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_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 #[derive(Copy, Clone)]
  57 enum Case {
  58     Option,
  59     Result,
  60 }
  61
  62 impl Case {
  63     fn unwrap_fn_path(&self) -> &str {
  64         match self {
  65             Case::Option => "Option::unwrap_or",
  66             Case::Result => "Result::unwrap_or",
  67         }
  68     }
  69 }
  70
  71 fn lint_manual_unwrap_or<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  72     fn applicable_or_arm<'a>(cx: &LateContext<'_>, arms: &'a [Arm<'a>]) -> Option<&'a Arm<'a>> {
  73         if_chain! {
  74             if arms.len() == 2;
  75             if arms.iter().all(|arm| arm.guard.is_none());
  76             if let Some((idx, or_arm)) = arms.iter().enumerate().find(|(_, arm)| {
  77                 match arm.pat.kind {
  78                     PatKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
  79                     PatKind::TupleStruct(ref qpath, &[pat], _) =>
  80                         matches!(pat.kind, PatKind::Wild) && is_lang_ctor(cx, qpath, ResultErr),
  81                     _ => false,
  82                 }
  83             });
  84             let unwrap_arm = &arms[1 - idx];
  85             if let PatKind::TupleStruct(ref qpath, &[unwrap_pat], _) = unwrap_arm.pat.kind;
  86             if is_lang_ctor(cx, qpath, OptionSome) || is_lang_ctor(cx, qpath, ResultOk);
  87             if let PatKind::Binding(_, binding_hir_id, ..) = unwrap_pat.kind;
  88             if path_to_local_id(unwrap_arm.body, binding_hir_id);
  89             if !contains_return_break_continue_macro(or_arm.body);
  90             then {
  91                 Some(or_arm)
  92             } else {
  93                 None
  94             }
  95         }
  96     }
  97
  98     if_chain! {
  99         if let ExprKind::Match(scrutinee, match_arms, _) = expr.kind;
 100         let ty = cx.typeck_results().expr_ty(scrutinee);
 101         if let Some(case) = if is_type_diagnostic_item(cx, ty, sym::option_type) {
 102             Some(Case::Option)
 103         } else if is_type_diagnostic_item(cx, ty, sym::result_type) {
 104             Some(Case::Result)
 105         } else {
 106             None
 107         };
 108         if let Some(or_arm) = applicable_or_arm(cx, match_arms);
 109         if let Some(or_body_snippet) = snippet_opt(cx, or_arm.body.span);
 110         if let Some(indent) = indent_of(cx, expr.span);
 111         if constant_simple(cx, cx.typeck_results(), or_arm.body).is_some();
 112         then {
 113             let reindented_or_body =
 114                 reindent_multiline(or_body_snippet.into(), true, Some(indent));
 115
 116             let suggestion = if scrutinee.span.from_expansion() {
 117                     // we don't want parenthesis around macro, e.g. `(some_macro!()).unwrap_or(0)`
 118                     sugg::Sugg::hir_with_macro_callsite(cx, scrutinee, "..")
 119                 }
 120                 else {
 121                     sugg::Sugg::hir(cx, scrutinee, "..").maybe_par()
 122                 };
 123
 124             span_lint_and_sugg(
 125                 cx,
 126                 MANUAL_UNWRAP_OR, expr.span,
 127                 &format!("this pattern reimplements `{}`", case.unwrap_fn_path()),
 128                 "replace with",
 129                 format!(
 130                     "{}.unwrap_or({})",
 131                     suggestion,
 132                     reindented_or_body,
 133                 ),
 134                 Applicability::MachineApplicable,
 135             );
 136         }
 137     }
 138 }