clippy_lints/src/useless_conversion.rs

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