clippy_lints/src/redundant_pattern_matching.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10 use crate::rustc::hir::*;
  11 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  12 use crate::rustc::{declare_tool_lint, lint_array};
  13 use crate::rustc_errors::Applicability;
  14 use crate::syntax::ast::LitKind;
  15 use crate::syntax::ptr::P;
  16 use crate::utils::{match_qpath, paths, snippet, span_lint_and_then};
  17
  18 /// **What it does:** Lint for redundant pattern matching over `Result` or
  19 /// `Option`
  20 ///
  21 /// **Why is this bad?** It's more concise and clear to just use the proper
  22 /// utility function
  23 ///
  24 /// **Known problems:** None.
  25 ///
  26 /// **Example:**
  27 ///
  28 /// ```rust
  29 /// if let Ok(_) = Ok::<i32, i32>(42) {}
  30 /// if let Err(_) = Err::<i32, i32>(42) {}
  31 /// if let None = None::<()> {}
  32 /// if let Some(_) = Some(42) {}
  33 /// match Ok::<i32, i32>(42) {
  34 ///     Ok(_) => true,
  35 ///     Err(_) => false,
  36 /// };
  37 /// ```
  38 ///
  39 /// The more idiomatic use would be:
  40 ///
  41 /// ```rust
  42 /// if Ok::<i32, i32>(42).is_ok() {}
  43 /// if Err::<i32, i32>(42).is_err() {}
  44 /// if None::<()>.is_none() {}
  45 /// if Some(42).is_some() {}
  46 /// Ok::<i32, i32>(42).is_ok();
  47 /// ```
  48 declare_clippy_lint! {
  49     pub REDUNDANT_PATTERN_MATCHING,
  50     style,
  51     "use the proper utility function avoiding an `if let`"
  52 }
  53
  54 #[derive(Copy, Clone)]
  55 pub struct Pass;
  56
  57 impl LintPass for Pass {
  58     fn get_lints(&self) -> LintArray {
  59         lint_array!(REDUNDANT_PATTERN_MATCHING)
  60     }
  61 }
  62
  63 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  64     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  65         if let ExprKind::Match(ref op, ref arms, ref match_source) = expr.node {
  66             match match_source {
  67                 MatchSource::Normal => find_sugg_for_match(cx, expr, op, arms),
  68                 MatchSource::IfLetDesugar { .. } => find_sugg_for_if_let(cx, expr, op, arms),
  69                 _ => return,
  70             }
  71         }
  72     }
  73 }
  74
  75 fn find_sugg_for_if_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, op: &P<Expr>, arms: &HirVec<Arm>) {
  76     if arms[0].pats.len() == 1 {
  77         let good_method = match arms[0].pats[0].node {
  78             PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
  79                 if let PatKind::Wild = patterns[0].node {
  80                     if match_qpath(path, &paths::RESULT_OK) {
  81                         "is_ok()"
  82                     } else if match_qpath(path, &paths::RESULT_ERR) {
  83                         "is_err()"
  84                     } else if match_qpath(path, &paths::OPTION_SOME) {
  85                         "is_some()"
  86                     } else {
  87                         return;
  88                     }
  89                 } else {
  90                     return;
  91                 }
  92             },
  93
  94             PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
  95
  96             _ => return,
  97         };
  98
  99         span_lint_and_then(
 100             cx,
 101             REDUNDANT_PATTERN_MATCHING,
 102             arms[0].pats[0].span,
 103             &format!("redundant pattern matching, consider using `{}`", good_method),
 104             |db| {
 105                 let span = expr.span.to(op.span);
 106                 db.span_suggestion_with_applicability(
 107                     span,
 108                     "try this",
 109                     format!("if {}.{}", snippet(cx, op.span, "_"), good_method),
 110                     Applicability::MachineApplicable, // snippet
 111                 );
 112             },
 113         );
 114     } else {
 115         return;
 116     }
 117 }
 118
 119 fn find_sugg_for_match<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, op: &P<Expr>, arms: &HirVec<Arm>) {
 120     if arms.len() == 2 {
 121         let node_pair = (&arms[0].pats[0].node, &arms[1].pats[0].node);
 122
 123         let found_good_method = match node_pair {
 124             (
 125                 PatKind::TupleStruct(ref path_left, ref patterns_left, _),
 126                 PatKind::TupleStruct(ref path_right, ref patterns_right, _),
 127             ) if patterns_left.len() == 1 && patterns_right.len() == 1 => {
 128                 if let (PatKind::Wild, PatKind::Wild) = (&patterns_left[0].node, &patterns_right[0].node) {
 129                     find_good_method_for_match(
 130                         arms,
 131                         path_left,
 132                         path_right,
 133                         &paths::RESULT_OK,
 134                         &paths::RESULT_ERR,
 135                         "is_ok()",
 136                         "is_err()",
 137                     )
 138                 } else {
 139                     None
 140                 }
 141             },
 142             (PatKind::TupleStruct(ref path_left, ref patterns, _), PatKind::Path(ref path_right))
 143             | (PatKind::Path(ref path_left), PatKind::TupleStruct(ref path_right, ref patterns, _))
 144                 if patterns.len() == 1 =>
 145             {
 146                 if let PatKind::Wild = patterns[0].node {
 147                     find_good_method_for_match(
 148                         arms,
 149                         path_left,
 150                         path_right,
 151                         &paths::OPTION_SOME,
 152                         &paths::OPTION_NONE,
 153                         "is_some()",
 154                         "is_none()",
 155                     )
 156                 } else {
 157                     None
 158                 }
 159             },
 160             _ => None,
 161         };
 162
 163         if let Some(good_method) = found_good_method {
 164             span_lint_and_then(
 165                 cx,
 166                 REDUNDANT_PATTERN_MATCHING,
 167                 expr.span,
 168                 &format!("redundant pattern matching, consider using `{}`", good_method),
 169                 |db| {
 170                     let span = expr.span.to(op.span);
 171                     db.span_suggestion_with_applicability(
 172                         span,
 173                         "try this",
 174                         format!("{}.{}", snippet(cx, op.span, "_"), good_method),
 175                         Applicability::MachineApplicable, // snippet
 176                     );
 177                 },
 178             );
 179         }
 180     } else {
 181         return;
 182     }
 183 }
 184
 185 fn find_good_method_for_match<'a>(
 186     arms: &HirVec<Arm>,
 187     path_left: &QPath,
 188     path_right: &QPath,
 189     expected_left: &[&str],
 190     expected_right: &[&str],
 191     should_be_left: &'a str,
 192     should_be_right: &'a str,
 193 ) -> Option<&'a str> {
 194     let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
 195         (&(*arms[0].body).node, &(*arms[1].body).node)
 196     } else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
 197         (&(*arms[1].body).node, &(*arms[0].body).node)
 198     } else {
 199         return None;
 200     };
 201
 202     match body_node_pair {
 203         (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
 204             (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
 205             (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
 206             _ => None,
 207         },
 208         _ => None,
 209     }
 210 }