clippy_lints/src/identity_conversion.rs

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