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
  11 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  12 use crate::rustc::{declare_tool_lint, lint_array};
  13 use crate::rustc::hir::*;
  14 use crate::syntax::ptr::P;
  15 use crate::syntax::ast::LitKind;
  16 use crate::utils::{match_qpath, paths, snippet, span_lint_and_then};
  17 use crate::rustc_errors::Applicability;
  18
  19 /// **What it does:** Lint for redundant pattern matching over `Result` or
  20 /// `Option`
  21 ///
  22 /// **Why is this bad?** It's more concise and clear to just use the proper
  23 /// utility function
  24 ///
  25 /// **Known problems:** None.
  26 ///
  27 /// **Example:**
  28 ///
  29 /// ```rust
  30 /// if let Ok(_) = Ok::<i32, i32>(42) {}
  31 /// if let Err(_) = Err::<i32, i32>(42) {}
  32 /// if let None = None::<()> {}
  33 /// if let Some(_) = Some(42) {}
  34 /// match Ok::<i32, i32>(42) {
  35 ///     Ok(_) => true,
  36 ///     Err(_) => false,
  37 /// };
  38 /// ```
  39 ///
  40 /// The more idiomatic use would be:
  41 ///
  42 /// ```rust
  43 /// if Ok::<i32, i32>(42).is_ok() {}
  44 /// if Err::<i32, i32>(42).is_err() {}
  45 /// if None::<()>.is_none() {}
  46 /// if Some(42).is_some() {}
  47 /// Ok::<i32, i32>(42).is_ok();
  48 /// ```
  49 ///
  50 declare_clippy_lint! {
  51     pub REDUNDANT_PATTERN_MATCHING,
  52     style,
  53     "use the proper utility function avoiding an `if let`"
  54 }
  55
  56 #[derive(Copy, Clone)]
  57 pub struct Pass;
  58
  59 impl LintPass for Pass {
  60     fn get_lints(&self) -> LintArray {
  61         lint_array!(REDUNDANT_PATTERN_MATCHING)
  62     }
  63 }
  64
  65 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  66     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  67         if let ExprKind::Match(ref op, ref arms, ref match_source) = expr.node {
  68             match match_source {
  69                 MatchSource::Normal => find_sugg_for_match(cx, expr, op, arms),
  70                 MatchSource::IfLetDesugar { .. } => find_sugg_for_if_let(cx, expr, op, arms),
  71                 _ => return,
  72             }
  73         }
  74     }
  75 }
  76
  77 fn find_sugg_for_if_let<'a, 'tcx>(
  78     cx: &LateContext<'a, 'tcx>,
  79     expr: &'tcx Expr,
  80     op: &P<Expr>,
  81     arms: &HirVec<Arm>
  82 ) {
  83     if arms[0].pats.len() == 1 {
  84         let good_method = match arms[0].pats[0].node {
  85             PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
  86                 if let PatKind::Wild = patterns[0].node {
  87                     if match_qpath(path, &paths::RESULT_OK) {
  88                         "is_ok()"
  89                     } else if match_qpath(path, &paths::RESULT_ERR) {
  90                         "is_err()"
  91                     } else if match_qpath(path, &paths::OPTION_SOME) {
  92                         "is_some()"
  93                     } else {
  94                         return;
  95                     }
  96                 } else {
  97                     return;
  98                 }
  99             },
 100
 101             PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
 102
 103             _ => return,
 104         };
 105
 106         span_lint_and_then(
 107             cx,
 108             REDUNDANT_PATTERN_MATCHING,
 109             arms[0].pats[0].span,
 110             &format!("redundant pattern matching, consider using `{}`", good_method),
 111             |db| {
 112                 let span = expr.span.to(op.span);
 113                 db.span_suggestion_with_applicability(
 114                     span,
 115                     "try this",
 116                     format!("if {}.{}", snippet(cx, op.span, "_"), good_method),
 117                     Applicability::MachineApplicable, // snippet
 118                 );
 119             },
 120         );
 121     } else {
 122         return;
 123     }
 124 }
 125
 126 fn find_sugg_for_match<'a, 'tcx>(
 127     cx: &LateContext<'a, 'tcx>,
 128     expr: &'tcx Expr,
 129     op: &P<Expr>,
 130     arms: &HirVec<Arm>
 131 ) {
 132     if arms.len() == 2 {
 133         let node_pair = (&arms[0].pats[0].node, &arms[1].pats[0].node);
 134
 135         let found_good_method = match node_pair {
 136             (
 137                 PatKind::TupleStruct(ref path_left, ref patterns_left, _),
 138                 PatKind::TupleStruct(ref path_right, ref patterns_right, _)
 139             ) if patterns_left.len() == 1 && patterns_right.len() == 1 => {
 140                 if let (PatKind::Wild, PatKind::Wild) = (&patterns_left[0].node, &patterns_right[0].node) {
 141                     find_good_method_for_match(
 142                         arms,
 143                         path_left,
 144                         path_right,
 145                         &paths::RESULT_OK,
 146                         &paths::RESULT_ERR,
 147                         "is_ok()",
 148                         "is_err()"
 149                     )
 150                 } else {
 151                     None
 152                 }
 153             },
 154             (
 155                 PatKind::TupleStruct(ref path_left, ref patterns, _),
 156                 PatKind::Path(ref path_right)
 157             ) | (
 158                 PatKind::Path(ref path_left),
 159                 PatKind::TupleStruct(ref path_right, ref patterns, _)
 160             ) if patterns.len() == 1 => {
 161                 if let PatKind::Wild = patterns[0].node {
 162                     find_good_method_for_match(
 163                         arms,
 164                         path_left,
 165                         path_right,
 166                         &paths::OPTION_SOME,
 167                         &paths::OPTION_NONE,
 168                         "is_some()",
 169                         "is_none()"
 170                     )
 171                 } else {
 172                     None
 173                 }
 174             },
 175             _ => None,
 176         };
 177
 178         if let Some(good_method) = found_good_method {
 179             span_lint_and_then(
 180                 cx,
 181                 REDUNDANT_PATTERN_MATCHING,
 182                 expr.span,
 183                 &format!("redundant pattern matching, consider using `{}`", good_method),
 184                 |db| {
 185                     let span = expr.span.to(op.span);
 186                     db.span_suggestion_with_applicability(
 187                         span,
 188                         "try this",
 189                         format!("{}.{}", snippet(cx, op.span, "_"), good_method),
 190                         Applicability::MachineApplicable, // snippet
 191                     );
 192                 },
 193             );
 194         }
 195     } else {
 196         return;
 197     }
 198 }
 199
 200 fn find_good_method_for_match<'a>(
 201     arms: &HirVec<Arm>,
 202     path_left: &QPath,
 203     path_right: &QPath,
 204     expected_left: &[&str],
 205     expected_right: &[&str],
 206     should_be_left: &'a str,
 207     should_be_right: &'a str
 208 ) -> Option<&'a str> {
 209     let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
 210         (&(*arms[0].body).node, &(*arms[1].body).node)
 211     } else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
 212         (&(*arms[1].body).node, &(*arms[0].body).node)
 213     } else {
 214         return None;
 215     };
 216
 217     match body_node_pair {
 218         (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => {
 219             match (&lit_left.node, &lit_right.node) {
 220                 (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
 221                 (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
 222                 _ => None,
 223             }
 224         },
 225         _ => None,
 226     }
 227 }