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.kind {
  50             match match_source {
  51                 MatchSource::Normal => find_sugg_for_match(cx, expr, op, arms),
  52                 MatchSource::IfLetDesugar { contains_else_clause } => {
  53                     find_sugg_for_if_let(cx, expr, op, arms, *contains_else_clause)
  54                 },
  55                 _ => return,
  56             }
  57         }
  58     }
  59 }
  60
  61 fn find_sugg_for_if_let<'a, 'tcx>(
  62     cx: &LateContext<'a, 'tcx>,
  63     expr: &'tcx Expr,
  64     op: &P<Expr>,
  65     arms: &HirVec<Arm>,
  66     has_else: bool,
  67 ) {
  68     let good_method = match arms[0].pat.kind {
  69         PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
  70             if let PatKind::Wild = patterns[0].kind {
  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     let maybe_semi = if has_else { "" } else { ";" };
  91
  92     span_lint_and_then(
  93         cx,
  94         REDUNDANT_PATTERN_MATCHING,
  95         arms[0].pat.span,
  96         &format!("redundant pattern matching, consider using `{}`", good_method),
  97         |db| {
  98             let span = expr.span.to(op.span);
  99             db.span_suggestion(
 100                 span,
 101                 "try this",
 102                 format!("{}.{}{}", snippet(cx, op.span, "_"), good_method, maybe_semi),
 103                 Applicability::MaybeIncorrect, // snippet
 104             );
 105         },
 106     );
 107 }
 108
 109 fn find_sugg_for_match<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, op: &P<Expr>, arms: &HirVec<Arm>) {
 110     if arms.len() == 2 {
 111         let node_pair = (&arms[0].pat.kind, &arms[1].pat.kind);
 112
 113         let found_good_method = match node_pair {
 114             (
 115                 PatKind::TupleStruct(ref path_left, ref patterns_left, _),
 116                 PatKind::TupleStruct(ref path_right, ref patterns_right, _),
 117             ) if patterns_left.len() == 1 && patterns_right.len() == 1 => {
 118                 if let (PatKind::Wild, PatKind::Wild) = (&patterns_left[0].kind, &patterns_right[0].kind) {
 119                     find_good_method_for_match(
 120                         arms,
 121                         path_left,
 122                         path_right,
 123                         &paths::RESULT_OK,
 124                         &paths::RESULT_ERR,
 125                         "is_ok()",
 126                         "is_err()",
 127                     )
 128                 } else {
 129                     None
 130                 }
 131             },
 132             (PatKind::TupleStruct(ref path_left, ref patterns, _), PatKind::Path(ref path_right))
 133             | (PatKind::Path(ref path_left), PatKind::TupleStruct(ref path_right, ref patterns, _))
 134                 if patterns.len() == 1 =>
 135             {
 136                 if let PatKind::Wild = patterns[0].kind {
 137                     find_good_method_for_match(
 138                         arms,
 139                         path_left,
 140                         path_right,
 141                         &paths::OPTION_SOME,
 142                         &paths::OPTION_NONE,
 143                         "is_some()",
 144                         "is_none()",
 145                     )
 146                 } else {
 147                     None
 148                 }
 149             },
 150             _ => None,
 151         };
 152
 153         if let Some(good_method) = found_good_method {
 154             span_lint_and_then(
 155                 cx,
 156                 REDUNDANT_PATTERN_MATCHING,
 157                 expr.span,
 158                 &format!("redundant pattern matching, consider using `{}`", good_method),
 159                 |db| {
 160                     let span = expr.span.to(op.span);
 161                     db.span_suggestion(
 162                         span,
 163                         "try this",
 164                         format!("{}.{}", snippet(cx, op.span, "_"), good_method),
 165                         Applicability::MaybeIncorrect, // snippet
 166                     );
 167                 },
 168             );
 169         }
 170     }
 171 }
 172
 173 fn find_good_method_for_match<'a>(
 174     arms: &HirVec<Arm>,
 175     path_left: &QPath,
 176     path_right: &QPath,
 177     expected_left: &[&str],
 178     expected_right: &[&str],
 179     should_be_left: &'a str,
 180     should_be_right: &'a str,
 181 ) -> Option<&'a str> {
 182     let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
 183         (&(*arms[0].body).kind, &(*arms[1].body).kind)
 184     } else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
 185         (&(*arms[1].body).kind, &(*arms[0].body).kind)
 186     } else {
 187         return None;
 188     };
 189
 190     match body_node_pair {
 191         (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
 192             (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
 193             (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
 194             _ => None,
 195         },
 196         _ => None,
 197     }
 198 }