tcx Body<'tcx>> { |
| 133 | + if_chain! { |
| 134 | + if let Some(block_expr) = block.expr; |
| 135 | + if let Some(args) = match_function_call(cx, block_expr, &FUTURE_FROM_GENERATOR); |
| 136 | + if args.len() == 1; |
| 137 | + if let Expr{kind: ExprKind::Closure(_, _, body_id, ..), ..} = args[0]; |
| 138 | + let closure_body = cx.tcx.hir().body(body_id); |
| 139 | + if let Some(GeneratorKind::Async(AsyncGeneratorKind::Block)) = closure_body.generator_kind; |
| 140 | + then { |
| 141 | + return Some(closure_body); |
| 142 | + } |
| 143 | + } |
| 144 | + |
| 145 | + None |
| 146 | +} |
| 147 | + |
| 148 | +fn suggested_ret(cx: &LateContext<'_, '_>, output: &Ty<'_>) -> Option<(&'static str, String)> { |
| 149 | + match output.kind { |
| 150 | + TyKind::Tup(tys) if tys.is_empty() => { |
| 151 | + let sugg = "remove the return type"; |
| 152 | + Some((sugg, "".into())) |
| 153 | + }, |
| 154 | + _ => { |
| 155 | + let sugg = "return the output of the future directly"; |
| 156 | + snippet_opt(cx, output.span).map(|snip| (sugg, format!("-> {}", snip))) |
| 157 | + }, |
| 158 | + } |
| 159 | +} |
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