clippy_lints/src/redundant_pattern_matching.rs

   1 use crate::utils::{match_qpath, match_trait_method, paths, snippet, span_lint_and_then};
   2 use if_chain::if_chain;
   3 use rustc_ast::ast::LitKind;
   4 use rustc_errors::Applicability;
   5 use rustc_hir::{Arm, Expr, ExprKind, MatchSource, PatKind, QPath};
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_session::{declare_lint_pass, declare_tool_lint};
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** Lint for redundant pattern matching over `Result` or
  11     /// `Option`
  12     ///
  13     /// **Why is this bad?** It's more concise and clear to just use the proper
  14     /// utility function
  15     ///
  16     /// **Known problems:** None.
  17     ///
  18     /// **Example:**
  19     ///
  20     /// ```rust
  21     /// if let Ok(_) = Ok::<i32, i32>(42) {}
  22     /// if let Err(_) = Err::<i32, i32>(42) {}
  23     /// if let None = None::<()> {}
  24     /// if let Some(_) = Some(42) {}
  25     /// match Ok::<i32, i32>(42) {
  26     ///     Ok(_) => true,
  27     ///     Err(_) => false,
  28     /// };
  29     /// ```
  30     ///
  31     /// The more idiomatic use would be:
  32     ///
  33     /// ```rust
  34     /// if Ok::<i32, i32>(42).is_ok() {}
  35     /// if Err::<i32, i32>(42).is_err() {}
  36     /// if None::<()>.is_none() {}
  37     /// if Some(42).is_some() {}
  38     /// Ok::<i32, i32>(42).is_ok();
  39     /// ```
  40     pub REDUNDANT_PATTERN_MATCHING,
  41     style,
  42     "use the proper utility function avoiding an `if let`"
  43 }
  44
  45 declare_lint_pass!(RedundantPatternMatching => [REDUNDANT_PATTERN_MATCHING]);
  46
  47 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantPatternMatching {
  48     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
  49         if let ExprKind::Match(op, arms, ref match_source) = &expr.kind {
  50             match match_source {
  51                 MatchSource::Normal => find_sugg_for_match(cx, expr, op, arms),
  52                 MatchSource::IfLetDesugar { .. } => find_sugg_for_if_let(cx, expr, op, arms, "if"),
  53                 MatchSource::WhileLetDesugar => find_sugg_for_if_let(cx, expr, op, arms, "while"),
  54                 _ => return,
  55             }
  56         }
  57     }
  58 }
  59
  60 fn find_sugg_for_if_let<'a, 'tcx>(
  61     cx: &LateContext<'a, 'tcx>,
  62     expr: &'tcx Expr<'_>,
  63     op: &Expr<'_>,
  64     arms: &[Arm<'_>],
  65     keyword: &'static str,
  66 ) {
  67     let good_method = match arms[0].pat.kind {
  68         PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
  69             if let PatKind::Wild = patterns[0].kind {
  70                 if match_qpath(path, &paths::RESULT_OK) {
  71                     "is_ok()"
  72                 } else if match_qpath(path, &paths::RESULT_ERR) {
  73                     "is_err()"
  74                 } else if match_qpath(path, &paths::OPTION_SOME) {
  75                     "is_some()"
  76                 } else {
  77                     return;
  78                 }
  79             } else {
  80                 return;
  81             }
  82         },
  83
  84         PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
  85
  86         _ => return,
  87     };
  88
  89     // check that `while_let_on_iterator` lint does not trigger
  90     if_chain! {
  91         if keyword == "while";
  92         if let ExprKind::MethodCall(method_path, _, _) = op.kind;
  93         if method_path.ident.name == sym!(next);
  94         if match_trait_method(cx, op, &paths::ITERATOR);
  95         then {
  96             return;
  97         }
  98     }
  99
 100     span_lint_and_then(
 101         cx,
 102         REDUNDANT_PATTERN_MATCHING,
 103         arms[0].pat.span,
 104         &format!("redundant pattern matching, consider using `{}`", good_method),
 105         |diag| {
 106             // in the case of WhileLetDesugar expr.span == op.span incorrectly.
 107             // this is a workaround to restore true value of expr.span
 108             let expr_span = expr.span.to(arms[1].span);
 109             let span = expr_span.until(op.span.shrink_to_hi());
 110             diag.span_suggestion(
 111                 span,
 112                 "try this",
 113                 format!("{} {}.{}", keyword, snippet(cx, op.span, "_"), good_method),
 114                 Applicability::MachineApplicable, // snippet
 115             );
 116         },
 117     );
 118 }
 119
 120 fn find_sugg_for_match<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>, op: &Expr<'_>, arms: &[Arm<'_>]) {
 121     if arms.len() == 2 {
 122         let node_pair = (&arms[0].pat.kind, &arms[1].pat.kind);
 123
 124         let found_good_method = match node_pair {
 125             (
 126                 PatKind::TupleStruct(ref path_left, ref patterns_left, _),
 127                 PatKind::TupleStruct(ref path_right, ref patterns_right, _),
 128             ) if patterns_left.len() == 1 && patterns_right.len() == 1 => {
 129                 if let (PatKind::Wild, PatKind::Wild) = (&patterns_left[0].kind, &patterns_right[0].kind) {
 130                     find_good_method_for_match(
 131                         arms,
 132                         path_left,
 133                         path_right,
 134                         &paths::RESULT_OK,
 135                         &paths::RESULT_ERR,
 136                         "is_ok()",
 137                         "is_err()",
 138                     )
 139                 } else {
 140                     None
 141                 }
 142             },
 143             (PatKind::TupleStruct(ref path_left, ref patterns, _), PatKind::Path(ref path_right))
 144             | (PatKind::Path(ref path_left), PatKind::TupleStruct(ref path_right, ref patterns, _))
 145                 if patterns.len() == 1 =>
 146             {
 147                 if let PatKind::Wild = patterns[0].kind {
 148                     find_good_method_for_match(
 149                         arms,
 150                         path_left,
 151                         path_right,
 152                         &paths::OPTION_SOME,
 153                         &paths::OPTION_NONE,
 154                         "is_some()",
 155                         "is_none()",
 156                     )
 157                 } else {
 158                     None
 159                 }
 160             },
 161             _ => None,
 162         };
 163
 164         if let Some(good_method) = found_good_method {
 165             span_lint_and_then(
 166                 cx,
 167                 REDUNDANT_PATTERN_MATCHING,
 168                 expr.span,
 169                 &format!("redundant pattern matching, consider using `{}`", good_method),
 170                 |diag| {
 171                     let span = expr.span.to(op.span);
 172                     diag.span_suggestion(
 173                         span,
 174                         "try this",
 175                         format!("{}.{}", snippet(cx, op.span, "_"), good_method),
 176                         Applicability::MaybeIncorrect, // snippet
 177                     );
 178                 },
 179             );
 180         }
 181     }
 182 }
 183
 184 fn find_good_method_for_match<'a>(
 185     arms: &[Arm<'_>],
 186     path_left: &QPath<'_>,
 187     path_right: &QPath<'_>,
 188     expected_left: &[&str],
 189     expected_right: &[&str],
 190     should_be_left: &'a str,
 191     should_be_right: &'a str,
 192 ) -> Option<&'a str> {
 193     let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
 194         (&(*arms[0].body).kind, &(*arms[1].body).kind)
 195     } else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
 196         (&(*arms[1].body).kind, &(*arms[0].body).kind)
 197     } else {
 198         return None;
 199     };
 200
 201     match body_node_pair {
 202         (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
 203             (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
 204             (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
 205             _ => None,
 206         },
 207         _ => None,
 208     }
 209 }