clippy_lints/src/matches/needless_match.rs

   1 use super::NEEDLESS_MATCH;
   2 use clippy_utils::diagnostics::span_lint_and_sugg;
   3 use clippy_utils::source::snippet_with_applicability;
   4 use clippy_utils::ty::{is_type_diagnostic_item, same_type_and_consts};
   5 use clippy_utils::{
   6     eq_expr_value, get_parent_expr_for_hir, get_parent_node, higher, is_else_clause, is_lang_ctor, over,
   7     peel_blocks_with_stmt,
   8 };
   9 use rustc_errors::Applicability;
  10 use rustc_hir::LangItem::OptionNone;
  11 use rustc_hir::{Arm, BindingAnnotation, Expr, ExprKind, FnRetTy, Node, Pat, PatKind, Path, QPath};
  12 use rustc_lint::LateContext;
  13 use rustc_span::sym;
  14 use rustc_typeck::hir_ty_to_ty;
  15
  16 pub(crate) fn check_match(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
  17     if arms.len() > 1 && expr_ty_matches_p_ty(cx, ex, expr) && check_all_arms(cx, ex, arms) {
  18         let mut applicability = Applicability::MachineApplicable;
  19         span_lint_and_sugg(
  20             cx,
  21             NEEDLESS_MATCH,
  22             expr.span,
  23             "this match expression is unnecessary",
  24             "replace it with",
  25             snippet_with_applicability(cx, ex.span, "..", &mut applicability).to_string(),
  26             applicability,
  27         );
  28     }
  29 }
  30
  31 /// Check for nop `if let` expression that assembled as unnecessary match
  32 ///
  33 /// ```rust,ignore
  34 /// if let Some(a) = option {
  35 ///     Some(a)
  36 /// } else {
  37 ///     None
  38 /// }
  39 /// ```
  40 /// OR
  41 /// ```rust,ignore
  42 /// if let SomeEnum::A = some_enum {
  43 ///     SomeEnum::A
  44 /// } else if let SomeEnum::B = some_enum {
  45 ///     SomeEnum::B
  46 /// } else {
  47 ///     some_enum
  48 /// }
  49 /// ```
  50 pub(crate) fn check_if_let<'tcx>(cx: &LateContext<'tcx>, ex: &Expr<'_>, if_let: &higher::IfLet<'tcx>) {
  51     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) {
  52         let mut applicability = Applicability::MachineApplicable;
  53         span_lint_and_sugg(
  54             cx,
  55             NEEDLESS_MATCH,
  56             ex.span,
  57             "this if-let expression is unnecessary",
  58             "replace it with",
  59             snippet_with_applicability(cx, if_let.let_expr.span, "..", &mut applicability).to_string(),
  60             applicability,
  61         );
  62     }
  63 }
  64
  65 fn check_all_arms(cx: &LateContext<'_>, match_expr: &Expr<'_>, arms: &[Arm<'_>]) -> bool {
  66     for arm in arms {
  67         let arm_expr = peel_blocks_with_stmt(arm.body);
  68         if let PatKind::Wild = arm.pat.kind {
  69             return eq_expr_value(cx, match_expr, strip_return(arm_expr));
  70         } else if !pat_same_as_expr(arm.pat, arm_expr) {
  71             return false;
  72         }
  73     }
  74
  75     true
  76 }
  77
  78 fn check_if_let_inner(cx: &LateContext<'_>, if_let: &higher::IfLet<'_>) -> bool {
  79     if let Some(if_else) = if_let.if_else {
  80         if !pat_same_as_expr(if_let.let_pat, peel_blocks_with_stmt(if_let.if_then)) {
  81             return false;
  82         }
  83
  84         // Recursively check for each `else if let` phrase,
  85         if let Some(ref nested_if_let) = higher::IfLet::hir(cx, if_else) {
  86             return check_if_let_inner(cx, nested_if_let);
  87         }
  88
  89         if matches!(if_else.kind, ExprKind::Block(..)) {
  90             let else_expr = peel_blocks_with_stmt(if_else);
  91             if matches!(else_expr.kind, ExprKind::Block(..)) {
  92                 return false;
  93             }
  94             let ret = strip_return(else_expr);
  95             let let_expr_ty = cx.typeck_results().expr_ty(if_let.let_expr);
  96             if is_type_diagnostic_item(cx, let_expr_ty, sym::Option) {
  97                 if let ExprKind::Path(ref qpath) = ret.kind {
  98                     return is_lang_ctor(cx, qpath, OptionNone) || eq_expr_value(cx, if_let.let_expr, ret);
  99                 }
 100                 return false;
 101             }
 102             return eq_expr_value(cx, if_let.let_expr, ret);
 103         }
 104     }
 105
 106     false
 107 }
 108
 109 /// Strip `return` keyword if the expression type is `ExprKind::Ret`.
 110 fn strip_return<'hir>(expr: &'hir Expr<'hir>) -> &'hir Expr<'hir> {
 111     if let ExprKind::Ret(Some(ret)) = expr.kind {
 112         ret
 113     } else {
 114         expr
 115     }
 116 }
 117
 118 /// Manually check for coercion casting by checking if the type of the match operand or let expr
 119 /// differs with the assigned local variable or the function return type.
 120 fn expr_ty_matches_p_ty(cx: &LateContext<'_>, expr: &Expr<'_>, p_expr: &Expr<'_>) -> bool {
 121     if let Some(p_node) = get_parent_node(cx.tcx, p_expr.hir_id) {
 122         match p_node {
 123             // Compare match_expr ty with local in `let local = match match_expr {..}`
 124             Node::Local(local) => {
 125                 let results = cx.typeck_results();
 126                 return same_type_and_consts(results.node_type(local.hir_id), results.expr_ty(expr));
 127             },
 128             // compare match_expr ty with RetTy in `fn foo() -> RetTy`
 129             Node::Item(..) => {
 130                 if let Some(fn_decl) = p_node.fn_decl() {
 131                     if let FnRetTy::Return(ret_ty) = fn_decl.output {
 132                         return same_type_and_consts(hir_ty_to_ty(cx.tcx, ret_ty), cx.typeck_results().expr_ty(expr));
 133                     }
 134                 }
 135             },
 136             // check the parent expr for this whole block `{ match match_expr {..} }`
 137             Node::Block(block) => {
 138                 if let Some(block_parent_expr) = get_parent_expr_for_hir(cx, block.hir_id) {
 139                     return expr_ty_matches_p_ty(cx, expr, block_parent_expr);
 140                 }
 141             },
 142             // recursively call on `if xxx {..}` etc.
 143             Node::Expr(p_expr) => {
 144                 return expr_ty_matches_p_ty(cx, expr, p_expr);
 145             },
 146             _ => {},
 147         }
 148     }
 149     false
 150 }
 151
 152 fn pat_same_as_expr(pat: &Pat<'_>, expr: &Expr<'_>) -> bool {
 153     let expr = strip_return(expr);
 154     match (&pat.kind, &expr.kind) {
 155         // Example: `Some(val) => Some(val)`
 156         (PatKind::TupleStruct(QPath::Resolved(_, path), tuple_params, _), ExprKind::Call(call_expr, call_params)) => {
 157             if let ExprKind::Path(QPath::Resolved(_, call_path)) = call_expr.kind {
 158                 return over(path.segments, call_path.segments, |pat_seg, call_seg| {
 159                     pat_seg.ident.name == call_seg.ident.name
 160                 }) && same_non_ref_symbols(tuple_params, call_params);
 161             }
 162         },
 163         // Example: `val => val`
 164         (
 165             PatKind::Binding(annot, _, pat_ident, _),
 166             ExprKind::Path(QPath::Resolved(
 167                 _,
 168                 Path {
 169                     segments: [first_seg, ..],
 170                     ..
 171                 },
 172             )),
 173         ) => {
 174             return !matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut)
 175                 && pat_ident.name == first_seg.ident.name;
 176         },
 177         // Example: `Custom::TypeA => Custom::TypeB`, or `None => None`
 178         (PatKind::Path(QPath::Resolved(_, p_path)), ExprKind::Path(QPath::Resolved(_, e_path))) => {
 179             return over(p_path.segments, e_path.segments, |p_seg, e_seg| {
 180                 p_seg.ident.name == e_seg.ident.name
 181             });
 182         },
 183         // Example: `5 => 5`
 184         (PatKind::Lit(pat_lit_expr), ExprKind::Lit(expr_spanned)) => {
 185             if let ExprKind::Lit(pat_spanned) = &pat_lit_expr.kind {
 186                 return pat_spanned.node == expr_spanned.node;
 187             }
 188         },
 189         _ => {},
 190     }
 191
 192     false
 193 }
 194
 195 fn same_non_ref_symbols(pats: &[Pat<'_>], exprs: &[Expr<'_>]) -> bool {
 196     if pats.len() != exprs.len() {
 197         return false;
 198     }
 199
 200     for i in 0..pats.len() {
 201         if !pat_same_as_expr(&pats[i], &exprs[i]) {
 202             return false;
 203         }
 204     }
 205
 206     true
 207 }