clippy_lints/src/redundant_pattern_matching.rs

   1 use crate::utils::{match_qpath, paths, snippet, span_lint_and_then};
   2 use rustc::declare_lint_pass;
   3 use rustc::hir::ptr::P;
   4 use rustc::hir::*;
   5 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   6 use rustc_errors::Applicability;
   7 use rustc_session::declare_tool_lint;
   8 use syntax::ast::LitKind;
   9
  10 declare_clippy_lint! {
  11     /// **What it does:** Lint for redundant pattern matching over `Result` or
  12     /// `Option`
  13     ///
  14     /// **Why is this bad?** It's more concise and clear to just use the proper
  15     /// utility function
  16     ///
  17     /// **Known problems:** None.
  18     ///
  19     /// **Example:**
  20     ///
  21     /// ```rust
  22     /// if let Ok(_) = Ok::<i32, i32>(42) {}
  23     /// if let Err(_) = Err::<i32, i32>(42) {}
  24     /// if let None = None::<()> {}
  25     /// if let Some(_) = Some(42) {}
  26     /// match Ok::<i32, i32>(42) {
  27     ///     Ok(_) => true,
  28     ///     Err(_) => false,
  29     /// };
  30     /// ```
  31     ///
  32     /// The more idiomatic use would be:
  33     ///
  34     /// ```rust
  35     /// if Ok::<i32, i32>(42).is_ok() {}
  36     /// if Err::<i32, i32>(42).is_err() {}
  37     /// if None::<()>.is_none() {}
  38     /// if Some(42).is_some() {}
  39     /// Ok::<i32, i32>(42).is_ok();
  40     /// ```
  41     pub REDUNDANT_PATTERN_MATCHING,
  42     style,
  43     "use the proper utility function avoiding an `if let`"
  44 }
  45
  46 declare_lint_pass!(RedundantPatternMatching => [REDUNDANT_PATTERN_MATCHING]);
  47
  48 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantPatternMatching {
  49     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  50         if let ExprKind::Match(ref op, ref arms, ref match_source) = expr.kind {
  51             match match_source {
  52                 MatchSource::Normal => find_sugg_for_match(cx, expr, op, arms),
  53                 MatchSource::IfLetDesugar { contains_else_clause } => {
  54                     find_sugg_for_if_let(cx, expr, op, arms, *contains_else_clause)
  55                 },
  56                 _ => return,
  57             }
  58         }
  59     }
  60 }
  61
  62 fn find_sugg_for_if_let<'a, 'tcx>(
  63     cx: &LateContext<'a, 'tcx>,
  64     expr: &'tcx Expr,
  65     op: &P<Expr>,
  66     arms: &HirVec<Arm>,
  67     has_else: bool,
  68 ) {
  69     let good_method = match arms[0].pat.kind {
  70         PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
  71             if let PatKind::Wild = patterns[0].kind {
  72                 if match_qpath(path, &paths::RESULT_OK) {
  73                     "is_ok()"
  74                 } else if match_qpath(path, &paths::RESULT_ERR) {
  75                     "is_err()"
  76                 } else if match_qpath(path, &paths::OPTION_SOME) {
  77                     "is_some()"
  78                 } else {
  79                     return;
  80                 }
  81             } else {
  82                 return;
  83             }
  84         },
  85
  86         PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
  87
  88         _ => return,
  89     };
  90
  91     let maybe_semi = if has_else { "" } else { ";" };
  92
  93     span_lint_and_then(
  94         cx,
  95         REDUNDANT_PATTERN_MATCHING,
  96         arms[0].pat.span,
  97         &format!("redundant pattern matching, consider using `{}`", good_method),
  98         |db| {
  99             let span = expr.span.to(op.span);
 100             db.span_suggestion(
 101                 span,
 102                 "try this",
 103                 format!("{}.{}{}", snippet(cx, op.span, "_"), good_method, maybe_semi),
 104                 Applicability::MaybeIncorrect, // snippet
 105             );
 106         },
 107     );
 108 }
 109
 110 fn find_sugg_for_match<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, op: &P<Expr>, arms: &HirVec<Arm>) {
 111     if arms.len() == 2 {
 112         let node_pair = (&arms[0].pat.kind, &arms[1].pat.kind);
 113
 114         let found_good_method = match node_pair {
 115             (
 116                 PatKind::TupleStruct(ref path_left, ref patterns_left, _),
 117                 PatKind::TupleStruct(ref path_right, ref patterns_right, _),
 118             ) if patterns_left.len() == 1 && patterns_right.len() == 1 => {
 119                 if let (PatKind::Wild, PatKind::Wild) = (&patterns_left[0].kind, &patterns_right[0].kind) {
 120                     find_good_method_for_match(
 121                         arms,
 122                         path_left,
 123                         path_right,
 124                         &paths::RESULT_OK,
 125                         &paths::RESULT_ERR,
 126                         "is_ok()",
 127                         "is_err()",
 128                     )
 129                 } else {
 130                     None
 131                 }
 132             },
 133             (PatKind::TupleStruct(ref path_left, ref patterns, _), PatKind::Path(ref path_right))
 134             | (PatKind::Path(ref path_left), PatKind::TupleStruct(ref path_right, ref patterns, _))
 135                 if patterns.len() == 1 =>
 136             {
 137                 if let PatKind::Wild = patterns[0].kind {
 138                     find_good_method_for_match(
 139                         arms,
 140                         path_left,
 141                         path_right,
 142                         &paths::OPTION_SOME,
 143                         &paths::OPTION_NONE,
 144                         "is_some()",
 145                         "is_none()",
 146                     )
 147                 } else {
 148                     None
 149                 }
 150             },
 151             _ => None,
 152         };
 153
 154         if let Some(good_method) = found_good_method {
 155             span_lint_and_then(
 156                 cx,
 157                 REDUNDANT_PATTERN_MATCHING,
 158                 expr.span,
 159                 &format!("redundant pattern matching, consider using `{}`", good_method),
 160                 |db| {
 161                     let span = expr.span.to(op.span);
 162                     db.span_suggestion(
 163                         span,
 164                         "try this",
 165                         format!("{}.{}", snippet(cx, op.span, "_"), good_method),
 166                         Applicability::MaybeIncorrect, // snippet
 167                     );
 168                 },
 169             );
 170         }
 171     }
 172 }
 173
 174 fn find_good_method_for_match<'a>(
 175     arms: &HirVec<Arm>,
 176     path_left: &QPath,
 177     path_right: &QPath,
 178     expected_left: &[&str],
 179     expected_right: &[&str],
 180     should_be_left: &'a str,
 181     should_be_right: &'a str,
 182 ) -> Option<&'a str> {
 183     let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
 184         (&(*arms[0].body).kind, &(*arms[1].body).kind)
 185     } else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
 186         (&(*arms[1].body).kind, &(*arms[0].body).kind)
 187     } else {
 188         return None;
 189     };
 190
 191     match body_node_pair {
 192         (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
 193             (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
 194             (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
 195             _ => None,
 196         },
 197         _ => None,
 198     }
 199 }