clippy_lints/src/manual_unwrap_or.rs

   1 use crate::consts::constant_simple;
   2 use crate::utils;
   3 use if_chain::if_chain;
   4 use rustc_errors::Applicability;
   5 use rustc_hir::{def, Arm, Expr, ExprKind, PatKind, QPath};
   6 use rustc_lint::LintContext;
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_middle::lint::in_external_macro;
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10
  11 declare_clippy_lint! {
  12     /// **What it does:**
  13     /// Finds patterns that reimplement `Option::unwrap_or`.
  14     ///
  15     /// **Why is this bad?**
  16     /// Concise code helps focusing on behavior instead of boilerplate.
  17     ///
  18     /// **Known problems:** None.
  19     ///
  20     /// **Example:**
  21     /// ```rust
  22     /// let foo: Option<i32> = None;
  23     /// match foo {
  24     ///     Some(v) => v,
  25     ///     None => 1,
  26     /// };
  27     /// ```
  28     ///
  29     /// Use instead:
  30     /// ```rust
  31     /// let foo: Option<i32> = None;
  32     /// foo.unwrap_or(1);
  33     /// ```
  34     pub MANUAL_UNWRAP_OR,
  35     complexity,
  36     "finds patterns that can be encoded more concisely with `Option::unwrap_or(_else)`"
  37 }
  38
  39 declare_lint_pass!(ManualUnwrapOr => [MANUAL_UNWRAP_OR]);
  40
  41 impl LateLintPass<'_> for ManualUnwrapOr {
  42     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  43         if in_external_macro(cx.sess(), expr.span) {
  44             return;
  45         }
  46         lint_option_unwrap_or_case(cx, expr);
  47     }
  48 }
  49
  50 fn lint_option_unwrap_or_case<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
  51     fn applicable_none_arm<'a>(arms: &'a [Arm<'a>]) -> Option<&'a Arm<'a>> {
  52         if_chain! {
  53             if arms.len() == 2;
  54             if arms.iter().all(|arm| arm.guard.is_none());
  55             if let Some((idx, none_arm)) = arms.iter().enumerate().find(|(_, arm)|
  56                 if let PatKind::Path(ref qpath) = arm.pat.kind {
  57                     utils::match_qpath(qpath, &utils::paths::OPTION_NONE)
  58                 } else {
  59                     false
  60                 }
  61             );
  62             let some_arm = &arms[1 - idx];
  63             if let PatKind::TupleStruct(ref some_qpath, &[some_binding], _) = some_arm.pat.kind;
  64             if utils::match_qpath(some_qpath, &utils::paths::OPTION_SOME);
  65             if let PatKind::Binding(_, binding_hir_id, ..) = some_binding.kind;
  66             if let ExprKind::Path(QPath::Resolved(_, body_path)) = some_arm.body.kind;
  67             if let def::Res::Local(body_path_hir_id) = body_path.res;
  68             if body_path_hir_id == binding_hir_id;
  69             if !utils::usage::contains_return_break_continue_macro(none_arm.body);
  70             then {
  71                 Some(none_arm)
  72             }
  73             else {
  74                 None
  75             }
  76         }
  77     }
  78
  79     if_chain! {
  80         if let ExprKind::Match(scrutinee, match_arms, _) = expr.kind;
  81         let ty = cx.typeck_results().expr_ty(scrutinee);
  82         if utils::is_type_diagnostic_item(cx, ty, sym!(option_type));
  83         if let Some(none_arm) = applicable_none_arm(match_arms);
  84         if let Some(scrutinee_snippet) = utils::snippet_opt(cx, scrutinee.span);
  85         if let Some(none_body_snippet) = utils::snippet_opt(cx, none_arm.body.span);
  86         if let Some(indent) = utils::indent_of(cx, expr.span);
  87         then {
  88             let reindented_none_body =
  89                 utils::reindent_multiline(none_body_snippet.into(), true, Some(indent));
  90             let eager_eval = constant_simple(cx, cx.typeck_results(), none_arm.body).is_some();
  91             let method = if eager_eval {
  92                 "unwrap_or"
  93             } else {
  94                 "unwrap_or_else"
  95             };
  96             utils::span_lint_and_sugg(
  97                 cx,
  98                 MANUAL_UNWRAP_OR, expr.span,
  99                 &format!("this pattern reimplements `Option::{}`", &method),
 100                 "replace with",
 101                 format!(
 102                     "{}.{}({}{})",
 103                     scrutinee_snippet,
 104                     method,
 105                     if eager_eval { ""} else { "|| " },
 106                     reindented_none_body
 107                 ),
 108                 Applicability::MachineApplicable,
 109             );
 110             true
 111         } else {
 112             false
 113         }
 114     }
 115 }