clippy_lints/src/unnecessary_wrap.rs

   1 use crate::utils::{
   2     in_macro, is_type_diagnostic_item, match_qpath, paths, return_ty, snippet, span_lint_and_then,
   3     visitors::find_all_ret_expressions,
   4 };
   5 use if_chain::if_chain;
   6 use rustc_errors::Applicability;
   7 use rustc_hir::intravisit::FnKind;
   8 use rustc_hir::*;
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_middle::ty::subst::GenericArgKind;
  11 use rustc_session::{declare_lint_pass, declare_tool_lint};
  12 use rustc_span::Span;
  13
  14 declare_clippy_lint! {
  15     /// **What it does:** Checks for private functions that only return `Ok` or `Some`.
  16     ///
  17     /// **Why is this bad?** It is not meaningful to wrap values when no `None` or `Err` is returned.
  18     ///
  19     /// **Known problems:** Since this lint changes function type signature, you may need to
  20     /// adjust some code at callee side.
  21     ///
  22     /// **Example:**
  23     ///
  24     /// ```rust
  25     /// fn get_cool_number(a: bool, b: bool) -> Option<i32> {
  26     ///     if a && b {
  27     ///         return Some(50);
  28     ///     }
  29     ///     if a {
  30     ///         Some(0)
  31     ///     } else {
  32     ///         Some(10)
  33     ///     }
  34     /// }
  35     /// ```
  36     /// Use instead:
  37     /// ```rust
  38     /// fn get_cool_number(a: bool, b: bool) -> i32 {
  39     ///     if a && b {
  40     ///         return 50;
  41     ///     }
  42     ///     if a {
  43     ///         0
  44     ///     } else {
  45     ///         10
  46     ///     }
  47     /// }
  48     /// ```
  49     pub UNNECESSARY_WRAP,
  50     complexity,
  51     "functions that only return `Ok` or `Some`"
  52 }
  53
  54 declare_lint_pass!(UnnecessaryWrap => [UNNECESSARY_WRAP]);
  55
  56 impl<'tcx> LateLintPass<'tcx> for UnnecessaryWrap {
  57     fn check_fn(
  58         &mut self,
  59         cx: &LateContext<'tcx>,
  60         fn_kind: FnKind<'tcx>,
  61         fn_decl: &FnDecl<'tcx>,
  62         body: &Body<'tcx>,
  63         span: Span,
  64         hir_id: HirId,
  65     ) {
  66         match fn_kind {
  67             FnKind::ItemFn(.., visibility, _) | FnKind::Method(.., Some(visibility), _) => {
  68                 if visibility.node.is_pub() {
  69                     return;
  70                 }
  71             },
  72             FnKind::Closure(..) => return,
  73             _ => (),
  74         }
  75
  76         let (return_type, path) = if is_type_diagnostic_item(cx, return_ty(cx, hir_id), sym!(option_type)) {
  77             ("Option", &paths::OPTION_SOME)
  78         } else if is_type_diagnostic_item(cx, return_ty(cx, hir_id), sym!(result_type)) {
  79             ("Result", &paths::RESULT_OK)
  80         } else {
  81             return;
  82         };
  83
  84         let mut suggs = Vec::new();
  85         let can_sugg = find_all_ret_expressions(cx, &body.value, |ret_expr| {
  86             if_chain! {
  87                 if !in_macro(ret_expr.span);
  88                 if let ExprKind::Call(ref func, ref args) = ret_expr.kind;
  89                 if let ExprKind::Path(ref qpath) = func.kind;
  90                 if match_qpath(qpath, path);
  91                 if args.len() == 1;
  92                 then {
  93                     suggs.push((ret_expr.span, snippet(cx, args[0].span.source_callsite(), "..").to_string()));
  94                     true
  95                 } else {
  96                     false
  97                 }
  98             }
  99         });
 100
 101         if can_sugg {
 102             span_lint_and_then(
 103                 cx,
 104                 UNNECESSARY_WRAP,
 105                 span,
 106                 format!(
 107                     "this function's return value is unnecessarily wrapped by `{}`",
 108                     return_type
 109                 )
 110                 .as_str(),
 111                 |diag| {
 112                     let inner_ty = return_ty(cx, hir_id)
 113                         .walk()
 114                         .skip(1) // skip `std::option::Option` or `std::result::Result`
 115                         .take(1) // take the first outermost inner type
 116                         .filter_map(|inner| match inner.unpack() {
 117                             GenericArgKind::Type(inner_ty) => Some(inner_ty.to_string()),
 118                             _ => None,
 119                         });
 120                     inner_ty.for_each(|inner_ty| {
 121                         diag.span_suggestion(
 122                             fn_decl.output.span(),
 123                             format!("remove `{}` from the return type...", return_type).as_str(),
 124                             inner_ty,
 125                             Applicability::MachineApplicable,
 126                         );
 127                     });
 128                     diag.multipart_suggestion(
 129                         "...and change the returning expressions",
 130                         suggs,
 131                         Applicability::MachineApplicable,
 132                     );
 133                 },
 134             );
 135         }
 136     }
 137 }