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     #[allow(clippy::similar_names)]
  67     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  68         if let ExprKind::Match(ref op, ref arms, ref match_source) = expr.node {
  69             match match_source {
  70                 MatchSource::Normal => find_sugg_for_match(cx, expr, op, arms),
  71                 MatchSource::IfLetDesugar { .. } => find_sugg_for_if_let(cx, expr, op, arms),
  72                 _ => return,
  73             }
  74         }
  75     }
  76 }
  77
  78 fn find_sugg_for_if_let<'a, 'tcx>(
  79     cx: &LateContext<'a, 'tcx>,
  80     expr: &'tcx Expr,
  81     op: &P<Expr>,
  82     arms: &HirVec<Arm>
  83 ) {
  84     if arms[0].pats.len() == 1 {
  85         let good_method = match arms[0].pats[0].node {
  86             PatKind::TupleStruct(ref path, ref pats, _) if pats.len() == 1 => {
  87                 if let PatKind::Wild = pats[0].node {
  88                     if match_qpath(path, &paths::RESULT_OK) {
  89                         "is_ok()"
  90                     } else if match_qpath(path, &paths::RESULT_ERR) {
  91                         "is_err()"
  92                     } else if match_qpath(path, &paths::OPTION_SOME) {
  93                         "is_some()"
  94                     } else {
  95                         return;
  96                     }
  97                 } else {
  98                     return;
  99                 }
 100             },
 101
 102             PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
 103
 104             _ => return,
 105         };
 106
 107         span_lint_and_then(
 108             cx,
 109             REDUNDANT_PATTERN_MATCHING,
 110             arms[0].pats[0].span,
 111             &format!("redundant pattern matching, consider using `{}`", good_method),
 112             |db| {
 113                 let span = expr.span.to(op.span);
 114                 db.span_suggestion_with_applicability(
 115                     span,
 116                     "try this",
 117                     format!("if {}.{}", snippet(cx, op.span, "_"), good_method),
 118                     Applicability::MachineApplicable, // snippet
 119                 );
 120             },
 121         );
 122     } else {
 123         return;
 124     }
 125 }
 126
 127 fn find_sugg_for_match<'a, 'tcx>(
 128     cx: &LateContext<'a, 'tcx>,
 129     expr: &'tcx Expr,
 130     op: &P<Expr>,
 131     arms: &HirVec<Arm>
 132 ) {
 133     if arms.len() == 2 {
 134         let node_pair = (&arms[0].pats[0].node, &arms[1].pats[0].node);
 135
 136         let found_good_method = match node_pair {
 137             (
 138                 PatKind::TupleStruct(ref path_left, ref pats_left, _),
 139                 PatKind::TupleStruct(ref path_right, ref pats_right, _)
 140             ) if pats_left.len() == 1 && pats_right.len() == 1 => {
 141                 if let (PatKind::Wild, PatKind::Wild) = (&pats_left[0].node, &pats_right[0].node) {
 142                     find_good_method_for_match(
 143                         arms,
 144                         path_left,
 145                         path_right,
 146                         &paths::RESULT_OK,
 147                         &paths::RESULT_ERR,
 148                         "is_ok()",
 149                         "is_err()"
 150                     )
 151                 } else {
 152                     None
 153                 }
 154             },
 155             (
 156                 PatKind::TupleStruct(ref path_left, ref pats, _),
 157                 PatKind::Path(ref path_right)
 158             ) | (
 159                 PatKind::Path(ref path_left),
 160                 PatKind::TupleStruct(ref path_right, ref pats, _)
 161             ) if pats.len() == 1 => {
 162                 if let PatKind::Wild = pats[0].node {
 163                     find_good_method_for_match(
 164                         arms,
 165                         path_left,
 166                         path_right,
 167                         &paths::OPTION_SOME,
 168                         &paths::OPTION_NONE,
 169                         "is_some()",
 170                         "is_none()"
 171                     )
 172                 } else {
 173                     None
 174                 }
 175             },
 176             _ => None,
 177         };
 178
 179         if let Some(good_method) = found_good_method {
 180             span_lint_and_then(
 181                 cx,
 182                 REDUNDANT_PATTERN_MATCHING,
 183                 expr.span,
 184                 &format!("redundant pattern matching, consider using `{}`", good_method),
 185                 |db| {
 186                     let span = expr.span.to(op.span);
 187                     db.span_suggestion_with_applicability(
 188                         span,
 189                         "try this",
 190                         format!("{}.{}", snippet(cx, op.span, "_"), good_method),
 191                         Applicability::MachineApplicable, // snippet
 192                     );
 193                 },
 194             );
 195         }
 196     } else {
 197         return;
 198     }
 199 }
 200
 201 fn find_good_method_for_match<'a>(
 202     arms: &HirVec<Arm>,
 203     path_left: &QPath,
 204     path_right: &QPath,
 205     expected_left: &[&str],
 206     expected_right: &[&str],
 207     should_be_left: &'a str,
 208     should_be_right: &'a str
 209 ) -> Option<&'a str> {
 210     let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
 211         (&(*arms[0].body).node, &(*arms[1].body).node)
 212     } else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
 213         (&(*arms[1].body).node, &(*arms[0].body).node)
 214     } else {
 215         return None;
 216     };
 217
 218     match body_node_pair {
 219         (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => {
 220             match (&lit_left.node, &lit_right.node) {
 221                 (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
 222                 (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
 223                 _ => None,
 224             }
 225         },
 226         _ => None,
 227     }
 228 }