clippy_lints/src/manual_unwrap_or.rs

   1 use crate::consts::constant_simple;
   2 use crate::utils;
   3 use crate::utils::{path_to_local_id, sugg};
   4 use clippy_utils::ty::is_type_diagnostic_item;
   5 use if_chain::if_chain;
   6 use rustc_errors::Applicability;
   7 use rustc_hir::{Arm, Expr, ExprKind, Pat, PatKind};
   8 use rustc_lint::LintContext;
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_middle::lint::in_external_macro;
  11 use rustc_session::{declare_lint_pass, declare_tool_lint};
  12 use rustc_span::sym;
  13
  14 declare_clippy_lint! {
  15     /// **What it does:**
  16     /// Finds patterns that reimplement `Option::unwrap_or` or `Result::unwrap_or`.
  17     ///
  18     /// **Why is this bad?**
  19     /// Concise code helps focusing on behavior instead of boilerplate.
  20     ///
  21     /// **Known problems:** None.
  22     ///
  23     /// **Example:**
  24     /// ```rust
  25     /// let foo: Option<i32> = None;
  26     /// match foo {
  27     ///     Some(v) => v,
  28     ///     None => 1,
  29     /// };
  30     /// ```
  31     ///
  32     /// Use instead:
  33     /// ```rust
  34     /// let foo: Option<i32> = None;
  35     /// foo.unwrap_or(1);
  36     /// ```
  37     pub MANUAL_UNWRAP_OR,
  38     complexity,
  39     "finds patterns that can be encoded more concisely with `Option::unwrap_or` or `Result::unwrap_or`"
  40 }
  41
  42 declare_lint_pass!(ManualUnwrapOr => [MANUAL_UNWRAP_OR]);
  43
  44 impl LateLintPass<'_> for ManualUnwrapOr {
  45     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  46         if in_external_macro(cx.sess(), expr.span) {
  47             return;
  48         }
  49         lint_manual_unwrap_or(cx, expr);
  50     }
  51 }
  52
  53 #[derive(Copy, Clone)]
  54 enum Case {
  55     Option,
  56     Result,
  57 }
  58
  59 impl Case {
  60     fn unwrap_fn_path(&self) -> &str {
  61         match self {
  62             Case::Option => "Option::unwrap_or",
  63             Case::Result => "Result::unwrap_or",
  64         }
  65     }
  66 }
  67
  68 fn lint_manual_unwrap_or<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  69     fn applicable_or_arm<'a>(arms: &'a [Arm<'a>]) -> Option<&'a Arm<'a>> {
  70         if_chain! {
  71             if arms.len() == 2;
  72             if arms.iter().all(|arm| arm.guard.is_none());
  73             if let Some((idx, or_arm)) = arms.iter().enumerate().find(|(_, arm)|
  74                 match arm.pat.kind {
  75                     PatKind::Path(ref some_qpath) =>
  76                         utils::match_qpath(some_qpath, &utils::paths::OPTION_NONE),
  77                     PatKind::TupleStruct(ref err_qpath, &[Pat { kind: PatKind::Wild, .. }], _) =>
  78                         utils::match_qpath(err_qpath, &utils::paths::RESULT_ERR),
  79                     _ => false,
  80                 }
  81             );
  82             let unwrap_arm = &arms[1 - idx];
  83             if let PatKind::TupleStruct(ref unwrap_qpath, &[unwrap_pat], _) = unwrap_arm.pat.kind;
  84             if utils::match_qpath(unwrap_qpath, &utils::paths::OPTION_SOME)
  85                 || utils::match_qpath(unwrap_qpath, &utils::paths::RESULT_OK);
  86             if let PatKind::Binding(_, binding_hir_id, ..) = unwrap_pat.kind;
  87             if path_to_local_id(unwrap_arm.body, binding_hir_id);
  88             if !utils::usage::contains_return_break_continue_macro(or_arm.body);
  89             then {
  90                 Some(or_arm)
  91             } else {
  92                 None
  93             }
  94         }
  95     }
  96
  97     if_chain! {
  98         if let ExprKind::Match(scrutinee, match_arms, _) = expr.kind;
  99         let ty = cx.typeck_results().expr_ty(scrutinee);
 100         if let Some(case) = if is_type_diagnostic_item(cx, ty, sym::option_type) {
 101             Some(Case::Option)
 102         } else if is_type_diagnostic_item(cx, ty, sym::result_type) {
 103             Some(Case::Result)
 104         } else {
 105             None
 106         };
 107         if let Some(or_arm) = applicable_or_arm(match_arms);
 108         if let Some(or_body_snippet) = utils::snippet_opt(cx, or_arm.body.span);
 109         if let Some(indent) = utils::indent_of(cx, expr.span);
 110         if constant_simple(cx, cx.typeck_results(), or_arm.body).is_some();
 111         then {
 112             let reindented_or_body =
 113                 utils::reindent_multiline(or_body_snippet.into(), true, Some(indent));
 114             utils::span_lint_and_sugg(
 115                 cx,
 116                 MANUAL_UNWRAP_OR, expr.span,
 117                 &format!("this pattern reimplements `{}`", case.unwrap_fn_path()),
 118                 "replace with",
 119                 format!(
 120                     "{}.unwrap_or({})",
 121                     sugg::Sugg::hir(cx, scrutinee, "..").maybe_par(),
 122                     reindented_or_body,
 123                 ),
 124                 Applicability::MachineApplicable,
 125             );
 126         }
 127     }
 128 }