use super::NEEDLESS_MATCH; use clippy_utils::diagnostics::span_lint_and_sugg; use clippy_utils::source::snippet_with_applicability; use clippy_utils::ty::{is_type_diagnostic_item, same_type_and_consts}; use clippy_utils::{ eq_expr_value, get_parent_expr_for_hir, get_parent_node, higher, is_else_clause, is_lang_ctor, over, peel_blocks_with_stmt, }; use rustc_errors::Applicability; use rustc_hir::LangItem::OptionNone; use rustc_hir::{Arm, BindingAnnotation, ByRef, Expr, ExprKind, FnRetTy, Guard, Node, Pat, PatKind, Path, QPath}; use rustc_lint::LateContext; use rustc_span::sym; use rustc_typeck::hir_ty_to_ty; pub(crate) fn check_match(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) { if arms.len() > 1 && expr_ty_matches_p_ty(cx, ex, expr) && check_all_arms(cx, ex, arms) { let mut applicability = Applicability::MachineApplicable; span_lint_and_sugg( cx, NEEDLESS_MATCH, expr.span, "this match expression is unnecessary", "replace it with", snippet_with_applicability(cx, ex.span, "..", &mut applicability).to_string(), applicability, ); } } /// Check for nop `if let` expression that assembled as unnecessary match /// /// ```rust,ignore /// if let Some(a) = option { /// Some(a) /// } else { /// None /// } /// ``` /// OR /// ```rust,ignore /// if let SomeEnum::A = some_enum { /// SomeEnum::A /// } else if let SomeEnum::B = some_enum { /// SomeEnum::B /// } else { /// some_enum /// } /// ``` pub(crate) fn check_if_let<'tcx>(cx: &LateContext<'tcx>, ex: &Expr<'_>, if_let: &higher::IfLet<'tcx>) { if !is_else_clause(cx.tcx, ex) && expr_ty_matches_p_ty(cx, if_let.let_expr, ex) && check_if_let_inner(cx, if_let) { let mut applicability = Applicability::MachineApplicable; span_lint_and_sugg( cx, NEEDLESS_MATCH, ex.span, "this if-let expression is unnecessary", "replace it with", snippet_with_applicability(cx, if_let.let_expr.span, "..", &mut applicability).to_string(), applicability, ); } } fn check_all_arms(cx: &LateContext<'_>, match_expr: &Expr<'_>, arms: &[Arm<'_>]) -> bool { for arm in arms { let arm_expr = peel_blocks_with_stmt(arm.body); if let Some(guard_expr) = &arm.guard { match guard_expr { // gives up if `pat if expr` can have side effects Guard::If(if_cond) => { if if_cond.can_have_side_effects() { return false; } }, // gives up `pat if let ...` arm Guard::IfLet(_) => { return false; }, }; } if let PatKind::Wild = arm.pat.kind { if !eq_expr_value(cx, match_expr, strip_return(arm_expr)) { return false; } } else if !pat_same_as_expr(arm.pat, arm_expr) { return false; } } true } fn check_if_let_inner(cx: &LateContext<'_>, if_let: &higher::IfLet<'_>) -> bool { if let Some(if_else) = if_let.if_else { if !pat_same_as_expr(if_let.let_pat, peel_blocks_with_stmt(if_let.if_then)) { return false; } // Recursively check for each `else if let` phrase, if let Some(ref nested_if_let) = higher::IfLet::hir(cx, if_else) { return check_if_let_inner(cx, nested_if_let); } if matches!(if_else.kind, ExprKind::Block(..)) { let else_expr = peel_blocks_with_stmt(if_else); if matches!(else_expr.kind, ExprKind::Block(..)) { return false; } let ret = strip_return(else_expr); let let_expr_ty = cx.typeck_results().expr_ty(if_let.let_expr); if is_type_diagnostic_item(cx, let_expr_ty, sym::Option) { if let ExprKind::Path(ref qpath) = ret.kind { return is_lang_ctor(cx, qpath, OptionNone) || eq_expr_value(cx, if_let.let_expr, ret); } return false; } return eq_expr_value(cx, if_let.let_expr, ret); } } false } /// Strip `return` keyword if the expression type is `ExprKind::Ret`. fn strip_return<'hir>(expr: &'hir Expr<'hir>) -> &'hir Expr<'hir> { if let ExprKind::Ret(Some(ret)) = expr.kind { ret } else { expr } } /// Manually check for coercion casting by checking if the type of the match operand or let expr /// differs with the assigned local variable or the function return type. fn expr_ty_matches_p_ty(cx: &LateContext<'_>, expr: &Expr<'_>, p_expr: &Expr<'_>) -> bool { if let Some(p_node) = get_parent_node(cx.tcx, p_expr.hir_id) { match p_node { // Compare match_expr ty with local in `let local = match match_expr {..}` Node::Local(local) => { let results = cx.typeck_results(); return same_type_and_consts(results.node_type(local.hir_id), results.expr_ty(expr)); }, // compare match_expr ty with RetTy in `fn foo() -> RetTy` Node::Item(..) => { if let Some(fn_decl) = p_node.fn_decl() { if let FnRetTy::Return(ret_ty) = fn_decl.output { return same_type_and_consts(hir_ty_to_ty(cx.tcx, ret_ty), cx.typeck_results().expr_ty(expr)); } } }, // check the parent expr for this whole block `{ match match_expr {..} }` Node::Block(block) => { if let Some(block_parent_expr) = get_parent_expr_for_hir(cx, block.hir_id) { return expr_ty_matches_p_ty(cx, expr, block_parent_expr); } }, // recursively call on `if xxx {..}` etc. Node::Expr(p_expr) => { return expr_ty_matches_p_ty(cx, expr, p_expr); }, _ => {}, } } false } fn pat_same_as_expr(pat: &Pat<'_>, expr: &Expr<'_>) -> bool { let expr = strip_return(expr); match (&pat.kind, &expr.kind) { // Example: `Some(val) => Some(val)` (PatKind::TupleStruct(QPath::Resolved(_, path), tuple_params, _), ExprKind::Call(call_expr, call_params)) => { if let ExprKind::Path(QPath::Resolved(_, call_path)) = call_expr.kind { return over(path.segments, call_path.segments, |pat_seg, call_seg| { pat_seg.ident.name == call_seg.ident.name }) && same_non_ref_symbols(tuple_params, call_params); } }, // Example: `val => val` ( PatKind::Binding(annot, _, pat_ident, _), ExprKind::Path(QPath::Resolved( _, Path { segments: [first_seg, ..], .. }, )), ) => { return !matches!(annot, BindingAnnotation(ByRef::Yes, _)) && pat_ident.name == first_seg.ident.name; }, // Example: `Custom::TypeA => Custom::TypeB`, or `None => None` (PatKind::Path(QPath::Resolved(_, p_path)), ExprKind::Path(QPath::Resolved(_, e_path))) => { return over(p_path.segments, e_path.segments, |p_seg, e_seg| { p_seg.ident.name == e_seg.ident.name }); }, // Example: `5 => 5` (PatKind::Lit(pat_lit_expr), ExprKind::Lit(expr_spanned)) => { if let ExprKind::Lit(pat_spanned) = &pat_lit_expr.kind { return pat_spanned.node == expr_spanned.node; } }, _ => {}, } false } fn same_non_ref_symbols(pats: &[Pat<'_>], exprs: &[Expr<'_>]) -> bool { if pats.len() != exprs.len() { return false; } for i in 0..pats.len() { if !pat_same_as_expr(&pats[i], &exprs[i]) { return false; } } true }