clippy_lints/src/identity_conversion.rs

   1 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   2 use crate::rustc::{declare_tool_lint, lint_array};
   3 use crate::rustc::hir::*;
   4 use crate::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 use crate::rustc_errors::Applicability;
   8
   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 declare_clippy_lint! {
  21     pub IDENTITY_CONVERSION,
  22     complexity,
  23     "using always-identical `Into`/`From`/`IntoIter` conversions"
  24 }
  25
  26 #[derive(Default)]
  27 pub struct IdentityConversion {
  28     try_desugar_arm: Vec<NodeId>,
  29 }
  30
  31 impl LintPass for IdentityConversion {
  32     fn get_lints(&self) -> LintArray {
  33         lint_array!(IDENTITY_CONVERSION)
  34     }
  35 }
  36
  37 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityConversion {
  38     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  39         if in_macro(e.span) {
  40             return;
  41         }
  42
  43         if Some(&e.id) == self.try_desugar_arm.last() {
  44             return;
  45         }
  46
  47         match e.node {
  48             ExprKind::Match(_, ref arms, MatchSource::TryDesugar) => {
  49                 let e = match arms[0].body.node {
  50                     ExprKind::Ret(Some(ref e)) | ExprKind::Break(_, Some(ref e)) => e,
  51                     _ => return,
  52                 };
  53                 if let ExprKind::Call(_, ref args) = e.node {
  54                     self.try_desugar_arm.push(args[0].id);
  55                 } else {
  56                     return;
  57                 }
  58             },
  59
  60             ExprKind::MethodCall(ref name, .., ref args) => {
  61                 if match_trait_method(cx, e, &paths::INTO[..]) && &*name.ident.as_str() == "into" {
  62                     let a = cx.tables.expr_ty(e);
  63                     let b = cx.tables.expr_ty(&args[0]);
  64                     if same_tys(cx, a, b) {
  65                         let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
  66                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  67                             db.span_suggestion_with_applicability(
  68                                 e.span,
  69                                 "consider removing `.into()`",
  70                                 sugg,
  71                                 Applicability::MachineApplicable, // snippet
  72                             );
  73                         });
  74                     }
  75                 }
  76                 if match_trait_method(cx, e, &paths::INTO_ITERATOR) && &*name.ident.as_str() == "into_iter" {
  77                     let a = cx.tables.expr_ty(e);
  78                     let b = cx.tables.expr_ty(&args[0]);
  79                     if same_tys(cx, a, b) {
  80                         let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
  81                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  82                             db.span_suggestion_with_applicability(
  83                                 e.span,
  84                                 "consider removing `.into_iter()`",
  85                                 sugg,
  86                                 Applicability::MachineApplicable, // snippet
  87                             );
  88                         });
  89                     }
  90                 }
  91             },
  92
  93             ExprKind::Call(ref path, ref args) => if let ExprKind::Path(ref qpath) = path.node {
  94                 if let Some(def_id) = opt_def_id(resolve_node(cx, qpath, path.hir_id)) {
  95                     if match_def_path(cx.tcx, 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 = 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_with_applicability(
 103                                     e.span,
 104                                     &sugg_msg,
 105                                     sugg,
 106                                     Applicability::MachineApplicable, // snippet
 107                                 );
 108                             });
 109                         }
 110                     }
 111                 }
 112             },
 113
 114             _ => {},
 115         }
 116     }
 117
 118     fn check_expr_post(&mut self, _: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 119         if Some(&e.id) == self.try_desugar_arm.last() {
 120             self.try_desugar_arm.pop();
 121         }
 122     }
 123 }