use clippy_utils::diagnostics::span_lint_and_sugg; use clippy_utils::higher; use clippy_utils::sugg::Sugg; use clippy_utils::ty::is_type_diagnostic_item; use clippy_utils::{ can_move_expr_to_closure, eager_or_lazy, in_constant, in_macro, is_else_clause, is_lang_ctor, peel_hir_expr_while, CaptureKind, }; use if_chain::if_chain; use rustc_errors::Applicability; use rustc_hir::LangItem::OptionSome; use rustc_hir::{def::Res, BindingAnnotation, Block, Expr, ExprKind, Mutability, PatKind, Path, QPath, UnOp}; use rustc_lint::{LateContext, LateLintPass}; use rustc_session::{declare_lint_pass, declare_tool_lint}; use rustc_span::sym; declare_clippy_lint! { /// ### What it does /// Lints usage of `if let Some(v) = ... { y } else { x }` which is more /// idiomatically done with `Option::map_or` (if the else bit is a pure /// expression) or `Option::map_or_else` (if the else bit is an impure /// expression). /// /// ### Why is this bad? /// Using the dedicated functions of the Option type is clearer and /// more concise than an `if let` expression. /// /// ### Known problems /// This lint uses a deliberately conservative metric for checking /// if the inside of either body contains breaks or continues which will /// cause it to not suggest a fix if either block contains a loop with /// continues or breaks contained within the loop. /// /// ### Example /// ```rust /// # let optional: Option = Some(0); /// # fn do_complicated_function() -> u32 { 5 }; /// let _ = if let Some(foo) = optional { /// foo /// } else { /// 5 /// }; /// let _ = if let Some(foo) = optional { /// foo /// } else { /// let y = do_complicated_function(); /// y*y /// }; /// ``` /// /// should be /// /// ```rust /// # let optional: Option = Some(0); /// # fn do_complicated_function() -> u32 { 5 }; /// let _ = optional.map_or(5, |foo| foo); /// let _ = optional.map_or_else(||{ /// let y = do_complicated_function(); /// y*y /// }, |foo| foo); /// ``` pub OPTION_IF_LET_ELSE, nursery, "reimplementation of Option::map_or" } declare_lint_pass!(OptionIfLetElse => [OPTION_IF_LET_ELSE]); /// Returns true iff the given expression is the result of calling `Result::ok` fn is_result_ok(cx: &LateContext<'_>, expr: &'_ Expr<'_>) -> bool { if let ExprKind::MethodCall(path, _, &[ref receiver], _) = &expr.kind { path.ident.name.as_str() == "ok" && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(receiver), sym::result_type) } else { false } } /// A struct containing information about occurrences of the /// `if let Some(..) = .. else` construct that this lint detects. struct OptionIfLetElseOccurence { option: String, method_sugg: String, some_expr: String, none_expr: String, } /// Extracts the body of a given arm. If the arm contains only an expression, /// then it returns the expression. Otherwise, it returns the entire block fn extract_body_from_expr<'a>(expr: &'a Expr<'a>) -> Option<&'a Expr<'a>> { if let ExprKind::Block( Block { stmts: block_stmts, expr: Some(block_expr), .. }, _, ) = expr.kind { if let [] = block_stmts { Some(block_expr) } else { Some(expr) } } else { None } } fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String { format!( "{}{}", Sugg::hir(cx, cond_expr, "..").maybe_par(), if as_mut { ".as_mut()" } else if as_ref { ".as_ref()" } else { "" } ) } /// If this expression is the option if let/else construct we're detecting, then /// this function returns an `OptionIfLetElseOccurence` struct with details if /// this construct is found, or None if this construct is not found. fn detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option { if_chain! { if !in_macro(expr.span); // Don't lint macros, because it behaves weirdly if !in_constant(cx, expr.hir_id); if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: Some(if_else) }) = higher::IfLet::hir(cx, expr); if !is_else_clause(cx.tcx, expr); if !is_result_ok(cx, let_expr); // Don't lint on Result::ok because a different lint does it already if let PatKind::TupleStruct(struct_qpath, [inner_pat], _) = &let_pat.kind; if is_lang_ctor(cx, struct_qpath, OptionSome); if let PatKind::Binding(bind_annotation, _, id, _) = &inner_pat.kind; if let Some(some_captures) = can_move_expr_to_closure(cx, if_then); if let Some(none_captures) = can_move_expr_to_closure(cx, if_else); if some_captures .iter() .filter_map(|(id, &c)| none_captures.get(id).map(|&c2| (c, c2))) .all(|(x, y)| x.is_imm_ref() && y.is_imm_ref()); then { let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" }; let some_body = extract_body_from_expr(if_then)?; let none_body = extract_body_from_expr(if_else)?; let method_sugg = if eager_or_lazy::is_eagerness_candidate(cx, none_body) { "map_or" } else { "map_or_else" }; let capture_name = id.name.to_ident_string(); let (as_ref, as_mut) = match &let_expr.kind { ExprKind::AddrOf(_, Mutability::Not, _) => (true, false), ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true), _ => (bind_annotation == &BindingAnnotation::Ref, bind_annotation == &BindingAnnotation::RefMut), }; let cond_expr = match let_expr.kind { // Pointer dereferencing happens automatically, so we can omit it in the suggestion ExprKind::Unary(UnOp::Deref, expr) | ExprKind::AddrOf(_, _, expr) => expr, _ => let_expr, }; // Check if captures the closure will need conflict with borrows made in the scrutinee. // TODO: check all the references made in the scrutinee expression. This will require interacting // with the borrow checker. Currently only `[.]*` is checked for. if as_ref || as_mut { let e = peel_hir_expr_while(cond_expr, |e| match e.kind { ExprKind::Field(e, _) | ExprKind::AddrOf(_, _, e) => Some(e), _ => None, }); if let ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(local_id), .. })) = e.kind { match some_captures.get(local_id) .or_else(|| (method_sugg == "map_or_else").then(|| ()).and_then(|_| none_captures.get(local_id))) { Some(CaptureKind::Value | CaptureKind::Ref(Mutability::Mut)) => return None, Some(CaptureKind::Ref(Mutability::Not)) if as_mut => return None, Some(CaptureKind::Ref(Mutability::Not)) | None => (), } } } Some(OptionIfLetElseOccurence { option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut), method_sugg: method_sugg.to_string(), some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir(cx, some_body, "..")), none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir(cx, none_body, "..")), }) } else { None } } } impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse { fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) { if let Some(detection) = detect_option_if_let_else(cx, expr) { span_lint_and_sugg( cx, OPTION_IF_LET_ELSE, expr.span, format!("use Option::{} instead of an if let/else", detection.method_sugg).as_str(), "try", format!( "{}.{}({}, {})", detection.option, detection.method_sugg, detection.none_expr, detection.some_expr, ), Applicability::MaybeIncorrect, ); } } }