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;
   5 use clippy_utils::{eq_expr_value, get_parent_expr, higher, is_else_clause, is_lang_ctor, peel_blocks_with_stmt};
   6 use rustc_errors::Applicability;
   7 use rustc_hir::LangItem::OptionNone;
   8 use rustc_hir::{Arm, BindingAnnotation, Expr, ExprKind, Pat, PatKind, Path, PathSegment, QPath, UnOp};
   9 use rustc_lint::LateContext;
  10 use rustc_span::sym;
  11
  12 pub(crate) fn check_match(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>]) {
  13     // This is for avoiding collision with `match_single_binding`.
  14     if arms.len() < 2 {
  15         return;
  16     }
  17
  18     for arm in arms {
  19         if let PatKind::Wild = arm.pat.kind {
  20             let ret_expr = strip_return(arm.body);
  21             if !eq_expr_value(cx, ex, ret_expr) {
  22                 return;
  23             }
  24         } else if !pat_same_as_expr(arm.pat, arm.body) {
  25             return;
  26         }
  27     }
  28
  29     if let Some(match_expr) = get_parent_expr(cx, ex) {
  30         let mut applicability = Applicability::MachineApplicable;
  31         span_lint_and_sugg(
  32             cx,
  33             NEEDLESS_MATCH,
  34             match_expr.span,
  35             "this match expression is unnecessary",
  36             "replace it with",
  37             snippet_with_applicability(cx, ex.span, "..", &mut applicability).to_string(),
  38             applicability,
  39         );
  40     }
  41 }
  42
  43 /// Check for nop `if let` expression that assembled as unnecessary match
  44 ///
  45 /// ```rust,ignore
  46 /// if let Some(a) = option {
  47 ///     Some(a)
  48 /// } else {
  49 ///     None
  50 /// }
  51 /// ```
  52 /// OR
  53 /// ```rust,ignore
  54 /// if let SomeEnum::A = some_enum {
  55 ///     SomeEnum::A
  56 /// } else if let SomeEnum::B = some_enum {
  57 ///     SomeEnum::B
  58 /// } else {
  59 ///     some_enum
  60 /// }
  61 /// ```
  62 pub(crate) fn check(cx: &LateContext<'_>, ex: &Expr<'_>) {
  63     if_chain! {
  64         if let Some(ref if_let) = higher::IfLet::hir(cx, ex);
  65         if !is_else_clause(cx.tcx, ex);
  66         if check_if_let(cx, if_let);
  67         then {
  68             let mut applicability = Applicability::MachineApplicable;
  69             span_lint_and_sugg(
  70                 cx,
  71                 NEEDLESS_MATCH,
  72                 ex.span,
  73                 "this if-let expression is unnecessary",
  74                 "replace it with",
  75                 snippet_with_applicability(cx, if_let.let_expr.span, "..", &mut applicability).to_string(),
  76                 applicability,
  77             );
  78         }
  79     }
  80 }
  81
  82 fn check_if_let(cx: &LateContext<'_>, if_let: &higher::IfLet<'_>) -> bool {
  83     if let Some(if_else) = if_let.if_else {
  84         if !pat_same_as_expr(if_let.let_pat, peel_blocks_with_stmt(if_let.if_then)) {
  85             return false;
  86         }
  87
  88         // Recurrsively check for each `else if let` phrase,
  89         if let Some(ref nested_if_let) = higher::IfLet::hir(cx, if_else) {
  90             return check_if_let(cx, nested_if_let);
  91         }
  92
  93         if matches!(if_else.kind, ExprKind::Block(..)) {
  94             let else_expr = peel_blocks_with_stmt(if_else);
  95             let ret = strip_return(else_expr);
  96             let let_expr_ty = cx.typeck_results().expr_ty(if_let.let_expr);
  97             if is_type_diagnostic_item(cx, let_expr_ty, sym::Option) {
  98                 if let ExprKind::Path(ref qpath) = ret.kind {
  99                     return is_lang_ctor(cx, qpath, OptionNone) || eq_expr_value(cx, if_let.let_expr, ret);
 100                 }
 101             } else {
 102                 return eq_expr_value(cx, if_let.let_expr, ret);
 103             }
 104             return true;
 105         }
 106     }
 107     false
 108 }
 109
 110 /// Strip `return` keyword if the expression type is `ExprKind::Ret`.
 111 fn strip_return<'hir>(expr: &'hir Expr<'hir>) -> &'hir Expr<'hir> {
 112     if let ExprKind::Ret(Some(ret)) = expr.kind {
 113         ret
 114     } else {
 115         expr
 116     }
 117 }
 118
 119 fn pat_same_as_expr(pat: &Pat<'_>, expr: &Expr<'_>) -> bool {
 120     let expr = strip_return(expr);
 121     match (&pat.kind, &expr.kind) {
 122         // Example: `Some(val) => Some(val)`
 123         (
 124             PatKind::TupleStruct(QPath::Resolved(_, path), [first_pat, ..], _),
 125             ExprKind::Call(call_expr, [first_param, ..]),
 126         ) => {
 127             if let ExprKind::Path(QPath::Resolved(_, call_path)) = call_expr.kind {
 128                 if has_identical_segments(path.segments, call_path.segments)
 129                     && has_same_non_ref_symbol(first_pat, first_param)
 130                 {
 131                     return true;
 132                 }
 133             }
 134         },
 135         // Example: `val => val`, or `ref val => *val`
 136         (PatKind::Binding(annot, _, pat_ident, _), _) => {
 137             let new_expr = if let (
 138                 BindingAnnotation::Ref | BindingAnnotation::RefMut,
 139                 ExprKind::Unary(UnOp::Deref, operand_expr),
 140             ) = (annot, &expr.kind)
 141             {
 142                 operand_expr
 143             } else {
 144                 expr
 145             };
 146
 147             if let ExprKind::Path(QPath::Resolved(
 148                 _,
 149                 Path {
 150                     segments: [first_seg, ..],
 151                     ..
 152                 },
 153             )) = new_expr.kind
 154             {
 155                 return pat_ident.name == first_seg.ident.name;
 156             }
 157         },
 158         // Example: `Custom::TypeA => Custom::TypeB`, or `None => None`
 159         (PatKind::Path(QPath::Resolved(_, p_path)), ExprKind::Path(QPath::Resolved(_, e_path))) => {
 160             return has_identical_segments(p_path.segments, e_path.segments);
 161         },
 162         // Example: `5 => 5`
 163         (PatKind::Lit(pat_lit_expr), ExprKind::Lit(expr_spanned)) => {
 164             if let ExprKind::Lit(pat_spanned) = &pat_lit_expr.kind {
 165                 return pat_spanned.node == expr_spanned.node;
 166             }
 167         },
 168         _ => {},
 169     }
 170
 171     false
 172 }
 173
 174 fn has_identical_segments(left_segs: &[PathSegment<'_>], right_segs: &[PathSegment<'_>]) -> bool {
 175     if left_segs.len() != right_segs.len() {
 176         return false;
 177     }
 178     for i in 0..left_segs.len() {
 179         if left_segs[i].ident.name != right_segs[i].ident.name {
 180             return false;
 181         }
 182     }
 183     true
 184 }
 185
 186 fn has_same_non_ref_symbol(pat: &Pat<'_>, expr: &Expr<'_>) -> bool {
 187     if_chain! {
 188         if let PatKind::Binding(annot, _, pat_ident, _) = pat.kind;
 189         if !matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
 190         if let ExprKind::Path(QPath::Resolved(_, Path {segments: [first_seg, ..], .. })) = expr.kind;
 191         then {
 192             return pat_ident.name == first_seg.ident.name;
 193         }
 194     }
 195
 196     false
 197 }