use clippy_utils::diagnostics::span_lint_and_sugg; use clippy_utils::sugg::Sugg; use clippy_utils::{ can_move_expr_to_closure, eager_or_lazy, higher, in_constant, is_else_clause, is_lang_ctor, peel_blocks, peel_hir_expr_while, CaptureKind, }; use if_chain::if_chain; use rustc_errors::Applicability; use rustc_hir::LangItem::{OptionNone, OptionSome, ResultErr, ResultOk}; use rustc_hir::{ def::Res, Arm, BindingAnnotation, Expr, ExprKind, MatchSource, Mutability, Pat, PatKind, Path, QPath, UnOp, }; use rustc_lint::{LateContext, LateLintPass}; use rustc_session::{declare_lint_pass, declare_tool_lint}; declare_clippy_lint! { /// ### What it does /// Lints usage of `if let Some(v) = ... { y } else { x }` and /// `match .. { Some(v) => y, None/_ => x }` which are 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<u32> = Some(0); /// # fn do_complicated_function() -> u32 { 5 }; /// let _ = if let Some(foo) = optional { /// foo /// } else { /// 5 /// }; /// let _ = match optional { /// Some(val) => val + 1, /// None => 5 /// }; /// let _ = if let Some(foo) = optional { /// foo /// } else { /// let y = do_complicated_function(); /// y*y /// }; /// ``` /// /// should be /// /// ```rust /// # let optional: Option<u32> = Some(0); /// # fn do_complicated_function() -> u32 { 5 }; /// let _ = optional.map_or(5, |foo| foo); /// let _ = optional.map_or(5, |val| val + 1); /// let _ = optional.map_or_else(||{ /// let y = do_complicated_function(); /// y*y /// }, |foo| foo); /// ``` // FIXME: Before moving this lint out of nursery, the lint name needs to be updated. It now also // covers matches and `Result`. #[clippy::version = "1.47.0"] pub OPTION_IF_LET_ELSE, nursery, "reimplementation of Option::map_or" } declare_lint_pass!(OptionIfLetElse => [OPTION_IF_LET_ELSE]); /// A struct containing information about occurrences of construct that this lint detects /// /// Such as: /// /// ```ignore /// if let Some(..) = {..} else {..} /// ``` /// or /// ```ignore /// match x { /// Some(..) => {..}, /// None/_ => {..} /// } /// ``` struct OptionOccurence { option: String, method_sugg: String, some_expr: String, none_expr: String, } fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String { format!( "{}{}", Sugg::hir_with_macro_callsite(cx, cond_expr, "..").maybe_par(), if as_mut { ".as_mut()" } else if as_ref { ".as_ref()" } else { "" } ) } fn try_get_option_occurence<'tcx>( cx: &LateContext<'tcx>, pat: &Pat<'tcx>, expr: &Expr<'_>, if_then: &'tcx Expr<'_>, if_else: &'tcx Expr<'_>, ) -> Option<OptionOccurence> { let cond_expr = match expr.kind { ExprKind::Unary(UnOp::Deref, inner_expr) | ExprKind::AddrOf(_, _, inner_expr) => inner_expr, _ => expr, }; let inner_pat = try_get_inner_pat(cx, pat)?; if_chain! { if let PatKind::Binding(bind_annotation, _, id, None) = 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::MUT { "mut " } else { "" }; let some_body = peel_blocks(if_then); let none_body = peel_blocks(if_else); let method_sugg = if eager_or_lazy::switch_to_eager_eval(cx, none_body) { "map_or" } else { "map_or_else" }; let capture_name = id.name.to_ident_string(); let (as_ref, as_mut) = match &expr.kind { ExprKind::AddrOf(_, Mutability::Not, _) => (true, false), ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true), _ => (bind_annotation == BindingAnnotation::REF, bind_annotation == BindingAnnotation::REF_MUT), }; // 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 `<local>[.<field>]*` 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_some(()).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 => (), } } } return Some(OptionOccurence { 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_with_macro_callsite(cx, some_body, "..")), none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir_with_macro_callsite(cx, none_body, "..")), }); } } None } fn try_get_inner_pat<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'tcx>) -> Option<&'tcx Pat<'tcx>> { if let PatKind::TupleStruct(ref qpath, [inner_pat], ..) = pat.kind { if is_lang_ctor(cx, qpath, OptionSome) || is_lang_ctor(cx, qpath, ResultOk) { return Some(inner_pat); } } None } /// If this expression is the option if let/else construct we're detecting, then /// this function returns an `OptionOccurence` 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<OptionOccurence> { 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) { return try_get_option_occurence(cx, let_pat, let_expr, if_then, if_else); } } None } fn detect_option_match<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionOccurence> { if let ExprKind::Match(ex, arms, MatchSource::Normal) = expr.kind { if let Some((let_pat, if_then, if_else)) = try_convert_match(cx, arms) { return try_get_option_occurence(cx, let_pat, ex, if_then, if_else); } } None } fn try_convert_match<'tcx>( cx: &LateContext<'tcx>, arms: &[Arm<'tcx>], ) -> Option<(&'tcx Pat<'tcx>, &'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> { if arms.len() == 2 { return if is_none_or_err_arm(cx, &arms[1]) { Some((arms[0].pat, arms[0].body, arms[1].body)) } else if is_none_or_err_arm(cx, &arms[0]) { Some((arms[1].pat, arms[1].body, arms[0].body)) } else { None }; } None } fn is_none_or_err_arm(cx: &LateContext<'_>, arm: &Arm<'_>) -> bool { match arm.pat.kind { PatKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone), PatKind::TupleStruct(ref qpath, [first_pat], _) => { is_lang_ctor(cx, qpath, ResultErr) && matches!(first_pat.kind, PatKind::Wild) }, PatKind::Wild => true, _ => false, } } impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse { fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) { // Don't lint macros and constants if expr.span.from_expansion() || in_constant(cx, expr.hir_id) { return; } let detection = detect_option_if_let_else(cx, expr).or_else(|| detect_option_match(cx, expr)); if let Some(det) = detection { span_lint_and_sugg( cx, OPTION_IF_LET_ELSE, expr.span, format!("use Option::{} instead of an if let/else", det.method_sugg).as_str(), "try", format!( "{}.{}({}, {})", det.option, det.method_sugg, det.none_expr, det.some_expr ), Applicability::MaybeIncorrect, ); } } }