rustdoc: Refactor Impl.{synthetic,blanket_impl} into enum

This change has two advantages:

1. It makes the possible states clearer, and it makes it impossible to
   construct invalid states, such as a blanket impl that is also an auto
   trait impl.

2. It shrinks the size of `Impl` a bit, since now there is only one
   field, rather than two.

src/librustdoc/clean/auto_trait.rs

@@ -121,8 +121,7 @@ fn generate_for_trait(
                 for_: ty.clean(self.cx),
                 items: Vec::new(),
                 negative_polarity,
-                synthetic: true,
-                blanket_impl: None,
+                kind: ImplKind::Auto,
             }),
             cfg: None,
         })

src/librustdoc/clean/blanket_impl.rs

@@ -124,8 +124,7 @@ impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
                             .collect::<Vec<_>>()
                             .clean(self.cx),
                         negative_polarity: false,
-                        synthetic: false,
-                        blanket_impl: Some(box trait_ref.self_ty().clean(self.cx)),
+                        kind: ImplKind::Blanket(box trait_ref.self_ty().clean(self.cx)),
                     }),
                     cfg: None,
                 });

src/librustdoc/clean/inline.rs

@@ -14,7 +14,9 @@
 use rustc_span::hygiene::MacroKind;
 use rustc_span::symbol::{kw, sym, Symbol};
 
-use crate::clean::{self, utils, Attributes, AttributesExt, ItemId, NestedAttributesExt, Type};
+use crate::clean::{
+    self, utils, Attributes, AttributesExt, ImplKind, ItemId, NestedAttributesExt, Type,
+};
 use crate::core::DocContext;
 use crate::formats::item_type::ItemType;
 
@@ -496,8 +498,7 @@ fn merge_attrs(
             for_,
             items: trait_items,
             negative_polarity: polarity.clean(cx),
-            synthetic: false,
-            blanket_impl: None,
+            kind: ImplKind::Normal,
         }),
         box merged_attrs,
         cx,

src/librustdoc/clean/mod.rs

@@ -1895,8 +1895,7 @@ fn clean_impl(impl_: &hir::Impl<'_>, hir_id: hir::HirId, cx: &mut DocContext<'_>
             for_,
             items,
             negative_polarity: tcx.impl_polarity(def_id).clean(cx),
-            synthetic: false,
-            blanket_impl: None,
+            kind: ImplKind::Normal,
         });
         Item::from_hir_id_and_parts(hir_id, None, kind, cx)
     };

src/librustdoc/clean/types.rs

@@ -393,8 +393,8 @@ impl Item {
         };
         match kind {
             ItemKind::ModuleItem(Module { span, .. }) => *span,
-            ItemKind::ImplItem(Impl { synthetic: true, .. }) => Span::dummy(),
-            ItemKind::ImplItem(Impl { blanket_impl: Some(_), .. }) => {
+            ItemKind::ImplItem(Impl { kind: ImplKind::Auto, .. }) => Span::dummy(),
+            ItemKind::ImplItem(Impl { kind: ImplKind::Blanket(_), .. }) => {
                 if let ItemId::Blanket { impl_id, .. } = self.def_id {
                     rustc_span(impl_id, tcx)
                 } else {
@@ -2178,11 +2178,22 @@ impl Constant {
     crate for_: Type,
     crate items: Vec<Item>,
     crate negative_polarity: bool,
-    crate synthetic: bool,
-    crate blanket_impl: Option<Box<Type>>,
+    crate kind: ImplKind,
 }
 
 impl Impl {
+    crate fn is_auto_impl(&self) -> bool {
+        self.kind.is_auto()
+    }
+
+    crate fn is_blanket_impl(&self) -> bool {
+        self.kind.is_blanket()
+    }
+
+    crate fn blanket_impl_ty(&self) -> Option<&Type> {
+        self.kind.as_blanket_ty()
+    }
+
     crate fn provided_trait_methods(&self, tcx: TyCtxt<'_>) -> FxHashSet<Symbol> {
         self.trait_
             .as_ref()
@@ -2192,6 +2203,30 @@ impl Impl {
     }
 }
 
+#[derive(Clone, Debug)]
+crate enum ImplKind {
+    Normal,
+    Auto,
+    Blanket(Box<Type>),
+}
+
+impl ImplKind {
+    crate fn is_auto(&self) -> bool {
+        matches!(self, ImplKind::Auto)
+    }
+
+    crate fn is_blanket(&self) -> bool {
+        matches!(self, ImplKind::Blanket(_))
+    }
+
+    crate fn as_blanket_ty(&self) -> Option<&Type> {
+        match self {
+            ImplKind::Blanket(ty) => Some(ty),
+            _ => None,
+        }
+    }
+}
+
 #[derive(Clone, Debug)]
 crate struct Import {
     crate kind: ImportKind,

src/librustdoc/formats/cache.rs

@@ -228,7 +228,7 @@ fn fold_item(&mut self, item: clean::Item) -> Option<clean::Item> {
         // Collect all the implementors of traits.
         if let clean::ImplItem(ref i) = *item.kind {
             if let Some(trait_) = &i.trait_ {
-                if i.blanket_impl.is_none() {
+                if !i.is_blanket_impl() {
                     self.cache
                         .implementors
                         .entry(trait_.def_id())

src/librustdoc/html/format.rs

@@ -997,7 +997,7 @@ impl clean::Impl {
                 write!(f, " for ")?;
             }
 
-            if let Some(ref ty) = self.blanket_impl {
+            if let Some(ref ty) = self.blanket_impl_ty() {
                 fmt_type(ty, f, use_absolute, cx)?;
             } else {
                 fmt_type(&self.for_, f, use_absolute, cx)?;

src/librustdoc/html/render/mod.rs

@@ -1147,9 +1147,9 @@ fn render_assoc_items_inner(
         }
 
         let (synthetic, concrete): (Vec<&&Impl>, Vec<&&Impl>) =
-            traits.iter().partition(|t| t.inner_impl().synthetic);
+            traits.iter().partition(|t| t.inner_impl().is_auto_impl());
         let (blanket_impl, concrete): (Vec<&&Impl>, _) =
-            concrete.into_iter().partition(|t| t.inner_impl().blanket_impl.is_some());
+            concrete.into_iter().partition(|t| t.inner_impl().is_blanket_impl());
 
         let mut impls = Buffer::empty_from(w);
         render_impls(cx, &mut impls, &concrete, containing_item);
@@ -2058,10 +2058,9 @@ fn sidebar_assoc_items(cx: &Context<'_>, out: &mut Buffer, it: &clean::Item) {
             };
 
             let (synthetic, concrete): (Vec<&Impl>, Vec<&Impl>) =
-                v.iter().partition::<Vec<_>, _>(|i| i.inner_impl().synthetic);
-            let (blanket_impl, concrete): (Vec<&Impl>, Vec<&Impl>) = concrete
-                .into_iter()
-                .partition::<Vec<_>, _>(|i| i.inner_impl().blanket_impl.is_some());
+                v.iter().partition::<Vec<_>, _>(|i| i.inner_impl().is_auto_impl());
+            let (blanket_impl, concrete): (Vec<&Impl>, Vec<&Impl>) =
+                concrete.into_iter().partition::<Vec<_>, _>(|i| i.inner_impl().is_blanket_impl());
 
             let concrete_format = format_impls(concrete);
             let synthetic_format = format_impls(synthetic);

src/librustdoc/html/render/print_item.rs

@@ -746,7 +746,7 @@ fn trait_item(w: &mut Buffer, cx: &Context<'_>, m: &clean::Item, t: &clean::Item
         });
 
         let (mut synthetic, mut concrete): (Vec<&&Impl>, Vec<&&Impl>) =
-            local.iter().partition(|i| i.inner_impl().synthetic);
+            local.iter().partition(|i| i.inner_impl().is_auto_impl());
 
         synthetic.sort_by(|a, b| compare_impl(a, b, cx));
         concrete.sort_by(|a, b| compare_impl(a, b, cx));

src/librustdoc/html/render/write_shared.rs

@@ -585,7 +585,7 @@ struct Implementor {
                 } else {
                     Some(Implementor {
                         text: imp.inner_impl().print(false, cx).to_string(),
-                        synthetic: imp.inner_impl().synthetic,
+                        synthetic: imp.inner_impl().is_auto_impl(),
                         types: collect_paths_for_type(imp.inner_impl().for_.clone(), cache),
                     })
                 }

src/librustdoc/json/conversions.rs

@@ -500,21 +500,19 @@ fn from_tcx(trait_: clean::Trait, tcx: TyCtxt<'_>) -> Self {
 impl FromWithTcx<clean::Impl> for Impl {
     fn from_tcx(impl_: clean::Impl, tcx: TyCtxt<'_>) -> Self {
         let provided_trait_methods = impl_.provided_trait_methods(tcx);
-        let clean::Impl {
-            unsafety,
-            generics,
-            trait_,
-            for_,
-            items,
-            negative_polarity,
-            synthetic,
-            blanket_impl,
-        } = impl_;
+        let clean::Impl { unsafety, generics, trait_, for_, items, negative_polarity, kind } =
+            impl_;
         // FIXME: should `trait_` be a clean::Path equivalent in JSON?
         let trait_ = trait_.map(|path| {
             let did = path.def_id();
             clean::ResolvedPath { path, did }.into_tcx(tcx)
         });
+        // FIXME: use something like ImplKind in JSON?
+        let (synthetic, blanket_impl) = match kind {
+            clean::ImplKind::Normal => (false, None),
+            clean::ImplKind::Auto => (true, None),
+            clean::ImplKind::Blanket(ty) => (false, Some(*ty)),
+        };
         Impl {
             is_unsafe: unsafety == rustc_hir::Unsafety::Unsafe,
             generics: generics.into_tcx(tcx),
@@ -527,7 +525,7 @@ fn from_tcx(impl_: clean::Impl, tcx: TyCtxt<'_>) -> Self {
             items: ids(items),
             negative: negative_polarity,
             synthetic,
-            blanket_impl: blanket_impl.map(|x| (*x).into_tcx(tcx)),
+            blanket_impl: blanket_impl.map(|x| x.into_tcx(tcx)),
         }
     }
 }

src/librustdoc/passes/collect_trait_impls.rs

@@ -111,12 +111,12 @@ fn add_deref_target(
     }
 
     new_items.retain(|it| {
-        if let ImplItem(Impl { ref for_, ref trait_, ref blanket_impl, .. }) = *it.kind {
+        if let ImplItem(Impl { ref for_, ref trait_, ref kind, .. }) = *it.kind {
             cleaner.keep_impl(
                 for_,
                 trait_.as_ref().map(|t| t.def_id()) == cx.tcx.lang_items().deref_trait(),
             ) || trait_.as_ref().map_or(false, |t| cleaner.keep_impl_with_def_id(t.def_id().into()))
-                || blanket_impl.is_some()
+                || kind.is_blanket()
         } else {
             true
         }