Use same FxHashMap in rustdoc-json-types and librustdoc.

The original motivation was me trying to remove the
`#![allow(rustc::default_hash_types)]`, as after #108626, we should be using
`FxHashMap` here. I then realized I should also be able to remove the
`.into_iter().collect()`, as we no longer need to convert from `FxHashMap` to `std::HashMap`.

However, this didn't work, and I got the following error

```
error[E0308]: mismatched types
   --> src/librustdoc/json/mod.rs:235:13
    |
235 |             index,
    |             ^^^^^ expected `rustc_hash::FxHasher`, found `FxHasher`
    |
    = note: `FxHasher` and `rustc_hash::FxHasher` have similar names, but are actually distinct types
note: `FxHasher` is defined in crate `rustc_hash`
   --> /cargo/registry/src/index.crates.io-6f17d22bba15001f/rustc-hash-1.1.0/src/lib.rs:60:1
note: `rustc_hash::FxHasher` is defined in crate `rustc_hash`
   --> /home/alona/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rustc-hash-1.1.0/src/lib.rs:60:1
    |
60  | pub struct FxHasher {
    | ^^^^^^^^^^^^^^^^^^^
    = note: perhaps two different versions of crate `rustc_hash` are being used?
```

This is because `librustdoc` got it's `FxHashMap` via the sysroot
`rustc-data-strucures`, whereas `rustdoc-json-types` got it via
`rustc-hash` on crates.io.

To avoid this, `rustdoc-json-types` now uses
`#![feature(rustc_private)]` to load the same version as `librustdoc`.

However, this needs to be placed behind a feature, as
`rustdoc-json-types` is also dependency of `src/tools/jsondocck`, which
means need needs to be buildable without nightly features.

Author: aDotInTheVoid

Diff for: Cargo.lock

@@ -2900,7 +2900,6 @@ dependencies = [
  "anyhow",
  "clap 4.2.1",
  "fs-err",
- "rustc-hash",
  "rustdoc-json-types",
  "serde",
  "serde_json",
@@ -5543,7 +5542,6 @@ dependencies = [
 name = "rustdoc-json-types"
 version = "0.1.0"
 dependencies = [
- "rustc-hash",
  "serde",
  "serde_json",
 ]

Diff for: src/librustdoc/Cargo.toml

@@ -13,7 +13,7 @@ itertools = "0.10.1"
 minifier = "0.2.2"
 once_cell = "1.10.0"
 regex = "1"
-rustdoc-json-types = { path = "../rustdoc-json-types" }
+rustdoc-json-types = { path = "../rustdoc-json-types", features = ["rustc_hash"] }
 serde_json = "1.0"
 serde = { version = "1.0", features = ["derive"] }
 smallvec = "1.8.1"

Diff for: src/librustdoc/json/mod.rs

@@ -228,14 +228,11 @@ impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
         let index = (*self.index).clone().into_inner();
 
         debug!("Constructing Output");
-        // This needs to be the default HashMap for compatibility with the public interface for
-        // rustdoc-json-types
-        #[allow(rustc::default_hash_types)]
         let output = types::Crate {
             root: types::Id(format!("0:0:{}", e.name(self.tcx).as_u32())),
             crate_version: self.cache.crate_version.clone(),
             includes_private: self.cache.document_private,
-            index: index.into_iter().collect(),
+            index,
             paths: self
                 .cache
                 .paths

Diff for: src/rustdoc-json-types/Cargo.toml

@@ -8,7 +8,9 @@ path = "lib.rs"
 
 [dependencies]
 serde = { version = "1.0", features = ["derive"] }
-rustc-hash = "1.1.0"
 
 [dev-dependencies]
 serde_json = "1.0"
+
+[features]
+rustc_hash = []

Diff for: src/rustdoc-json-types/lib.rs

@@ -3,7 +3,14 @@
 //! These types are the public API exposed through the `--output-format json` flag. The [`Crate`]
 //! struct is the root of the JSON blob and all other items are contained within.
 
-use rustc_hash::FxHashMap;
+#![cfg_attr(feature = "rustc_hash", feature(rustc_private))]
+#[cfg(feature = "rustc_hash")]
+extern crate rustc_hash;
+#[cfg(feature = "rustc_hash")]
+use rustc_hash::FxHashMap as HashMap;
+#[cfg(not(feature = "rustc_hash"))]
+use std::collections::HashMap;
+
 use serde::{Deserialize, Serialize};
 use std::path::PathBuf;
 
@@ -23,11 +30,11 @@ pub struct Crate {
     pub includes_private: bool,
     /// A collection of all items in the local crate as well as some external traits and their
     /// items that are referenced locally.
-    pub index: FxHashMap<Id, Item>,
+    pub index: HashMap<Id, Item>,
     /// Maps IDs to fully qualified paths and other info helpful for generating links.
-    pub paths: FxHashMap<Id, ItemSummary>,
+    pub paths: HashMap<Id, ItemSummary>,
     /// Maps `crate_id` of items to a crate name and html_root_url if it exists.
-    pub external_crates: FxHashMap<u32, ExternalCrate>,
+    pub external_crates: HashMap<u32, ExternalCrate>,
     /// A single version number to be used in the future when making backwards incompatible changes
     /// to the JSON output.
     pub format_version: u32,
@@ -79,7 +86,7 @@ pub struct Item {
     /// Some("") if there is some documentation but it is empty (EG `#[doc = ""]`).
     pub docs: Option<String>,
     /// This mapping resolves [intra-doc links](https://github.com/rust-lang/rfcs/blob/master/text/1946-intra-rustdoc-links.md) from the docstring to their IDs
-    pub links: FxHashMap<String, Id>,
+    pub links: HashMap<String, Id>,
     /// Stringified versions of the attributes on this item (e.g. `"#[inline]"`)
     pub attrs: Vec<String>,
     pub deprecation: Option<Deprecation>,

Diff for: src/tools/jsondoclint/Cargo.toml

@@ -9,7 +9,6 @@ edition = "2021"
 anyhow = "1.0.62"
 clap = { version = "4.0.15", features = ["derive"] }
 fs-err = "2.8.1"
-rustc-hash = "1.1.0"
 rustdoc-json-types = { version = "0.1.0", path = "../../rustdoc-json-types" }
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0.85"

Diff for: src/tools/jsondoclint/src/validator/tests.rs

@@ -1,5 +1,5 @@
-use rustc_hash::FxHashMap;
 use rustdoc_json_types::{Crate, Item, ItemKind, ItemSummary, Visibility, FORMAT_VERSION};
+use std::collections::HashMap;
 
 use crate::json_find::SelectorPart;
 
@@ -26,7 +26,7 @@ fn errors_on_missing_links() {
         root: id("0"),
         crate_version: None,
         includes_private: false,
-        index: FxHashMap::from_iter([(
+        index: HashMap::from_iter([(
             id("0"),
             Item {
                 name: Some("root".to_owned()),
@@ -35,7 +35,7 @@ fn errors_on_missing_links() {
                 span: None,
                 visibility: Visibility::Public,
                 docs: None,
-                links: FxHashMap::from_iter([("Not Found".to_owned(), id("1"))]),
+                links: HashMap::from_iter([("Not Found".to_owned(), id("1"))]),
                 attrs: vec![],
                 deprecation: None,
                 inner: ItemEnum::Module(Module {
@@ -45,8 +45,8 @@ fn errors_on_missing_links() {
                 }),
             },
         )]),
-        paths: FxHashMap::default(),
-        external_crates: FxHashMap::default(),
+        paths: HashMap::default(),
+        external_crates: HashMap::default(),
         format_version: rustdoc_json_types::FORMAT_VERSION,
     };
 
@@ -72,7 +72,7 @@ fn errors_on_local_in_paths_and_not_index() {
         root: id("0:0:1572"),
         crate_version: None,
         includes_private: false,
-        index: FxHashMap::from_iter([
+        index: HashMap::from_iter([
             (
                 id("0:0:1572"),
                 Item {
@@ -82,7 +82,7 @@ fn errors_on_local_in_paths_and_not_index() {
                     span: None,
                     visibility: Visibility::Public,
                     docs: None,
-                    links: FxHashMap::from_iter([(("prim@i32".to_owned(), id("0:1:1571")))]),
+                    links: HashMap::from_iter([(("prim@i32".to_owned(), id("0:1:1571")))]),
                     attrs: Vec::new(),
                     deprecation: None,
                     inner: ItemEnum::Module(Module {
@@ -101,22 +101,22 @@ fn errors_on_local_in_paths_and_not_index() {
                     span: None,
                     visibility: Visibility::Public,
                     docs: None,
-                    links: FxHashMap::default(),
+                    links: HashMap::default(),
                     attrs: Vec::new(),
                     deprecation: None,
                     inner: ItemEnum::Primitive(Primitive { name: "i32".to_owned(), impls: vec![] }),
                 },
             ),
         ]),
-        paths: FxHashMap::from_iter([(
+        paths: HashMap::from_iter([(
             id("0:1:1571"),
             ItemSummary {
                 crate_id: 0,
                 path: vec!["microcore".to_owned(), "i32".to_owned()],
                 kind: ItemKind::Primitive,
             },
         )]),
-        external_crates: FxHashMap::default(),
+        external_crates: HashMap::default(),
         format_version: rustdoc_json_types::FORMAT_VERSION,
     };
 
@@ -136,7 +136,7 @@ fn checks_local_crate_id_is_correct() {
         root: id("root"),
         crate_version: None,
         includes_private: false,
-        index: FxHashMap::from_iter([(
+        index: HashMap::from_iter([(
             id("root"),
             Item {
                 id: id("root"),
@@ -145,7 +145,7 @@ fn checks_local_crate_id_is_correct() {
                 span: None,
                 visibility: Visibility::Public,
                 docs: None,
-                links: FxHashMap::default(),
+                links: HashMap::default(),
                 attrs: Vec::new(),
                 deprecation: None,
                 inner: ItemEnum::Module(Module {
@@ -155,8 +155,8 @@ fn checks_local_crate_id_is_correct() {
                 }),
             },
         )]),
-        paths: FxHashMap::default(),
-        external_crates: FxHashMap::default(),
+        paths: HashMap::default(),
+        external_crates: HashMap::default(),
         format_version: FORMAT_VERSION,
     };
     check(&krate, &[]);