clippy_lints/src/identity_conversion.rs

   1 use crate::utils::{
   2     in_macro, match_def_path, match_trait_method, same_tys, snippet, snippet_with_macro_callsite, span_lint_and_then,
   3 };
   4 use crate::utils::{opt_def_id, paths, resolve_node};
   5 use rustc::hir::*;
   6 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   7 use rustc::{declare_tool_lint, lint_array};
   8 use rustc_errors::Applicability;
   9 use syntax::ast::NodeId;
  10
  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 declare_clippy_lint! {
  23     pub IDENTITY_CONVERSION,
  24     complexity,
  25     "using always-identical `Into`/`From`/`IntoIter` conversions"
  26 }
  27
  28 #[derive(Default)]
  29 pub struct IdentityConversion {
  30     try_desugar_arm: Vec<NodeId>,
  31 }
  32
  33 impl LintPass for IdentityConversion {
  34     fn get_lints(&self) -> LintArray {
  35         lint_array!(IDENTITY_CONVERSION)
  36     }
  37 }
  38
  39 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityConversion {
  40     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  41         if in_macro(e.span) {
  42             return;
  43         }
  44
  45         if Some(&e.id) == self.try_desugar_arm.last() {
  46             return;
  47         }
  48
  49         match e.node {
  50             ExprKind::Match(_, ref arms, MatchSource::TryDesugar) => {
  51                 let e = match arms[0].body.node {
  52                     ExprKind::Ret(Some(ref e)) | ExprKind::Break(_, Some(ref e)) => e,
  53                     _ => return,
  54                 };
  55                 if let ExprKind::Call(_, ref args) = e.node {
  56                     self.try_desugar_arm.push(args[0].id);
  57                 } else {
  58                     return;
  59                 }
  60             },
  61
  62             ExprKind::MethodCall(ref name, .., ref args) => {
  63                 if match_trait_method(cx, e, &paths::INTO[..]) && &*name.ident.as_str() == "into" {
  64                     let a = cx.tables.expr_ty(e);
  65                     let b = cx.tables.expr_ty(&args[0]);
  66                     if same_tys(cx, a, b) {
  67                         let sugg = snippet_with_macro_callsite(cx, args[0].span, "<expr>").to_string();
  68
  69                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  70                             db.span_suggestion_with_applicability(
  71                                 e.span,
  72                                 "consider removing `.into()`",
  73                                 sugg,
  74                                 Applicability::MachineApplicable, // snippet
  75                             );
  76                         });
  77                     }
  78                 }
  79                 if match_trait_method(cx, e, &paths::INTO_ITERATOR) && &*name.ident.as_str() == "into_iter" {
  80                     let a = cx.tables.expr_ty(e);
  81                     let b = cx.tables.expr_ty(&args[0]);
  82                     if same_tys(cx, a, b) {
  83                         let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
  84                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  85                             db.span_suggestion_with_applicability(
  86                                 e.span,
  87                                 "consider removing `.into_iter()`",
  88                                 sugg,
  89                                 Applicability::MachineApplicable, // snippet
  90                             );
  91                         });
  92                     }
  93                 }
  94             },
  95
  96             ExprKind::Call(ref path, ref args) => {
  97                 if let ExprKind::Path(ref qpath) = path.node {
  98                     if let Some(def_id) = opt_def_id(resolve_node(cx, qpath, path.hir_id)) {
  99                         if match_def_path(cx.tcx, def_id, &paths::FROM_FROM[..]) {
 100                             let a = cx.tables.expr_ty(e);
 101                             let b = cx.tables.expr_ty(&args[0]);
 102                             if same_tys(cx, a, b) {
 103                                 let sugg = snippet(cx, args[0].span.source_callsite(), "<expr>").into_owned();
 104                                 let sugg_msg =
 105                                     format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
 106                                 span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
 107                                     db.span_suggestion_with_applicability(
 108                                         e.span,
 109                                         &sugg_msg,
 110                                         sugg,
 111                                         Applicability::MachineApplicable, // snippet
 112                                     );
 113                                 });
 114                             }
 115                         }
 116                     }
 117                 }
 118             },
 119
 120             _ => {},
 121         }
 122     }
 123
 124     fn check_expr_post(&mut self, _: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 125         if Some(&e.id) == self.try_desugar_arm.last() {
 126             self.try_desugar_arm.pop();
 127         }
 128     }
 129 }