clippy_lints/src/default_trait_access.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::hir::*;
  12 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  13 use crate::rustc::{declare_tool_lint, lint_array};
  14 use if_chain::if_chain;
  15 use crate::rustc::ty::TyKind;
  16
  17 use crate::utils::{any_parent_is_automatically_derived, match_def_path, opt_def_id, paths, span_lint_and_sugg};
  18
  19
  20 /// **What it does:** Checks for literal calls to `Default::default()`.
  21 ///
  22 /// **Why is this bad?** It's more clear to the reader to use the name of the type whose default is
  23 /// being gotten than the generic `Default`.
  24 ///
  25 /// **Known problems:** None.
  26 ///
  27 /// **Example:**
  28 /// ```rust
  29 /// // Bad
  30 /// let s: String = Default::default();
  31 ///
  32 /// // Good
  33 /// let s = String::default();
  34 /// ```
  35 declare_clippy_lint! {
  36     pub DEFAULT_TRAIT_ACCESS,
  37     pedantic,
  38     "checks for literal calls to Default::default()"
  39 }
  40
  41 #[derive(Copy, Clone)]
  42 pub struct DefaultTraitAccess;
  43
  44 impl LintPass for DefaultTraitAccess {
  45     fn get_lints(&self) -> LintArray {
  46         lint_array!(DEFAULT_TRAIT_ACCESS)
  47     }
  48 }
  49
  50 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DefaultTraitAccess {
  51     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  52         if_chain! {
  53             if let ExprKind::Call(ref path, ..) = expr.node;
  54             if !any_parent_is_automatically_derived(cx.tcx, expr.id);
  55             if let ExprKind::Path(ref qpath) = path.node;
  56             if let Some(def_id) = opt_def_id(cx.tables.qpath_def(qpath, path.hir_id));
  57             if match_def_path(cx.tcx, def_id, &paths::DEFAULT_TRAIT_METHOD);
  58             then {
  59                 match qpath {
  60                     QPath::Resolved(..) => {
  61                         if_chain! {
  62                             // Detect and ignore <Foo as Default>::default() because these calls do
  63                             // explicitly name the type.
  64                             if let ExprKind::Call(ref method, ref _args) = expr.node;
  65                             if let ExprKind::Path(ref p) = method.node;
  66                             if let QPath::Resolved(Some(_ty), _path) = p;
  67                             then {
  68                                 return;
  69                             }
  70                         }
  71
  72                         // TODO: Work out a way to put "whatever the imported way of referencing
  73                         // this type in this file" rather than a fully-qualified type.
  74                         let expr_ty = cx.tables.expr_ty(expr);
  75                         if let TyKind::Adt(..) = expr_ty.sty {
  76                             let replacement = format!("{}::default()", expr_ty);
  77                             span_lint_and_sugg(
  78                                 cx,
  79                                 DEFAULT_TRAIT_ACCESS,
  80                                 expr.span,
  81                                 &format!("Calling {} is more clear than this expression", replacement),
  82                                 "try",
  83                                 replacement);
  84                          }
  85                     },
  86                     QPath::TypeRelative(..) => {},
  87                 }
  88             }
  89          }
  90     }
  91 }