clippy_lints/src/identity_conversion.rs

   1 use crate::utils::{in_macro, match_trait_method, same_tys, snippet, snippet_with_macro_callsite, span_lint_and_then};
   2 use crate::utils::{paths, resolve_node};
   3 use rustc::hir::*;
   4 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   5 use rustc::{declare_tool_lint, lint_array};
   6 use rustc_errors::Applicability;
   7
   8 declare_clippy_lint! {
   9     /// **What it does:** Checks for always-identical `Into`/`From`/`IntoIter` conversions.
  10     ///
  11     /// **Why is this bad?** Redundant code.
  12     ///
  13     /// **Known problems:** None.
  14     ///
  15     /// **Example:**
  16     /// ```rust
  17     /// // format!() returns a `String`
  18     /// let s: String = format!("hello").into();
  19     /// ```
  20     pub IDENTITY_CONVERSION,
  21     complexity,
  22     "using always-identical `Into`/`From`/`IntoIter` conversions"
  23 }
  24
  25 #[derive(Default)]
  26 pub struct IdentityConversion {
  27     try_desugar_arm: Vec<HirId>,
  28 }
  29
  30 impl LintPass for IdentityConversion {
  31     fn get_lints(&self) -> LintArray {
  32         lint_array!(IDENTITY_CONVERSION)
  33     }
  34
  35     fn name(&self) -> &'static str {
  36         "IdentityConversion"
  37     }
  38 }
  39
  40 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityConversion {
  41     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  42         if in_macro(e.span) {
  43             return;
  44         }
  45
  46         if Some(&e.hir_id) == self.try_desugar_arm.last() {
  47             return;
  48         }
  49
  50         match e.node {
  51             ExprKind::Match(_, ref arms, MatchSource::TryDesugar) => {
  52                 let e = match arms[0].body.node {
  53                     ExprKind::Ret(Some(ref e)) | ExprKind::Break(_, Some(ref e)) => e,
  54                     _ => return,
  55                 };
  56                 if let ExprKind::Call(_, ref args) = e.node {
  57                     self.try_desugar_arm.push(args[0].hir_id);
  58                 } else {
  59                     return;
  60                 }
  61             },
  62
  63             ExprKind::MethodCall(ref name, .., ref args) => {
  64                 if match_trait_method(cx, e, &paths::INTO[..]) && &*name.ident.as_str() == "into" {
  65                     let a = cx.tables.expr_ty(e);
  66                     let b = cx.tables.expr_ty(&args[0]);
  67                     if same_tys(cx, a, b) {
  68                         let sugg = snippet_with_macro_callsite(cx, args[0].span, "<expr>").to_string();
  69
  70                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  71                             db.span_suggestion(
  72                                 e.span,
  73                                 "consider removing `.into()`",
  74                                 sugg,
  75                                 Applicability::MachineApplicable, // snippet
  76                             );
  77                         });
  78                     }
  79                 }
  80                 if match_trait_method(cx, e, &paths::INTO_ITERATOR) && &*name.ident.as_str() == "into_iter" {
  81                     let a = cx.tables.expr_ty(e);
  82                     let b = cx.tables.expr_ty(&args[0]);
  83                     if same_tys(cx, a, b) {
  84                         let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
  85                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  86                             db.span_suggestion(
  87                                 e.span,
  88                                 "consider removing `.into_iter()`",
  89                                 sugg,
  90                                 Applicability::MachineApplicable, // snippet
  91                             );
  92                         });
  93                     }
  94                 }
  95             },
  96
  97             ExprKind::Call(ref path, ref args) => {
  98                 if let ExprKind::Path(ref qpath) = path.node {
  99                     if let Some(def_id) = resolve_node(cx, qpath, path.hir_id).opt_def_id() {
 100                         if cx.match_def_path(def_id, &paths::FROM_FROM[..]) {
 101                             let a = cx.tables.expr_ty(e);
 102                             let b = cx.tables.expr_ty(&args[0]);
 103                             if same_tys(cx, a, b) {
 104                                 let sugg = snippet(cx, args[0].span.source_callsite(), "<expr>").into_owned();
 105                                 let sugg_msg =
 106                                     format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
 107                                 span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
 108                                     db.span_suggestion(
 109                                         e.span,
 110                                         &sugg_msg,
 111                                         sugg,
 112                                         Applicability::MachineApplicable, // snippet
 113                                     );
 114                                 });
 115                             }
 116                         }
 117                     }
 118                 }
 119             },
 120
 121             _ => {},
 122         }
 123     }
 124
 125     fn check_expr_post(&mut self, _: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 126         if Some(&e.hir_id) == self.try_desugar_arm.last() {
 127             self.try_desugar_arm.pop();
 128         }
 129     }
 130 }