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_tool_lint, lint_array};
   5 use rustc_errors::Applicability;
   6 use syntax::ast::LitKind;
   7 use syntax::ptr::P;
   8
   9 /// **What it does:** Lint for redundant pattern matching over `Result` or
  10 /// `Option`
  11 ///
  12 /// **Why is this bad?** It's more concise and clear to just use the proper
  13 /// utility function
  14 ///
  15 /// **Known problems:** None.
  16 ///
  17 /// **Example:**
  18 ///
  19 /// ```rust
  20 /// if let Ok(_) = Ok::<i32, i32>(42) {}
  21 /// if let Err(_) = Err::<i32, i32>(42) {}
  22 /// if let None = None::<()> {}
  23 /// if let Some(_) = Some(42) {}
  24 /// match Ok::<i32, i32>(42) {
  25 ///     Ok(_) => true,
  26 ///     Err(_) => false,
  27 /// };
  28 /// ```
  29 ///
  30 /// The more idiomatic use would be:
  31 ///
  32 /// ```rust
  33 /// if Ok::<i32, i32>(42).is_ok() {}
  34 /// if Err::<i32, i32>(42).is_err() {}
  35 /// if None::<()>.is_none() {}
  36 /// if Some(42).is_some() {}
  37 /// Ok::<i32, i32>(42).is_ok();
  38 /// ```
  39 declare_clippy_lint! {
  40     pub REDUNDANT_PATTERN_MATCHING,
  41     style,
  42     "use the proper utility function avoiding an `if let`"
  43 }
  44
  45 #[derive(Copy, Clone)]
  46 pub struct Pass;
  47
  48 impl LintPass for Pass {
  49     fn get_lints(&self) -> LintArray {
  50         lint_array!(REDUNDANT_PATTERN_MATCHING)
  51     }
  52
  53     fn name(&self) -> &'static str {
  54         "RedundantPatternMatching"
  55     }
  56 }
  57
  58 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  59     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  60         if let ExprKind::Match(ref op, ref arms, ref match_source) = expr.node {
  61             match match_source {
  62                 MatchSource::Normal => find_sugg_for_match(cx, expr, op, arms),
  63                 MatchSource::IfLetDesugar { .. } => find_sugg_for_if_let(cx, expr, op, arms),
  64                 _ => return,
  65             }
  66         }
  67     }
  68 }
  69
  70 fn find_sugg_for_if_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, op: &P<Expr>, arms: &HirVec<Arm>) {
  71     if arms[0].pats.len() == 1 {
  72         let good_method = match arms[0].pats[0].node {
  73             PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
  74                 if let PatKind::Wild = patterns[0].node {
  75                     if match_qpath(path, &paths::RESULT_OK) {
  76                         "is_ok()"
  77                     } else if match_qpath(path, &paths::RESULT_ERR) {
  78                         "is_err()"
  79                     } else if match_qpath(path, &paths::OPTION_SOME) {
  80                         "is_some()"
  81                     } else {
  82                         return;
  83                     }
  84                 } else {
  85                     return;
  86                 }
  87             },
  88
  89             PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
  90
  91             _ => return,
  92         };
  93
  94         span_lint_and_then(
  95             cx,
  96             REDUNDANT_PATTERN_MATCHING,
  97             arms[0].pats[0].span,
  98             &format!("redundant pattern matching, consider using `{}`", good_method),
  99             |db| {
 100                 let span = expr.span.to(op.span);
 101                 db.span_suggestion(
 102                     span,
 103                     "try this",
 104                     format!("if {}.{}", snippet(cx, op.span, "_"), good_method),
 105                     Applicability::MachineApplicable, // snippet
 106                 );
 107             },
 108         );
 109     } else {
 110         return;
 111     }
 112 }
 113
 114 fn find_sugg_for_match<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, op: &P<Expr>, arms: &HirVec<Arm>) {
 115     if arms.len() == 2 {
 116         let node_pair = (&arms[0].pats[0].node, &arms[1].pats[0].node);
 117
 118         let found_good_method = match node_pair {
 119             (
 120                 PatKind::TupleStruct(ref path_left, ref patterns_left, _),
 121                 PatKind::TupleStruct(ref path_right, ref patterns_right, _),
 122             ) if patterns_left.len() == 1 && patterns_right.len() == 1 => {
 123                 if let (PatKind::Wild, PatKind::Wild) = (&patterns_left[0].node, &patterns_right[0].node) {
 124                     find_good_method_for_match(
 125                         arms,
 126                         path_left,
 127                         path_right,
 128                         &paths::RESULT_OK,
 129                         &paths::RESULT_ERR,
 130                         "is_ok()",
 131                         "is_err()",
 132                     )
 133                 } else {
 134                     None
 135                 }
 136             },
 137             (PatKind::TupleStruct(ref path_left, ref patterns, _), PatKind::Path(ref path_right))
 138             | (PatKind::Path(ref path_left), PatKind::TupleStruct(ref path_right, ref patterns, _))
 139                 if patterns.len() == 1 =>
 140             {
 141                 if let PatKind::Wild = patterns[0].node {
 142                     find_good_method_for_match(
 143                         arms,
 144                         path_left,
 145                         path_right,
 146                         &paths::OPTION_SOME,
 147                         &paths::OPTION_NONE,
 148                         "is_some()",
 149                         "is_none()",
 150                     )
 151                 } else {
 152                     None
 153                 }
 154             },
 155             _ => None,
 156         };
 157
 158         if let Some(good_method) = found_good_method {
 159             span_lint_and_then(
 160                 cx,
 161                 REDUNDANT_PATTERN_MATCHING,
 162                 expr.span,
 163                 &format!("redundant pattern matching, consider using `{}`", good_method),
 164                 |db| {
 165                     let span = expr.span.to(op.span);
 166                     db.span_suggestion(
 167                         span,
 168                         "try this",
 169                         format!("{}.{}", snippet(cx, op.span, "_"), good_method),
 170                         Applicability::MachineApplicable, // snippet
 171                     );
 172                 },
 173             );
 174         }
 175     } else {
 176         return;
 177     }
 178 }
 179
 180 fn find_good_method_for_match<'a>(
 181     arms: &HirVec<Arm>,
 182     path_left: &QPath,
 183     path_right: &QPath,
 184     expected_left: &[&str],
 185     expected_right: &[&str],
 186     should_be_left: &'a str,
 187     should_be_right: &'a str,
 188 ) -> Option<&'a str> {
 189     let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
 190         (&(*arms[0].body).node, &(*arms[1].body).node)
 191     } else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
 192         (&(*arms[1].body).node, &(*arms[0].body).node)
 193     } else {
 194         return None;
 195     };
 196
 197     match body_node_pair {
 198         (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
 199             (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
 200             (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
 201             _ => None,
 202         },
 203         _ => None,
 204     }
 205 }