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::{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
  10 declare_clippy_lint! {
  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     pub IDENTITY_CONVERSION,
  23     complexity,
  24     "using always-identical `Into`/`From`/`IntoIter` conversions"
  25 }
  26
  27 #[derive(Default)]
  28 pub struct IdentityConversion {
  29     try_desugar_arm: Vec<HirId>,
  30 }
  31
  32 impl LintPass for IdentityConversion {
  33     fn get_lints(&self) -> LintArray {
  34         lint_array!(IDENTITY_CONVERSION)
  35     }
  36
  37     fn name(&self) -> &'static str {
  38         "IdentityConversion"
  39     }
  40 }
  41
  42 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityConversion {
  43     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  44         if in_macro(e.span) {
  45             return;
  46         }
  47
  48         if Some(&e.hir_id) == self.try_desugar_arm.last() {
  49             return;
  50         }
  51
  52         match e.node {
  53             ExprKind::Match(_, ref arms, MatchSource::TryDesugar) => {
  54                 let e = match arms[0].body.node {
  55                     ExprKind::Ret(Some(ref e)) | ExprKind::Break(_, Some(ref e)) => e,
  56                     _ => return,
  57                 };
  58                 if let ExprKind::Call(_, ref args) = e.node {
  59                     self.try_desugar_arm.push(args[0].hir_id);
  60                 } else {
  61                     return;
  62                 }
  63             },
  64
  65             ExprKind::MethodCall(ref name, .., ref args) => {
  66                 if match_trait_method(cx, e, &paths::INTO[..]) && &*name.ident.as_str() == "into" {
  67                     let a = cx.tables.expr_ty(e);
  68                     let b = cx.tables.expr_ty(&args[0]);
  69                     if same_tys(cx, a, b) {
  70                         let sugg = snippet_with_macro_callsite(cx, args[0].span, "<expr>").to_string();
  71
  72                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  73                             db.span_suggestion(
  74                                 e.span,
  75                                 "consider removing `.into()`",
  76                                 sugg,
  77                                 Applicability::MachineApplicable, // snippet
  78                             );
  79                         });
  80                     }
  81                 }
  82                 if match_trait_method(cx, e, &paths::INTO_ITERATOR) && &*name.ident.as_str() == "into_iter" {
  83                     let a = cx.tables.expr_ty(e);
  84                     let b = cx.tables.expr_ty(&args[0]);
  85                     if same_tys(cx, a, b) {
  86                         let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
  87                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  88                             db.span_suggestion(
  89                                 e.span,
  90                                 "consider removing `.into_iter()`",
  91                                 sugg,
  92                                 Applicability::MachineApplicable, // snippet
  93                             );
  94                         });
  95                     }
  96                 }
  97             },
  98
  99             ExprKind::Call(ref path, ref args) => {
 100                 if let ExprKind::Path(ref qpath) = path.node {
 101                     if let Some(def_id) = resolve_node(cx, qpath, path.hir_id).opt_def_id() {
 102                         if match_def_path(cx.tcx, def_id, &paths::FROM_FROM[..]) {
 103                             let a = cx.tables.expr_ty(e);
 104                             let b = cx.tables.expr_ty(&args[0]);
 105                             if same_tys(cx, a, b) {
 106                                 let sugg = snippet(cx, args[0].span.source_callsite(), "<expr>").into_owned();
 107                                 let sugg_msg =
 108                                     format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
 109                                 span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
 110                                     db.span_suggestion(
 111                                         e.span,
 112                                         &sugg_msg,
 113                                         sugg,
 114                                         Applicability::MachineApplicable, // snippet
 115                                     );
 116                                 });
 117                             }
 118                         }
 119                     }
 120                 }
 121             },
 122
 123             _ => {},
 124         }
 125     }
 126
 127     fn check_expr_post(&mut self, _: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 128         if Some(&e.hir_id) == self.try_desugar_arm.last() {
 129             self.try_desugar_arm.pop();
 130         }
 131     }
 132 }