clippy_lints/src/identity_conversion.rs

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