clippy_lints/src/manual_unwrap_or.rs

   1 use crate::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_middle::ty::adjustment::Adjust;
  15 use rustc_session::{declare_lint_pass, declare_tool_lint};
  16 use rustc_span::sym;
  17
  18 declare_clippy_lint! {
  19     /// **What it does:**
  20     /// Finds patterns that reimplement `Option::unwrap_or` or `Result::unwrap_or`.
  21     ///
  22     /// **Why is this bad?**
  23     /// Concise code helps focusing on behavior instead of boilerplate.
  24     ///
  25     /// **Known problems:** None.
  26     ///
  27     /// **Example:**
  28     /// ```rust
  29     /// let foo: Option<i32> = None;
  30     /// match foo {
  31     ///     Some(v) => v,
  32     ///     None => 1,
  33     /// };
  34     /// ```
  35     ///
  36     /// Use instead:
  37     /// ```rust
  38     /// let foo: Option<i32> = None;
  39     /// foo.unwrap_or(1);
  40     /// ```
  41     pub MANUAL_UNWRAP_OR,
  42     complexity,
  43     "finds patterns that can be encoded more concisely with `Option::unwrap_or` or `Result::unwrap_or`"
  44 }
  45
  46 declare_lint_pass!(ManualUnwrapOr => [MANUAL_UNWRAP_OR]);
  47
  48 impl LateLintPass<'_> for ManualUnwrapOr {
  49     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  50         if in_external_macro(cx.sess(), expr.span) || in_constant(cx, expr.hir_id) {
  51             return;
  52         }
  53         lint_manual_unwrap_or(cx, expr);
  54     }
  55 }
  56
  57 #[derive(Copy, Clone)]
  58 enum Case {
  59     Option,
  60     Result,
  61 }
  62
  63 impl Case {
  64     fn unwrap_fn_path(&self) -> &str {
  65         match self {
  66             Case::Option => "Option::unwrap_or",
  67             Case::Result => "Result::unwrap_or",
  68         }
  69     }
  70 }
  71
  72 fn lint_manual_unwrap_or<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  73     fn applicable_or_arm<'a>(cx: &LateContext<'_>, arms: &'a [Arm<'a>]) -> Option<&'a Arm<'a>> {
  74         if_chain! {
  75             if arms.len() == 2;
  76             if arms.iter().all(|arm| arm.guard.is_none());
  77             if let Some((idx, or_arm)) = arms.iter().enumerate().find(|(_, arm)| {
  78                 match arm.pat.kind {
  79                     PatKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
  80                     PatKind::TupleStruct(ref qpath, &[pat], _) =>
  81                         matches!(pat.kind, PatKind::Wild) && is_lang_ctor(cx, qpath, ResultErr),
  82                     _ => false,
  83                 }
  84             });
  85             let unwrap_arm = &arms[1 - idx];
  86             if let PatKind::TupleStruct(ref qpath, &[unwrap_pat], _) = unwrap_arm.pat.kind;
  87             if is_lang_ctor(cx, qpath, OptionSome) || is_lang_ctor(cx, qpath, ResultOk);
  88             if let PatKind::Binding(_, binding_hir_id, ..) = unwrap_pat.kind;
  89             if path_to_local_id(unwrap_arm.body, binding_hir_id);
  90             if !contains_return_break_continue_macro(or_arm.body);
  91             if !cx.typeck_results().expr_adjustments(unwrap_arm.body).iter()
  92                 .any(|a| matches!(a.kind, Adjust::Deref(Some(..))));
  93             then {
  94                 Some(or_arm)
  95             } else {
  96                 None
  97             }
  98         }
  99     }
 100
 101     if_chain! {
 102         if let ExprKind::Match(scrutinee, match_arms, _) = expr.kind;
 103         let ty = cx.typeck_results().expr_ty(scrutinee);
 104         if let Some(case) = if is_type_diagnostic_item(cx, ty, sym::option_type) {
 105             Some(Case::Option)
 106         } else if is_type_diagnostic_item(cx, ty, sym::result_type) {
 107             Some(Case::Result)
 108         } else {
 109             None
 110         };
 111         if let Some(or_arm) = applicable_or_arm(cx, match_arms);
 112         if let Some(or_body_snippet) = snippet_opt(cx, or_arm.body.span);
 113         if let Some(indent) = indent_of(cx, expr.span);
 114         if constant_simple(cx, cx.typeck_results(), or_arm.body).is_some();
 115         then {
 116             let reindented_or_body =
 117                 reindent_multiline(or_body_snippet.into(), true, Some(indent));
 118
 119             let suggestion = if scrutinee.span.from_expansion() {
 120                     // we don't want parenthesis around macro, e.g. `(some_macro!()).unwrap_or(0)`
 121                     sugg::Sugg::hir_with_macro_callsite(cx, scrutinee, "..")
 122                 }
 123                 else {
 124                     sugg::Sugg::hir(cx, scrutinee, "..").maybe_par()
 125                 };
 126
 127             span_lint_and_sugg(
 128                 cx,
 129                 MANUAL_UNWRAP_OR, expr.span,
 130                 &format!("this pattern reimplements `{}`", case.unwrap_fn_path()),
 131                 "replace with",
 132                 format!(
 133                     "{}.unwrap_or({})",
 134                     suggestion,
 135                     reindented_or_body,
 136                 ),
 137                 Applicability::MachineApplicable,
 138             );
 139         }
 140     }
 141 }