Auto merge of #86698 - cjgillot:modc, r=estebank

Move OnDiskCache to rustc_query_impl.

This should be the last remnant of the query implementation that was still in rustc_middle.

5 files changed, 54 insertions, 1249 deletions

diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 1651853a552..cb99ae19ee7 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -724,7 +724,7 @@ rustc_queries! {
         cache_on_disk_if { true }
         load_cached(tcx, id) {
             let typeck_results: Option<ty::TypeckResults<'tcx>> = tcx
-                .on_disk_cache.as_ref()
+                .on_disk_cache().as_ref()
                 .and_then(|c| c.try_load_query_result(*tcx, id));
 
             typeck_results.map(|x| &*tcx.arena.alloc(x))
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index f52686c9b5f..b8405801106 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -1,7 +1,7 @@
 //! Type context book-keeping.
 
 use crate::arena::Arena;
-use crate::dep_graph::DepGraph;
+use crate::dep_graph::{DepGraph, DepNode};
 use crate::hir::place::Place as HirPlace;
 use crate::ich::{NodeIdHashingMode, StableHashingContext};
 use crate::infer::canonical::{Canonical, CanonicalVarInfo, CanonicalVarInfos};
@@ -14,7 +14,7 @@ use crate::mir::interpret::{self, AllocId, Allocation, ConstValue, Scalar};
 use crate::mir::{Body, Field, Local, Place, PlaceElem, ProjectionKind, Promoted};
 use crate::thir::Thir;
 use crate::traits;
-use crate::ty::query::{self, OnDiskCache, TyCtxtAt};
+use crate::ty::query::{self, TyCtxtAt};
 use crate::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, Subst, SubstsRef, UserSubsts};
 use crate::ty::TyKind::*;
 use crate::ty::{
@@ -52,8 +52,8 @@ use rustc_session::config::{BorrowckMode, CrateType, OutputFilenames};
 use rustc_session::lint::{Level, Lint};
 use rustc_session::Limit;
 use rustc_session::Session;
-use rustc_span::def_id::StableCrateId;
-use rustc_span::source_map::MultiSpan;
+use rustc_span::def_id::{DefPathHash, StableCrateId};
+use rustc_span::source_map::{MultiSpan, SourceMap};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_target::abi::{Layout, TargetDataLayout, VariantIdx};
@@ -71,6 +71,40 @@ use std::mem;
 use std::ops::{Bound, Deref};
 use std::sync::Arc;
 
+pub trait OnDiskCache<'tcx>: rustc_data_structures::sync::Sync {
+    /// Creates a new `OnDiskCache` instance from the serialized data in `data`.
+    fn new(sess: &'tcx Session, data: Vec<u8>, start_pos: usize) -> Self
+    where
+        Self: Sized;
+
+    fn new_empty(source_map: &'tcx SourceMap) -> Self
+    where
+        Self: Sized;
+
+    /// Converts a `DefPathHash` to its corresponding `DefId` in the current compilation
+    /// session, if it still exists. This is used during incremental compilation to
+    /// turn a deserialized `DefPathHash` into its current `DefId`.
+    fn def_path_hash_to_def_id(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        def_path_hash: DefPathHash,
+    ) -> Option<DefId>;
+
+    /// If the given `dep_node`'s hash still exists in the current compilation,
+    /// and its current `DefId` is foreign, calls `store_foreign_def_id` with it.
+    ///
+    /// Normally, `store_foreign_def_id_hash` can be called directly by
+    /// the dependency graph when we construct a `DepNode`. However,
+    /// when we re-use a deserialized `DepNode` from the previous compilation
+    /// session, we only have the `DefPathHash` available. This method is used
+    /// to that any `DepNode` that we re-use has a `DefPathHash` -> `RawId` written
+    /// out for usage in the next compilation session.
+    fn register_reused_dep_node(&self, tcx: TyCtxt<'tcx>, dep_node: &DepNode);
+    fn store_foreign_def_id_hash(&self, def_id: DefId, hash: DefPathHash);
+
+    fn serialize(&self, tcx: TyCtxt<'tcx>, encoder: &mut FileEncoder) -> FileEncodeResult;
+}
+
 /// A type that is not publicly constructable. This prevents people from making [`TyKind::Error`]s
 /// except through the error-reporting functions on a [`tcx`][TyCtxt].
 #[derive(Copy, Clone, Debug, Eq, Hash, PartialEq, PartialOrd, Ord)]
@@ -993,7 +1027,7 @@ pub struct GlobalCtxt<'tcx> {
     /// Do not access this directly. It is only meant to be used by
     /// `DepGraph::try_mark_green()` and the query infrastructure.
     /// This is `None` if we are not incremental compilation mode
-    pub on_disk_cache: Option<OnDiskCache<'tcx>>,
+    pub on_disk_cache: Option<&'tcx dyn OnDiskCache<'tcx>>,
 
     pub queries: &'tcx dyn query::QueryEngine<'tcx>,
     pub query_caches: query::QueryCaches<'tcx>,
@@ -1141,7 +1175,7 @@ impl<'tcx> TyCtxt<'tcx> {
         resolutions: ty::ResolverOutputs,
         krate: &'tcx hir::Crate<'tcx>,
         dep_graph: DepGraph,
-        on_disk_cache: Option<query::OnDiskCache<'tcx>>,
+        on_disk_cache: Option<&'tcx dyn OnDiskCache<'tcx>>,
         queries: &'tcx dyn query::QueryEngine<'tcx>,
         crate_name: &str,
         output_filenames: OutputFilenames,
@@ -1308,10 +1342,16 @@ impl<'tcx> TyCtxt<'tcx> {
         self.untracked_resolutions.cstore.encode_metadata(self)
     }
 
-    // Note that this is *untracked* and should only be used within the query
-    // system if the result is otherwise tracked through queries
-    pub fn cstore_as_any(self) -> &'tcx dyn Any {
-        self.untracked_resolutions.cstore.as_any()
+    /// Note that this is *untracked* and should only be used within the query
+    /// system if the result is otherwise tracked through queries
+    pub fn cstore_untracked(self) -> &'tcx ty::CrateStoreDyn {
+        &*self.untracked_resolutions.cstore
+    }
+
+    /// Note that this is *untracked* and should only be used within the query
+    /// system if the result is otherwise tracked through queries
+    pub fn definitions_untracked(self) -> &'tcx hir::definitions::Definitions {
+        &self.untracked_resolutions.definitions
     }
 
     #[inline(always)]
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index bfc942e6f10..a6aff424790 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -59,7 +59,7 @@ pub use self::consts::{Const, ConstInt, ConstKind, InferConst, ScalarInt, Uneval
 pub use self::context::{
     tls, CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations,
     CtxtInterners, DelaySpanBugEmitted, FreeRegionInfo, GeneratorInteriorTypeCause, GlobalCtxt,
-    Lift, TyCtxt, TypeckResults, UserType, UserTypeAnnotationIndex,
+    Lift, OnDiskCache, TyCtxt, TypeckResults, UserType, UserTypeAnnotationIndex,
 };
 pub use self::instance::{Instance, InstanceDef};
 pub use self::list::List;
diff --git a/compiler/rustc_middle/src/ty/query/mod.rs b/compiler/rustc_middle/src/ty/query.rs
index 2ed9ede8951..15a8888ee65 100644
--- a/compiler/rustc_middle/src/ty/query/mod.rs
+++ b/compiler/rustc_middle/src/ty/query.rs
@@ -38,14 +38,13 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
 use rustc_data_structures::steal::Steal;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::Lrc;
-use rustc_errors::{ErrorReported, Handler};
+use rustc_errors::ErrorReported;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, DefIdSet, LocalDefId};
 use rustc_hir::lang_items::{LangItem, LanguageItems};
 use rustc_hir::{Crate, ItemLocalId, TraitCandidate};
 use rustc_index::{bit_set::FiniteBitSet, vec::IndexVec};
-use rustc_serialize::opaque;
 use rustc_session::config::{EntryFnType, OptLevel, OutputFilenames, SymbolManglingVersion};
 use rustc_session::utils::NativeLibKind;
 use rustc_session::Limits;
@@ -63,9 +62,6 @@ use std::sync::Arc;
 pub(crate) use rustc_query_system::query::QueryJobId;
 use rustc_query_system::query::*;
 
-pub mod on_disk_cache;
-pub use self::on_disk_cache::OnDiskCache;
-
 #[derive(Copy, Clone)]
 pub struct TyCtxtAt<'tcx> {
     pub tcx: TyCtxt<'tcx>,
@@ -235,28 +231,10 @@ macro_rules! define_callbacks {
         }
 
         pub trait QueryEngine<'tcx>: rustc_data_structures::sync::Sync {
-            #[cfg(parallel_compiler)]
-            unsafe fn deadlock(&'tcx self, tcx: TyCtxt<'tcx>, registry: &rustc_rayon_core::Registry);
-
-            fn encode_query_results(
-                &'tcx self,
-                tcx: TyCtxt<'tcx>,
-                encoder: &mut on_disk_cache::CacheEncoder<'a, 'tcx, opaque::FileEncoder>,
-                query_result_index: &mut on_disk_cache::EncodedQueryResultIndex,
-            ) -> opaque::FileEncodeResult;
-
-            fn exec_cache_promotions(&'tcx self, tcx: TyCtxt<'tcx>);
+            fn as_any(&'tcx self) -> &'tcx dyn std::any::Any;
 
             fn try_mark_green(&'tcx self, tcx: TyCtxt<'tcx>, dep_node: &dep_graph::DepNode) -> bool;
 
-            fn try_print_query_stack(
-                &'tcx self,
-                tcx: TyCtxt<'tcx>,
-                query: Option<QueryJobId<dep_graph::DepKind>>,
-                handler: &Handler,
-                num_frames: Option<usize>,
-            ) -> usize;
-
             $($(#[$attr])*
             fn $name(
                 &'tcx self,
diff --git a/compiler/rustc_middle/src/ty/query/on_disk_cache.rs b/compiler/rustc_middle/src/ty/query/on_disk_cache.rs
deleted file mode 100644
index 0ac80ebd636..00000000000
--- a/compiler/rustc_middle/src/ty/query/on_disk_cache.rs
+++ /dev/null
@@ -1,1213 +0,0 @@
-use crate::dep_graph::{DepNode, DepNodeIndex, SerializedDepNodeIndex};
-use crate::mir::interpret::{AllocDecodingSession, AllocDecodingState};
-use crate::mir::{self, interpret};
-use crate::ty::codec::{RefDecodable, TyDecoder, TyEncoder};
-use crate::ty::context::TyCtxt;
-use crate::ty::{self, Ty};
-use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
-use rustc_data_structures::sync::{HashMapExt, Lock, Lrc, OnceCell};
-use rustc_data_structures::thin_vec::ThinVec;
-use rustc_data_structures::unhash::UnhashMap;
-use rustc_errors::Diagnostic;
-use rustc_hir::def_id::{CrateNum, DefId, DefIndex, LocalDefId, StableCrateId, LOCAL_CRATE};
-use rustc_hir::definitions::DefPathHash;
-use rustc_index::vec::{Idx, IndexVec};
-use rustc_query_system::dep_graph::DepContext;
-use rustc_query_system::query::QueryContext;
-use rustc_serialize::{
-    opaque::{self, FileEncodeResult, FileEncoder, IntEncodedWithFixedSize},
-    Decodable, Decoder, Encodable, Encoder,
-};
-use rustc_session::Session;
-use rustc_span::hygiene::{
-    ExpnId, HygieneDecodeContext, HygieneEncodeContext, SyntaxContext, SyntaxContextData,
-};
-use rustc_span::source_map::{SourceMap, StableSourceFileId};
-use rustc_span::CachingSourceMapView;
-use rustc_span::{BytePos, ExpnData, ExpnHash, SourceFile, Span, DUMMY_SP};
-use std::collections::hash_map::Entry;
-use std::mem;
-
-const TAG_FILE_FOOTER: u128 = 0xC0FFEE_C0FFEE_C0FFEE_C0FFEE_C0FFEE;
-
-// A normal span encoded with both location information and a `SyntaxContext`
-const TAG_FULL_SPAN: u8 = 0;
-// A partial span with no location information, encoded only with a `SyntaxContext`
-const TAG_PARTIAL_SPAN: u8 = 1;
-
-const TAG_SYNTAX_CONTEXT: u8 = 0;
-const TAG_EXPN_DATA: u8 = 1;
-
-/// Provides an interface to incremental compilation data cached from the
-/// previous compilation session. This data will eventually include the results
-/// of a few selected queries (like `typeck` and `mir_optimized`) and
-/// any diagnostics that have been emitted during a query.
-pub struct OnDiskCache<'sess> {
-    // The complete cache data in serialized form.
-    serialized_data: Vec<u8>,
-
-    // Collects all `Diagnostic`s emitted during the current compilation
-    // session.
-    current_diagnostics: Lock<FxHashMap<DepNodeIndex, Vec<Diagnostic>>>,
-
-    cnum_map: OnceCell<UnhashMap<StableCrateId, CrateNum>>,
-
-    source_map: &'sess SourceMap,
-    file_index_to_stable_id: FxHashMap<SourceFileIndex, EncodedSourceFileId>,
-
-    // Caches that are populated lazily during decoding.
-    file_index_to_file: Lock<FxHashMap<SourceFileIndex, Lrc<SourceFile>>>,
-
-    // A map from dep-node to the position of the cached query result in
-    // `serialized_data`.
-    query_result_index: FxHashMap<SerializedDepNodeIndex, AbsoluteBytePos>,
-
-    // A map from dep-node to the position of any associated diagnostics in
-    // `serialized_data`.
-    prev_diagnostics_index: FxHashMap<SerializedDepNodeIndex, AbsoluteBytePos>,
-
-    alloc_decoding_state: AllocDecodingState,
-
-    // A map from syntax context ids to the position of their associated
-    // `SyntaxContextData`. We use a `u32` instead of a `SyntaxContext`
-    // to represent the fact that we are storing *encoded* ids. When we decode
-    // a `SyntaxContext`, a new id will be allocated from the global `HygieneData`,
-    // which will almost certainly be different than the serialized id.
-    syntax_contexts: FxHashMap<u32, AbsoluteBytePos>,
-    // A map from the `DefPathHash` of an `ExpnId` to the position
-    // of their associated `ExpnData`. Ideally, we would store a `DefId`,
-    // but we need to decode this before we've constructed a `TyCtxt` (which
-    // makes it difficult to decode a `DefId`).
-
-    // Note that these `DefPathHashes` correspond to both local and foreign
-    // `ExpnData` (e.g `ExpnData.krate` may not be `LOCAL_CRATE`). Alternatively,
-    // we could look up the `ExpnData` from the metadata of foreign crates,
-    // but it seemed easier to have `OnDiskCache` be independent of the `CStore`.
-    expn_data: UnhashMap<ExpnHash, AbsoluteBytePos>,
-    // Additional information used when decoding hygiene data.
-    hygiene_context: HygieneDecodeContext,
-    // Maps `DefPathHash`es to their `RawDefId`s from the *previous*
-    // compilation session. This is used as an initial 'guess' when
-    // we try to map a `DefPathHash` to its `DefId` in the current compilation
-    // session.
-    foreign_def_path_hashes: UnhashMap<DefPathHash, RawDefId>,
-    // Likewise for ExpnId.
-    foreign_expn_data: UnhashMap<ExpnHash, u32>,
-
-    // The *next* compilation sessison's `foreign_def_path_hashes` - at
-    // the end of our current compilation session, this will get written
-    // out to the `foreign_def_path_hashes` field of the `Footer`, which
-    // will become `foreign_def_path_hashes` of the next compilation session.
-    // This stores any `DefPathHash` that we may need to map to a `DefId`
-    // during the next compilation session.
-    latest_foreign_def_path_hashes: Lock<UnhashMap<DefPathHash, RawDefId>>,
-
-    // Caches all lookups of `DefPathHashes`, both for local and foreign
-    // definitions. A definition from the previous compilation session
-    // may no longer exist in the current compilation session, so
-    // we use `Option<DefId>` so that we can cache a lookup failure.
-    def_path_hash_to_def_id_cache: Lock<UnhashMap<DefPathHash, Option<DefId>>>,
-}
-
-// This type is used only for serialization and deserialization.
-#[derive(Encodable, Decodable)]
-struct Footer {
-    file_index_to_stable_id: FxHashMap<SourceFileIndex, EncodedSourceFileId>,
-    query_result_index: EncodedQueryResultIndex,
-    diagnostics_index: EncodedQueryResultIndex,
-    // The location of all allocations.
-    interpret_alloc_index: Vec<u32>,
-    // See `OnDiskCache.syntax_contexts`
-    syntax_contexts: FxHashMap<u32, AbsoluteBytePos>,
-    // See `OnDiskCache.expn_data`
-    expn_data: UnhashMap<ExpnHash, AbsoluteBytePos>,
-    foreign_def_path_hashes: UnhashMap<DefPathHash, RawDefId>,
-    foreign_expn_data: UnhashMap<ExpnHash, u32>,
-}
-
-pub type EncodedQueryResultIndex = Vec<(SerializedDepNodeIndex, AbsoluteBytePos)>;
-type EncodedDiagnosticsIndex = Vec<(SerializedDepNodeIndex, AbsoluteBytePos)>;
-type EncodedDiagnostics = Vec<Diagnostic>;
-
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, Encodable, Decodable)]
-struct SourceFileIndex(u32);
-
-#[derive(Copy, Clone, Debug, Hash, Eq, PartialEq, Encodable, Decodable)]
-pub struct AbsoluteBytePos(u32);
-
-impl AbsoluteBytePos {
-    fn new(pos: usize) -> AbsoluteBytePos {
-        debug_assert!(pos <= u32::MAX as usize);
-        AbsoluteBytePos(pos as u32)
-    }
-
-    fn to_usize(self) -> usize {
-        self.0 as usize
-    }
-}
-
-/// Represents a potentially invalid `DefId`. This is used during incremental
-/// compilation to represent a `DefId` from the *previous* compilation session,
-/// which may no longer be valid. This is used to help map a `DefPathHash`
-/// to a `DefId` in the current compilation session.
-#[derive(Encodable, Decodable, Copy, Clone, Debug)]
-crate struct RawDefId {
-    // We deliberately do not use `CrateNum` and `DefIndex`
-    // here, since a crate/index from the previous compilation
-    // session may no longer exist.
-    pub krate: u32,
-    pub index: u32,
-}
-
-/// An `EncodedSourceFileId` is the same as a `StableSourceFileId` except that
-/// the source crate is represented as a [StableCrateId] instead of as a
-/// `CrateNum`. This way `EncodedSourceFileId` can be encoded and decoded
-/// without any additional context, i.e. with a simple `opaque::Decoder` (which
-/// is the only thing available when decoding the cache's [Footer].
-#[derive(Encodable, Decodable, Clone, Debug)]
-struct EncodedSourceFileId {
-    file_name_hash: u64,
-    stable_crate_id: StableCrateId,
-}
-
-impl EncodedSourceFileId {
-    fn translate(&self, cnum_map: &UnhashMap<StableCrateId, CrateNum>) -> StableSourceFileId {
-        let cnum = cnum_map[&self.stable_crate_id];
-        StableSourceFileId { file_name_hash: self.file_name_hash, cnum }
-    }
-
-    fn new(tcx: TyCtxt<'_>, file: &SourceFile) -> EncodedSourceFileId {
-        let source_file_id = StableSourceFileId::new(file);
-        EncodedSourceFileId {
-            file_name_hash: source_file_id.file_name_hash,
-            stable_crate_id: tcx.stable_crate_id(source_file_id.cnum),
-        }
-    }
-}
-
-impl<'sess> OnDiskCache<'sess> {
-    /// Creates a new `OnDiskCache` instance from the serialized data in `data`.
-    pub fn new(sess: &'sess Session, data: Vec<u8>, start_pos: usize) -> Self {
-        debug_assert!(sess.opts.incremental.is_some());
-
-        // Wrap in a scope so we can borrow `data`.
-        let footer: Footer = {
-            let mut decoder = opaque::Decoder::new(&data[..], start_pos);
-
-            // Decode the *position* of the footer, which can be found in the
-            // last 8 bytes of the file.
-            decoder.set_position(data.len() - IntEncodedWithFixedSize::ENCODED_SIZE);
-            let footer_pos = IntEncodedWithFixedSize::decode(&mut decoder)
-                .expect("error while trying to decode footer position")
-                .0 as usize;
-
-            // Decode the file footer, which contains all the lookup tables, etc.
-            decoder.set_position(footer_pos);
-
-            decode_tagged(&mut decoder, TAG_FILE_FOOTER)
-                .expect("error while trying to decode footer position")
-        };
-
-        Self {
-            serialized_data: data,
-            file_index_to_stable_id: footer.file_index_to_stable_id,
-            file_index_to_file: Default::default(),
-            cnum_map: OnceCell::new(),
-            source_map: sess.source_map(),
-            current_diagnostics: Default::default(),
-            query_result_index: footer.query_result_index.into_iter().collect(),
-            prev_diagnostics_index: footer.diagnostics_index.into_iter().collect(),
-            alloc_decoding_state: AllocDecodingState::new(footer.interpret_alloc_index),
-            syntax_contexts: footer.syntax_contexts,
-            expn_data: footer.expn_data,
-            foreign_expn_data: footer.foreign_expn_data,
-            hygiene_context: Default::default(),
-            foreign_def_path_hashes: footer.foreign_def_path_hashes,
-            latest_foreign_def_path_hashes: Default::default(),
-            def_path_hash_to_def_id_cache: Default::default(),
-        }
-    }
-
-    pub fn new_empty(source_map: &'sess SourceMap) -> Self {
-        Self {
-            serialized_data: Vec::new(),
-            file_index_to_stable_id: Default::default(),
-            file_index_to_file: Default::default(),
-            cnum_map: OnceCell::new(),
-            source_map,
-            current_diagnostics: Default::default(),
-            query_result_index: Default::default(),
-            prev_diagnostics_index: Default::default(),
-            alloc_decoding_state: AllocDecodingState::new(Vec::new()),
-            syntax_contexts: FxHashMap::default(),
-            expn_data: UnhashMap::default(),
-            foreign_expn_data: UnhashMap::default(),
-            hygiene_context: Default::default(),
-            foreign_def_path_hashes: Default::default(),
-            latest_foreign_def_path_hashes: Default::default(),
-            def_path_hash_to_def_id_cache: Default::default(),
-        }
-    }
-
-    pub fn serialize<'tcx>(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        encoder: &mut FileEncoder,
-    ) -> FileEncodeResult {
-        // Serializing the `DepGraph` should not modify it.
-        tcx.dep_graph.with_ignore(|| {
-            // Allocate `SourceFileIndex`es.
-            let (file_to_file_index, file_index_to_stable_id) = {
-                let files = tcx.sess.source_map().files();
-                let mut file_to_file_index =
-                    FxHashMap::with_capacity_and_hasher(files.len(), Default::default());
-                let mut file_index_to_stable_id =
-                    FxHashMap::with_capacity_and_hasher(files.len(), Default::default());
-
-                for (index, file) in files.iter().enumerate() {
-                    let index = SourceFileIndex(index as u32);
-                    let file_ptr: *const SourceFile = &**file as *const _;
-                    file_to_file_index.insert(file_ptr, index);
-                    let source_file_id = EncodedSourceFileId::new(tcx, &file);
-                    file_index_to_stable_id.insert(index, source_file_id);
-                }
-
-                (file_to_file_index, file_index_to_stable_id)
-            };
-
-            // Register any dep nodes that we reused from the previous session,
-            // but didn't `DepNode::construct` in this session. This ensures
-            // that their `DefPathHash` to `RawDefId` mappings are registered
-            // in 'latest_foreign_def_path_hashes' if necessary, since that
-            // normally happens in `DepNode::construct`.
-            tcx.dep_graph.register_reused_dep_nodes(tcx);
-
-            // Load everything into memory so we can write it out to the on-disk
-            // cache. The vast majority of cacheable query results should already
-            // be in memory, so this should be a cheap operation.
-            // Do this *before* we clone 'latest_foreign_def_path_hashes', since
-            // loading existing queries may cause us to create new DepNodes, which
-            // may in turn end up invoking `store_foreign_def_id_hash`
-            tcx.queries.exec_cache_promotions(tcx);
-
-            let latest_foreign_def_path_hashes = self.latest_foreign_def_path_hashes.lock().clone();
-            let hygiene_encode_context = HygieneEncodeContext::default();
-
-            let mut encoder = CacheEncoder {
-                tcx,
-                encoder,
-                type_shorthands: Default::default(),
-                predicate_shorthands: Default::default(),
-                interpret_allocs: Default::default(),
-                source_map: CachingSourceMapView::new(tcx.sess.source_map()),
-                file_to_file_index,
-                hygiene_context: &hygiene_encode_context,
-                latest_foreign_def_path_hashes,
-            };
-
-            // Encode query results.
-            let mut query_result_index = EncodedQueryResultIndex::new();
-
-            tcx.sess.time("encode_query_results", || -> FileEncodeResult {
-                let enc = &mut encoder;
-                let qri = &mut query_result_index;
-                tcx.queries.encode_query_results(tcx, enc, qri)
-            })?;
-
-            // Encode diagnostics.
-            let diagnostics_index: EncodedDiagnosticsIndex = self
-                .current_diagnostics
-                .borrow()
-                .iter()
-                .map(
-                    |(dep_node_index, diagnostics)| -> Result<_, <FileEncoder as Encoder>::Error> {
-                        let pos = AbsoluteBytePos::new(encoder.position());
-                        // Let's make sure we get the expected type here.
-                        let diagnostics: &EncodedDiagnostics = diagnostics;
-                        let dep_node_index = SerializedDepNodeIndex::new(dep_node_index.index());
-                        encoder.encode_tagged(dep_node_index, diagnostics)?;
-
-                        Ok((dep_node_index, pos))
-                    },
-                )
-                .collect::<Result<_, _>>()?;
-
-            let interpret_alloc_index = {
-                let mut interpret_alloc_index = Vec::new();
-                let mut n = 0;
-                loop {
-                    let new_n = encoder.interpret_allocs.len();
-                    // If we have found new IDs, serialize those too.
-                    if n == new_n {
-                        // Otherwise, abort.
-                        break;
-                    }
-                    interpret_alloc_index.reserve(new_n - n);
-                    for idx in n..new_n {
-                        let id = encoder.interpret_allocs[idx];
-                        let pos = encoder.position() as u32;
-                        interpret_alloc_index.push(pos);
-                        interpret::specialized_encode_alloc_id(&mut encoder, tcx, id)?;
-                    }
-                    n = new_n;
-                }
-                interpret_alloc_index
-            };
-
-            let mut syntax_contexts = FxHashMap::default();
-            let mut expn_data = UnhashMap::default();
-            let mut foreign_expn_data = UnhashMap::default();
-
-            // Encode all hygiene data (`SyntaxContextData` and `ExpnData`) from the current
-            // session.
-
-            hygiene_encode_context.encode(
-                &mut encoder,
-                |encoder, index, ctxt_data| -> FileEncodeResult {
-                    let pos = AbsoluteBytePos::new(encoder.position());
-                    encoder.encode_tagged(TAG_SYNTAX_CONTEXT, ctxt_data)?;
-                    syntax_contexts.insert(index, pos);
-                    Ok(())
-                },
-                |encoder, expn_id, data, hash| -> FileEncodeResult {
-                    if expn_id.krate == LOCAL_CRATE {
-                        let pos = AbsoluteBytePos::new(encoder.position());
-                        encoder.encode_tagged(TAG_EXPN_DATA, data)?;
-                        expn_data.insert(hash, pos);
-                    } else {
-                        foreign_expn_data.insert(hash, expn_id.local_id.as_u32());
-                    }
-                    Ok(())
-                },
-            )?;
-
-            let foreign_def_path_hashes =
-                std::mem::take(&mut encoder.latest_foreign_def_path_hashes);
-
-            // `Encode the file footer.
-            let footer_pos = encoder.position() as u64;
-            encoder.encode_tagged(
-                TAG_FILE_FOOTER,
-                &Footer {
-                    file_index_to_stable_id,
-                    query_result_index,
-                    diagnostics_index,
-                    interpret_alloc_index,
-                    syntax_contexts,
-                    expn_data,
-                    foreign_expn_data,
-                    foreign_def_path_hashes,
-                },
-            )?;
-
-            // Encode the position of the footer as the last 8 bytes of the
-            // file so we know where to look for it.
-            IntEncodedWithFixedSize(footer_pos).encode(encoder.encoder)?;
-
-            // DO NOT WRITE ANYTHING TO THE ENCODER AFTER THIS POINT! The address
-            // of the footer must be the last thing in the data stream.
-
-            Ok(())
-        })
-    }
-
-    /// Loads a diagnostic emitted during the previous compilation session.
-    pub fn load_diagnostics(
-        &self,
-        tcx: TyCtxt<'_>,
-        dep_node_index: SerializedDepNodeIndex,
-    ) -> Vec<Diagnostic> {
-        let diagnostics: Option<EncodedDiagnostics> =
-            self.load_indexed(tcx, dep_node_index, &self.prev_diagnostics_index, "diagnostics");
-
-        diagnostics.unwrap_or_default()
-    }
-
-    /// Stores a diagnostic emitted during the current compilation session.
-    /// Anything stored like this will be available via `load_diagnostics` in
-    /// the next compilation session.
-    #[inline(never)]
-    #[cold]
-    pub fn store_diagnostics(
-        &self,
-        dep_node_index: DepNodeIndex,
-        diagnostics: ThinVec<Diagnostic>,
-    ) {
-        let mut current_diagnostics = self.current_diagnostics.borrow_mut();
-        let prev = current_diagnostics.insert(dep_node_index, diagnostics.into());
-        debug_assert!(prev.is_none());
-    }
-
-    fn get_raw_def_id(&self, hash: &DefPathHash) -> Option<RawDefId> {
-        self.foreign_def_path_hashes.get(hash).copied()
-    }
-
-    fn try_remap_cnum(&self, tcx: TyCtxt<'_>, stable_crate_id: StableCrateId) -> Option<CrateNum> {
-        let cnum_map = self.cnum_map.get_or_init(|| Self::compute_cnum_map(tcx));
-        debug!("try_remap_cnum({:?}): cnum_map={:?}", stable_crate_id, cnum_map);
-
-        cnum_map.get(&stable_crate_id).copied()
-    }
-
-    pub(crate) fn store_foreign_def_id_hash(&self, def_id: DefId, hash: DefPathHash) {
-        // We may overwrite an existing entry, but it will have the same value,
-        // so it's fine
-        self.latest_foreign_def_path_hashes
-            .lock()
-            .insert(hash, RawDefId { krate: def_id.krate.as_u32(), index: def_id.index.as_u32() });
-    }
-
-    /// If the given `dep_node`'s hash still exists in the current compilation,
-    /// and its current `DefId` is foreign, calls `store_foreign_def_id` with it.
-    ///
-    /// Normally, `store_foreign_def_id_hash` can be called directly by
-    /// the dependency graph when we construct a `DepNode`. However,
-    /// when we re-use a deserialized `DepNode` from the previous compilation
-    /// session, we only have the `DefPathHash` available. This method is used
-    /// to that any `DepNode` that we re-use has a `DefPathHash` -> `RawId` written
-    /// out for usage in the next compilation session.
-    pub fn register_reused_dep_node(&self, tcx: TyCtxt<'tcx>, dep_node: &DepNode) {
-        // For reused dep nodes, we only need to store the mapping if the node
-        // is one whose query key we can reconstruct from the hash. We use the
-        // mapping to aid that reconstruction in the next session. While we also
-        // use it to decode `DefId`s we encoded in the cache as `DefPathHashes`,
-        // they're already registered during `DefId` encoding.
-        if dep_node.kind.can_reconstruct_query_key() {
-            let hash = DefPathHash(dep_node.hash.into());
-
-            // We can't simply copy the `RawDefId` from `foreign_def_path_hashes` to
-            // `latest_foreign_def_path_hashes`, since the `RawDefId` might have
-            // changed in the current compilation session (e.g. we've added/removed crates,
-            // or added/removed definitions before/after the target definition).
-            if let Some(def_id) = self.def_path_hash_to_def_id(tcx, hash) {
-                if !def_id.is_local() {
-                    self.store_foreign_def_id_hash(def_id, hash);
-                }
-            }
-        }
-    }
-
-    /// Returns the cached query result if there is something in the cache for
-    /// the given `SerializedDepNodeIndex`; otherwise returns `None`.
-    pub fn try_load_query_result<'tcx, T>(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        dep_node_index: SerializedDepNodeIndex,
-    ) -> Option<T>
-    where
-        T: for<'a> Decodable<CacheDecoder<'a, 'tcx>>,
-    {
-        self.load_indexed(tcx, dep_node_index, &self.query_result_index, "query result")
-    }
-
-    /// Stores a diagnostic emitted during computation of an anonymous query.
-    /// Since many anonymous queries can share the same `DepNode`, we aggregate
-    /// them -- as opposed to regular queries where we assume that there is a
-    /// 1:1 relationship between query-key and `DepNode`.
-    #[inline(never)]
-    #[cold]
-    pub fn store_diagnostics_for_anon_node(
-        &self,
-        dep_node_index: DepNodeIndex,
-        diagnostics: ThinVec<Diagnostic>,
-    ) {
-        let mut current_diagnostics = self.current_diagnostics.borrow_mut();
-
-        let x = current_diagnostics.entry(dep_node_index).or_default();
-
-        x.extend(Into::<Vec<_>>::into(diagnostics));
-    }
-
-    fn load_indexed<'tcx, T>(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        dep_node_index: SerializedDepNodeIndex,
-        index: &FxHashMap<SerializedDepNodeIndex, AbsoluteBytePos>,
-        debug_tag: &'static str,
-    ) -> Option<T>
-    where
-        T: for<'a> Decodable<CacheDecoder<'a, 'tcx>>,
-    {
-        let pos = index.get(&dep_node_index).cloned()?;
-
-        self.with_decoder(tcx, pos, |decoder| match decode_tagged(decoder, dep_node_index) {
-            Ok(v) => Some(v),
-            Err(e) => bug!("could not decode cached {}: {}", debug_tag, e),
-        })
-    }
-
-    fn with_decoder<'a, 'tcx, T, F: FnOnce(&mut CacheDecoder<'sess, 'tcx>) -> T>(
-        &'sess self,
-        tcx: TyCtxt<'tcx>,
-        pos: AbsoluteBytePos,
-        f: F,
-    ) -> T
-    where
-        T: Decodable<CacheDecoder<'a, 'tcx>>,
-    {
-        let cnum_map = self.cnum_map.get_or_init(|| Self::compute_cnum_map(tcx));
-
-        let mut decoder = CacheDecoder {
-            tcx,
-            opaque: opaque::Decoder::new(&self.serialized_data[..], pos.to_usize()),
-            source_map: self.source_map,
-            cnum_map,
-            file_index_to_file: &self.file_index_to_file,
-            file_index_to_stable_id: &self.file_index_to_stable_id,
-            alloc_decoding_session: self.alloc_decoding_state.new_decoding_session(),
-            syntax_contexts: &self.syntax_contexts,
-            expn_data: &self.expn_data,
-            foreign_expn_data: &self.foreign_expn_data,
-            hygiene_context: &self.hygiene_context,
-        };
-        f(&mut decoder)
-    }
-
-    // This function builds mapping from previous-session-`CrateNum` to
-    // current-session-`CrateNum`. There might be `CrateNum`s from the previous
-    // `Session` that don't occur in the current one. For these, the mapping
-    // maps to None.
-    fn compute_cnum_map(tcx: TyCtxt<'_>) -> UnhashMap<StableCrateId, CrateNum> {
-        tcx.dep_graph.with_ignore(|| {
-            tcx.crates(())
-                .iter()
-                .chain(std::iter::once(&LOCAL_CRATE))
-                .map(|&cnum| {
-                    let hash = tcx.def_path_hash(cnum.as_def_id()).stable_crate_id();
-                    (hash, cnum)
-                })
-                .collect()
-        })
-    }
-
-    /// Converts a `DefPathHash` to its corresponding `DefId` in the current compilation
-    /// session, if it still exists. This is used during incremental compilation to
-    /// turn a deserialized `DefPathHash` into its current `DefId`.
-    pub(crate) fn def_path_hash_to_def_id(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        hash: DefPathHash,
-    ) -> Option<DefId> {
-        let mut cache = self.def_path_hash_to_def_id_cache.lock();
-        match cache.entry(hash) {
-            Entry::Occupied(e) => *e.get(),
-            Entry::Vacant(e) => {
-                debug!("def_path_hash_to_def_id({:?})", hash);
-                // Check if the `DefPathHash` corresponds to a definition in the current
-                // crate
-                if let Some(def_id) =
-                    tcx.untracked_resolutions.definitions.local_def_path_hash_to_def_id(hash)
-                {
-                    let def_id = def_id.to_def_id();
-                    e.insert(Some(def_id));
-                    return Some(def_id);
-                }
-                // This `raw_def_id` represents the `DefId` of this `DefPathHash` in
-                // the *previous* compliation session. The `DefPathHash` includes the
-                // owning crate, so if the corresponding definition still exists in the
-                // current compilation session, the crate is guaranteed to be the same
-                // (otherwise, we would compute a different `DefPathHash`).
-                let raw_def_id = self.get_raw_def_id(&hash)?;
-                debug!("def_path_hash_to_def_id({:?}): raw_def_id = {:?}", hash, raw_def_id);
-                // If the owning crate no longer exists, the corresponding definition definitely
-                // no longer exists.
-                let krate = self.try_remap_cnum(tcx, hash.stable_crate_id())?;
-                debug!("def_path_hash_to_def_id({:?}): krate = {:?}", hash, krate);
-                // If our `DefPathHash` corresponded to a definition in the local crate,
-                // we should have either found it in `local_def_path_hash_to_def_id`, or
-                // never attempted to load it in the first place. Any query result or `DepNode`
-                // that references a local `DefId` should depend on some HIR-related `DepNode`.
-                // If a local definition is removed/modified such that its old `DefPathHash`
-                // no longer has a corresponding definition, that HIR-related `DepNode` should
-                // end up red. This should prevent us from ever calling
-                // `tcx.def_path_hash_to_def_id`, since we'll end up recomputing any
-                // queries involved.
-                debug_assert_ne!(krate, LOCAL_CRATE);
-                // Try to find a definition in the current session, using the previous `DefIndex`
-                // as an initial guess.
-                let opt_def_id = tcx.untracked_resolutions.cstore.def_path_hash_to_def_id(
-                    krate,
-                    raw_def_id.index,
-                    hash,
-                );
-                debug!("def_path_to_def_id({:?}): opt_def_id = {:?}", hash, opt_def_id);
-                e.insert(opt_def_id);
-                opt_def_id
-            }
-        }
-    }
-}
-
-//- DECODING -------------------------------------------------------------------
-
-/// A decoder that can read from the incremental compilation cache. It is similar to the one
-/// we use for crate metadata decoding in that it can rebase spans and eventually
-/// will also handle things that contain `Ty` instances.
-pub struct CacheDecoder<'a, 'tcx> {
-    tcx: TyCtxt<'tcx>,
-    opaque: opaque::Decoder<'a>,
-    source_map: &'a SourceMap,
-    cnum_map: &'a UnhashMap<StableCrateId, CrateNum>,
-    file_index_to_file: &'a Lock<FxHashMap<SourceFileIndex, Lrc<SourceFile>>>,
-    file_index_to_stable_id: &'a FxHashMap<SourceFileIndex, EncodedSourceFileId>,
-    alloc_decoding_session: AllocDecodingSession<'a>,
-    syntax_contexts: &'a FxHashMap<u32, AbsoluteBytePos>,
-    expn_data: &'a UnhashMap<ExpnHash, AbsoluteBytePos>,
-    foreign_expn_data: &'a UnhashMap<ExpnHash, u32>,
-    hygiene_context: &'a HygieneDecodeContext,
-}
-
-impl<'a, 'tcx> CacheDecoder<'a, 'tcx> {
-    fn file_index_to_file(&self, index: SourceFileIndex) -> Lrc<SourceFile> {
-        let CacheDecoder {
-            ref file_index_to_file,
-            ref file_index_to_stable_id,
-            ref source_map,
-            ref cnum_map,
-            ..
-        } = *self;
-
-        file_index_to_file
-            .borrow_mut()
-            .entry(index)
-            .or_insert_with(|| {
-                let stable_id = file_index_to_stable_id[&index].translate(cnum_map);
-                source_map
-                    .source_file_by_stable_id(stable_id)
-                    .expect("failed to lookup `SourceFile` in new context")
-            })
-            .clone()
-    }
-}
-
-trait DecoderWithPosition: Decoder {
-    fn position(&self) -> usize;
-}
-
-impl<'a> DecoderWithPosition for opaque::Decoder<'a> {
-    fn position(&self) -> usize {
-        self.position()
-    }
-}
-
-impl<'a, 'tcx> DecoderWithPosition for CacheDecoder<'a, 'tcx> {
-    fn position(&self) -> usize {
-        self.opaque.position()
-    }
-}
-
-// Decodes something that was encoded with `encode_tagged()` and verify that the
-// tag matches and the correct amount of bytes was read.
-fn decode_tagged<D, T, V>(decoder: &mut D, expected_tag: T) -> Result<V, D::Error>
-where
-    T: Decodable<D> + Eq + std::fmt::Debug,
-    V: Decodable<D>,
-    D: DecoderWithPosition,
-{
-    let start_pos = decoder.position();
-
-    let actual_tag = T::decode(decoder)?;
-    assert_eq!(actual_tag, expected_tag);
-    let value = V::decode(decoder)?;
-    let end_pos = decoder.position();
-
-    let expected_len: u64 = Decodable::decode(decoder)?;
-    assert_eq!((end_pos - start_pos) as u64, expected_len);
-
-    Ok(value)
-}
-
-impl<'a, 'tcx> TyDecoder<'tcx> for CacheDecoder<'a, 'tcx> {
-    const CLEAR_CROSS_CRATE: bool = false;
-
-    #[inline]
-    fn tcx(&self) -> TyCtxt<'tcx> {
-        self.tcx
-    }
-
-    #[inline]
-    fn position(&self) -> usize {
-        self.opaque.position()
-    }
-
-    #[inline]
-    fn peek_byte(&self) -> u8 {
-        self.opaque.data[self.opaque.position()]
-    }
-
-    fn cached_ty_for_shorthand<F>(
-        &mut self,
-        shorthand: usize,
-        or_insert_with: F,
-    ) -> Result<Ty<'tcx>, Self::Error>
-    where
-        F: FnOnce(&mut Self) -> Result<Ty<'tcx>, Self::Error>,
-    {
-        let tcx = self.tcx();
-
-        let cache_key = ty::CReaderCacheKey { cnum: None, pos: shorthand };
-
-        if let Some(&ty) = tcx.ty_rcache.borrow().get(&cache_key) {
-            return Ok(ty);
-        }
-
-        let ty = or_insert_with(self)?;
-        // This may overwrite the entry, but it should overwrite with the same value.
-        tcx.ty_rcache.borrow_mut().insert_same(cache_key, ty);
-        Ok(ty)
-    }
-
-    fn with_position<F, R>(&mut self, pos: usize, f: F) -> R
-    where
-        F: FnOnce(&mut Self) -> R,
-    {
-        debug_assert!(pos < self.opaque.data.len());
-
-        let new_opaque = opaque::Decoder::new(self.opaque.data, pos);
-        let old_opaque = mem::replace(&mut self.opaque, new_opaque);
-        let r = f(self);
-        self.opaque = old_opaque;
-        r
-    }
-
-    fn decode_alloc_id(&mut self) -> Result<interpret::AllocId, Self::Error> {
-        let alloc_decoding_session = self.alloc_decoding_session;
-        alloc_decoding_session.decode_alloc_id(self)
-    }
-}
-
-crate::implement_ty_decoder!(CacheDecoder<'a, 'tcx>);
-
-// This ensures that the `Decodable<opaque::Decoder>::decode` specialization for `Vec<u8>` is used
-// when a `CacheDecoder` is passed to `Decodable::decode`. Unfortunately, we have to manually opt
-// into specializations this way, given how `CacheDecoder` and the decoding traits currently work.
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for Vec<u8> {
-    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        Decodable::decode(&mut d.opaque)
-    }
-}
-
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for SyntaxContext {
-    fn decode(decoder: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        let syntax_contexts = decoder.syntax_contexts;
-        rustc_span::hygiene::decode_syntax_context(decoder, decoder.hygiene_context, |this, id| {
-            // This closure is invoked if we haven't already decoded the data for the `SyntaxContext` we are deserializing.
-            // We look up the position of the associated `SyntaxData` and decode it.
-            let pos = syntax_contexts.get(&id).unwrap();
-            this.with_position(pos.to_usize(), |decoder| {
-                let data: SyntaxContextData = decode_tagged(decoder, TAG_SYNTAX_CONTEXT)?;
-                Ok(data)
-            })
-        })
-    }
-}
-
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for ExpnId {
-    fn decode(decoder: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        let hash = ExpnHash::decode(decoder)?;
-        if hash.is_root() {
-            return Ok(ExpnId::root());
-        }
-
-        if let Some(expn_id) = ExpnId::from_hash(hash) {
-            return Ok(expn_id);
-        }
-
-        let krate = decoder.cnum_map[&hash.stable_crate_id()];
-
-        let expn_id = if krate == LOCAL_CRATE {
-            // We look up the position of the associated `ExpnData` and decode it.
-            let pos = decoder
-                .expn_data
-                .get(&hash)
-                .unwrap_or_else(|| panic!("Bad hash {:?} (map {:?})", hash, decoder.expn_data));
-
-            let data: ExpnData = decoder
-                .with_position(pos.to_usize(), |decoder| decode_tagged(decoder, TAG_EXPN_DATA))?;
-            rustc_span::hygiene::register_local_expn_id(data, hash)
-        } else {
-            let index_guess = decoder.foreign_expn_data[&hash];
-            decoder.tcx.untracked_resolutions.cstore.expn_hash_to_expn_id(krate, index_guess, hash)
-        };
-
-        #[cfg(debug_assertions)]
-        {
-            use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
-            let mut hcx = decoder.tcx.create_stable_hashing_context();
-            let mut hasher = StableHasher::new();
-            hcx.while_hashing_spans(true, |hcx| expn_id.expn_data().hash_stable(hcx, &mut hasher));
-            let local_hash: u64 = hasher.finish();
-            debug_assert_eq!(hash.local_hash(), local_hash);
-        }
-
-        Ok(expn_id)
-    }
-}
-
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for Span {
-    fn decode(decoder: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        let tag: u8 = Decodable::decode(decoder)?;
-
-        if tag == TAG_PARTIAL_SPAN {
-            let ctxt = SyntaxContext::decode(decoder)?;
-            return Ok(DUMMY_SP.with_ctxt(ctxt));
-        } else {
-            debug_assert_eq!(tag, TAG_FULL_SPAN);
-        }
-
-        let file_lo_index = SourceFileIndex::decode(decoder)?;
-        let line_lo = usize::decode(decoder)?;
-        let col_lo = BytePos::decode(decoder)?;
-        let len = BytePos::decode(decoder)?;
-        let ctxt = SyntaxContext::decode(decoder)?;
-
-        let file_lo = decoder.file_index_to_file(file_lo_index);
-        let lo = file_lo.lines[line_lo - 1] + col_lo;
-        let hi = lo + len;
-
-        Ok(Span::new(lo, hi, ctxt))
-    }
-}
-
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for CrateNum {
-    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        let stable_id = StableCrateId::decode(d)?;
-        let cnum = d.cnum_map[&stable_id];
-        Ok(cnum)
-    }
-}
-
-// This impl makes sure that we get a runtime error when we try decode a
-// `DefIndex` that is not contained in a `DefId`. Such a case would be problematic
-// because we would not know how to transform the `DefIndex` to the current
-// context.
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for DefIndex {
-    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Result<DefIndex, String> {
-        Err(d.error("trying to decode `DefIndex` outside the context of a `DefId`"))
-    }
-}
-
-// Both the `CrateNum` and the `DefIndex` of a `DefId` can change in between two
-// compilation sessions. We use the `DefPathHash`, which is stable across
-// sessions, to map the old `DefId` to the new one.
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for DefId {
-    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        // Load the `DefPathHash` which is was we encoded the `DefId` as.
-        let def_path_hash = DefPathHash::decode(d)?;
-
-        // Using the `DefPathHash`, we can lookup the new `DefId`.
-        // Subtle: We only encode a `DefId` as part of a query result.
-        // If we get to this point, then all of the query inputs were green,
-        // which means that the definition with this hash is guaranteed to
-        // still exist in the current compilation session.
-        Ok(d.tcx()
-            .on_disk_cache
-            .as_ref()
-            .unwrap()
-            .def_path_hash_to_def_id(d.tcx(), def_path_hash)
-            .unwrap())
-    }
-}
-
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx FxHashSet<LocalDefId> {
-    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        RefDecodable::decode(d)
-    }
-}
-
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>>
-    for &'tcx IndexVec<mir::Promoted, mir::Body<'tcx>>
-{
-    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        RefDecodable::decode(d)
-    }
-}
-
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx [mir::abstract_const::Node<'tcx>] {
-    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        RefDecodable::decode(d)
-    }
-}
-
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx [(ty::Predicate<'tcx>, Span)] {
-    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        RefDecodable::decode(d)
-    }
-}
-
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx [rustc_ast::InlineAsmTemplatePiece] {
-    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        RefDecodable::decode(d)
-    }
-}
-
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx [Span] {
-    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        RefDecodable::decode(d)
-    }
-}
-
-//- ENCODING -------------------------------------------------------------------
-
-pub trait OpaqueEncoder: Encoder {
-    fn position(&self) -> usize;
-}
-
-impl OpaqueEncoder for FileEncoder {
-    #[inline]
-    fn position(&self) -> usize {
-        FileEncoder::position(self)
-    }
-}
-
-/// An encoder that can write to the incremental compilation cache.
-pub struct CacheEncoder<'a, 'tcx, E: OpaqueEncoder> {
-    tcx: TyCtxt<'tcx>,
-    encoder: &'a mut E,
-    type_shorthands: FxHashMap<Ty<'tcx>, usize>,
-    predicate_shorthands: FxHashMap<ty::PredicateKind<'tcx>, usize>,
-    interpret_allocs: FxIndexSet<interpret::AllocId>,
-    source_map: CachingSourceMapView<'tcx>,
-    file_to_file_index: FxHashMap<*const SourceFile, SourceFileIndex>,
-    hygiene_context: &'a HygieneEncodeContext,
-    latest_foreign_def_path_hashes: UnhashMap<DefPathHash, RawDefId>,
-}
-
-impl<'a, 'tcx, E> CacheEncoder<'a, 'tcx, E>
-where
-    E: 'a + OpaqueEncoder,
-{
-    fn source_file_index(&mut self, source_file: Lrc<SourceFile>) -> SourceFileIndex {
-        self.file_to_file_index[&(&*source_file as *const SourceFile)]
-    }
-
-    /// Encode something with additional information that allows to do some
-    /// sanity checks when decoding the data again. This method will first
-    /// encode the specified tag, then the given value, then the number of
-    /// bytes taken up by tag and value. On decoding, we can then verify that
-    /// we get the expected tag and read the expected number of bytes.
-    fn encode_tagged<T: Encodable<Self>, V: Encodable<Self>>(
-        &mut self,
-        tag: T,
-        value: &V,
-    ) -> Result<(), E::Error> {
-        let start_pos = self.position();
-
-        tag.encode(self)?;
-        value.encode(self)?;
-
-        let end_pos = self.position();
-        ((end_pos - start_pos) as u64).encode(self)
-    }
-}
-
-impl<'a, 'tcx, E> Encodable<CacheEncoder<'a, 'tcx, E>> for SyntaxContext
-where
-    E: 'a + OpaqueEncoder,
-{
-    fn encode(&self, s: &mut CacheEncoder<'a, 'tcx, E>) -> Result<(), E::Error> {
-        rustc_span::hygiene::raw_encode_syntax_context(*self, s.hygiene_context, s)
-    }
-}
-
-impl<'a, 'tcx, E> Encodable<CacheEncoder<'a, 'tcx, E>> for ExpnId
-where
-    E: 'a + OpaqueEncoder,
-{
-    fn encode(&self, s: &mut CacheEncoder<'a, 'tcx, E>) -> Result<(), E::Error> {
-        s.hygiene_context.schedule_expn_data_for_encoding(*self);
-        self.expn_hash().encode(s)
-    }
-}
-
-impl<'a, 'tcx, E> Encodable<CacheEncoder<'a, 'tcx, E>> for Span
-where
-    E: 'a + OpaqueEncoder,
-{
-    fn encode(&self, s: &mut CacheEncoder<'a, 'tcx, E>) -> Result<(), E::Error> {
-        let span_data = self.data();
-        if self.is_dummy() {
-            TAG_PARTIAL_SPAN.encode(s)?;
-            return span_data.ctxt.encode(s);
-        }
-
-        let pos = s.source_map.byte_pos_to_line_and_col(span_data.lo);
-        let partial_span = match &pos {
-            Some((file_lo, _, _)) => !file_lo.contains(span_data.hi),
-            None => true,
-        };
-
-        if partial_span {
-            TAG_PARTIAL_SPAN.encode(s)?;
-            return span_data.ctxt.encode(s);
-        }
-
-        let (file_lo, line_lo, col_lo) = pos.unwrap();
-
-        let len = span_data.hi - span_data.lo;
-
-        let source_file_index = s.source_file_index(file_lo);
-
-        TAG_FULL_SPAN.encode(s)?;
-        source_file_index.encode(s)?;
-        line_lo.encode(s)?;
-        col_lo.encode(s)?;
-        len.encode(s)?;
-        span_data.ctxt.encode(s)
-    }
-}
-
-impl<'a, 'tcx, E> TyEncoder<'tcx> for CacheEncoder<'a, 'tcx, E>
-where
-    E: 'a + OpaqueEncoder,
-{
-    const CLEAR_CROSS_CRATE: bool = false;
-
-    fn position(&self) -> usize {
-        self.encoder.position()
-    }
-    fn type_shorthands(&mut self) -> &mut FxHashMap<Ty<'tcx>, usize> {
-        &mut self.type_shorthands
-    }
-    fn predicate_shorthands(&mut self) -> &mut FxHashMap<ty::PredicateKind<'tcx>, usize> {
-        &mut self.predicate_shorthands
-    }
-    fn encode_alloc_id(&mut self, alloc_id: &interpret::AllocId) -> Result<(), Self::Error> {
-        let (index, _) = self.interpret_allocs.insert_full(*alloc_id);
-
-        index.encode(self)
-    }
-}
-
-impl<'a, 'tcx, E> Encodable<CacheEncoder<'a, 'tcx, E>> for CrateNum
-where
-    E: 'a + OpaqueEncoder,
-{
-    fn encode(&self, s: &mut CacheEncoder<'a, 'tcx, E>) -> Result<(), E::Error> {
-        s.tcx.stable_crate_id(*self).encode(s)
-    }
-}
-
-impl<'a, 'tcx, E> Encodable<CacheEncoder<'a, 'tcx, E>> for DefId
-where
-    E: 'a + OpaqueEncoder,
-{
-    fn encode(&self, s: &mut CacheEncoder<'a, 'tcx, E>) -> Result<(), E::Error> {
-        let def_path_hash = s.tcx.def_path_hash(*self);
-        // Store additional information when we encode a foreign `DefId`,
-        // so that we can map its `DefPathHash` back to a `DefId` in the next
-        // compilation session.
-        if !self.is_local() {
-            s.latest_foreign_def_path_hashes.insert(
-                def_path_hash,
-                RawDefId { krate: self.krate.as_u32(), index: self.index.as_u32() },
-            );
-        }
-        def_path_hash.encode(s)
-    }
-}
-
-impl<'a, 'tcx, E> Encodable<CacheEncoder<'a, 'tcx, E>> for DefIndex
-where
-    E: 'a + OpaqueEncoder,
-{
-    fn encode(&self, _: &mut CacheEncoder<'a, 'tcx, E>) -> Result<(), E::Error> {
-        bug!("encoding `DefIndex` without context");
-    }
-}
-
-macro_rules! encoder_methods {
-    ($($name:ident($ty:ty);)*) => {
-        #[inline]
-        $(fn $name(&mut self, value: $ty) -> Result<(), Self::Error> {
-            self.encoder.$name(value)
-        })*
-    }
-}
-
-impl<'a, 'tcx, E> Encoder for CacheEncoder<'a, 'tcx, E>
-where
-    E: 'a + OpaqueEncoder,
-{
-    type Error = E::Error;
-
-    #[inline]
-    fn emit_unit(&mut self) -> Result<(), Self::Error> {
-        Ok(())
-    }
-
-    encoder_methods! {
-        emit_usize(usize);
-        emit_u128(u128);
-        emit_u64(u64);
-        emit_u32(u32);
-        emit_u16(u16);
-        emit_u8(u8);
-
-        emit_isize(isize);
-        emit_i128(i128);
-        emit_i64(i64);
-        emit_i32(i32);
-        emit_i16(i16);
-        emit_i8(i8);
-
-        emit_bool(bool);
-        emit_f64(f64);
-        emit_f32(f32);
-        emit_char(char);
-        emit_str(&str);
-        emit_raw_bytes(&[u8]);
-    }
-}
-
-// This ensures that the `Encodable<opaque::FileEncoder>::encode` specialization for byte slices
-// is used when a `CacheEncoder` having an `opaque::FileEncoder` is passed to `Encodable::encode`.
-// Unfortunately, we have to manually opt into specializations this way, given how `CacheEncoder`
-// and the encoding traits currently work.
-impl<'a, 'tcx> Encodable<CacheEncoder<'a, 'tcx, FileEncoder>> for [u8] {
-    fn encode(&self, e: &mut CacheEncoder<'a, 'tcx, FileEncoder>) -> FileEncodeResult {
-        self.encode(e.encoder)
-    }
-}
-
-pub fn encode_query_results<'a, 'tcx, CTX, Q>(
-    tcx: CTX,
-    encoder: &mut CacheEncoder<'a, 'tcx, FileEncoder>,
-    query_result_index: &mut EncodedQueryResultIndex,
-) -> FileEncodeResult
-where
-    CTX: QueryContext + 'tcx,
-    Q: super::QueryDescription<CTX> + super::QueryAccessors<CTX>,
-    Q::Value: Encodable<CacheEncoder<'a, 'tcx, FileEncoder>>,
-{
-    let _timer = tcx
-        .dep_context()
-        .profiler()
-        .extra_verbose_generic_activity("encode_query_results_for", std::any::type_name::<Q>());
-
-    assert!(Q::query_state(tcx).all_inactive());
-    let cache = Q::query_cache(tcx);
-    let mut res = Ok(());
-    cache.iter_results(&mut |key, value, dep_node| {
-        if res.is_err() {
-            return;
-        }
-        if Q::cache_on_disk(tcx, &key, Some(value)) {
-            let dep_node = SerializedDepNodeIndex::new(dep_node.index());
-
-            // Record position of the cache entry.
-            query_result_index.push((dep_node, AbsoluteBytePos::new(encoder.encoder.position())));
-
-            // Encode the type check tables with the `SerializedDepNodeIndex`
-            // as tag.
-            match encoder.encode_tagged(dep_node, value) {
-                Ok(()) => {}
-                Err(e) => {
-                    res = Err(e);
-                }
-            }
-        }
-    });
-
-    res
-}