clippy_lints/src/unnecessary_wraps.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::source::snippet;
   3 use clippy_utils::{contains_return, in_macro, is_lang_ctor, return_ty, visitors::find_all_ret_expressions};
   4 use if_chain::if_chain;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::intravisit::FnKind;
   7 use rustc_hir::LangItem::{OptionSome, ResultOk};
   8 use rustc_hir::{Body, ExprKind, FnDecl, HirId, Impl, ItemKind, Node};
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_middle::ty;
  11 use rustc_session::{declare_lint_pass, declare_tool_lint};
  12 use rustc_span::symbol::sym;
  13 use rustc_span::Span;
  14
  15 declare_clippy_lint! {
  16     /// **What it does:** Checks for private functions that only return `Ok` or `Some`.
  17     ///
  18     /// **Why is this bad?** It is not meaningful to wrap values when no `None` or `Err` is returned.
  19     ///
  20     /// **Known problems:** There can be false positives if the function signature is designed to
  21     /// fit some external requirement.
  22     ///
  23     /// **Example:**
  24     ///
  25     /// ```rust
  26     /// fn get_cool_number(a: bool, b: bool) -> Option<i32> {
  27     ///     if a && b {
  28     ///         return Some(50);
  29     ///     }
  30     ///     if a {
  31     ///         Some(0)
  32     ///     } else {
  33     ///         Some(10)
  34     ///     }
  35     /// }
  36     /// ```
  37     /// Use instead:
  38     /// ```rust
  39     /// fn get_cool_number(a: bool, b: bool) -> i32 {
  40     ///     if a && b {
  41     ///         return 50;
  42     ///     }
  43     ///     if a {
  44     ///         0
  45     ///     } else {
  46     ///         10
  47     ///     }
  48     /// }
  49     /// ```
  50     pub UNNECESSARY_WRAPS,
  51     pedantic,
  52     "functions that only return `Ok` or `Some`"
  53 }
  54
  55 declare_lint_pass!(UnnecessaryWraps => [UNNECESSARY_WRAPS]);
  56
  57 impl<'tcx> LateLintPass<'tcx> for UnnecessaryWraps {
  58     fn check_fn(
  59         &mut self,
  60         cx: &LateContext<'tcx>,
  61         fn_kind: FnKind<'tcx>,
  62         fn_decl: &FnDecl<'tcx>,
  63         body: &Body<'tcx>,
  64         span: Span,
  65         hir_id: HirId,
  66     ) {
  67         // Abort if public function/method or closure.
  68         match fn_kind {
  69             FnKind::ItemFn(.., visibility) | FnKind::Method(.., Some(visibility)) => {
  70                 if visibility.node.is_pub() {
  71                     return;
  72                 }
  73             },
  74             FnKind::Closure => return,
  75             FnKind::Method(..) => (),
  76         }
  77
  78         // Abort if the method is implementing a trait or of it a trait method.
  79         if let Some(Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(hir_id)) {
  80             if matches!(
  81                 item.kind,
  82                 ItemKind::Impl(Impl { of_trait: Some(_), .. }) | ItemKind::Trait(..)
  83             ) {
  84                 return;
  85             }
  86         }
  87
  88         // Get the wrapper and inner types, if can't, abort.
  89         let (return_type_label, lang_item, inner_type) = if let ty::Adt(adt_def, subst) = return_ty(cx, hir_id).kind() {
  90             if cx.tcx.is_diagnostic_item(sym::option_type, adt_def.did) {
  91                 ("Option", OptionSome, subst.type_at(0))
  92             } else if cx.tcx.is_diagnostic_item(sym::result_type, adt_def.did) {
  93                 ("Result", ResultOk, subst.type_at(0))
  94             } else {
  95                 return;
  96             }
  97         } else {
  98             return;
  99         };
 100
 101         // Check if all return expression respect the following condition and collect them.
 102         let mut suggs = Vec::new();
 103         let can_sugg = find_all_ret_expressions(cx, &body.value, |ret_expr| {
 104             if_chain! {
 105                 if !in_macro(ret_expr.span);
 106                 // Check if a function call.
 107                 if let ExprKind::Call(func, [arg]) = ret_expr.kind;
 108                 // Check if OPTION_SOME or RESULT_OK, depending on return type.
 109                 if let ExprKind::Path(qpath) = &func.kind;
 110                 if is_lang_ctor(cx, qpath, lang_item);
 111                 // Make sure the function argument does not contain a return expression.
 112                 if !contains_return(arg);
 113                 then {
 114                     suggs.push(
 115                         (
 116                             ret_expr.span,
 117                             if inner_type.is_unit() {
 118                                 "".to_string()
 119                             } else {
 120                                 snippet(cx, arg.span.source_callsite(), "..").to_string()
 121                             }
 122                         )
 123                     );
 124                     true
 125                 } else {
 126                     false
 127                 }
 128             }
 129         });
 130
 131         if can_sugg && !suggs.is_empty() {
 132             let (lint_msg, return_type_sugg_msg, return_type_sugg, body_sugg_msg) = if inner_type.is_unit() {
 133                 (
 134                     "this function's return value is unnecessary".to_string(),
 135                     "remove the return type...".to_string(),
 136                     snippet(cx, fn_decl.output.span(), "..").to_string(),
 137                     "...and then remove returned values",
 138                 )
 139             } else {
 140                 (
 141                     format!(
 142                         "this function's return value is unnecessarily wrapped by `{}`",
 143                         return_type_label
 144                     ),
 145                     format!("remove `{}` from the return type...", return_type_label),
 146                     inner_type.to_string(),
 147                     "...and then change returning expressions",
 148                 )
 149             };
 150
 151             span_lint_and_then(cx, UNNECESSARY_WRAPS, span, lint_msg.as_str(), |diag| {
 152                 diag.span_suggestion(
 153                     fn_decl.output.span(),
 154                     return_type_sugg_msg.as_str(),
 155                     return_type_sugg,
 156                     Applicability::MaybeIncorrect,
 157                 );
 158                 diag.multipart_suggestion(body_sugg_msg, suggs, Applicability::MaybeIncorrect);
 159             });
 160         }
 161     }
 162 }