Store a Symbol instead of an Ident in VariantDef/FieldDef

The field is also renamed from `ident` to `name. In most cases,
we don't actually need the `Span`. A new `ident` method is added
to `VariantDef` and `FieldDef`, which constructs the full `Ident`
using `tcx.def_ident_span()`. This method is used in the cases
where we actually need an `Ident`.

This makes incremental compilation properly track changes
to the `Span`, without all of the invalidations caused by storing
a `Span` directly via an `Ident`.

Author: Aaron1011

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -372,7 +372,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     } else {
                         def.non_enum_variant()
                     };
-                    variant.fields[field.index()].ident.to_string()
+                    variant.fields[field.index()].name.to_string()
                 }
                 ty::Tuple(_) => field.index().to_string(),
                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {

compiler/rustc_codegen_cranelift/src/debuginfo/mod.rs

@@ -174,7 +174,7 @@ impl<'tcx> DebugContext<'tcx> {
 
                     field_entry.set(
                         gimli::DW_AT_name,
-                        AttributeValue::String(field_def.ident.as_str().to_string().into_bytes()),
+                        AttributeValue::String(field_def.name.as_str().to_string().into_bytes()),
                     );
                     field_entry.set(
                         gimli::DW_AT_data_member_location,

compiler/rustc_codegen_gcc/src/type_of.rs

@@ -57,7 +57,7 @@ pub fn uncached_gcc_type<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, layout: TyAndLa
                 (layout.ty.kind(), &layout.variants)
             {
                 if def.is_enum() && !def.variants.is_empty() {
-                    write!(&mut name, "::{}", def.variants[index].ident).unwrap();
+                    write!(&mut name, "::{}", def.variants[index].name).unwrap();
                 }
             }
             if let (&ty::Generator(_, _, _), &Variants::Single { index }) =

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -1300,7 +1300,7 @@ impl<'tcx> StructMemberDescriptionFactory<'tcx> {
                 let name = if self.variant.ctor_kind == CtorKind::Fn {
                     format!("__{}", i)
                 } else {
-                    f.ident.to_string()
+                    f.name.to_string()
                 };
                 let field = layout.field(cx, i);
                 MemberDescription {
@@ -1480,7 +1480,7 @@ impl<'tcx> UnionMemberDescriptionFactory<'tcx> {
             .map(|(i, f)| {
                 let field = self.layout.field(cx, i);
                 MemberDescription {
-                    name: f.ident.to_string(),
+                    name: f.name.to_string(),
                     type_metadata: type_metadata(cx, field.ty, self.span),
                     offset: Size::ZERO,
                     size: field.size,
@@ -1950,7 +1950,7 @@ enum VariantInfo<'a, 'tcx> {
 impl<'tcx> VariantInfo<'_, 'tcx> {
     fn map_struct_name<R>(&self, f: impl FnOnce(&str) -> R) -> R {
         match self {
-            VariantInfo::Adt(variant) => f(variant.ident.as_str()),
+            VariantInfo::Adt(variant) => f(variant.name.as_str()),
             VariantInfo::Generator { variant_index, .. } => {
                 f(&GeneratorSubsts::variant_name(*variant_index))
             }
@@ -1959,7 +1959,7 @@ impl<'tcx> VariantInfo<'_, 'tcx> {
 
     fn variant_name(&self) -> String {
         match self {
-            VariantInfo::Adt(variant) => variant.ident.to_string(),
+            VariantInfo::Adt(variant) => variant.name.to_string(),
             VariantInfo::Generator { variant_index, .. } => {
                 // Since GDB currently prints out the raw discriminant along
                 // with every variant, make each variant name be just the value
@@ -1973,7 +1973,7 @@ impl<'tcx> VariantInfo<'_, 'tcx> {
     fn field_name(&self, i: usize) -> String {
         let field_name = match *self {
             VariantInfo::Adt(variant) if variant.ctor_kind != CtorKind::Fn => {
-                Some(variant.fields[i].ident.name)
+                Some(variant.fields[i].name)
             }
             VariantInfo::Generator {
                 generator_layout,
@@ -2063,7 +2063,7 @@ fn prepare_enum_metadata<'ll, 'tcx>(
         let enumerators_metadata: Vec<_> = match enum_type.kind() {
             ty::Adt(def, _) => iter::zip(def.discriminants(tcx), &def.variants)
                 .map(|((_, discr), v)| {
-                    let name = v.ident.as_str();
+                    let name = v.name.as_str();
                     let is_unsigned = match discr.ty.kind() {
                         ty::Int(_) => false,
                         ty::Uint(_) => true,

compiler/rustc_codegen_llvm/src/type_of.rs

@@ -49,7 +49,7 @@ fn uncached_llvm_type<'a, 'tcx>(
                 (layout.ty.kind(), &layout.variants)
             {
                 if def.is_enum() && !def.variants.is_empty() {
-                    write!(&mut name, "::{}", def.variants[index].ident).unwrap();
+                    write!(&mut name, "::{}", def.variants[index].name).unwrap();
                 }
             }
             if let (&ty::Generator(_, _, _), &Variants::Single { index }) =

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -409,14 +409,14 @@ fn push_debuginfo_type_name<'tcx>(
             let max = dataful_discriminant_range.end;
             let max = tag.value.size(&tcx).truncate(max);
 
-            let dataful_variant_name = def.variants[*dataful_variant].ident.as_str();
+            let dataful_variant_name = def.variants[*dataful_variant].name.as_str();
 
             output.push_str(&format!(", {}, {}, {}", min, max, dataful_variant_name));
         } else if let Variants::Single { index: variant_idx } = &layout.variants {
             // Uninhabited enums can't be constructed and should never need to be visualized so
             // skip this step for them.
             if def.variants.len() != 0 {
-                let variant = def.variants[*variant_idx].ident.as_str();
+                let variant = def.variants[*variant_idx].name.as_str();
 
                 output.push_str(&format!(", {}", variant));
             }

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -267,14 +267,14 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                 match layout.variants {
                     Variants::Single { index } => {
                         // Inside a variant
-                        PathElem::Field(def.variants[index].fields[field].ident.name)
+                        PathElem::Field(def.variants[index].fields[field].name)
                     }
                     Variants::Multiple { .. } => bug!("we handled variants above"),
                 }
             }
 
             // other ADTs
-            ty::Adt(def, _) => PathElem::Field(def.non_enum_variant().fields[field].ident.name),
+            ty::Adt(def, _) => PathElem::Field(def.non_enum_variant().fields[field].name),
 
             // arrays/slices
             ty::Array(..) | ty::Slice(..) => PathElem::ArrayElem(field),
@@ -726,7 +726,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
         new_op: &OpTy<'tcx, M::PointerTag>,
     ) -> InterpResult<'tcx> {
         let name = match old_op.layout.ty.kind() {
-            ty::Adt(adt, _) => PathElem::Variant(adt.variants[variant_id].ident.name),
+            ty::Adt(adt, _) => PathElem::Variant(adt.variants[variant_id].name),
             // Generators also have variants
             ty::Generator(..) => PathElem::GeneratorState(variant_id),
             _ => bug!("Unexpected type with variant: {:?}", old_op.layout.ty),

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -1924,7 +1924,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 .fields
                 .iter()
                 .filter(|field| field.vis.is_accessible_from(field.did, self.tcx))
-                .map(|field| (field.ident.name, field.ty(self.tcx, expected_substs)))
+                .map(|field| (field.name, field.ty(self.tcx, expected_substs)))
                 .find(|(_, ty)| same_type_modulo_infer(ty, exp_found.found))
             {
                 if let ObligationCauseCode::Pattern { span: Some(span), .. } = *cause.code() {

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -862,7 +862,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         let ctor_did = data.ctor.map(|index| self.local_def_id(index));
 
         ty::VariantDef::new(
-            self.item_ident(index, sess),
+            self.item_ident(index, sess).name,
             variant_did,
             ctor_did,
             data.discr,
@@ -874,7 +874,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                 .decode(self)
                 .map(|index| ty::FieldDef {
                     did: self.local_def_id(index),
-                    ident: self.item_ident(index, sess),
+                    name: self.item_ident(index, sess).name,
                     vis: self.get_visibility(index),
                 })
                 .collect(),

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1052,7 +1052,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             assert!(f.did.is_local());
             f.did.index
         }));
-        self.encode_ident_span(def_id, variant.ident);
+        self.encode_ident_span(def_id, variant.ident(tcx));
         self.encode_item_type(def_id);
         if variant.ctor_kind == CtorKind::Fn {
             // FIXME(eddyb) encode signature only in `encode_enum_variant_ctor`.
@@ -1138,7 +1138,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         debug!("EncodeContext::encode_field({:?})", def_id);
 
         record!(self.tables.kind[def_id] <- EntryKind::Field);
-        self.encode_ident_span(def_id, field.ident);
+        self.encode_ident_span(def_id, field.ident(self.tcx));
         self.encode_item_type(def_id);
     }
 

compiler/rustc_middle/src/mir/mod.rs

@@ -2439,7 +2439,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
                                 CtorKind::Fictive => {
                                     let mut struct_fmt = fmt.debug_struct(&name);
                                     for (field, place) in iter::zip(&variant_def.fields, places) {
-                                        struct_fmt.field(field.ident.as_str(), place);
+                                        struct_fmt.field(field.name.as_str(), place);
                                     }
                                     struct_fmt.finish()
                                 }
@@ -2785,7 +2785,7 @@ impl UserTypeProjection {
         field: Field,
     ) -> Self {
         self.projs.push(ProjectionElem::Downcast(
-            Some(adt_def.variants[variant_index].ident.name),
+            Some(adt_def.variants[variant_index].name),
             variant_index,
         ));
         self.projs.push(ProjectionElem::Field(field, ()));

compiler/rustc_middle/src/thir.rs

@@ -726,7 +726,7 @@ impl<'tcx> fmt::Display for Pat<'tcx> {
                 };
 
                 if let Some(variant) = variant {
-                    write!(f, "{}", variant.ident)?;
+                    write!(f, "{}", variant.name)?;
 
                     // Only for Adt we can have `S {...}`,
                     // which we handle separately here.
@@ -738,7 +738,7 @@ impl<'tcx> fmt::Display for Pat<'tcx> {
                             if let PatKind::Wild = *p.pattern.kind {
                                 continue;
                             }
-                            let name = variant.fields[p.field.index()].ident;
+                            let name = variant.fields[p.field.index()].name;
                             write!(f, "{}{}: {}", start_or_comma(), name, p.pattern)?;
                             printed += 1;
                         }

compiler/rustc_middle/src/ty/closure.rs

@@ -178,7 +178,7 @@ impl<'tcx> CapturedPlace<'tcx> {
                         write!(
                             &mut symbol,
                             "__{}",
-                            def.variants[variant].fields[idx as usize].ident.name.as_str(),
+                            def.variants[variant].fields[idx as usize].name.as_str(),
                         )
                         .unwrap();
                     }
@@ -344,7 +344,7 @@ pub fn place_to_string_for_capture<'tcx>(tcx: TyCtxt<'tcx>, place: &HirPlace<'tc
                     curr_string = format!(
                         "{}.{}",
                         curr_string,
-                        def.variants[variant].fields[idx as usize].ident.name.as_str()
+                        def.variants[variant].fields[idx as usize].name.as_str()
                     );
                 }
                 ty::Tuple(_) => {

compiler/rustc_middle/src/ty/context.rs

@@ -2452,7 +2452,7 @@ impl<'tcx> TyCtxt<'tcx> {
     ) -> Place<'tcx> {
         self.mk_place_elem(
             place,
-            PlaceElem::Downcast(Some(adt_def.variants[variant_index].ident.name), variant_index),
+            PlaceElem::Downcast(Some(adt_def.variants[variant_index].name), variant_index),
         )
     }
 

compiler/rustc_middle/src/ty/layout.rs

@@ -10,7 +10,7 @@ use rustc_hir::lang_items::LangItem;
 use rustc_index::bit_set::BitSet;
 use rustc_index::vec::{Idx, IndexVec};
 use rustc_session::{config::OptLevel, DataTypeKind, FieldInfo, SizeKind, VariantInfo};
-use rustc_span::symbol::{Ident, Symbol};
+use rustc_span::symbol::Symbol;
 use rustc_span::{Span, DUMMY_SP};
 use rustc_target::abi::call::{
     ArgAbi, ArgAttribute, ArgAttributes, ArgExtension, Conv, FnAbi, PassMode, Reg, RegKind,
@@ -1810,7 +1810,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
         let adt_kind = adt_def.adt_kind();
         let adt_packed = adt_def.repr.pack.is_some();
 
-        let build_variant_info = |n: Option<Ident>, flds: &[Symbol], layout: TyAndLayout<'tcx>| {
+        let build_variant_info = |n: Option<Symbol>, flds: &[Symbol], layout: TyAndLayout<'tcx>| {
             let mut min_size = Size::ZERO;
             let field_info: Vec<_> = flds
                 .iter()
@@ -1845,15 +1845,15 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
                 if !adt_def.variants.is_empty() && layout.fields != FieldsShape::Primitive {
                     debug!(
                         "print-type-size `{:#?}` variant {}",
-                        layout, adt_def.variants[index].ident
+                        layout, adt_def.variants[index].name
                     );
                     let variant_def = &adt_def.variants[index];
-                    let fields: Vec<_> = variant_def.fields.iter().map(|f| f.ident.name).collect();
+                    let fields: Vec<_> = variant_def.fields.iter().map(|f| f.name).collect();
                     record(
                         adt_kind.into(),
                         adt_packed,
                         None,
-                        vec![build_variant_info(Some(variant_def.ident), &fields, layout)],
+                        vec![build_variant_info(Some(variant_def.name), &fields, layout)],
                     );
                 } else {
                     // (This case arises for *empty* enums; so give it
@@ -1872,10 +1872,9 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
                     .variants
                     .iter_enumerated()
                     .map(|(i, variant_def)| {
-                        let fields: Vec<_> =
-                            variant_def.fields.iter().map(|f| f.ident.name).collect();
+                        let fields: Vec<_> = variant_def.fields.iter().map(|f| f.name).collect();
                         build_variant_info(
-                            Some(variant_def.ident),
+                            Some(variant_def.name),
                             &fields,
                             layout.for_variant(self, i),
                         )

compiler/rustc_middle/src/ty/mod.rs

@@ -1504,8 +1504,7 @@ pub struct VariantDef {
     /// If this variant is a struct variant, then this is `None`.
     pub ctor_def_id: Option<DefId>,
     /// Variant or struct name.
-    #[stable_hasher(project(name))]
-    pub ident: Ident,
+    pub name: Symbol,
     /// Discriminant of this variant.
     pub discr: VariantDiscr,
     /// Fields of this variant.
@@ -1534,7 +1533,7 @@ impl VariantDef {
     /// If someone speeds up attribute loading to not be a performance concern, they can
     /// remove this hack and use the constructor `DefId` everywhere.
     pub fn new(
-        ident: Ident,
+        name: Symbol,
         variant_did: Option<DefId>,
         ctor_def_id: Option<DefId>,
         discr: VariantDiscr,
@@ -1546,9 +1545,9 @@ impl VariantDef {
         is_field_list_non_exhaustive: bool,
     ) -> Self {
         debug!(
-            "VariantDef::new(ident = {:?}, variant_did = {:?}, ctor_def_id = {:?}, discr = {:?},
+            "VariantDef::new(name = {:?}, variant_did = {:?}, ctor_def_id = {:?}, discr = {:?},
              fields = {:?}, ctor_kind = {:?}, adt_kind = {:?}, parent_did = {:?})",
-            ident, variant_did, ctor_def_id, discr, fields, ctor_kind, adt_kind, parent_did,
+            name, variant_did, ctor_def_id, discr, fields, ctor_kind, adt_kind, parent_did,
         );
 
         let mut flags = VariantFlags::NO_VARIANT_FLAGS;
@@ -1563,7 +1562,7 @@ impl VariantDef {
         VariantDef {
             def_id: variant_did.unwrap_or(parent_did),
             ctor_def_id,
-            ident,
+            name,
             discr,
             fields,
             ctor_kind,
@@ -1582,6 +1581,11 @@ impl VariantDef {
     pub fn is_recovered(&self) -> bool {
         self.flags.intersects(VariantFlags::IS_RECOVERED)
     }
+
+    /// Computes the `Ident` of this variant by looking up the `Span`
+    pub fn ident(&self, tcx: TyCtxt<'_>) -> Ident {
+        Ident::new(self.name, tcx.def_ident_span(self.def_id).unwrap())
+    }
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
@@ -1600,8 +1604,7 @@ pub enum VariantDiscr {
 #[derive(Debug, HashStable, TyEncodable, TyDecodable)]
 pub struct FieldDef {
     pub did: DefId,
-    #[stable_hasher(project(name))]
-    pub ident: Ident,
+    pub name: Symbol,
     pub vis: Visibility,
 }
 
@@ -1776,6 +1779,11 @@ impl<'tcx> FieldDef {
     pub fn ty(&self, tcx: TyCtxt<'tcx>, subst: SubstsRef<'tcx>) -> Ty<'tcx> {
         tcx.type_of(self.did).subst(tcx, subst)
     }
+
+    /// Computes the `Ident` of this variant by looking up the `Span`
+    pub fn ident(&self, tcx: TyCtxt<'_>) -> Ident {
+        Ident::new(self.name, tcx.def_ident_span(self.did).unwrap())
+    }
 }
 
 pub type Attributes<'tcx> = &'tcx [ast::Attribute];
@@ -1892,7 +1900,10 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     pub fn find_field_index(self, ident: Ident, variant: &VariantDef) -> Option<usize> {
-        variant.fields.iter().position(|field| self.hygienic_eq(ident, field.ident, variant.def_id))
+        variant
+            .fields
+            .iter()
+            .position(|field| self.hygienic_eq(ident, field.ident(self), variant.def_id))
     }
 
     /// Returns `true` if the impls are the same polarity and the trait either

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -1475,7 +1475,7 @@ pub trait PrettyPrinter<'tcx>:
                                     if !first {
                                         p!(", ");
                                     }
-                                    p!(write("{}: ", field_def.ident), print(field));
+                                    p!(write("{}: ", field_def.name), print(field));
                                     first = false;
                                 }
                                 p!(" }}");

compiler/rustc_mir_build/src/build/expr/as_place.rs

@@ -336,10 +336,7 @@ impl<'tcx> PlaceBuilder<'tcx> {
     }
 
     crate fn downcast(self, adt_def: &'tcx AdtDef, variant_index: VariantIdx) -> Self {
-        self.project(PlaceElem::Downcast(
-            Some(adt_def.variants[variant_index].ident.name),
-            variant_index,
-        ))
+        self.project(PlaceElem::Downcast(Some(adt_def.variants[variant_index].name), variant_index))
     }
 
     fn index(self, index: Local) -> Self {