Update directly tagged enums to visualize the same as niche-layout enums

Previously, directly tagged enums had a `variant$` field which would
show the name of the active variant. We now show the variant using a
`[variant]` synthetic item just like we do for niche-layout enums.

Author: wesleywiser

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -1,4 +1,3 @@
-use self::EnumTagInfo::*;
 use self::MemberDescriptionFactory::*;
 use self::RecursiveTypeDescription::*;
 
@@ -28,7 +27,7 @@ use rustc_hir::def::CtorKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_index::vec::{Idx, IndexVec};
 use rustc_middle::ich::NodeIdHashingMode;
-use rustc_middle::mir::{self, Field, GeneratorLayout};
+use rustc_middle::mir::{self, GeneratorLayout};
 use rustc_middle::ty::layout::{self, IntegerExt, PrimitiveExt, TyAndLayout};
 use rustc_middle::ty::subst::GenericArgKind;
 use rustc_middle::ty::Instance;
@@ -1188,7 +1187,7 @@ enum MemberDescriptionFactory<'ll, 'tcx> {
     TupleMDF(TupleMemberDescriptionFactory<'tcx>),
     EnumMDF(EnumMemberDescriptionFactory<'ll, 'tcx>),
     UnionMDF(UnionMemberDescriptionFactory<'tcx>),
-    VariantMDF(VariantMemberDescriptionFactory<'ll, 'tcx>),
+    VariantMDF(VariantMemberDescriptionFactory<'tcx>),
 }
 
 impl MemberDescriptionFactory<'ll, 'tcx> {
@@ -1505,14 +1504,8 @@ impl EnumMemberDescriptionFactory<'ll, 'tcx> {
                 }
 
                 let variant_info = variant_info_for(index);
-                let (variant_type_metadata, member_description_factory) = describe_enum_variant(
-                    cx,
-                    self.layout,
-                    variant_info,
-                    None,
-                    self_metadata,
-                    self.span,
-                );
+                let (variant_type_metadata, member_description_factory) =
+                    describe_enum_variant(cx, self.layout, variant_info, self_metadata, self.span);
 
                 let member_descriptions = member_description_factory.create_member_descriptions(cx);
 
@@ -1540,28 +1533,38 @@ impl EnumMemberDescriptionFactory<'ll, 'tcx> {
                 ref variants,
                 ..
             } => {
-                let tag_info = if fallback {
-                    // For MSVC, we generate a union of structs for each variant with an explicit
-                    // discriminant field roughly equivalent to the following C:
+                let fallback_discr_variant = if fallback {
+                    // For MSVC, we generate a union of structs for each variant and an
+                    // explicit discriminant field roughly equivalent to the following C:
                     // ```c
                     // union enum$<{name}> {
                     //   struct {variant 0 name} {
-                    //     tag$ variant$;
                     //     <variant 0 fields>
                     //   } variant0;
                     //   <other variant structs>
+                    //   {name} discriminant;
                     // }
                     // ```
-                    // The natvis in `intrinsic.nativs` then matches on `this.variant0.variant$` to
+                    // The natvis in `intrinsic.nativs` then matches on `this.discriminant` to
                     // determine which variant is active and then displays it.
-                    Some(DirectTag {
-                        tag_field: Field::from(tag_field),
-                        tag_type_metadata: self.tag_type_metadata.unwrap(),
+                    let enum_layout = self.layout;
+                    let offset = enum_layout.fields.offset(tag_field);
+                    let discr_ty = enum_layout.field(cx, tag_field).ty;
+                    let (size, align) = cx.size_and_align_of(discr_ty);
+                    Some(MemberDescription {
+                        name: "discriminant".into(),
+                        type_metadata: self.tag_type_metadata.unwrap(),
+                        offset,
+                        size,
+                        align,
+                        flags: DIFlags::FlagZero,
+                        discriminant: None,
+                        source_info: None,
                     })
                 } else {
-                    // This doesn't matter in this case.
                     None
                 };
+
                 variants
                     .iter_enumerated()
                     .map(|(i, _)| {
@@ -1571,7 +1574,6 @@ impl EnumMemberDescriptionFactory<'ll, 'tcx> {
                             cx,
                             variant,
                             variant_info,
-                            tag_info,
                             self_metadata,
                             self.span,
                         );
@@ -1605,6 +1607,7 @@ impl EnumMemberDescriptionFactory<'ll, 'tcx> {
                             source_info: variant_info.source_info(cx),
                         }
                     })
+                    .chain(fallback_discr_variant.into_iter())
                     .collect()
             }
             Variants::Multiple {
@@ -1702,7 +1705,6 @@ impl EnumMemberDescriptionFactory<'ll, 'tcx> {
                         cx,
                         dataful_variant_layout,
                         variant_info,
-                        Some(NicheTag),
                         self_metadata,
                         self.span,
                     );
@@ -1754,7 +1756,6 @@ impl EnumMemberDescriptionFactory<'ll, 'tcx> {
                                     cx,
                                     variant,
                                     variant_info,
-                                    Some(NicheTag),
                                     self_metadata,
                                     self.span,
                                 );
@@ -1791,39 +1792,27 @@ impl EnumMemberDescriptionFactory<'ll, 'tcx> {
 }
 
 // Creates `MemberDescription`s for the fields of a single enum variant.
-struct VariantMemberDescriptionFactory<'ll, 'tcx> {
+struct VariantMemberDescriptionFactory<'tcx> {
     /// Cloned from the `layout::Struct` describing the variant.
     offsets: Vec<Size>,
     args: Vec<(String, Ty<'tcx>)>,
-    tag_type_metadata: Option<&'ll DIType>,
     span: Span,
 }
 
-impl VariantMemberDescriptionFactory<'ll, 'tcx> {
+impl VariantMemberDescriptionFactory<'tcx> {
     fn create_member_descriptions(&self, cx: &CodegenCx<'ll, 'tcx>) -> Vec<MemberDescription<'ll>> {
         self.args
             .iter()
             .enumerate()
             .map(|(i, &(ref name, ty))| {
-                // Discriminant is always the first field of our variant
-                // when using the enum fallback.
-                let is_artificial_discr = use_enum_fallback(cx) && i == 0;
                 let (size, align) = cx.size_and_align_of(ty);
                 MemberDescription {
                     name: name.to_string(),
-                    type_metadata: if is_artificial_discr {
-                        self.tag_type_metadata.unwrap_or_else(|| type_metadata(cx, ty, self.span))
-                    } else {
-                        type_metadata(cx, ty, self.span)
-                    },
+                    type_metadata: type_metadata(cx, ty, self.span),
                     offset: self.offsets[i],
                     size,
                     align,
-                    flags: if is_artificial_discr {
-                        DIFlags::FlagArtificial
-                    } else {
-                        DIFlags::FlagZero
-                    },
+                    flags: DIFlags::FlagZero,
                     discriminant: None,
                     source_info: None,
                 }
@@ -1832,12 +1821,6 @@ impl VariantMemberDescriptionFactory<'ll, 'tcx> {
     }
 }
 
-#[derive(Copy, Clone)]
-enum EnumTagInfo<'ll> {
-    DirectTag { tag_field: Field, tag_type_metadata: &'ll DIType },
-    NicheTag,
-}
-
 #[derive(Copy, Clone)]
 enum VariantInfo<'a, 'tcx> {
     Adt(&'tcx ty::VariantDef),
@@ -1916,7 +1899,6 @@ fn describe_enum_variant(
     cx: &CodegenCx<'ll, 'tcx>,
     layout: layout::TyAndLayout<'tcx>,
     variant: VariantInfo<'_, 'tcx>,
-    discriminant_info: Option<EnumTagInfo<'ll>>,
     containing_scope: &'ll DIScope,
     span: Span,
 ) -> (&'ll DICompositeType, MemberDescriptionFactory<'ll, 'tcx>) {
@@ -1935,50 +1917,13 @@ fn describe_enum_variant(
         )
     });
 
-    // Build an array of (field name, field type) pairs to be captured in the factory closure.
-    let (offsets, args) = if use_enum_fallback(cx) {
-        // If this is not a univariant enum, there is also the discriminant field.
-        let (discr_offset, discr_arg) = match discriminant_info {
-            Some(DirectTag { tag_field, .. }) => {
-                // We have the layout of an enum variant, we need the layout of the outer enum
-                let enum_layout = cx.layout_of(layout.ty);
-                let offset = enum_layout.fields.offset(tag_field.as_usize());
-                let args = ("variant$".to_owned(), enum_layout.field(cx, tag_field.as_usize()).ty);
-                (Some(offset), Some(args))
-            }
-            _ => (None, None),
-        };
-        (
-            discr_offset
-                .into_iter()
-                .chain((0..layout.fields.count()).map(|i| layout.fields.offset(i)))
-                .collect(),
-            discr_arg
-                .into_iter()
-                .chain(
-                    (0..layout.fields.count())
-                        .map(|i| (variant.field_name(i), layout.field(cx, i).ty)),
-                )
-                .collect(),
-        )
-    } else {
-        (
-            (0..layout.fields.count()).map(|i| layout.fields.offset(i)).collect(),
-            (0..layout.fields.count())
-                .map(|i| (variant.field_name(i), layout.field(cx, i).ty))
-                .collect(),
-        )
-    };
+    let offsets = (0..layout.fields.count()).map(|i| layout.fields.offset(i)).collect();
+    let args = (0..layout.fields.count())
+        .map(|i| (variant.field_name(i), layout.field(cx, i).ty))
+        .collect();
 
-    let member_description_factory = VariantMDF(VariantMemberDescriptionFactory {
-        offsets,
-        args,
-        tag_type_metadata: match discriminant_info {
-            Some(DirectTag { tag_type_metadata, .. }) => Some(tag_type_metadata),
-            _ => None,
-        },
-        span,
-    });
+    let member_description_factory =
+        VariantMDF(VariantMemberDescriptionFactory { offsets, args, span });
 
     (metadata_stub, member_description_factory)
 }

src/etc/natvis/intrinsic.natvis

@@ -150,7 +150,7 @@
     </Expand>
   </Type>
   <Type Name="enum$&lt;*&gt;">
-    <Intrinsic Name="tag" Expression="variant0.variant$" />
+    <Intrinsic Name="tag" Expression="discriminant" />
     <DisplayString Condition="tag() == 0">{tag(),en}</DisplayString>
     <DisplayString Condition="tag() == 1" Optional="true">{tag(),en}</DisplayString>
     <DisplayString Condition="tag() == 2" Optional="true">{tag(),en}</DisplayString>
@@ -169,6 +169,9 @@
     <DisplayString Condition="tag() == 15" Optional="true">{tag(),en}</DisplayString>
 
     <Expand>
+      <Synthetic Name="[variant]">
+        <DisplayString>{tag(),en}</DisplayString>
+      </Synthetic>
       <ExpandedItem Condition="tag() == 0">variant0</ExpandedItem>
       <ExpandedItem Condition="tag() == 1" Optional="true">variant1</ExpandedItem>
       <ExpandedItem Condition="tag() == 2" Optional="true">variant2</ExpandedItem>

src/test/debuginfo/msvc-pretty-enums.rs

@@ -48,14 +48,30 @@
 // cdb-check:        [+0x000] __0              : 0x0 [Type: unsigned int *]
 // cdb-check:    [+0x000] discriminant     : None (0x0) [Type: enum$<core::option::Option<ref$<u32> >, 1, [...], Some>::Discriminant$]
 
+// cdb-command: dx -r2 h,!
+// cdb-check:h,!              : Some [Type: enum$<core::option::Option<u32> >]
+// cdb-check:    [+0x000] variant0         [Type: enum$<core::option::Option<u32> >::None]
+// cdb-check:    [+0x000] variant1         [Type: enum$<core::option::Option<u32> >::Some]
+// cdb-check:        [+0x004] __0              : 0xc [Type: unsigned int]
+// cdb-check:    [+0x000] discriminant     : Some (0x1) [Type: core::option::Option]
+
 // cdb-command: dx h
 // cdb-check:h                : Some [Type: enum$<core::option::Option<u32> >]
-// cdb-check:    [+0x000] variant$         : Some (0x1) [Type: core::option::Option]
+// cdb-check:    [<Raw View>]     [Type: enum$<core::option::Option<u32> >]
+// cdb-check:    [variant]        : Some
 // cdb-check:    [+0x004] __0              : 0xc [Type: unsigned int]
 
+// cdb-command: dx -r2 i,!
+// cdb-check:i,!              : None [Type: enum$<core::option::Option<u32> >]
+// cdb-check:    [+0x000] variant0         [Type: enum$<core::option::Option<u32> >::None]
+// cdb-check:    [+0x000] variant1         [Type: enum$<core::option::Option<u32> >::Some]
+// cdb-check:        [+0x004] __0              : 0x5c0065 [Type: unsigned int]
+// cdb-check:    [+0x000] discriminant     : None (0x0) [Type: core::option::Option]
+
 // cdb-command: dx i
 // cdb-check:i                : None [Type: enum$<core::option::Option<u32> >]
-// cdb-check:    [+0x000] variant$         : None (0x0) [Type: core::option::Option]
+// cdb-check:    [<Raw View>]     [Type: enum$<core::option::Option<u32> >]
+// cdb-check:    [variant]        : None
 
 // cdb-command: dx j
 // cdb-check:j                : High (0x10) [Type: msvc_pretty_enums::CStyleEnum]

src/test/debuginfo/pretty-std.rs

@@ -116,12 +116,14 @@
 
 // cdb-command: dx some
 // cdb-check:some             : Some [Type: enum$<core::option::Option<i16> >]
-// cdb-check:    [...] variant$         : Some (0x1) [Type: core::option::Option]
-// cdb-check:    [...] __0              : 8 [Type: short]
+// cdb-check:    [<Raw View>]     [Type: enum$<core::option::Option<i16> >]
+// cdb-check:    [variant]        : Some
+// cdb-check:    [+0x002] __0              : 8 [Type: short]
 
 // cdb-command: dx none
 // cdb-check:none             : None [Type: enum$<core::option::Option<i64> >]
-// cdb-check:    [...] variant$         : None (0x0) [Type: core::option::Option]
+// cdb-check:    [<Raw View>]     [Type: enum$<core::option::Option<i64> >]
+// cdb-check:    [variant]        : None
 
 // cdb-command: dx some_string
 // NOTE: cdb fails to interpret debug info of Option enums on i686.