src/tools/clippy/clippy_lints/src/manual_unwrap_or.rs

   1 use clippy_utils::consts::constant_simple;
   2 use clippy_utils::diagnostics::span_lint_and_sugg;
   3 use clippy_utils::source::{indent_of, reindent_multiline, snippet_opt};
   4 use clippy_utils::ty::is_type_diagnostic_item;
   5 use clippy_utils::usage::contains_return_break_continue_macro;
   6 use clippy_utils::{in_constant, is_lang_ctor, path_to_local_id, sugg};
   7 use if_chain::if_chain;
   8 use rustc_errors::Applicability;
   9 use rustc_hir::LangItem::{OptionNone, OptionSome, ResultErr, ResultOk};
  10 use rustc_hir::{Arm, Expr, ExprKind, PatKind};
  11 use rustc_lint::LintContext;
  12 use rustc_lint::{LateContext, LateLintPass};
  13 use rustc_middle::lint::in_external_macro;
  14 use rustc_session::{declare_lint_pass, declare_tool_lint};
  15 use rustc_span::sym;
  16
  17 declare_clippy_lint! {
  18     /// ### What it does
  19     /// Finds patterns that reimplement `Option::unwrap_or` or `Result::unwrap_or`.
  20     ///
  21     /// ### Why is this bad?
  22     /// Concise code helps focusing on behavior instead of boilerplate.
  23     ///
  24     /// ### Example
  25     /// ```rust
  26     /// let foo: Option<i32> = None;
  27     /// match foo {
  28     ///     Some(v) => v,
  29     ///     None => 1,
  30     /// };
  31     /// ```
  32     ///
  33     /// Use instead:
  34     /// ```rust
  35     /// let foo: Option<i32> = None;
  36     /// foo.unwrap_or(1);
  37     /// ```
  38     pub MANUAL_UNWRAP_OR,
  39     complexity,
  40     "finds patterns that can be encoded more concisely with `Option::unwrap_or` or `Result::unwrap_or`"
  41 }
  42
  43 declare_lint_pass!(ManualUnwrapOr => [MANUAL_UNWRAP_OR]);
  44
  45 impl LateLintPass<'_> for ManualUnwrapOr {
  46     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  47         if in_external_macro(cx.sess(), expr.span) || in_constant(cx, expr.hir_id) {
  48             return;
  49         }
  50         lint_manual_unwrap_or(cx, expr);
  51     }
  52 }
  53
  54 fn lint_manual_unwrap_or<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  55     fn applicable_or_arm<'a>(cx: &LateContext<'_>, arms: &'a [Arm<'a>]) -> Option<&'a Arm<'a>> {
  56         if_chain! {
  57             if arms.len() == 2;
  58             if arms.iter().all(|arm| arm.guard.is_none());
  59             if let Some((idx, or_arm)) = arms.iter().enumerate().find(|(_, arm)| {
  60                 match arm.pat.kind {
  61                     PatKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
  62                     PatKind::TupleStruct(ref qpath, [pat], _) =>
  63                         matches!(pat.kind, PatKind::Wild) && is_lang_ctor(cx, qpath, ResultErr),
  64                     _ => false,
  65                 }
  66             });
  67             let unwrap_arm = &arms[1 - idx];
  68             if let PatKind::TupleStruct(ref qpath, [unwrap_pat], _) = unwrap_arm.pat.kind;
  69             if is_lang_ctor(cx, qpath, OptionSome) || is_lang_ctor(cx, qpath, ResultOk);
  70             if let PatKind::Binding(_, binding_hir_id, ..) = unwrap_pat.kind;
  71             if path_to_local_id(unwrap_arm.body, binding_hir_id);
  72             if cx.typeck_results().expr_adjustments(unwrap_arm.body).is_empty();
  73             if !contains_return_break_continue_macro(or_arm.body);
  74             then {
  75                 Some(or_arm)
  76             } else {
  77                 None
  78             }
  79         }
  80     }
  81
  82     if_chain! {
  83         if let ExprKind::Match(scrutinee, match_arms, _) = expr.kind;
  84         let ty = cx.typeck_results().expr_ty(scrutinee);
  85         if let Some(ty_name) = if is_type_diagnostic_item(cx, ty, sym::option_type) {
  86             Some("Option")
  87         } else if is_type_diagnostic_item(cx, ty, sym::result_type) {
  88             Some("Result")
  89         } else {
  90             None
  91         };
  92         if let Some(or_arm) = applicable_or_arm(cx, match_arms);
  93         if let Some(or_body_snippet) = snippet_opt(cx, or_arm.body.span);
  94         if let Some(indent) = indent_of(cx, expr.span);
  95         if constant_simple(cx, cx.typeck_results(), or_arm.body).is_some();
  96         then {
  97             let reindented_or_body =
  98                 reindent_multiline(or_body_snippet.into(), true, Some(indent));
  99
 100             let suggestion = if scrutinee.span.from_expansion() {
 101                     // we don't want parenthesis around macro, e.g. `(some_macro!()).unwrap_or(0)`
 102                     sugg::Sugg::hir_with_macro_callsite(cx, scrutinee, "..")
 103                 }
 104                 else {
 105                     sugg::Sugg::hir(cx, scrutinee, "..").maybe_par()
 106                 };
 107
 108             span_lint_and_sugg(
 109                 cx,
 110                 MANUAL_UNWRAP_OR, expr.span,
 111                 &format!("this pattern reimplements `{}::unwrap_or`", ty_name),
 112                 "replace with",
 113                 format!(
 114                     "{}.unwrap_or({})",
 115                     suggestion,
 116                     reindented_or_body,
 117                 ),
 118                 Applicability::MachineApplicable,
 119             );
 120         }
 121     }
 122 }