clippy_lints/src/useless_conversion.rs

   1 use crate::utils::sugg::Sugg;
   2 use crate::utils::{
   3     get_parent_expr, is_type_diagnostic_item, match_def_path, match_trait_method, paths, snippet,
   4     snippet_with_macro_callsite, span_lint_and_help, span_lint_and_sugg,
   5 };
   6 use if_chain::if_chain;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::{Expr, ExprKind, HirId, MatchSource};
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_middle::ty::{self, TyS};
  11 use rustc_session::{declare_tool_lint, impl_lint_pass};
  12 use rustc_span::sym;
  13
  14 declare_clippy_lint! {
  15     /// **What it does:** Checks for `Into`, `TryInto`, `From`, `TryFrom`, or `IntoIter` calls
  16     /// which uselessly convert to the same type.
  17     ///
  18     /// **Why is this bad?** Redundant code.
  19     ///
  20     /// **Known problems:** None.
  21     ///
  22     /// **Example:**
  23     ///
  24     /// ```rust
  25     /// // Bad
  26     /// // format!() returns a `String`
  27     /// let s: String = format!("hello").into();
  28     ///
  29     /// // Good
  30     /// let s: String = format!("hello");
  31     /// ```
  32     pub USELESS_CONVERSION,
  33     complexity,
  34     "calls to `Into`, `TryInto`, `From`, `TryFrom`, or `IntoIter` which perform useless conversions to the same type"
  35 }
  36
  37 #[derive(Default)]
  38 pub struct UselessConversion {
  39     try_desugar_arm: Vec<HirId>,
  40 }
  41
  42 impl_lint_pass!(UselessConversion => [USELESS_CONVERSION]);
  43
  44 #[allow(clippy::too_many_lines)]
  45 impl<'tcx> LateLintPass<'tcx> for UselessConversion {
  46     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
  47         if e.span.from_expansion() {
  48             return;
  49         }
  50
  51         if Some(&e.hir_id) == self.try_desugar_arm.last() {
  52             return;
  53         }
  54
  55         match e.kind {
  56             ExprKind::Match(_, ref arms, MatchSource::TryDesugar) => {
  57                 let e = match arms[0].body.kind {
  58                     ExprKind::Ret(Some(ref e)) | ExprKind::Break(_, Some(ref e)) => e,
  59                     _ => return,
  60                 };
  61                 if let ExprKind::Call(_, ref args) = e.kind {
  62                     self.try_desugar_arm.push(args[0].hir_id);
  63                 }
  64             },
  65
  66             ExprKind::MethodCall(ref name, .., ref args, _) => {
  67                 if match_trait_method(cx, e, &paths::INTO) && &*name.ident.as_str() == "into" {
  68                     let a = cx.typeck_results().expr_ty(e);
  69                     let b = cx.typeck_results().expr_ty(&args[0]);
  70                     if TyS::same_type(a, b) {
  71                         let sugg = snippet_with_macro_callsite(cx, args[0].span, "<expr>").to_string();
  72                         span_lint_and_sugg(
  73                             cx,
  74                             USELESS_CONVERSION,
  75                             e.span,
  76                             &format!("useless conversion to the same type: `{}`", b),
  77                             "consider removing `.into()`",
  78                             sugg,
  79                             Applicability::MachineApplicable, // snippet
  80                         );
  81                     }
  82                 }
  83                 if match_trait_method(cx, e, &paths::INTO_ITERATOR) && &*name.ident.as_str() == "into_iter" {
  84                     if let Some(parent_expr) = get_parent_expr(cx, e) {
  85                         if let ExprKind::MethodCall(ref parent_name, ..) = parent_expr.kind {
  86                             if &*parent_name.ident.as_str() != "into_iter" {
  87                                 return;
  88                             }
  89                         }
  90                     }
  91                     let a = cx.typeck_results().expr_ty(e);
  92                     let b = cx.typeck_results().expr_ty(&args[0]);
  93                     if TyS::same_type(a, b) {
  94                         let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
  95                         span_lint_and_sugg(
  96                             cx,
  97                             USELESS_CONVERSION,
  98                             e.span,
  99                             &format!("useless conversion to the same type: `{}`", b),
 100                             "consider removing `.into_iter()`",
 101                             sugg,
 102                             Applicability::MachineApplicable, // snippet
 103                         );
 104                     }
 105                 }
 106                 if match_trait_method(cx, e, &paths::TRY_INTO_TRAIT) && &*name.ident.as_str() == "try_into" {
 107                     if_chain! {
 108                         let a = cx.typeck_results().expr_ty(e);
 109                         let b = cx.typeck_results().expr_ty(&args[0]);
 110                         if is_type_diagnostic_item(cx, a, sym::result_type);
 111                         if let ty::Adt(_, substs) = a.kind();
 112                         if let Some(a_type) = substs.types().next();
 113                         if TyS::same_type(a_type, b);
 114
 115                         then {
 116                             span_lint_and_help(
 117                                 cx,
 118                                 USELESS_CONVERSION,
 119                                 e.span,
 120                                 &format!("useless conversion to the same type: `{}`", b),
 121                                 None,
 122                                 "consider removing `.try_into()`",
 123                             );
 124                         }
 125                     }
 126                 }
 127             },
 128
 129             ExprKind::Call(ref path, ref args) => {
 130                 if_chain! {
 131                     if args.len() == 1;
 132                     if let ExprKind::Path(ref qpath) = path.kind;
 133                     if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id();
 134                     let a = cx.typeck_results().expr_ty(e);
 135                     let b = cx.typeck_results().expr_ty(&args[0]);
 136
 137                     then {
 138                         if_chain! {
 139                             if match_def_path(cx, def_id, &paths::TRY_FROM);
 140                             if is_type_diagnostic_item(cx, a, sym::result_type);
 141                             if let ty::Adt(_, substs) = a.kind();
 142                             if let Some(a_type) = substs.types().next();
 143                             if TyS::same_type(a_type, b);
 144
 145                             then {
 146                                 let hint = format!("consider removing `{}()`", snippet(cx, path.span, "TryFrom::try_from"));
 147                                 span_lint_and_help(
 148                                     cx,
 149                                     USELESS_CONVERSION,
 150                                     e.span,
 151                                     &format!("useless conversion to the same type: `{}`", b),
 152                                     None,
 153                                     &hint,
 154                                 );
 155                             }
 156                         }
 157
 158                         if_chain! {
 159                             if match_def_path(cx, def_id, &paths::FROM_FROM);
 160                             if TyS::same_type(a, b);
 161
 162                             then {
 163                                 let sugg = Sugg::hir_with_macro_callsite(cx, &args[0], "<expr>").maybe_par();
 164                                 let sugg_msg =
 165                                     format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
 166                                 span_lint_and_sugg(
 167                                     cx,
 168                                     USELESS_CONVERSION,
 169                                     e.span,
 170                                     &format!("useless conversion to the same type: `{}`", b),
 171                                     &sugg_msg,
 172                                     sugg.to_string(),
 173                                     Applicability::MachineApplicable, // snippet
 174                                 );
 175                             }
 176                         }
 177                     }
 178                 }
 179             },
 180
 181             _ => {},
 182         }
 183     }
 184
 185     fn check_expr_post(&mut self, _: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
 186         if Some(&e.hir_id) == self.try_desugar_arm.last() {
 187             self.try_desugar_arm.pop();
 188         }
 189     }
 190 }