clippy_lints/src/redundant_pattern_matching.rs

   1 use crate::utils::{match_qpath, paths, snippet, span_lint_and_then};
   2 use rustc::hir::ptr::P;
   3 use rustc::hir::*;
   4 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   5 use rustc::{declare_lint_pass, declare_tool_lint};
   6 use rustc_errors::Applicability;
   7 use syntax::ast::LitKind;
   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(ref op, ref arms, ref match_source) = expr.node {
  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),
  53                 _ => return,
  54             }
  55         }
  56     }
  57 }
  58
  59 fn find_sugg_for_if_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, op: &P<Expr>, arms: &HirVec<Arm>) {
  60     let good_method = match arms[0].pat.node {
  61         PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
  62             if let PatKind::Wild = patterns[0].node {
  63                 if match_qpath(path, &paths::RESULT_OK) {
  64                     "is_ok()"
  65                 } else if match_qpath(path, &paths::RESULT_ERR) {
  66                     "is_err()"
  67                 } else if match_qpath(path, &paths::OPTION_SOME) {
  68                     "is_some()"
  69                 } else {
  70                     return;
  71                 }
  72             } else {
  73                 return;
  74             }
  75         },
  76
  77         PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
  78
  79         _ => return,
  80     };
  81
  82     span_lint_and_then(
  83         cx,
  84         REDUNDANT_PATTERN_MATCHING,
  85         arms[0].pat.span,
  86         &format!("redundant pattern matching, consider using `{}`", good_method),
  87         |db| {
  88             let span = expr.span.to(op.span);
  89             db.span_suggestion(
  90                 span,
  91                 "try this",
  92                 format!("{}.{}", snippet(cx, op.span, "_"), good_method),
  93                 Applicability::MaybeIncorrect, // snippet
  94             );
  95         },
  96     );
  97 }
  98
  99 fn find_sugg_for_match<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, op: &P<Expr>, arms: &HirVec<Arm>) {
 100     if arms.len() == 2 {
 101         let node_pair = (&arms[0].pat.node, &arms[1].pat.node);
 102
 103         let found_good_method = match node_pair {
 104             (
 105                 PatKind::TupleStruct(ref path_left, ref patterns_left, _),
 106                 PatKind::TupleStruct(ref path_right, ref patterns_right, _),
 107             ) if patterns_left.len() == 1 && patterns_right.len() == 1 => {
 108                 if let (PatKind::Wild, PatKind::Wild) = (&patterns_left[0].node, &patterns_right[0].node) {
 109                     find_good_method_for_match(
 110                         arms,
 111                         path_left,
 112                         path_right,
 113                         &paths::RESULT_OK,
 114                         &paths::RESULT_ERR,
 115                         "is_ok()",
 116                         "is_err()",
 117                     )
 118                 } else {
 119                     None
 120                 }
 121             },
 122             (PatKind::TupleStruct(ref path_left, ref patterns, _), PatKind::Path(ref path_right))
 123             | (PatKind::Path(ref path_left), PatKind::TupleStruct(ref path_right, ref patterns, _))
 124                 if patterns.len() == 1 =>
 125             {
 126                 if let PatKind::Wild = patterns[0].node {
 127                     find_good_method_for_match(
 128                         arms,
 129                         path_left,
 130                         path_right,
 131                         &paths::OPTION_SOME,
 132                         &paths::OPTION_NONE,
 133                         "is_some()",
 134                         "is_none()",
 135                     )
 136                 } else {
 137                     None
 138                 }
 139             },
 140             _ => None,
 141         };
 142
 143         if let Some(good_method) = found_good_method {
 144             span_lint_and_then(
 145                 cx,
 146                 REDUNDANT_PATTERN_MATCHING,
 147                 expr.span,
 148                 &format!("redundant pattern matching, consider using `{}`", good_method),
 149                 |db| {
 150                     let span = expr.span.to(op.span);
 151                     db.span_suggestion(
 152                         span,
 153                         "try this",
 154                         format!("{}.{}", snippet(cx, op.span, "_"), good_method),
 155                         Applicability::MaybeIncorrect, // snippet
 156                     );
 157                 },
 158             );
 159         }
 160     }
 161 }
 162
 163 fn find_good_method_for_match<'a>(
 164     arms: &HirVec<Arm>,
 165     path_left: &QPath,
 166     path_right: &QPath,
 167     expected_left: &[&str],
 168     expected_right: &[&str],
 169     should_be_left: &'a str,
 170     should_be_right: &'a str,
 171 ) -> Option<&'a str> {
 172     let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
 173         (&(*arms[0].body).node, &(*arms[1].body).node)
 174     } else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
 175         (&(*arms[1].body).node, &(*arms[0].body).node)
 176     } else {
 177         return None;
 178     };
 179
 180     match body_node_pair {
 181         (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
 182             (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
 183             (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
 184             _ => None,
 185         },
 186         _ => None,
 187     }
 188 }