clippy_lints/src/redundant_pattern_matching.rs

   1 use crate::utils::{match_qpath, paths, snippet, span_lint_and_then};
   2 use rustc::hir::*;
   3 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   4 use rustc::{declare_lint_pass, declare_tool_lint};
   5 use rustc_errors::Applicability;
   6 use syntax::ast::LitKind;
   7 use syntax::ptr::P;
   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     if arms[0].pats.len() == 1 {
  61         let good_method = match arms[0].pats[0].node {
  62             PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
  63                 if let PatKind::Wild = patterns[0].node {
  64                     if match_qpath(path, &paths::RESULT_OK) {
  65                         "is_ok()"
  66                     } else if match_qpath(path, &paths::RESULT_ERR) {
  67                         "is_err()"
  68                     } else if match_qpath(path, &paths::OPTION_SOME) {
  69                         "is_some()"
  70                     } else {
  71                         return;
  72                     }
  73                 } else {
  74                     return;
  75                 }
  76             },
  77
  78             PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
  79
  80             _ => return,
  81         };
  82
  83         span_lint_and_then(
  84             cx,
  85             REDUNDANT_PATTERN_MATCHING,
  86             arms[0].pats[0].span,
  87             &format!("redundant pattern matching, consider using `{}`", good_method),
  88             |db| {
  89                 let span = expr.span.to(op.span);
  90                 db.span_suggestion(
  91                     span,
  92                     "try this",
  93                     format!("if {}.{}", snippet(cx, op.span, "_"), good_method),
  94                     Applicability::MachineApplicable, // snippet
  95                 );
  96             },
  97         );
  98     } else {
  99         return;
 100     }
 101 }
 102
 103 fn find_sugg_for_match<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, op: &P<Expr>, arms: &HirVec<Arm>) {
 104     if arms.len() == 2 {
 105         let node_pair = (&arms[0].pats[0].node, &arms[1].pats[0].node);
 106
 107         let found_good_method = match node_pair {
 108             (
 109                 PatKind::TupleStruct(ref path_left, ref patterns_left, _),
 110                 PatKind::TupleStruct(ref path_right, ref patterns_right, _),
 111             ) if patterns_left.len() == 1 && patterns_right.len() == 1 => {
 112                 if let (PatKind::Wild, PatKind::Wild) = (&patterns_left[0].node, &patterns_right[0].node) {
 113                     find_good_method_for_match(
 114                         arms,
 115                         path_left,
 116                         path_right,
 117                         &paths::RESULT_OK,
 118                         &paths::RESULT_ERR,
 119                         "is_ok()",
 120                         "is_err()",
 121                     )
 122                 } else {
 123                     None
 124                 }
 125             },
 126             (PatKind::TupleStruct(ref path_left, ref patterns, _), PatKind::Path(ref path_right))
 127             | (PatKind::Path(ref path_left), PatKind::TupleStruct(ref path_right, ref patterns, _))
 128                 if patterns.len() == 1 =>
 129             {
 130                 if let PatKind::Wild = patterns[0].node {
 131                     find_good_method_for_match(
 132                         arms,
 133                         path_left,
 134                         path_right,
 135                         &paths::OPTION_SOME,
 136                         &paths::OPTION_NONE,
 137                         "is_some()",
 138                         "is_none()",
 139                     )
 140                 } else {
 141                     None
 142                 }
 143             },
 144             _ => None,
 145         };
 146
 147         if let Some(good_method) = found_good_method {
 148             span_lint_and_then(
 149                 cx,
 150                 REDUNDANT_PATTERN_MATCHING,
 151                 expr.span,
 152                 &format!("redundant pattern matching, consider using `{}`", good_method),
 153                 |db| {
 154                     let span = expr.span.to(op.span);
 155                     db.span_suggestion(
 156                         span,
 157                         "try this",
 158                         format!("{}.{}", snippet(cx, op.span, "_"), good_method),
 159                         Applicability::MachineApplicable, // snippet
 160                     );
 161                 },
 162             );
 163         }
 164     } else {
 165         return;
 166     }
 167 }
 168
 169 fn find_good_method_for_match<'a>(
 170     arms: &HirVec<Arm>,
 171     path_left: &QPath,
 172     path_right: &QPath,
 173     expected_left: &[&str],
 174     expected_right: &[&str],
 175     should_be_left: &'a str,
 176     should_be_right: &'a str,
 177 ) -> Option<&'a str> {
 178     let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
 179         (&(*arms[0].body).node, &(*arms[1].body).node)
 180     } else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
 181         (&(*arms[1].body).node, &(*arms[0].body).node)
 182     } else {
 183         return None;
 184     };
 185
 186     match body_node_pair {
 187         (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
 188             (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
 189             (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
 190             _ => None,
 191         },
 192         _ => None,
 193     }
 194 }