clippy_lints/src/identity_conversion.rs

   1 use crate::utils::{
   2     match_def_path, match_trait_method, paths, same_tys, snippet, snippet_with_macro_callsite, span_lint_and_sugg,
   3 };
   4 use rustc_errors::Applicability;
   5 use rustc_hir::{Expr, ExprKind, HirId, MatchSource};
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_session::{declare_tool_lint, impl_lint_pass};
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** Checks for always-identical `Into`/`From`/`IntoIter` conversions.
  11     ///
  12     /// **Why is this bad?** Redundant code.
  13     ///
  14     /// **Known problems:** None.
  15     ///
  16     /// **Example:**
  17     /// ```rust
  18     /// // format!() returns a `String`
  19     /// let s: String = format!("hello").into();
  20     /// ```
  21     pub IDENTITY_CONVERSION,
  22     complexity,
  23     "using always-identical `Into`/`From`/`IntoIter` conversions"
  24 }
  25
  26 #[derive(Default)]
  27 pub struct IdentityConversion {
  28     try_desugar_arm: Vec<HirId>,
  29 }
  30
  31 impl_lint_pass!(IdentityConversion => [IDENTITY_CONVERSION]);
  32
  33 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityConversion {
  34     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
  35         if e.span.from_expansion() {
  36             return;
  37         }
  38
  39         if Some(&e.hir_id) == self.try_desugar_arm.last() {
  40             return;
  41         }
  42
  43         match e.kind {
  44             ExprKind::Match(_, ref arms, MatchSource::TryDesugar) => {
  45                 let e = match arms[0].body.kind {
  46                     ExprKind::Ret(Some(ref e)) | ExprKind::Break(_, Some(ref e)) => e,
  47                     _ => return,
  48                 };
  49                 if let ExprKind::Call(_, ref args) = e.kind {
  50                     self.try_desugar_arm.push(args[0].hir_id);
  51                 }
  52             },
  53
  54             ExprKind::MethodCall(ref name, .., ref args) => {
  55                 if match_trait_method(cx, e, &paths::INTO) && &*name.ident.as_str() == "into" {
  56                     let a = cx.tables.expr_ty(e);
  57                     let b = cx.tables.expr_ty(&args[0]);
  58                     if same_tys(cx, a, b) {
  59                         let sugg = snippet_with_macro_callsite(cx, args[0].span, "<expr>").to_string();
  60
  61                         span_lint_and_sugg(
  62                             cx,
  63                             IDENTITY_CONVERSION,
  64                             e.span,
  65                             "identical conversion",
  66                             "consider removing `.into()`",
  67                             sugg,
  68                             Applicability::MachineApplicable, // snippet
  69                         );
  70                     }
  71                 }
  72                 if match_trait_method(cx, e, &paths::INTO_ITERATOR) && &*name.ident.as_str() == "into_iter" {
  73                     let a = cx.tables.expr_ty(e);
  74                     let b = cx.tables.expr_ty(&args[0]);
  75                     if same_tys(cx, a, b) {
  76                         let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
  77                         span_lint_and_sugg(
  78                             cx,
  79                             IDENTITY_CONVERSION,
  80                             e.span,
  81                             "identical conversion",
  82                             "consider removing `.into_iter()`",
  83                             sugg,
  84                             Applicability::MachineApplicable, // snippet
  85                         );
  86                     }
  87                 }
  88             },
  89
  90             ExprKind::Call(ref path, ref args) => {
  91                 if let ExprKind::Path(ref qpath) = path.kind {
  92                     if let Some(def_id) = cx.tables.qpath_res(qpath, path.hir_id).opt_def_id() {
  93                         if match_def_path(cx, def_id, &paths::FROM_FROM) {
  94                             let a = cx.tables.expr_ty(e);
  95                             let b = cx.tables.expr_ty(&args[0]);
  96                             if same_tys(cx, a, b) {
  97                                 let sugg = snippet(cx, args[0].span.source_callsite(), "<expr>").into_owned();
  98                                 let sugg_msg =
  99                                     format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
 100                                 span_lint_and_sugg(
 101                                     cx,
 102                                     IDENTITY_CONVERSION,
 103                                     e.span,
 104                                     "identical conversion",
 105                                     &sugg_msg,
 106                                     sugg,
 107                                     Applicability::MachineApplicable, // snippet
 108                                 );
 109                             }
 110                         }
 111                     }
 112                 }
 113             },
 114
 115             _ => {},
 116         }
 117     }
 118
 119     fn check_expr_post(&mut self, _: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
 120         if Some(&e.hir_id) == self.try_desugar_arm.last() {
 121             self.try_desugar_arm.pop();
 122         }
 123     }
 124 }