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                 if self.avoid_breaking_exported_api && cx.access_levels.is_exported(hir_id) {
  85                     return;
  86                 }
  87             },
  88             FnKind::Closure => return,
  89         }
  90
  91         // Abort if the method is implementing a trait or of it a trait method.
  92         if let Some(Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(hir_id)) {
  93             if matches!(
  94                 item.kind,
  95                 ItemKind::Impl(Impl { of_trait: Some(_), .. }) | ItemKind::Trait(..)
  96             ) {
  97                 return;
  98             }
  99         }
 100
 101         // Get the wrapper and inner types, if can't, abort.
 102         let (return_type_label, lang_item, inner_type) = if let ty::Adt(adt_def, subst) = return_ty(cx, hir_id).kind() {
 103             if cx.tcx.is_diagnostic_item(sym::option_type, adt_def.did) {
 104                 ("Option", OptionSome, subst.type_at(0))
 105             } else if cx.tcx.is_diagnostic_item(sym::result_type, adt_def.did) {
 106                 ("Result", ResultOk, subst.type_at(0))
 107             } else {
 108                 return;
 109             }
 110         } else {
 111             return;
 112         };
 113
 114         // Check if all return expression respect the following condition and collect them.
 115         let mut suggs = Vec::new();
 116         let can_sugg = find_all_ret_expressions(cx, &body.value, |ret_expr| {
 117             if_chain! {
 118                 if !in_macro(ret_expr.span);
 119                 // Check if a function call.
 120                 if let ExprKind::Call(func, [arg]) = ret_expr.kind;
 121                 // Check if OPTION_SOME or RESULT_OK, depending on return type.
 122                 if let ExprKind::Path(qpath) = &func.kind;
 123                 if is_lang_ctor(cx, qpath, lang_item);
 124                 // Make sure the function argument does not contain a return expression.
 125                 if !contains_return(arg);
 126                 then {
 127                     suggs.push(
 128                         (
 129                             ret_expr.span,
 130                             if inner_type.is_unit() {
 131                                 "".to_string()
 132                             } else {
 133                                 snippet(cx, arg.span.source_callsite(), "..").to_string()
 134                             }
 135                         )
 136                     );
 137                     true
 138                 } else {
 139                     false
 140                 }
 141             }
 142         });
 143
 144         if can_sugg && !suggs.is_empty() {
 145             let (lint_msg, return_type_sugg_msg, return_type_sugg, body_sugg_msg) = if inner_type.is_unit() {
 146                 (
 147                     "this function's return value is unnecessary".to_string(),
 148                     "remove the return type...".to_string(),
 149                     snippet(cx, fn_decl.output.span(), "..").to_string(),
 150                     "...and then remove returned values",
 151                 )
 152             } else {
 153                 (
 154                     format!(
 155                         "this function's return value is unnecessarily wrapped by `{}`",
 156                         return_type_label
 157                     ),
 158                     format!("remove `{}` from the return type...", return_type_label),
 159                     inner_type.to_string(),
 160                     "...and then change returning expressions",
 161                 )
 162             };
 163
 164             span_lint_and_then(cx, UNNECESSARY_WRAPS, span, lint_msg.as_str(), |diag| {
 165                 diag.span_suggestion(
 166                     fn_decl.output.span(),
 167                     return_type_sugg_msg.as_str(),
 168                     return_type_sugg,
 169                     Applicability::MaybeIncorrect,
 170                 );
 171                 diag.multipart_suggestion(body_sugg_msg, suggs, Applicability::MaybeIncorrect);
 172             });
 173         }
 174     }
 175 }