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_tool_lint, impl_lint_pass};
  12 use rustc_span::symbol::sym;
  13 use rustc_span::Span;
  14
  15 declare_clippy_lint! {
  16     /// ### What it does
  17     /// Checks for private functions that only return `Ok` or `Some`.
  18     ///
  19     /// ### Why is this bad?
  20     /// It is not meaningful to wrap values when no `None` or `Err` is returned.
  21     ///
  22     /// ### Known problems
  23     /// There can be false positives if the function signature is designed to
  24     /// fit some external requirement.
  25     ///
  26     /// ### Example
  27     /// ```rust
  28     /// fn get_cool_number(a: bool, b: bool) -> Option<i32> {
  29     ///     if a && b {
  30     ///         return Some(50);
  31     ///     }
  32     ///     if a {
  33     ///         Some(0)
  34     ///     } else {
  35     ///         Some(10)
  36     ///     }
  37     /// }
  38     /// ```
  39     /// Use instead:
  40     /// ```rust
  41     /// fn get_cool_number(a: bool, b: bool) -> i32 {
  42     ///     if a && b {
  43     ///         return 50;
  44     ///     }
  45     ///     if a {
  46     ///         0
  47     ///     } else {
  48     ///         10
  49     ///     }
  50     /// }
  51     /// ```
  52     pub UNNECESSARY_WRAPS,
  53     pedantic,
  54     "functions that only return `Ok` or `Some`"
  55 }
  56
  57 pub struct UnnecessaryWraps {
  58     avoid_breaking_exported_api: bool,
  59 }
  60
  61 impl_lint_pass!(UnnecessaryWraps => [UNNECESSARY_WRAPS]);
  62
  63 impl UnnecessaryWraps {
  64     pub fn new(avoid_breaking_exported_api: bool) -> Self {
  65         Self {
  66             avoid_breaking_exported_api,
  67         }
  68     }
  69 }
  70
  71 impl<'tcx> LateLintPass<'tcx> for UnnecessaryWraps {
  72     fn check_fn(
  73         &mut self,
  74         cx: &LateContext<'tcx>,
  75         fn_kind: FnKind<'tcx>,
  76         fn_decl: &FnDecl<'tcx>,
  77         body: &Body<'tcx>,
  78         span: Span,
  79         hir_id: HirId,
  80     ) {
  81         // Abort if public function/method or closure.
  82         match fn_kind {
  83             FnKind::ItemFn(..) | FnKind::Method(..) => {
  84                 let def_id = cx.tcx.hir().local_def_id(hir_id);
  85                 if self.avoid_breaking_exported_api && cx.access_levels.is_exported(def_id) {
  86                     return;
  87                 }
  88             },
  89             FnKind::Closure => return,
  90         }
  91
  92         // Abort if the method is implementing a trait or of it a trait method.
  93         if let Some(Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(hir_id)) {
  94             if matches!(
  95                 item.kind,
  96                 ItemKind::Impl(Impl { of_trait: Some(_), .. }) | ItemKind::Trait(..)
  97             ) {
  98                 return;
  99             }
 100         }
 101
 102         // Get the wrapper and inner types, if can't, abort.
 103         let (return_type_label, lang_item, inner_type) = if let ty::Adt(adt_def, subst) = return_ty(cx, hir_id).kind() {
 104             if cx.tcx.is_diagnostic_item(sym::Option, adt_def.did) {
 105                 ("Option", OptionSome, subst.type_at(0))
 106             } else if cx.tcx.is_diagnostic_item(sym::Result, adt_def.did) {
 107                 ("Result", ResultOk, subst.type_at(0))
 108             } else {
 109                 return;
 110             }
 111         } else {
 112             return;
 113         };
 114
 115         // Check if all return expression respect the following condition and collect them.
 116         let mut suggs = Vec::new();
 117         let can_sugg = find_all_ret_expressions(cx, &body.value, |ret_expr| {
 118             if_chain! {
 119                 if !in_macro(ret_expr.span);
 120                 // Check if a function call.
 121                 if let ExprKind::Call(func, [arg]) = ret_expr.kind;
 122                 // Check if OPTION_SOME or RESULT_OK, depending on return type.
 123                 if let ExprKind::Path(qpath) = &func.kind;
 124                 if is_lang_ctor(cx, qpath, lang_item);
 125                 // Make sure the function argument does not contain a return expression.
 126                 if !contains_return(arg);
 127                 then {
 128                     suggs.push(
 129                         (
 130                             ret_expr.span,
 131                             if inner_type.is_unit() {
 132                                 "".to_string()
 133                             } else {
 134                                 snippet(cx, arg.span.source_callsite(), "..").to_string()
 135                             }
 136                         )
 137                     );
 138                     true
 139                 } else {
 140                     false
 141                 }
 142             }
 143         });
 144
 145         if can_sugg && !suggs.is_empty() {
 146             let (lint_msg, return_type_sugg_msg, return_type_sugg, body_sugg_msg) = if inner_type.is_unit() {
 147                 (
 148                     "this function's return value is unnecessary".to_string(),
 149                     "remove the return type...".to_string(),
 150                     snippet(cx, fn_decl.output.span(), "..").to_string(),
 151                     "...and then remove returned values",
 152                 )
 153             } else {
 154                 (
 155                     format!(
 156                         "this function's return value is unnecessarily wrapped by `{}`",
 157                         return_type_label
 158                     ),
 159                     format!("remove `{}` from the return type...", return_type_label),
 160                     inner_type.to_string(),
 161                     "...and then change returning expressions",
 162                 )
 163             };
 164
 165             span_lint_and_then(cx, UNNECESSARY_WRAPS, span, lint_msg.as_str(), |diag| {
 166                 diag.span_suggestion(
 167                     fn_decl.output.span(),
 168                     return_type_sugg_msg.as_str(),
 169                     return_type_sugg,
 170                     Applicability::MaybeIncorrect,
 171                 );
 172                 diag.multipart_suggestion(body_sugg_msg, suggs, Applicability::MaybeIncorrect);
 173             });
 174         }
 175     }
 176 }