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     fn name(&self) -> &'static str {
  39         "IdentityConversion"
  40     }
  41 }
  42
  43 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityConversion {
  44     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  45         if in_macro(e.span) {
  46             return;
  47         }
  48
  49         if Some(&e.id) == self.try_desugar_arm.last() {
  50             return;
  51         }
  52
  53         match e.node {
  54             ExprKind::Match(_, ref arms, MatchSource::TryDesugar) => {
  55                 let e = match arms[0].body.node {
  56                     ExprKind::Ret(Some(ref e)) | ExprKind::Break(_, Some(ref e)) => e,
  57                     _ => return,
  58                 };
  59                 if let ExprKind::Call(_, ref args) = e.node {
  60                     self.try_desugar_arm.push(args[0].id);
  61                 } else {
  62                     return;
  63                 }
  64             },
  65
  66             ExprKind::MethodCall(ref name, .., ref args) => {
  67                 if match_trait_method(cx, e, &paths::INTO[..]) && &*name.ident.as_str() == "into" {
  68                     let a = cx.tables.expr_ty(e);
  69                     let b = cx.tables.expr_ty(&args[0]);
  70                     if same_tys(cx, a, b) {
  71                         let sugg = snippet_with_macro_callsite(cx, args[0].span, "<expr>").to_string();
  72
  73                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  74                             db.span_suggestion(
  75                                 e.span,
  76                                 "consider removing `.into()`",
  77                                 sugg,
  78                                 Applicability::MachineApplicable, // snippet
  79                             );
  80                         });
  81                     }
  82                 }
  83                 if match_trait_method(cx, e, &paths::INTO_ITERATOR) && &*name.ident.as_str() == "into_iter" {
  84                     let a = cx.tables.expr_ty(e);
  85                     let b = cx.tables.expr_ty(&args[0]);
  86                     if same_tys(cx, a, b) {
  87                         let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
  88                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  89                             db.span_suggestion(
  90                                 e.span,
  91                                 "consider removing `.into_iter()`",
  92                                 sugg,
  93                                 Applicability::MachineApplicable, // snippet
  94                             );
  95                         });
  96                     }
  97                 }
  98             },
  99
 100             ExprKind::Call(ref path, ref args) => {
 101                 if let ExprKind::Path(ref qpath) = path.node {
 102                     if let Some(def_id) = opt_def_id(resolve_node(cx, qpath, path.hir_id)) {
 103                         if match_def_path(cx.tcx, def_id, &paths::FROM_FROM[..]) {
 104                             let a = cx.tables.expr_ty(e);
 105                             let b = cx.tables.expr_ty(&args[0]);
 106                             if same_tys(cx, a, b) {
 107                                 let sugg = snippet(cx, args[0].span.source_callsite(), "<expr>").into_owned();
 108                                 let sugg_msg =
 109                                     format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
 110                                 span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
 111                                     db.span_suggestion(
 112                                         e.span,
 113                                         &sugg_msg,
 114                                         sugg,
 115                                         Applicability::MachineApplicable, // snippet
 116                                     );
 117                                 });
 118                             }
 119                         }
 120                     }
 121                 }
 122             },
 123
 124             _ => {},
 125         }
 126     }
 127
 128     fn check_expr_post(&mut self, _: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 129         if Some(&e.id) == self.try_desugar_arm.last() {
 130             self.try_desugar_arm.pop();
 131         }
 132     }
 133 }