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(cx: &LateContext<'_>, ex: &Expr<'_>) {
  51     if let Some(ref if_let) = higher::IfLet::hir(cx, ex) {
  52         if !is_else_clause(cx.tcx, ex) && expr_ty_matches_p_ty(cx, if_let.let_expr, ex) && check_if_let(cx, if_let) {
  53             let mut applicability = Applicability::MachineApplicable;
  54             span_lint_and_sugg(
  55                 cx,
  56                 NEEDLESS_MATCH,
  57                 ex.span,
  58                 "this if-let expression is unnecessary",
  59                 "replace it with",
  60                 snippet_with_applicability(cx, if_let.let_expr.span, "..", &mut applicability).to_string(),
  61                 applicability,
  62             );
  63         }
  64     }
  65 }
  66
  67 fn check_all_arms(cx: &LateContext<'_>, match_expr: &Expr<'_>, arms: &[Arm<'_>]) -> bool {
  68     for arm in arms {
  69         let arm_expr = peel_blocks_with_stmt(arm.body);
  70         if let PatKind::Wild = arm.pat.kind {
  71             return eq_expr_value(cx, match_expr, strip_return(arm_expr));
  72         } else if !pat_same_as_expr(arm.pat, arm_expr) {
  73             return false;
  74         }
  75     }
  76
  77     true
  78 }
  79
  80 fn check_if_let(cx: &LateContext<'_>, if_let: &higher::IfLet<'_>) -> bool {
  81     if let Some(if_else) = if_let.if_else {
  82         if !pat_same_as_expr(if_let.let_pat, peel_blocks_with_stmt(if_let.if_then)) {
  83             return false;
  84         }
  85
  86         // Recurrsively check for each `else if let` phrase,
  87         if let Some(ref nested_if_let) = higher::IfLet::hir(cx, if_else) {
  88             return check_if_let(cx, nested_if_let);
  89         }
  90
  91         if matches!(if_else.kind, ExprKind::Block(..)) {
  92             let else_expr = peel_blocks_with_stmt(if_else);
  93             if matches!(else_expr.kind, ExprKind::Block(..)) {
  94                 return false;
  95             }
  96             let ret = strip_return(else_expr);
  97             let let_expr_ty = cx.typeck_results().expr_ty(if_let.let_expr);
  98             if is_type_diagnostic_item(cx, let_expr_ty, sym::Option) {
  99                 if let ExprKind::Path(ref qpath) = ret.kind {
 100                     return is_lang_ctor(cx, qpath, OptionNone) || eq_expr_value(cx, if_let.let_expr, ret);
 101                 }
 102                 return true;
 103             }
 104             return eq_expr_value(cx, if_let.let_expr, ret);
 105         }
 106     }
 107
 108     false
 109 }
 110
 111 /// Strip `return` keyword if the expression type is `ExprKind::Ret`.
 112 fn strip_return<'hir>(expr: &'hir Expr<'hir>) -> &'hir Expr<'hir> {
 113     if let ExprKind::Ret(Some(ret)) = expr.kind {
 114         ret
 115     } else {
 116         expr
 117     }
 118 }
 119
 120 /// Manually check for coercion casting by checking if the type of the match operand or let expr
 121 /// differs with the assigned local variable or the funtion return type.
 122 fn expr_ty_matches_p_ty(cx: &LateContext<'_>, expr: &Expr<'_>, p_expr: &Expr<'_>) -> bool {
 123     if let Some(p_node) = get_parent_node(cx.tcx, p_expr.hir_id) {
 124         match p_node {
 125             // Compare match_expr ty with local in `let local = match match_expr {..}`
 126             Node::Local(local) => {
 127                 let results = cx.typeck_results();
 128                 return same_type_and_consts(results.node_type(local.hir_id), results.expr_ty(expr));
 129             },
 130             // compare match_expr ty with RetTy in `fn foo() -> RetTy`
 131             Node::Item(..) => {
 132                 if let Some(fn_decl) = p_node.fn_decl() {
 133                     if let FnRetTy::Return(ret_ty) = fn_decl.output {
 134                         return same_type_and_consts(hir_ty_to_ty(cx.tcx, ret_ty), cx.typeck_results().expr_ty(expr));
 135                     }
 136                 }
 137             },
 138             // check the parent expr for this whole block `{ match match_expr {..} }`
 139             Node::Block(block) => {
 140                 if let Some(block_parent_expr) = get_parent_expr_for_hir(cx, block.hir_id) {
 141                     return expr_ty_matches_p_ty(cx, expr, block_parent_expr);
 142                 }
 143             },
 144             // recursively call on `if xxx {..}` etc.
 145             Node::Expr(p_expr) => {
 146                 return expr_ty_matches_p_ty(cx, expr, p_expr);
 147             },
 148             _ => {},
 149         }
 150     }
 151     false
 152 }
 153
 154 fn pat_same_as_expr(pat: &Pat<'_>, expr: &Expr<'_>) -> bool {
 155     let expr = strip_return(expr);
 156     match (&pat.kind, &expr.kind) {
 157         // Example: `Some(val) => Some(val)`
 158         (PatKind::TupleStruct(QPath::Resolved(_, path), tuple_params, _), ExprKind::Call(call_expr, call_params)) => {
 159             if let ExprKind::Path(QPath::Resolved(_, call_path)) = call_expr.kind {
 160                 return over(path.segments, call_path.segments, |pat_seg, call_seg| {
 161                     pat_seg.ident.name == call_seg.ident.name
 162                 }) && same_non_ref_symbols(tuple_params, call_params);
 163             }
 164         },
 165         // Example: `val => val`
 166         (
 167             PatKind::Binding(annot, _, pat_ident, _),
 168             ExprKind::Path(QPath::Resolved(
 169                 _,
 170                 Path {
 171                     segments: [first_seg, ..],
 172                     ..
 173                 },
 174             )),
 175         ) => {
 176             return !matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut)
 177                 && pat_ident.name == first_seg.ident.name;
 178         },
 179         // Example: `Custom::TypeA => Custom::TypeB`, or `None => None`
 180         (PatKind::Path(QPath::Resolved(_, p_path)), ExprKind::Path(QPath::Resolved(_, e_path))) => {
 181             return over(p_path.segments, e_path.segments, |p_seg, e_seg| {
 182                 p_seg.ident.name == e_seg.ident.name
 183             });
 184         },
 185         // Example: `5 => 5`
 186         (PatKind::Lit(pat_lit_expr), ExprKind::Lit(expr_spanned)) => {
 187             if let ExprKind::Lit(pat_spanned) = &pat_lit_expr.kind {
 188                 return pat_spanned.node == expr_spanned.node;
 189             }
 190         },
 191         _ => {},
 192     }
 193
 194     false
 195 }
 196
 197 fn same_non_ref_symbols(pats: &[Pat<'_>], exprs: &[Expr<'_>]) -> bool {
 198     if pats.len() != exprs.len() {
 199         return false;
 200     }
 201
 202     for i in 0..pats.len() {
 203         if !pat_same_as_expr(&pats[i], &exprs[i]) {
 204             return false;
 205         }
 206     }
 207
 208     true
 209 }