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
  54 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  55     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  56         if let ExprKind::Match(ref op, ref arms, ref match_source) = expr.node {
  57             match match_source {
  58                 MatchSource::Normal => find_sugg_for_match(cx, expr, op, arms),
  59                 MatchSource::IfLetDesugar { .. } => find_sugg_for_if_let(cx, expr, op, arms),
  60                 _ => return,
  61             }
  62         }
  63     }
  64 }
  65
  66 fn find_sugg_for_if_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, op: &P<Expr>, arms: &HirVec<Arm>) {
  67     if arms[0].pats.len() == 1 {
  68         let good_method = match arms[0].pats[0].node {
  69             PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
  70                 if let PatKind::Wild = patterns[0].node {
  71                     if match_qpath(path, &paths::RESULT_OK) {
  72                         "is_ok()"
  73                     } else if match_qpath(path, &paths::RESULT_ERR) {
  74                         "is_err()"
  75                     } else if match_qpath(path, &paths::OPTION_SOME) {
  76                         "is_some()"
  77                     } else {
  78                         return;
  79                     }
  80                 } else {
  81                     return;
  82                 }
  83             },
  84
  85             PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
  86
  87             _ => return,
  88         };
  89
  90         span_lint_and_then(
  91             cx,
  92             REDUNDANT_PATTERN_MATCHING,
  93             arms[0].pats[0].span,
  94             &format!("redundant pattern matching, consider using `{}`", good_method),
  95             |db| {
  96                 let span = expr.span.to(op.span);
  97                 db.span_suggestion_with_applicability(
  98                     span,
  99                     "try this",
 100                     format!("if {}.{}", snippet(cx, op.span, "_"), good_method),
 101                     Applicability::MachineApplicable, // snippet
 102                 );
 103             },
 104         );
 105     } else {
 106         return;
 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].pats[0].node, &arms[1].pats[0].node);
 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].node, &patterns_right[0].node) {
 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].node {
 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_with_applicability(
 163                         span,
 164                         "try this",
 165                         format!("{}.{}", snippet(cx, op.span, "_"), good_method),
 166                         Applicability::MachineApplicable, // snippet
 167                     );
 168                 },
 169             );
 170         }
 171     } else {
 172         return;
 173     }
 174 }
 175
 176 fn find_good_method_for_match<'a>(
 177     arms: &HirVec<Arm>,
 178     path_left: &QPath,
 179     path_right: &QPath,
 180     expected_left: &[&str],
 181     expected_right: &[&str],
 182     should_be_left: &'a str,
 183     should_be_right: &'a str,
 184 ) -> Option<&'a str> {
 185     let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
 186         (&(*arms[0].body).node, &(*arms[1].body).node)
 187     } else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
 188         (&(*arms[1].body).node, &(*arms[0].body).node)
 189     } else {
 190         return None;
 191     };
 192
 193     match body_node_pair {
 194         (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
 195             (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
 196             (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
 197             _ => None,
 198         },
 199         _ => None,
 200     }
 201 }