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                 } else {
  54                     return;
  55                 }
  56             },
  57
  58             ExprKind::MethodCall(ref name, .., ref args) => {
  59                 if match_trait_method(cx, e, &*paths::INTO) && &*name.ident.as_str() == "into" {
  60                     let a = cx.tables.expr_ty(e);
  61                     let b = cx.tables.expr_ty(&args[0]);
  62                     if same_tys(cx, a, b) {
  63                         let sugg = snippet_with_macro_callsite(cx, args[0].span, "<expr>").to_string();
  64
  65                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  66                             db.span_suggestion(
  67                                 e.span,
  68                                 "consider removing `.into()`",
  69                                 sugg,
  70                                 Applicability::MachineApplicable, // snippet
  71                             );
  72                         });
  73                     }
  74                 }
  75                 if match_trait_method(cx, e, &*paths::INTO_ITERATOR) && &*name.ident.as_str() == "into_iter" {
  76                     let a = cx.tables.expr_ty(e);
  77                     let b = cx.tables.expr_ty(&args[0]);
  78                     if same_tys(cx, a, b) {
  79                         let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
  80                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  81                             db.span_suggestion(
  82                                 e.span,
  83                                 "consider removing `.into_iter()`",
  84                                 sugg,
  85                                 Applicability::MachineApplicable, // snippet
  86                             );
  87                         });
  88                     }
  89                 }
  90             },
  91
  92             ExprKind::Call(ref path, ref args) => {
  93                 if let ExprKind::Path(ref qpath) = path.node {
  94                     if let Some(def_id) = resolve_node(cx, qpath, path.hir_id).opt_def_id() {
  95                         if match_def_path(cx, def_id, &*paths::FROM_FROM) {
  96                             let a = cx.tables.expr_ty(e);
  97                             let b = cx.tables.expr_ty(&args[0]);
  98                             if same_tys(cx, a, b) {
  99                                 let sugg = snippet(cx, args[0].span.source_callsite(), "<expr>").into_owned();
 100                                 let sugg_msg =
 101                                     format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
 102                                 span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
 103                                     db.span_suggestion(
 104                                         e.span,
 105                                         &sugg_msg,
 106                                         sugg,
 107                                         Applicability::MachineApplicable, // snippet
 108                                     );
 109                                 });
 110                             }
 111                         }
 112                     }
 113                 }
 114             },
 115
 116             _ => {},
 117         }
 118     }
 119
 120     fn check_expr_post(&mut self, _: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 121         if Some(&e.hir_id) == self.try_desugar_arm.last() {
 122             self.try_desugar_arm.pop();
 123         }
 124     }
 125 }