clippy_lints/src/unnecessary_wrap.rs

   1 use crate::utils::{
   2     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         if_chain! {
  67             if let FnKind::ItemFn(.., visibility, _) = fn_kind;
  68             if visibility.node.is_pub();
  69             then {
  70                 return;
  71             }
  72         }
  73
  74         let (return_type, path) = if is_type_diagnostic_item(cx, return_ty(cx, hir_id), sym!(option_type)) {
  75             ("Option", &paths::OPTION_SOME)
  76         } else if is_type_diagnostic_item(cx, return_ty(cx, hir_id), sym!(result_type)) {
  77             ("Result", &paths::RESULT_OK)
  78         } else {
  79             return;
  80         };
  81
  82         let mut suggs = Vec::new();
  83         let can_sugg = find_all_ret_expressions(cx, &body.value, |ret_expr| {
  84             if_chain! {
  85                 if let ExprKind::Call(ref func, ref args) = ret_expr.kind;
  86                 if let ExprKind::Path(ref qpath) = func.kind;
  87                 if match_qpath(qpath, path);
  88                 if args.len() == 1;
  89                 then {
  90                     suggs.push((ret_expr.span, snippet(cx, args[0].span.source_callsite(), "..").to_string()));
  91                     true
  92                 } else {
  93                     false
  94                 }
  95             }
  96         });
  97
  98         if can_sugg {
  99             span_lint_and_then(
 100                 cx,
 101                 UNNECESSARY_WRAP,
 102                 span,
 103                 format!(
 104                     "this function's return value is unnecessarily wrapped by `{}`",
 105                     return_type
 106                 )
 107                 .as_str(),
 108                 |diag| {
 109                     let inner_ty = return_ty(cx, hir_id)
 110                         .walk()
 111                         .skip(1) // skip `std::option::Option` or `std::result::Result`
 112                         .take(1) // take the first outermost inner type
 113                         .filter_map(|inner| match inner.unpack() {
 114                             GenericArgKind::Type(inner_ty) => Some(inner_ty.to_string()),
 115                             _ => None,
 116                         });
 117                     inner_ty.for_each(|inner_ty| {
 118                         diag.span_suggestion(
 119                             fn_decl.output.span(),
 120                             format!("remove `{}` from the return type...", return_type).as_str(),
 121                             inner_ty,
 122                             Applicability::MachineApplicable,
 123                         );
 124                     });
 125                     diag.multipart_suggestion(
 126                         "...and change the returning expressions",
 127                         suggs,
 128                         Applicability::MachineApplicable,
 129                     );
 130                 },
 131             );
 132         }
 133     }
 134 }