clippy_lints/src/manual_unwrap_or.rs

   1 use crate::utils;
   2 use if_chain::if_chain;
   3 use rustc_errors::Applicability;
   4 use rustc_hir::{def, Arm, Expr, ExprKind, PatKind, QPath};
   5 use rustc_lint::LintContext;
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_middle::lint::in_external_macro;
   8 use rustc_session::{declare_lint_pass, declare_tool_lint};
   9
  10 declare_clippy_lint! {
  11     /// **What it does:**
  12     /// Finds patterns that reimplement `Option::unwrap_or`.
  13     ///
  14     /// **Why is this bad?**
  15     /// Concise code helps focusing on behavior instead of boilerplate.
  16     ///
  17     /// **Known problems:** None.
  18     ///
  19     /// **Example:**
  20     /// ```rust
  21     /// match int_option {
  22     ///     Some(v) => v,
  23     ///     None => 1,
  24     /// }
  25     /// ```
  26     ///
  27     /// Use instead:
  28     /// ```rust
  29     /// int_option.unwrap_or(1)
  30     /// ```
  31     pub MANUAL_UNWRAP_OR,
  32     complexity,
  33     "finds patterns that can be encoded more concisely with `Option::unwrap_or(_else)`"
  34 }
  35
  36 declare_lint_pass!(ManualUnwrapOr => [MANUAL_UNWRAP_OR]);
  37
  38 impl LateLintPass<'_> for ManualUnwrapOr {
  39     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  40         if in_external_macro(cx.sess(), expr.span) {
  41             return;
  42         }
  43         lint_option_unwrap_or_case(cx, expr);
  44     }
  45 }
  46
  47 fn lint_option_unwrap_or_case<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
  48     fn applicable_none_arm<'a>(arms: &'a [Arm<'a>]) -> Option<&'a Arm<'a>> {
  49         if_chain! {
  50             if arms.len() == 2;
  51             if arms.iter().all(|arm| arm.guard.is_none());
  52             if let Some((idx, none_arm)) = arms.iter().enumerate().find(|(_, arm)|
  53                 if let PatKind::Path(ref qpath) = arm.pat.kind {
  54                     utils::match_qpath(qpath, &utils::paths::OPTION_NONE)
  55                 } else {
  56                     false
  57                 }
  58             );
  59             let some_arm = &arms[1 - idx];
  60             if let PatKind::TupleStruct(ref some_qpath, &[some_binding], _) = some_arm.pat.kind;
  61             if utils::match_qpath(some_qpath, &utils::paths::OPTION_SOME);
  62             if let PatKind::Binding(_, binding_hir_id, ..) = some_binding.kind;
  63             if let ExprKind::Path(QPath::Resolved(_, body_path)) = some_arm.body.kind;
  64             if let def::Res::Local(body_path_hir_id) = body_path.res;
  65             if body_path_hir_id == binding_hir_id;
  66             if !utils::usage::contains_return_break_continue_macro(none_arm.body);
  67             then {
  68                 Some(none_arm)
  69             }
  70             else {
  71                 None
  72             }
  73         }
  74     }
  75
  76     if_chain! {
  77         if let ExprKind::Match(scrutinee, match_arms, _) = expr.kind;
  78         let ty = cx.typeck_results().expr_ty(scrutinee);
  79         if utils::is_type_diagnostic_item(cx, ty, sym!(option_type));
  80         if let Some(none_arm) = applicable_none_arm(match_arms);
  81         if let Some(scrutinee_snippet) = utils::snippet_opt(cx, scrutinee.span);
  82         if let Some(none_body_snippet) = utils::snippet_opt(cx, none_arm.body.span);
  83         if let Some(indent) = utils::indent_of(cx, expr.span);
  84         then {
  85             let reindented_none_body =
  86                 utils::reindent_multiline(none_body_snippet.into(), true, Some(indent));
  87             let eager_eval = utils::eager_or_lazy::is_eagerness_candidate(cx, none_arm.body);
  88             let method = if eager_eval {
  89                 "unwrap_or"
  90             } else {
  91                 "unwrap_or_else"
  92             };
  93             utils::span_lint_and_sugg(
  94                 cx,
  95                 MANUAL_UNWRAP_OR, expr.span,
  96                 &format!("this pattern reimplements `Option::{}`", &method),
  97                 "replace with",
  98                 format!(
  99                     "{}.{}({}{})",
 100                     scrutinee_snippet,
 101                     method,
 102                     if eager_eval { ""} else { "|| " },
 103                     reindented_none_body
 104                 ),
 105                 Applicability::MachineApplicable,
 106             );
 107             true
 108         } else {
 109             false
 110         }
 111     }
 112 }