Implement default_mismatches_new lint

CHANGELOG.md

@@ -6633,6 +6633,7 @@ Released 2018-09-13
 [`declare_interior_mutable_const`]: https://rust-lang.github.io/rust-clippy/master/index.html#declare_interior_mutable_const
 [`default_constructed_unit_structs`]: https://rust-lang.github.io/rust-clippy/master/index.html#default_constructed_unit_structs
 [`default_instead_of_iter_empty`]: https://rust-lang.github.io/rust-clippy/master/index.html#default_instead_of_iter_empty
+[`default_mismatches_new`]: https://rust-lang.github.io/rust-clippy/master/index.html#default_mismatches_new
 [`default_numeric_fallback`]: https://rust-lang.github.io/rust-clippy/master/index.html#default_numeric_fallback
 [`default_trait_access`]: https://rust-lang.github.io/rust-clippy/master/index.html#default_trait_access
 [`default_union_representation`]: https://rust-lang.github.io/rust-clippy/master/index.html#default_union_representation

clippy_lints/src/declared_lints.rs

@@ -567,7 +567,8 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
     crate::needless_update::NEEDLESS_UPDATE_INFO,
     crate::neg_cmp_op_on_partial_ord::NEG_CMP_OP_ON_PARTIAL_ORD_INFO,
     crate::neg_multiply::NEG_MULTIPLY_INFO,
-    crate::new_without_default::NEW_WITHOUT_DEFAULT_INFO,
+    crate::new_vs_default::DEFAULT_MISMATCHES_NEW_INFO,
+    crate::new_vs_default::NEW_WITHOUT_DEFAULT_INFO,
     crate::no_effect::NO_EFFECT_INFO,
     crate::no_effect::NO_EFFECT_UNDERSCORE_BINDING_INFO,
     crate::no_effect::UNNECESSARY_OPERATION_INFO,

clippy_lints/src/default_constructed_unit_structs.rs

@@ -1,12 +1,12 @@
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::is_ty_alias;
 use clippy_utils::source::SpanRangeExt as _;
+use clippy_utils::ty::is_unit_struct;
 use hir::ExprKind;
 use hir::def::Res;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::ty;
 use rustc_session::declare_lint_pass;
 use rustc_span::sym;
 
@@ -50,30 +50,20 @@ declare_lint_pass!(DefaultConstructedUnitStructs => [
     DEFAULT_CONSTRUCTED_UNIT_STRUCTS,
 ]);
 
-fn is_alias(ty: hir::Ty<'_>) -> bool {
-    if let hir::TyKind::Path(ref qpath) = ty.kind {
-        is_ty_alias(qpath)
-    } else {
-        false
-    }
-}
-
 impl LateLintPass<'_> for DefaultConstructedUnitStructs {
     fn check_expr<'tcx>(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
         if let ExprKind::Call(fn_expr, &[]) = expr.kind
             // make sure we have a call to `Default::default`
             && let ExprKind::Path(ref qpath @ hir::QPath::TypeRelative(base, _)) = fn_expr.kind
             // make sure this isn't a type alias:
             // `<Foo as Bar>::Assoc` cannot be used as a constructor
-            && !is_alias(*base)
+            && !matches!(base.kind, hir::TyKind::Path(ref qpath) if is_ty_alias(qpath))
             && let Res::Def(_, def_id) = cx.qpath_res(qpath, fn_expr.hir_id)
             && cx.tcx.is_diagnostic_item(sym::default_fn, def_id)
             // make sure we have a struct with no fields (unit struct)
-            && let ty::Adt(def, ..) = cx.typeck_results().expr_ty(expr).kind()
-            && def.is_struct()
-            && let var @ ty::VariantDef { ctor: Some((hir::def::CtorKind::Const, _)), .. } = def.non_enum_variant()
-            && !var.is_field_list_non_exhaustive()
-            && !expr.span.from_expansion() && !qpath.span().from_expansion()
+            && is_unit_struct(cx.typeck_results().expr_ty(expr))
+            && !expr.span.from_expansion()
+            && !qpath.span().from_expansion()
             // do not suggest replacing an expression by a type name with placeholders
             && !base.is_suggestable_infer_ty()
         {

clippy_lints/src/lib.rs

@@ -266,7 +266,7 @@ mod needless_question_mark;
 mod needless_update;
 mod neg_cmp_op_on_partial_ord;
 mod neg_multiply;
-mod new_without_default;
+mod new_vs_default;
 mod no_effect;
 mod no_mangle_with_rust_abi;
 mod non_canonical_impls;
@@ -616,7 +616,7 @@ pub fn register_lint_passes(store: &mut rustc_lint::LintStore, conf: &'static Co
         },
         Box::new(|_| Box::new(swap::Swap)),
         Box::new(|_| Box::new(panicking_overflow_checks::PanickingOverflowChecks)),
-        Box::new(|_| Box::<new_without_default::NewWithoutDefault>::default()),
+        Box::new(|_| Box::<new_vs_default::NewVsDefault>::default()),
         Box::new(move |_| Box::new(disallowed_names::DisallowedNames::new(conf))),
         Box::new(move |tcx| Box::new(functions::Functions::new(tcx, conf))),
         Box::new(move |_| Box::new(doc::Documentation::new(conf))),