clippy_lints/src/manual_unwrap_or.rs

   1 use crate::consts::constant_simple;
   2 use crate::utils;
   3 use if_chain::if_chain;
   4 use rustc_errors::Applicability;
   5 use rustc_hir::{def, Arm, Expr, ExprKind, Pat, PatKind, QPath};
   6 use rustc_lint::LintContext;
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_middle::lint::in_external_macro;
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10
  11 declare_clippy_lint! {
  12     /// **What it does:**
  13     /// Finds patterns that reimplement `Option::unwrap_or` or `Result::unwrap_or`.
  14     ///
  15     /// **Why is this bad?**
  16     /// Concise code helps focusing on behavior instead of boilerplate.
  17     ///
  18     /// **Known problems:** None.
  19     ///
  20     /// **Example:**
  21     /// ```rust
  22     /// let foo: Option<i32> = None;
  23     /// match foo {
  24     ///     Some(v) => v,
  25     ///     None => 1,
  26     /// };
  27     /// ```
  28     ///
  29     /// Use instead:
  30     /// ```rust
  31     /// let foo: Option<i32> = None;
  32     /// foo.unwrap_or(1);
  33     /// ```
  34     pub MANUAL_UNWRAP_OR,
  35     complexity,
  36     "finds patterns that can be encoded more concisely with `Option::unwrap_or` or `Result::unwrap_or`"
  37 }
  38
  39 declare_lint_pass!(ManualUnwrapOr => [MANUAL_UNWRAP_OR]);
  40
  41 impl LateLintPass<'_> for ManualUnwrapOr {
  42     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  43         if in_external_macro(cx.sess(), expr.span) {
  44             return;
  45         }
  46         lint_manual_unwrap_or(cx, expr);
  47     }
  48 }
  49
  50 #[derive(Copy, Clone)]
  51 enum Case {
  52     Option,
  53     Result,
  54 }
  55
  56 impl Case {
  57     fn unwrap_fn_path(&self) -> &str {
  58         match self {
  59             Case::Option => "Option::unwrap_or",
  60             Case::Result => "Result::unwrap_or",
  61         }
  62     }
  63 }
  64
  65 fn lint_manual_unwrap_or<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  66     fn applicable_or_arm<'a>(arms: &'a [Arm<'a>]) -> Option<&'a Arm<'a>> {
  67         if_chain! {
  68             if arms.len() == 2;
  69             if arms.iter().all(|arm| arm.guard.is_none());
  70             if let Some((idx, or_arm)) = arms.iter().enumerate().find(|(_, arm)|
  71                 match arm.pat.kind {
  72                     PatKind::Path(ref some_qpath) =>
  73                         utils::match_qpath(some_qpath, &utils::paths::OPTION_NONE),
  74                     PatKind::TupleStruct(ref err_qpath, &[Pat { kind: PatKind::Wild, .. }], _) =>
  75                         utils::match_qpath(err_qpath, &utils::paths::RESULT_ERR),
  76                     _ => false,
  77                 }
  78             );
  79             let unwrap_arm = &arms[1 - idx];
  80             if let PatKind::TupleStruct(ref unwrap_qpath, &[unwrap_pat], _) = unwrap_arm.pat.kind;
  81             if utils::match_qpath(unwrap_qpath, &utils::paths::OPTION_SOME)
  82                 || utils::match_qpath(unwrap_qpath, &utils::paths::RESULT_OK);
  83             if let PatKind::Binding(_, binding_hir_id, ..) = unwrap_pat.kind;
  84             if let ExprKind::Path(QPath::Resolved(_, body_path)) = unwrap_arm.body.kind;
  85             if let def::Res::Local(body_path_hir_id) = body_path.res;
  86             if body_path_hir_id == binding_hir_id;
  87             if !utils::usage::contains_return_break_continue_macro(or_arm.body);
  88             then {
  89                 Some(or_arm)
  90             } else {
  91                 None
  92             }
  93         }
  94     }
  95
  96     if_chain! {
  97         if let ExprKind::Match(scrutinee, match_arms, _) = expr.kind;
  98         let ty = cx.typeck_results().expr_ty(scrutinee);
  99         if let Some(case) = if utils::is_type_diagnostic_item(cx, ty, sym!(option_type)) {
 100             Some(Case::Option)
 101         } else if utils::is_type_diagnostic_item(cx, ty, sym!(result_type)) {
 102             Some(Case::Result)
 103         } else {
 104             None
 105         };
 106         if let Some(or_arm) = applicable_or_arm(match_arms);
 107         if let Some(scrutinee_snippet) = utils::snippet_opt(cx, scrutinee.span);
 108         if let Some(or_body_snippet) = utils::snippet_opt(cx, or_arm.body.span);
 109         if let Some(indent) = utils::indent_of(cx, expr.span);
 110         if constant_simple(cx, cx.typeck_results(), or_arm.body).is_some();
 111         then {
 112             let reindented_or_body =
 113                 utils::reindent_multiline(or_body_snippet.into(), true, Some(indent));
 114             let wrap_in_parens = !matches!(scrutinee, Expr { kind: ExprKind::Call(..), .. });
 115             let l_paren = if wrap_in_parens { "(" } else { "" };
 116             let r_paren = if wrap_in_parens { ")" } else { "" };
 117             utils::span_lint_and_sugg(
 118                 cx,
 119                 MANUAL_UNWRAP_OR, expr.span,
 120                 &format!("this pattern reimplements `{}`", case.unwrap_fn_path()),
 121                 "replace with",
 122                 format!(
 123                     "{}{}{}.unwrap_or({})",
 124                     l_paren,
 125                     scrutinee_snippet,
 126                     r_paren,
 127                     reindented_or_body,
 128                 ),
 129                 Applicability::MachineApplicable,
 130             );
 131         }
 132     }
 133 }