clippy_lints/src/default_trait_access.rs

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