Fix `#[derive(Default)]` on a generic `#[default]` enum adding unnecessary `Default` bounds

12 files changed, 35 insertions, 1 deletions

diff --git a/compiler/rustc_builtin_macros/src/deriving/bounds.rs b/compiler/rustc_builtin_macros/src/deriving/bounds.rs
index 77e0b6c55a8..7bd344467d0 100644
--- a/compiler/rustc_builtin_macros/src/deriving/bounds.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/bounds.rs
@@ -16,6 +16,7 @@ pub fn expand_deriving_copy(
     let trait_def = TraitDef {
         span,
         path: path_std!(marker::Copy),
+        skip_path_as_bound: false,
         additional_bounds: Vec::new(),
         generics: Bounds::empty(),
         supports_unions: true,
diff --git a/compiler/rustc_builtin_macros/src/deriving/clone.rs b/compiler/rustc_builtin_macros/src/deriving/clone.rs
index c7f2d95e72f..fa8685f5f4e 100644
--- a/compiler/rustc_builtin_macros/src/deriving/clone.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/clone.rs
@@ -72,6 +72,7 @@ pub fn expand_deriving_clone(
     let trait_def = TraitDef {
         span,
         path: path_std!(clone::Clone),
+        skip_path_as_bound: false,
         additional_bounds: bounds,
         generics: Bounds::empty(),
         supports_unions: true,
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
index 5b556c5c9b9..eab67b0d354 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
@@ -25,6 +25,7 @@ pub fn expand_deriving_eq(
     let trait_def = TraitDef {
         span,
         path: path_std!(cmp::Eq),
+        skip_path_as_bound: false,
         additional_bounds: Vec::new(),
         generics: Bounds::empty(),
         supports_unions: true,
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
index 72625869558..7f117981a9a 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
@@ -19,6 +19,7 @@ pub fn expand_deriving_ord(
     let trait_def = TraitDef {
         span,
         path: path_std!(cmp::Ord),
+        skip_path_as_bound: false,
         additional_bounds: Vec::new(),
         generics: Bounds::empty(),
         supports_unions: false,
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
index 42ee65b570a..236cbccaf9f 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
@@ -83,6 +83,7 @@ pub fn expand_deriving_partial_eq(
     let trait_def = TraitDef {
         span,
         path: path_std!(cmp::PartialEq),
+        skip_path_as_bound: false,
         additional_bounds: Vec::new(),
         generics: Bounds::empty(),
         supports_unions: false,
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
index 516892aeda9..4173403a1b8 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
@@ -37,6 +37,7 @@ pub fn expand_deriving_partial_ord(
     let trait_def = TraitDef {
         span,
         path: path_std!(cmp::PartialOrd),
+        skip_path_as_bound: false,
         additional_bounds: vec![],
         generics: Bounds::empty(),
         supports_unions: false,
diff --git a/compiler/rustc_builtin_macros/src/deriving/debug.rs b/compiler/rustc_builtin_macros/src/deriving/debug.rs
index 4af7fd81653..2cf614ed947 100644
--- a/compiler/rustc_builtin_macros/src/deriving/debug.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/debug.rs
@@ -20,6 +20,7 @@ pub fn expand_deriving_debug(
     let trait_def = TraitDef {
         span,
         path: path_std!(fmt::Debug),
+        skip_path_as_bound: false,
         additional_bounds: Vec::new(),
         generics: Bounds::empty(),
         supports_unions: false,
diff --git a/compiler/rustc_builtin_macros/src/deriving/decodable.rs b/compiler/rustc_builtin_macros/src/deriving/decodable.rs
index 7174dbbe7ea..d669f616802 100644
--- a/compiler/rustc_builtin_macros/src/deriving/decodable.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/decodable.rs
@@ -23,6 +23,7 @@ pub fn expand_deriving_rustc_decodable(
     let trait_def = TraitDef {
         span,
         path: Path::new_(vec![krate, sym::Decodable], vec![], PathKind::Global),
+        skip_path_as_bound: false,
         additional_bounds: Vec::new(),
         generics: Bounds::empty(),
         supports_unions: false,
diff --git a/compiler/rustc_builtin_macros/src/deriving/default.rs b/compiler/rustc_builtin_macros/src/deriving/default.rs
index a94c8a996e6..17df9fb279a 100644
--- a/compiler/rustc_builtin_macros/src/deriving/default.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/default.rs
@@ -24,6 +24,7 @@ pub fn expand_deriving_default(
     let trait_def = TraitDef {
         span,
         path: Path::new(vec![kw::Default, sym::Default]),
+        skip_path_as_bound: has_a_default_variant(item),
         additional_bounds: Vec::new(),
         generics: Bounds::empty(),
         supports_unions: false,
@@ -262,3 +263,22 @@ impl<'a, 'b> rustc_ast::visit::Visitor<'a> for DetectNonVariantDefaultAttr<'a, '
         }
     }
 }
+
+fn has_a_default_variant(item: &Annotatable) -> bool {
+    struct HasDefaultAttrOnVariant {
+        found: bool,
+    }
+
+    impl<'ast> rustc_ast::visit::Visitor<'ast> for HasDefaultAttrOnVariant {
+        fn visit_variant(&mut self, v: &'ast rustc_ast::Variant) {
+            if v.attrs.iter().any(|attr| attr.has_name(kw::Default)) {
+                self.found = true;
+            }
+            // no need to subrecurse.
+        }
+    }
+
+    let mut visitor = HasDefaultAttrOnVariant { found: false };
+    item.visit_with(&mut visitor);
+    visitor.found
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/encodable.rs b/compiler/rustc_builtin_macros/src/deriving/encodable.rs
index b220e54238f..f83f58b97d3 100644
--- a/compiler/rustc_builtin_macros/src/deriving/encodable.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/encodable.rs
@@ -107,6 +107,7 @@ pub fn expand_deriving_rustc_encodable(
     let trait_def = TraitDef {
         span,
         path: Path::new_(vec![krate, sym::Encodable], vec![], PathKind::Global),
+        skip_path_as_bound: false,
         additional_bounds: Vec::new(),
         generics: Bounds::empty(),
         supports_unions: false,
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
index adffebd3fd2..cd53050c61e 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -172,6 +172,7 @@ use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::Span;
 use std::cell::RefCell;
 use std::iter;
+use std::ops::Not;
 use std::vec;
 use thin_vec::thin_vec;
 use ty::{Bounds, Path, Ref, Self_, Ty};
@@ -185,6 +186,9 @@ pub struct TraitDef<'a> {
     /// Path of the trait, including any type parameters
     pub path: Path,
 
+    /// Whether to skip adding the current trait as a bound to the type parameters of the type.
+    pub skip_path_as_bound: bool,
+
     /// Additional bounds required of any type parameters of the type,
     /// other than the current trait
     pub additional_bounds: Vec<Ty>,
@@ -594,7 +598,7 @@ impl<'a> TraitDef<'a> {
                         cx.trait_bound(p.to_path(cx, self.span, type_ident, generics))
                     }).chain(
                         // require the current trait
-                        iter::once(cx.trait_bound(trait_path.clone()))
+                        self.skip_path_as_bound.not().then(|| cx.trait_bound(trait_path.clone()))
                     ).chain(
                         // also add in any bounds from the declaration
                         param.bounds.iter().cloned()
diff --git a/compiler/rustc_builtin_macros/src/deriving/hash.rs b/compiler/rustc_builtin_macros/src/deriving/hash.rs
index f1f02e7ce77..6e9d5f08b94 100644
--- a/compiler/rustc_builtin_macros/src/deriving/hash.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/hash.rs
@@ -22,6 +22,7 @@ pub fn expand_deriving_hash(
     let hash_trait_def = TraitDef {
         span,
         path,
+        skip_path_as_bound: false,
         additional_bounds: Vec::new(),
         generics: Bounds::empty(),
         supports_unions: false,