clippy_lints/src/identity_conversion.rs

   1 use rustc::lint::*;
   2 use rustc::hir::*;
   3 use syntax::ast::NodeId;
   4 use crate::utils::{in_macro, match_def_path, match_trait_method, same_tys, snippet, span_lint_and_then};
   5 use crate::utils::{opt_def_id, paths, resolve_node};
   6
   7 /// **What it does:** Checks for always-identical `Into`/`From` conversions.
   8 ///
   9 /// **Why is this bad?** Redundant code.
  10 ///
  11 /// **Known problems:** None.
  12 ///
  13 /// **Example:**
  14 /// ```rust
  15 /// // format!() returns a `String`
  16 /// let s: String = format!("hello").into();
  17 /// ```
  18 declare_clippy_lint! {
  19     pub IDENTITY_CONVERSION,
  20     complexity,
  21     "using always-identical `Into`/`From` conversions"
  22 }
  23
  24 #[derive(Default)]
  25 pub struct IdentityConversion {
  26     try_desugar_arm: Vec<NodeId>,
  27 }
  28
  29 impl LintPass for IdentityConversion {
  30     fn get_lints(&self) -> LintArray {
  31         lint_array!(IDENTITY_CONVERSION)
  32     }
  33 }
  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(e.span) {
  38             return;
  39         }
  40
  41         if Some(&e.id) == self.try_desugar_arm.last() {
  42             return;
  43         }
  44
  45         match e.node {
  46             ExprMatch(_, ref arms, MatchSource::TryDesugar) => {
  47                 let e = match arms[0].body.node {
  48                     ExprRet(Some(ref e)) | ExprBreak(_, Some(ref e)) => e,
  49                     _ => return,
  50                 };
  51                 if let ExprCall(_, ref args) = e.node {
  52                     self.try_desugar_arm.push(args[0].id);
  53                 } else {
  54                     return;
  55                 }
  56             },
  57
  58             ExprMethodCall(ref name, .., ref args) => {
  59                 if match_trait_method(cx, e, &paths::INTO[..]) && &*name.name.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(cx, args[0].span, "<expr>").into_owned();
  64                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  65                             db.span_suggestion(e.span, "consider removing `.into()`", sugg);
  66                         });
  67                     }
  68                 }
  69             },
  70
  71             ExprCall(ref path, ref args) => if let ExprPath(ref qpath) = path.node {
  72                 if let Some(def_id) = opt_def_id(resolve_node(cx, qpath, path.hir_id)) {
  73                     if match_def_path(cx.tcx, def_id, &paths::FROM_FROM[..]) {
  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                             let sugg_msg = format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
  79                             span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  80                                 db.span_suggestion(e.span, &sugg_msg, sugg);
  81                             });
  82                         }
  83                     }
  84                 }
  85             },
  86
  87             _ => {},
  88         }
  89     }
  90
  91     fn check_expr_post(&mut self, _: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  92         if Some(&e.id) == self.try_desugar_arm.last() {
  93             self.try_desugar_arm.pop();
  94         }
  95     }
  96 }