src/tools/clippy/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, is_res_lang_ctor, path_res, 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, Impl, ItemKind, Node};
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_middle::ty;
  11 use rustc_session::{declare_tool_lint, impl_lint_pass};
  12 use rustc_span::def_id::LocalDefId;
  13 use rustc_span::symbol::sym;
  14 use rustc_span::Span;
  15
  16 declare_clippy_lint! {
  17     /// ### What it does
  18     /// Checks for private functions that only return `Ok` or `Some`.
  19     ///
  20     /// ### Why is this bad?
  21     /// It is not meaningful to wrap values when no `None` or `Err` is returned.
  22     ///
  23     /// ### Known problems
  24     /// There can be false positives if the function signature is designed to
  25     /// fit some external requirement.
  26     ///
  27     /// ### Example
  28     /// ```rust
  29     /// fn get_cool_number(a: bool, b: bool) -> Option<i32> {
  30     ///     if a && b {
  31     ///         return Some(50);
  32     ///     }
  33     ///     if a {
  34     ///         Some(0)
  35     ///     } else {
  36     ///         Some(10)
  37     ///     }
  38     /// }
  39     /// ```
  40     /// Use instead:
  41     /// ```rust
  42     /// fn get_cool_number(a: bool, b: bool) -> i32 {
  43     ///     if a && b {
  44     ///         return 50;
  45     ///     }
  46     ///     if a {
  47     ///         0
  48     ///     } else {
  49     ///         10
  50     ///     }
  51     /// }
  52     /// ```
  53     #[clippy::version = "1.50.0"]
  54     pub UNNECESSARY_WRAPS,
  55     pedantic,
  56     "functions that only return `Ok` or `Some`"
  57 }
  58
  59 pub struct UnnecessaryWraps {
  60     avoid_breaking_exported_api: bool,
  61 }
  62
  63 impl_lint_pass!(UnnecessaryWraps => [UNNECESSARY_WRAPS]);
  64
  65 impl UnnecessaryWraps {
  66     pub fn new(avoid_breaking_exported_api: bool) -> Self {
  67         Self {
  68             avoid_breaking_exported_api,
  69         }
  70     }
  71 }
  72
  73 impl<'tcx> LateLintPass<'tcx> for UnnecessaryWraps {
  74     fn check_fn(
  75         &mut self,
  76         cx: &LateContext<'tcx>,
  77         fn_kind: FnKind<'tcx>,
  78         fn_decl: &FnDecl<'tcx>,
  79         body: &Body<'tcx>,
  80         span: Span,
  81         def_id: LocalDefId,
  82     ) {
  83         // Abort if public function/method or closure.
  84         match fn_kind {
  85             FnKind::ItemFn(..) | FnKind::Method(..) => {
  86                 if self.avoid_breaking_exported_api && cx.effective_visibilities.is_exported(def_id) {
  87                     return;
  88                 }
  89             },
  90             FnKind::Closure => return,
  91         }
  92
  93         // Abort if the method is implementing a trait or of it a trait method.
  94         let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
  95         if let Some(Node::Item(item)) = cx.tcx.hir().find_parent(hir_id) {
  96             if matches!(
  97                 item.kind,
  98                 ItemKind::Impl(Impl { of_trait: Some(_), .. }) | ItemKind::Trait(..)
  99             ) {
 100                 return;
 101             }
 102         }
 103
 104         // Get the wrapper and inner types, if can't, abort.
 105         let (return_type_label, lang_item, inner_type) =
 106             if let ty::Adt(adt_def, subst) = return_ty(cx, hir_id.expect_owner()).kind() {
 107                 if cx.tcx.is_diagnostic_item(sym::Option, adt_def.did()) {
 108                     ("Option", OptionSome, subst.type_at(0))
 109                 } else if cx.tcx.is_diagnostic_item(sym::Result, adt_def.did()) {
 110                     ("Result", ResultOk, subst.type_at(0))
 111                 } else {
 112                     return;
 113                 }
 114             } else {
 115                 return;
 116             };
 117
 118         // Check if all return expression respect the following condition and collect them.
 119         let mut suggs = Vec::new();
 120         let can_sugg = find_all_ret_expressions(cx, body.value, |ret_expr| {
 121             if_chain! {
 122                 if !ret_expr.span.from_expansion();
 123                 // Check if a function call.
 124                 if let ExprKind::Call(func, [arg]) = ret_expr.kind;
 125                 if is_res_lang_ctor(cx, path_res(cx, func), lang_item);
 126                 // Make sure the function argument does not contain a return expression.
 127                 if !contains_return(arg);
 128                 then {
 129                     suggs.push(
 130                         (
 131                             ret_expr.span,
 132                             if inner_type.is_unit() {
 133                                 String::new()
 134                             } else {
 135                                 snippet(cx, arg.span.source_callsite(), "..").to_string()
 136                             }
 137                         )
 138                     );
 139                     true
 140                 } else {
 141                     false
 142                 }
 143             }
 144         });
 145
 146         if can_sugg && !suggs.is_empty() {
 147             let (lint_msg, return_type_sugg_msg, return_type_sugg, body_sugg_msg) = if inner_type.is_unit() {
 148                 (
 149                     "this function's return value is unnecessary".to_string(),
 150                     "remove the return type...".to_string(),
 151                     snippet(cx, fn_decl.output.span(), "..").to_string(),
 152                     "...and then remove returned values",
 153                 )
 154             } else {
 155                 (
 156                     format!("this function's return value is unnecessarily wrapped by `{return_type_label}`"),
 157                     format!("remove `{return_type_label}` from the return type..."),
 158                     inner_type.to_string(),
 159                     "...and then change returning expressions",
 160                 )
 161             };
 162
 163             span_lint_and_then(cx, UNNECESSARY_WRAPS, span, lint_msg.as_str(), |diag| {
 164                 diag.span_suggestion(
 165                     fn_decl.output.span(),
 166                     return_type_sugg_msg.as_str(),
 167                     return_type_sugg,
 168                     Applicability::MaybeIncorrect,
 169                 );
 170                 diag.multipart_suggestion(body_sugg_msg, suggs, Applicability::MaybeIncorrect);
 171             });
 172         }
 173     }
 174 }