clippy_lints/src/default_trait_access.rs

   1 use rustc::hir::*;
   2 use rustc::lint::*;
   3 use rustc::{declare_lint, lint_array};
   4 use if_chain::if_chain;
   5 use rustc::ty::TyKind;
   6
   7 use crate::utils::{any_parent_is_automatically_derived, match_def_path, opt_def_id, paths, span_lint_and_sugg};
   8
   9
  10 /// **What it does:** Checks for literal calls to `Default::default()`.
  11 ///
  12 /// **Why is this bad?** It's more clear to the reader to use the name of the type whose default is
  13 /// being gotten than the generic `Default`.
  14 ///
  15 /// **Known problems:** None.
  16 ///
  17 /// **Example:**
  18 /// ```rust
  19 /// // Bad
  20 /// let s: String = Default::default();
  21 ///
  22 /// // Good
  23 /// let s = String::default();
  24 /// ```
  25 declare_clippy_lint! {
  26     pub DEFAULT_TRAIT_ACCESS,
  27     pedantic,
  28     "checks for literal calls to Default::default()"
  29 }
  30
  31 #[derive(Copy, Clone)]
  32 pub struct DefaultTraitAccess;
  33
  34 impl LintPass for DefaultTraitAccess {
  35     fn get_lints(&self) -> LintArray {
  36         lint_array!(DEFAULT_TRAIT_ACCESS)
  37     }
  38 }
  39
  40 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DefaultTraitAccess {
  41     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  42         if_chain! {
  43             if let ExprKind::Call(ref path, ..) = expr.node;
  44             if !any_parent_is_automatically_derived(cx.tcx, expr.id);
  45             if let ExprKind::Path(ref qpath) = path.node;
  46             if let Some(def_id) = opt_def_id(cx.tables.qpath_def(qpath, path.hir_id));
  47             if match_def_path(cx.tcx, def_id, &paths::DEFAULT_TRAIT_METHOD);
  48             then {
  49                 match qpath {
  50                     QPath::Resolved(..) => {
  51                         if let ExprKind::Call(ref method, ref _args) = expr.node {
  52                             if format!("{:?}", method).contains(" as Default>") {
  53                                 return
  54                             }
  55                         }
  56
  57
  58                         // TODO: Work out a way to put "whatever the imported way of referencing
  59                         // this type in this file" rather than a fully-qualified type.
  60                         let expr_ty = cx.tables.expr_ty(expr);
  61                         if let TyKind::Adt(..) = expr_ty.sty {
  62                             let replacement = format!("{}::default()", expr_ty);
  63                             span_lint_and_sugg(
  64                                 cx,
  65                                 DEFAULT_TRAIT_ACCESS,
  66                                 expr.span,
  67                                 &format!("Calling {} is more clear than this expression", replacement),
  68                                 "try",
  69                                 replacement);
  70                          }
  71                     },
  72                     QPath::TypeRelative(..) => {},
  73                 }
  74             }
  75          }
  76     }
  77 }