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     /// **Known problems:** None.
  25     ///
  26     /// **Example:**
  27     /// ```rust
  28     /// let foo: Option<i32> = None;
  29     /// match foo {
  30     ///     Some(v) => v,
  31     ///     None => 1,
  32     /// };
  33     /// ```
  34     ///
  35     /// Use instead:
  36     /// ```rust
  37     /// let foo: Option<i32> = None;
  38     /// foo.unwrap_or(1);
  39     /// ```
  40     pub MANUAL_UNWRAP_OR,
  41     complexity,
  42     "finds patterns that can be encoded more concisely with `Option::unwrap_or` or `Result::unwrap_or`"
  43 }
  44
  45 declare_lint_pass!(ManualUnwrapOr => [MANUAL_UNWRAP_OR]);
  46
  47 impl LateLintPass<'_> for ManualUnwrapOr {
  48     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  49         if in_external_macro(cx.sess(), expr.span) || in_constant(cx, expr.hir_id) {
  50             return;
  51         }
  52         lint_manual_unwrap_or(cx, expr);
  53     }
  54 }
  55
  56 fn lint_manual_unwrap_or<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  57     fn applicable_or_arm<'a>(cx: &LateContext<'_>, arms: &'a [Arm<'a>]) -> Option<&'a Arm<'a>> {
  58         if_chain! {
  59             if arms.len() == 2;
  60             if arms.iter().all(|arm| arm.guard.is_none());
  61             if let Some((idx, or_arm)) = arms.iter().enumerate().find(|(_, arm)| {
  62                 match arm.pat.kind {
  63                     PatKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
  64                     PatKind::TupleStruct(ref qpath, &[pat], _) =>
  65                         matches!(pat.kind, PatKind::Wild) && is_lang_ctor(cx, qpath, ResultErr),
  66                     _ => false,
  67                 }
  68             });
  69             let unwrap_arm = &arms[1 - idx];
  70             if let PatKind::TupleStruct(ref qpath, &[unwrap_pat], _) = unwrap_arm.pat.kind;
  71             if is_lang_ctor(cx, qpath, OptionSome) || is_lang_ctor(cx, qpath, ResultOk);
  72             if let PatKind::Binding(_, binding_hir_id, ..) = unwrap_pat.kind;
  73             if path_to_local_id(unwrap_arm.body, binding_hir_id);
  74             if cx.typeck_results().expr_adjustments(unwrap_arm.body).is_empty();
  75             if !contains_return_break_continue_macro(or_arm.body);
  76             then {
  77                 Some(or_arm)
  78             } else {
  79                 None
  80             }
  81         }
  82     }
  83
  84     if_chain! {
  85         if let ExprKind::Match(scrutinee, match_arms, _) = expr.kind;
  86         let ty = cx.typeck_results().expr_ty(scrutinee);
  87         if let Some(ty_name) = if is_type_diagnostic_item(cx, ty, sym::option_type) {
  88             Some("Option")
  89         } else if is_type_diagnostic_item(cx, ty, sym::result_type) {
  90             Some("Result")
  91         } else {
  92             None
  93         };
  94         if let Some(or_arm) = applicable_or_arm(cx, match_arms);
  95         if let Some(or_body_snippet) = snippet_opt(cx, or_arm.body.span);
  96         if let Some(indent) = indent_of(cx, expr.span);
  97         if constant_simple(cx, cx.typeck_results(), or_arm.body).is_some();
  98         then {
  99             let reindented_or_body =
 100                 reindent_multiline(or_body_snippet.into(), true, Some(indent));
 101
 102             let suggestion = if scrutinee.span.from_expansion() {
 103                     // we don't want parenthesis around macro, e.g. `(some_macro!()).unwrap_or(0)`
 104                     sugg::Sugg::hir_with_macro_callsite(cx, scrutinee, "..")
 105                 }
 106                 else {
 107                     sugg::Sugg::hir(cx, scrutinee, "..").maybe_par()
 108                 };
 109
 110             span_lint_and_sugg(
 111                 cx,
 112                 MANUAL_UNWRAP_OR, expr.span,
 113                 &format!("this pattern reimplements `{}::unwrap_or`", ty_name),
 114                 "replace with",
 115                 format!(
 116                     "{}.unwrap_or({})",
 117                     suggestion,
 118                     reindented_or_body,
 119                 ),
 120                 Applicability::MachineApplicable,
 121             );
 122         }
 123     }
 124 }