clippy_lints/src/identity_conversion.rs

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