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 use crate::utils::{
  11     in_macro, match_def_path, match_trait_method, same_tys, snippet, snippet_with_macro_callsite, span_lint_and_then,
  12 };
  13 use crate::utils::{opt_def_id, paths, resolve_node};
  14 use rustc::hir::*;
  15 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  16 use rustc::{declare_tool_lint, lint_array};
  17 use rustc_errors::Applicability;
  18 use syntax::ast::NodeId;
  19
  20 /// **What it does:** Checks for always-identical `Into`/`From`/`IntoIter` conversions.
  21 ///
  22 /// **Why is this bad?** Redundant code.
  23 ///
  24 /// **Known problems:** None.
  25 ///
  26 /// **Example:**
  27 /// ```rust
  28 /// // format!() returns a `String`
  29 /// let s: String = format!("hello").into();
  30 /// ```
  31 declare_clippy_lint! {
  32     pub IDENTITY_CONVERSION,
  33     complexity,
  34     "using always-identical `Into`/`From`/`IntoIter` conversions"
  35 }
  36
  37 #[derive(Default)]
  38 pub struct IdentityConversion {
  39     try_desugar_arm: Vec<NodeId>,
  40 }
  41
  42 impl LintPass for IdentityConversion {
  43     fn get_lints(&self) -> LintArray {
  44         lint_array!(IDENTITY_CONVERSION)
  45     }
  46 }
  47
  48 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityConversion {
  49     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  50         if in_macro(e.span) {
  51             return;
  52         }
  53
  54         if Some(&e.id) == self.try_desugar_arm.last() {
  55             return;
  56         }
  57
  58         match e.node {
  59             ExprKind::Match(_, ref arms, MatchSource::TryDesugar) => {
  60                 let e = match arms[0].body.node {
  61                     ExprKind::Ret(Some(ref e)) | ExprKind::Break(_, Some(ref e)) => e,
  62                     _ => return,
  63                 };
  64                 if let ExprKind::Call(_, ref args) = e.node {
  65                     self.try_desugar_arm.push(args[0].id);
  66                 } else {
  67                     return;
  68                 }
  69             },
  70
  71             ExprKind::MethodCall(ref name, .., ref args) => {
  72                 if match_trait_method(cx, e, &paths::INTO[..]) && &*name.ident.as_str() == "into" {
  73                     let a = cx.tables.expr_ty(e);
  74                     let b = cx.tables.expr_ty(&args[0]);
  75                     if same_tys(cx, a, b) {
  76                         let sugg = snippet_with_macro_callsite(cx, args[0].span, "<expr>").to_string();
  77
  78                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  79                             db.span_suggestion_with_applicability(
  80                                 e.span,
  81                                 "consider removing `.into()`",
  82                                 sugg,
  83                                 Applicability::MachineApplicable, // snippet
  84                             );
  85                         });
  86                     }
  87                 }
  88                 if match_trait_method(cx, e, &paths::INTO_ITERATOR) && &*name.ident.as_str() == "into_iter" {
  89                     let a = cx.tables.expr_ty(e);
  90                     let b = cx.tables.expr_ty(&args[0]);
  91                     if same_tys(cx, a, b) {
  92                         let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
  93                         span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
  94                             db.span_suggestion_with_applicability(
  95                                 e.span,
  96                                 "consider removing `.into_iter()`",
  97                                 sugg,
  98                                 Applicability::MachineApplicable, // snippet
  99                             );
 100                         });
 101                     }
 102                 }
 103             },
 104
 105             ExprKind::Call(ref path, ref args) => {
 106                 if let ExprKind::Path(ref qpath) = path.node {
 107                     if let Some(def_id) = opt_def_id(resolve_node(cx, qpath, path.hir_id)) {
 108                         if match_def_path(cx.tcx, def_id, &paths::FROM_FROM[..]) {
 109                             let a = cx.tables.expr_ty(e);
 110                             let b = cx.tables.expr_ty(&args[0]);
 111                             if same_tys(cx, a, b) {
 112                                 let sugg = snippet(cx, args[0].span.source_callsite(), "<expr>").into_owned();
 113                                 let sugg_msg =
 114                                     format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
 115                                 span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
 116                                     db.span_suggestion_with_applicability(
 117                                         e.span,
 118                                         &sugg_msg,
 119                                         sugg,
 120                                         Applicability::MachineApplicable, // snippet
 121                                     );
 122                                 });
 123                             }
 124                         }
 125                     }
 126                 }
 127             },
 128
 129             _ => {},
 130         }
 131     }
 132
 133     fn check_expr_post(&mut self, _: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 134         if Some(&e.id) == self.try_desugar_arm.last() {
 135             self.try_desugar_arm.pop();
 136         }
 137     }
 138 }