Replace custom_encodable with encodable.

By default, `newtype_index!` types get a default `Encodable`/`Decodable`
impl. You can opt out of this with `custom_encodable`. Opting out is the
opposite to how Rust normally works with autogenerated (derived) impls.

This commit inverts the behaviour, replacing `custom_encodable` with
`encodable` which opts into the default `Encodable`/`Decodable` impl.
Only 23 of the 59 `newtype_index!` occurrences need `encodable`.

Even better, there were eight crates with a dependency on
`rustc_serialize` just from unused default `Encodable`/`Decodable`
impls. This commit removes that dependency from those eight crates.

Cargo.lock

@@ -3524,7 +3524,6 @@ dependencies = [
  "rustc_macros",
  "rustc_middle",
  "rustc_mir_dataflow",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -3935,7 +3934,6 @@ dependencies = [
  "rustc_lint",
  "rustc_macros",
  "rustc_middle",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -3998,7 +3996,6 @@ dependencies = [
  "rustc_index",
  "rustc_macros",
  "rustc_middle",
- "rustc_serialize",
  "rustc_span",
  "rustc_target",
  "smallvec",
@@ -4216,7 +4213,6 @@ dependencies = [
  "rustc_infer",
  "rustc_macros",
  "rustc_middle",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -4240,7 +4236,6 @@ dependencies = [
  "rustc_index",
  "rustc_macros",
  "rustc_middle",
- "rustc_serialize",
  "rustc_span",
  "rustc_target",
  "smallvec",
@@ -4267,7 +4262,6 @@ dependencies = [
  "rustc_middle",
  "rustc_mir_build",
  "rustc_mir_dataflow",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -4341,7 +4335,6 @@ dependencies = [
  "rustc_lexer",
  "rustc_macros",
  "rustc_middle",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -4565,7 +4558,6 @@ dependencies = [
  "rustc_middle",
  "rustc_parse_format",
  "rustc_query_system",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",

compiler/rustc_ast/src/ast.rs

@@ -2574,7 +2574,6 @@ pub enum AttrStyle {
 }
 
 rustc_index::newtype_index! {
-    #[custom_encodable]
     #[debug_format = "AttrId({})"]
     pub struct AttrId {}
 }

compiler/rustc_ast/src/node_id.rs

@@ -8,6 +8,7 @@
     /// This is later turned into [`DefId`] and `HirId` for the HIR.
     ///
     /// [`DefId`]: rustc_span::def_id::DefId
+    #[encodable]
     #[debug_format = "NodeId({})"]
     pub struct NodeId {
         /// The [`NodeId`] used to represent the root of the crate.

compiler/rustc_borrowck/Cargo.toml

@@ -19,7 +19,6 @@ rustc_lexer = { path = "../rustc_lexer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
 rustc_mir_dataflow = { path = "../rustc_mir_dataflow" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

@@ -189,8 +189,6 @@ fn make_filenames_buffer(&self, tcx: TyCtxt<'_>) -> Vec<u8> {
 }
 
 rustc_index::newtype_index! {
-    // Tell the newtype macro to not generate `Encode`/`Decode` impls.
-    #[custom_encodable]
     struct LocalFileId {}
 }
 

compiler/rustc_hir/src/hir_id.rs

@@ -154,6 +154,7 @@ fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
     /// an "item-like" to something else can be implemented by a `Vec` instead of a
     /// tree or hash map.
     #[derive(HashStable_Generic)]
+    #[encodable]
     pub struct ItemLocalId {}
 }
 

compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs

@@ -198,7 +198,6 @@ fn check_item(&mut self, id: hir::ItemId) {
             // entire graph when there are many connected regions.
 
             rustc_index::newtype_index! {
-                #[custom_encodable]
                 pub struct RegionId {}
             }
 

compiler/rustc_hir_typeck/Cargo.toml

@@ -19,7 +19,6 @@ rustc_infer = { path = "../rustc_infer" }
 rustc_lint = { path = "../rustc_lint" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }

compiler/rustc_index_macros/src/newtype.rs

@@ -22,7 +22,7 @@ fn parse(input: ParseStream<'_>) -> Result<Self> {
         let mut debug_format: Option<Lit> = None;
         let mut max = None;
         let mut consts = Vec::new();
-        let mut encodable = true;
+        let mut encodable = false;
         let mut ord = true;
         let mut gate_rustc_only = quote! {};
         let mut gate_rustc_only_cfg = quote! { all() };
@@ -34,8 +34,8 @@ fn parse(input: ParseStream<'_>) -> Result<Self> {
                     gate_rustc_only_cfg = quote! { feature = "nightly" };
                     false
                 }
-                "custom_encodable" => {
-                    encodable = false;
+                "encodable" => {
+                    encodable = true;
                     false
                 }
                 "no_ord_impl" => {

compiler/rustc_infer/Cargo.toml

@@ -15,7 +15,6 @@ rustc_hir = { path = "../rustc_hir" }
 rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
 smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }

compiler/rustc_lint/src/levels.rs

@@ -56,7 +56,6 @@ struct LintLevelSets {
 }
 
 rustc_index::newtype_index! {
-    #[custom_encodable] // we don't need encoding
     struct LintStackIndex {
         const COMMAND_LINE = 0;
     }

compiler/rustc_middle/src/middle/region.rs

@@ -148,6 +148,7 @@ pub enum ScopeData {
     /// * The subscope with `first_statement_index == 1` is scope of `c`,
     ///   and thus does not include EXPR_2, but covers the `...`.
     #[derive(HashStable)]
+    #[encodable]
     pub struct FirstStatementIndex {}
 }
 

compiler/rustc_middle/src/mir/coverage.rs

@@ -17,6 +17,7 @@
     /// Note that LLVM handles counter IDs as `uint32_t`, so there is no need
     /// to use a larger representation on the Rust side.
     #[derive(HashStable)]
+    #[encodable]
     #[max = 0xFFFF_FFFF]
     #[debug_format = "CounterId({})"]
     pub struct CounterId {}
@@ -37,6 +38,7 @@ impl CounterId {
     /// Note that LLVM handles expression IDs as `uint32_t`, so there is no need
     /// to use a larger representation on the Rust side.
     #[derive(HashStable)]
+    #[encodable]
     #[max = 0xFFFF_FFFF]
     #[debug_format = "ExpressionId({})"]
     pub struct ExpressionId {}

compiler/rustc_middle/src/mir/mod.rs

@@ -736,6 +736,7 @@ pub fn outermost(span: Span) -> Self {
 
 rustc_index::newtype_index! {
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "_{}"]
     pub struct Local {
         const RETURN_PLACE = 0;
@@ -1171,6 +1172,7 @@ pub struct VarDebugInfo<'tcx> {
     /// [`CriticalCallEdges`]: ../../rustc_const_eval/transform/add_call_guards/enum.AddCallGuards.html#variant.CriticalCallEdges
     /// [guide-mir]: https://rustc-dev-guide.rust-lang.org/mir/
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "bb{}"]
     pub struct BasicBlock {
         const START_BLOCK = 0;
@@ -1305,6 +1307,7 @@ pub fn is_empty_unreachable(&self) -> bool {
 
 rustc_index::newtype_index! {
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "scope[{}]"]
     pub struct SourceScope {
         const OUTERMOST_SOURCE_SCOPE = 0;
@@ -1533,6 +1536,7 @@ pub(crate) fn variant(
 
 rustc_index::newtype_index! {
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "promoted[{}]"]
     pub struct Promoted {}
 }

compiler/rustc_middle/src/mir/query.rs

@@ -132,6 +132,7 @@ pub struct UnsafetyCheckResult {
 
 rustc_index::newtype_index! {
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "_{}"]
     pub struct CoroutineSavedLocal {}
 }

compiler/rustc_middle/src/ty/sty.rs

@@ -1612,6 +1612,7 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 rustc_index::newtype_index! {
     /// A **region** (lifetime) **v**ariable **ID**.
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "'?{}"]
     pub struct RegionVid {}
 }

compiler/rustc_middle/src/ty/typeck_results.rs

@@ -578,6 +578,7 @@ pub fn extend(
 
 rustc_index::newtype_index! {
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "UserType({})"]
     pub struct UserTypeAnnotationIndex {
         const START_INDEX = 0;

compiler/rustc_mir_build/Cargo.toml

@@ -17,7 +17,6 @@ rustc_index = { path = "../rustc_index" }
 rustc_infer = { path = "../rustc_infer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }

compiler/rustc_mir_dataflow/Cargo.toml

@@ -16,7 +16,6 @@ rustc_hir = { path = "../rustc_hir" }
 rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
 smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }

compiler/rustc_mir_transform/Cargo.toml

@@ -20,7 +20,6 @@ rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
 rustc_mir_build = { path = "../rustc_mir_build" }
 rustc_mir_dataflow = { path = "../rustc_mir_dataflow" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }

compiler/rustc_passes/Cargo.toml

@@ -19,7 +19,6 @@ rustc_index = { path = "../rustc_index" }
 rustc_lexer = { path = "../rustc_lexer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }

compiler/rustc_query_system/src/dep_graph/serialized.rs

@@ -54,6 +54,7 @@
 // unused so that we can store multiple index types in `CompressedHybridIndex`,
 // and use those bits to encode which index type it contains.
 rustc_index::newtype_index! {
+    #[encodable]
     #[max = 0x7FFF_FFFF]
     pub struct SerializedDepNodeIndex {}
 }

compiler/rustc_span/src/def_id.rs

@@ -13,7 +13,6 @@
     indexmap::IndexMap<StableCrateId, CrateNum, BuildHasherDefault<Unhasher>>;
 
 rustc_index::newtype_index! {
-    #[custom_encodable]
     #[debug_format = "crate{}"]
     pub struct CrateNum {}
 }
@@ -213,7 +212,6 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
     /// A DefIndex is an index into the hir-map for a crate, identifying a
     /// particular definition. It should really be considered an interned
     /// shorthand for a particular DefPath.
-    #[custom_encodable] // (only encodable in metadata)
     #[debug_format = "DefIndex({})"]
     pub struct DefIndex {
         /// The crate root is always assigned index 0 by the AST Map code,
@@ -222,6 +220,7 @@ pub struct DefIndex {
     }
 }
 
+// njn: I don't understand these
 impl<E: Encoder> Encodable<E> for DefIndex {
     default fn encode(&self, _: &mut E) {
         panic!("cannot encode `DefIndex` with `{}`", std::any::type_name::<E>());

compiler/rustc_span/src/hygiene.rs

@@ -60,7 +60,6 @@ pub struct SyntaxContextData {
 
 rustc_index::newtype_index! {
     /// A unique ID associated with a macro invocation and expansion.
-    #[custom_encodable]
     pub struct ExpnIndex {}
 }
 
@@ -80,7 +79,6 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 
 rustc_index::newtype_index! {
     /// A unique ID associated with a macro invocation and expansion.
-    #[custom_encodable]
     #[no_ord_impl]
     #[debug_format = "expn{}"]
     pub struct LocalExpnId {}

compiler/rustc_target/src/abi/mod.rs

@@ -42,6 +42,7 @@ fn to_json(&self) -> Json {
     /// `d` is `FieldIdx(1)` in `VariantIdx(1)`, and
     /// `f` is `FieldIdx(1)` in `VariantIdx(0)`.
     #[derive(HashStable_Generic)]
+    #[encodable]
     pub struct FieldIdx {}
 }
 
@@ -57,6 +58,7 @@ pub struct FieldIdx {}
     /// `struct`s, `tuples`, and `unions`s are considered to have a single variant
     /// with variant index zero, aka [`FIRST_VARIANT`].
     #[derive(HashStable_Generic)]
+    #[encodable]
     pub struct VariantIdx {
         /// Equivalent to `VariantIdx(0)`.
         const FIRST_VARIANT = 0;

compiler/rustc_trait_selection/Cargo.toml

@@ -17,7 +17,6 @@ rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
 rustc_parse_format = { path = "../rustc_parse_format" }
 rustc_query_system = { path = "../rustc_query_system" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }

compiler/rustc_type_ir/src/const_kind.rs

@@ -95,6 +95,7 @@ fn fmt<Infcx: InferCtxtLike<Interner = I>>(
 
 rustc_index::newtype_index! {
     /// A **`const`** **v**ariable **ID**.
+    #[encodable]
     #[debug_format = "?{}c"]
     #[gate_rustc_only]
     pub struct ConstVid {}
@@ -108,6 +109,7 @@ pub struct ConstVid {}
     /// relate an effect variable with a normal one, we would ICE, which can catch bugs
     /// where we are not correctly using the effect var for an effect param. Fallback
     /// is also implemented on top of having separate effect and normal const variables.
+    #[encodable]
     #[debug_format = "?{}e"]
     #[gate_rustc_only]
     pub struct EffectVid {}

compiler/rustc_type_ir/src/lib.rs

@@ -92,6 +92,7 @@
     ///
     /// [dbi]: https://en.wikipedia.org/wiki/De_Bruijn_index
     #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
+    #[encodable]
     #[debug_format = "DebruijnIndex({})"]
     #[gate_rustc_only]
     pub struct DebruijnIndex {
@@ -293,6 +294,7 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
     /// type -- an idealized representative of "types in general" that we
     /// use for checking generic functions.
     #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
+    #[encodable]
     #[debug_format = "U{}"]
     #[gate_rustc_only]
     pub struct UniverseIndex {}
@@ -335,6 +337,7 @@ pub fn cannot_name(self, other: UniverseIndex) -> bool {
 
 rustc_index::newtype_index! {
     #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
+    #[encodable]
     #[debug_format = "{}"]
     #[gate_rustc_only]
     pub struct BoundVar {}

compiler/rustc_type_ir/src/ty_kind.rs

@@ -622,6 +622,7 @@ pub enum IntVarValue {
 
 rustc_index::newtype_index! {
     /// A **ty**pe **v**ariable **ID**.
+    #[encodable]
     #[debug_format = "?{}t"]
     #[gate_rustc_only]
     pub struct TyVid {}
@@ -629,6 +630,7 @@ pub struct TyVid {}
 
 rustc_index::newtype_index! {
     /// An **int**egral (`u32`, `i32`, `usize`, etc.) type **v**ariable **ID**.
+    #[encodable]
     #[debug_format = "?{}i"]
     #[gate_rustc_only]
     pub struct IntVid {}
@@ -636,6 +638,7 @@ pub struct IntVid {}
 
 rustc_index::newtype_index! {
     /// A **float**ing-point (`f32` or `f64`) type **v**ariable **ID**.
+    #[encodable]
     #[debug_format = "?{}f"]
     #[gate_rustc_only]
     pub struct FloatVid {}