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::ty::TyKind;
  14 use crate::rustc::{declare_tool_lint, lint_array};
  15 use crate::rustc_errors::Applicability;
  16 use if_chain::if_chain;
  17
  18 use crate::utils::{any_parent_is_automatically_derived, match_def_path, opt_def_id, paths, span_lint_and_sugg};
  19
  20
  21 /// **What it does:** Checks for literal calls to `Default::default()`.
  22 ///
  23 /// **Why is this bad?** It's more clear to the reader to use the name of the type whose default is
  24 /// being gotten than the generic `Default`.
  25 ///
  26 /// **Known problems:** None.
  27 ///
  28 /// **Example:**
  29 /// ```rust
  30 /// // Bad
  31 /// let s: String = Default::default();
  32 ///
  33 /// // Good
  34 /// let s = String::default();
  35 /// ```
  36 declare_clippy_lint! {
  37     pub DEFAULT_TRAIT_ACCESS,
  38     pedantic,
  39     "checks for literal calls to Default::default()"
  40 }
  41
  42 #[derive(Copy, Clone)]
  43 pub struct DefaultTraitAccess;
  44
  45 impl LintPass for DefaultTraitAccess {
  46     fn get_lints(&self) -> LintArray {
  47         lint_array!(DEFAULT_TRAIT_ACCESS)
  48     }
  49 }
  50
  51 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DefaultTraitAccess {
  52     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  53         if_chain! {
  54             if let ExprKind::Call(ref path, ..) = expr.node;
  55             if !any_parent_is_automatically_derived(cx.tcx, expr.id);
  56             if let ExprKind::Path(ref qpath) = path.node;
  57             if let Some(def_id) = opt_def_id(cx.tables.qpath_def(qpath, path.hir_id));
  58             if match_def_path(cx.tcx, def_id, &paths::DEFAULT_TRAIT_METHOD);
  59             then {
  60                 match qpath {
  61                     QPath::Resolved(..) => {
  62                         if_chain! {
  63                             // Detect and ignore <Foo as Default>::default() because these calls do
  64                             // explicitly name the type.
  65                             if let ExprKind::Call(ref method, ref _args) = expr.node;
  66                             if let ExprKind::Path(ref p) = method.node;
  67                             if let QPath::Resolved(Some(_ty), _path) = p;
  68                             then {
  69                                 return;
  70                             }
  71                         }
  72
  73                         // TODO: Work out a way to put "whatever the imported way of referencing
  74                         // this type in this file" rather than a fully-qualified type.
  75                         let expr_ty = cx.tables.expr_ty(expr);
  76                         if let TyKind::Adt(..) = expr_ty.sty {
  77                             let replacement = format!("{}::default()", expr_ty);
  78                             span_lint_and_sugg(
  79                                 cx,
  80                                 DEFAULT_TRAIT_ACCESS,
  81                                 expr.span,
  82                                 &format!("Calling {} is more clear than this expression", replacement),
  83                                 "try",
  84                                 replacement,
  85                                 Applicability::Unspecified, // First resolve the TODO above
  86                             );
  87                          }
  88                     },
  89                     QPath::TypeRelative(..) => {},
  90                 }
  91             }
  92          }
  93     }
  94 }