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, match_qpath, path_to_local_id, paths, sugg};
   7 use if_chain::if_chain;
   8 use rustc_errors::Applicability;
   9 use rustc_hir::{Arm, Expr, ExprKind, Pat, PatKind};
  10 use rustc_lint::LintContext;
  11 use rustc_lint::{LateContext, LateLintPass};
  12 use rustc_middle::lint::in_external_macro;
  13 use rustc_session::{declare_lint_pass, declare_tool_lint};
  14 use rustc_span::sym;
  15
  16 declare_clippy_lint! {
  17     /// **What it does:**
  18     /// Finds patterns that reimplement `Option::unwrap_or` or `Result::unwrap_or`.
  19     ///
  20     /// **Why is this bad?**
  21     /// Concise code helps focusing on behavior instead of boilerplate.
  22     ///
  23     /// **Known problems:** None.
  24     ///
  25     /// **Example:**
  26     /// ```rust
  27     /// let foo: Option<i32> = None;
  28     /// match foo {
  29     ///     Some(v) => v,
  30     ///     None => 1,
  31     /// };
  32     /// ```
  33     ///
  34     /// Use instead:
  35     /// ```rust
  36     /// let foo: Option<i32> = None;
  37     /// foo.unwrap_or(1);
  38     /// ```
  39     pub MANUAL_UNWRAP_OR,
  40     complexity,
  41     "finds patterns that can be encoded more concisely with `Option::unwrap_or` or `Result::unwrap_or`"
  42 }
  43
  44 declare_lint_pass!(ManualUnwrapOr => [MANUAL_UNWRAP_OR]);
  45
  46 impl LateLintPass<'_> for ManualUnwrapOr {
  47     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  48         if in_external_macro(cx.sess(), expr.span) || in_constant(cx, expr.hir_id) {
  49             return;
  50         }
  51         lint_manual_unwrap_or(cx, expr);
  52     }
  53 }
  54
  55 #[derive(Copy, Clone)]
  56 enum Case {
  57     Option,
  58     Result,
  59 }
  60
  61 impl Case {
  62     fn unwrap_fn_path(&self) -> &str {
  63         match self {
  64             Case::Option => "Option::unwrap_or",
  65             Case::Result => "Result::unwrap_or",
  66         }
  67     }
  68 }
  69
  70 fn lint_manual_unwrap_or<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  71     fn applicable_or_arm<'a>(arms: &'a [Arm<'a>]) -> Option<&'a Arm<'a>> {
  72         if_chain! {
  73             if arms.len() == 2;
  74             if arms.iter().all(|arm| arm.guard.is_none());
  75             if let Some((idx, or_arm)) = arms.iter().enumerate().find(|(_, arm)|
  76                 match arm.pat.kind {
  77                     PatKind::Path(ref some_qpath) =>
  78                         match_qpath(some_qpath, &paths::OPTION_NONE),
  79                     PatKind::TupleStruct(ref err_qpath, &[Pat { kind: PatKind::Wild, .. }], _) =>
  80                         match_qpath(err_qpath, &paths::RESULT_ERR),
  81                     _ => false,
  82                 }
  83             );
  84             let unwrap_arm = &arms[1 - idx];
  85             if let PatKind::TupleStruct(ref unwrap_qpath, &[unwrap_pat], _) = unwrap_arm.pat.kind;
  86             if match_qpath(unwrap_qpath, &paths::OPTION_SOME)
  87                 || match_qpath(unwrap_qpath, &paths::RESULT_OK);
  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             then {
  92                 Some(or_arm)
  93             } else {
  94                 None
  95             }
  96         }
  97     }
  98
  99     if_chain! {
 100         if let ExprKind::Match(scrutinee, match_arms, _) = expr.kind;
 101         let ty = cx.typeck_results().expr_ty(scrutinee);
 102         if let Some(case) = if is_type_diagnostic_item(cx, ty, sym::option_type) {
 103             Some(Case::Option)
 104         } else if is_type_diagnostic_item(cx, ty, sym::result_type) {
 105             Some(Case::Result)
 106         } else {
 107             None
 108         };
 109         if let Some(or_arm) = applicable_or_arm(match_arms);
 110         if let Some(or_body_snippet) = snippet_opt(cx, or_arm.body.span);
 111         if let Some(indent) = indent_of(cx, expr.span);
 112         if constant_simple(cx, cx.typeck_results(), or_arm.body).is_some();
 113         then {
 114             let reindented_or_body =
 115                 reindent_multiline(or_body_snippet.into(), true, Some(indent));
 116             span_lint_and_sugg(
 117                 cx,
 118                 MANUAL_UNWRAP_OR, expr.span,
 119                 &format!("this pattern reimplements `{}`", case.unwrap_fn_path()),
 120                 "replace with",
 121                 format!(
 122                     "{}.unwrap_or({})",
 123                     sugg::Sugg::hir(cx, scrutinee, "..").maybe_par(),
 124                     reindented_or_body,
 125                 ),
 126                 Applicability::MachineApplicable,
 127             );
 128         }
 129     }
 130 }