clippy_lints/src/identity_conversion.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10
  11 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  12 use crate::rustc::{declare_tool_lint, lint_array};
  13 use crate::rustc::hir::*;
  14 use crate::syntax::ast::NodeId;
  15 use crate::utils::{in_macro, match_def_path, match_trait_method, same_tys, snippet, snippet_with_macro_callsite, span_lint_and_then};
  16 use crate::utils::{opt_def_id, paths, resolve_node};
  17 use crate::rustc_errors::Applicability;
  18
  19 /// **What it does:** Checks for always-identical `Into`/`From`/`IntoIter` conversions.
  20 ///
  21 /// **Why is this bad?** Redundant code.
  22 ///
  23 /// **Known problems:** None.
  24 ///
  25 /// **Example:**
  26 /// ```rust
  27 /// // format!() returns a `String`
  28 /// let s: String = format!("hello").into();
  29 /// ```
  30 declare_clippy_lint! {
  31     pub IDENTITY_CONVERSION,
  32     complexity,
  33     "using always-identical `Into`/`From`/`IntoIter` conversions"
  34 }
  35
  36 #[derive(Default)]
  37 pub struct IdentityConversion {
  38     try_desugar_arm: Vec<NodeId>,
  39 }
  40
  41 impl LintPass for IdentityConversion {
  42     fn get_lints(&self) -> LintArray {
  43         lint_array!(IDENTITY_CONVERSION)
  44     }
  45 }
  46
  47 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityConversion {
  48     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  49         if in_macro(e.span) {
  50             return;
  51         }
  52
  53         if Some(&e.id) == self.try_desugar_arm.last() {
  54             return;
  55         }
  56
  57         match e.node {
  58             ExprKind::Match(_, ref arms, MatchSource::TryDesugar) => {
  59                 let e = match arms[0].body.node {
  60                     ExprKind::Ret(Some(ref e)) | ExprKind::Break(_, Some(ref e)) => e,
  61                     _ => return,
  62                 };
  63                 if let ExprKind::Call(_, ref args) = e.node {
  64                     self.try_desugar_arm.push(args[0].id);
  65                 } else {
  66                     return;
  67                 }
  68             },
  69
  70             ExprKind::MethodCall(ref name, .., ref args) => {
  71                 if match_trait_method(cx, e, &paths::INTO[..]) && &*name.ident.as_str() == "into" {
  72                     let a = cx.tables.expr_ty(e);
  73                     let b = cx.tables.expr_ty(&args[0]);
  74                     if same_tys(cx, a, b) {
  75                         let sugg = snippet_with_macro_callsite(cx, args[0].span, "<expr>").to_string();
  76
  77                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  78                             db.span_suggestion_with_applicability(
  79                                 e.span,
  80                                 "consider removing `.into()`",
  81                                 sugg,
  82                                 Applicability::MachineApplicable, // snippet
  83                             );
  84                         });
  85                     }
  86                 }
  87                 if match_trait_method(cx, e, &paths::INTO_ITERATOR) && &*name.ident.as_str() == "into_iter" {
  88                     let a = cx.tables.expr_ty(e);
  89                     let b = cx.tables.expr_ty(&args[0]);
  90                     if same_tys(cx, a, b) {
  91                         let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
  92                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  93                             db.span_suggestion_with_applicability(
  94                                 e.span,
  95                                 "consider removing `.into_iter()`",
  96                                 sugg,
  97                                 Applicability::MachineApplicable, // snippet
  98                             );
  99                         });
 100                     }
 101                 }
 102             },
 103
 104             ExprKind::Call(ref path, ref args) => if let ExprKind::Path(ref qpath) = path.node {
 105                 if let Some(def_id) = opt_def_id(resolve_node(cx, qpath, path.hir_id)) {
 106                     if match_def_path(cx.tcx, def_id, &paths::FROM_FROM[..]) {
 107                         let a = cx.tables.expr_ty(e);
 108                         let b = cx.tables.expr_ty(&args[0]);
 109                         if same_tys(cx, a, b) {
 110                             let sugg = snippet(cx, args[0].span.source_callsite(), "<expr>").into_owned();
 111                             let sugg_msg = format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
 112                             span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
 113                                 db.span_suggestion_with_applicability(
 114                                     e.span,
 115                                     &sugg_msg,
 116                                     sugg,
 117                                     Applicability::MachineApplicable, // snippet
 118                                 );
 119                             });
 120                         }
 121                     }
 122                 }
 123             },
 124
 125             _ => {},
 126         }
 127     }
 128
 129     fn check_expr_post(&mut self, _: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 130         if Some(&e.id) == self.try_desugar_arm.last() {
 131             self.try_desugar_arm.pop();
 132         }
 133     }
 134 }