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