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