Generate unstable docs with items under feature

Add the items to the autogenerated stubs
Make unstable-book-gen use the top stage instead of stage 0
Generate the full docs, only print and save optional notes

Author: albertlarsan68

Cargo.lock

@@ -6045,6 +6045,9 @@ name = "unstable-book-gen"
 version = "0.1.0"
 dependencies = [
  "num-traits",
+ "rustdoc-json-types",
+ "serde_json",
+ "syn",
  "tidy",
 ]
 

src/bootstrap/builder/tests.rs

@@ -286,7 +286,7 @@ mod dist {
         // Make sure rustdoc is only built once.
         assert_eq!(
             first(cache.all::<tool::Rustdoc>()),
-            &[tool::Rustdoc { compiler: Compiler { host: a, stage: 2 } },]
+            &[tool::Rustdoc { compiler: Compiler { host: a, stage: 2 } }]
         );
     }
 
@@ -608,7 +608,7 @@ mod dist {
         // stage minus 1 if --stage is not 0. Very confusing!
         assert_eq!(
             first(builder.cache.all::<tool::Rustdoc>()),
-            &[tool::Rustdoc { compiler: Compiler { host: a, stage: 2 } },]
+            &[tool::Rustdoc { compiler: Compiler { host: a, stage: 2 } }]
         );
     }
 

src/bootstrap/doc.rs

@@ -931,6 +931,13 @@ impl Step for UnstableBookGen {
 
     fn run(self, builder: &Builder<'_>) {
         let target = self.target;
+        let host = builder.build.build;
+
+        builder.ensure(Std {
+            stage: builder.top_stage,
+            target: host,
+            format: DocumentationFormat::JSON,
+        });
 
         builder.info(&format!("Generating unstable book md files ({})", target));
         let out = builder.md_doc_out(target).join("unstable-book");
@@ -940,6 +947,7 @@ impl Step for UnstableBookGen {
         cmd.arg(builder.src.join("library"));
         cmd.arg(builder.src.join("compiler"));
         cmd.arg(builder.src.join("src"));
+        cmd.arg(builder.json_doc_out(host));
         cmd.arg(out);
 
         builder.run(&mut cmd);

src/doc/unstable-book/src/library-features/allocator-api.md

@@ -1,11 +1,3 @@
-# `allocator_api`
-
-The tracking issue for this feature is [#32838]
-
-[#32838]: https://github.com/rust-lang/rust/issues/32838
-
-------------------------
-
 Sometimes you want the memory for one collection to use a different
 allocator than the memory for another collection. In this case,
 replacing the global allocator is not a workable option. Instead,

src/doc/unstable-book/src/library-features/c-variadic.md

@@ -1,11 +1,3 @@
-# `c_variadic`
-
-The tracking issue for this feature is: [#44930]
-
-[#44930]: https://github.com/rust-lang/rust/issues/44930
-
-------------------------
-
 The `c_variadic` library feature exposes the `VaList` structure,
 Rust's analogue of C's `va_list` type.
 

src/doc/unstable-book/src/library-features/c-void-variant.md

@@ -1,11 +1,3 @@
-# `concat_idents`
-
-The tracking issue for this feature is: [#29599]
-
-[#29599]: https://github.com/rust-lang/rust/issues/29599
-
-------------------------
-
 The `concat_idents` feature adds a macro for concatenating multiple identifiers
 into one identifier.
 

src/doc/unstable-book/src/library-features/concat-idents.md

@@ -1,11 +1,3 @@
-# `default_free_fn`
-
-The tracking issue for this feature is: [#73014]
-
-[#73014]: https://github.com/rust-lang/rust/issues/73014
-
-------------------------
-
 Adds a free `default()` function to the `std::default` module.  This function
 just forwards to [`Default::default()`], but may remove repetition of the word
 "default" from the call site.

src/doc/unstable-book/src/library-features/core-intrinsics.md

@@ -1,13 +1,3 @@
-# `fn_traits`
-
-The tracking issue for this feature is [#29625]
-
-See Also: [`unboxed_closures`](../language-features/unboxed-closures.md)
-
-[#29625]: https://github.com/rust-lang/rust/issues/29625
-
-----
-
 The `fn_traits` feature allows for implementation of the [`Fn*`] traits
 for creating custom closure-like types.
 

src/doc/unstable-book/src/library-features/core-panic.md

@@ -1,11 +1,3 @@
-# `is_sorted`
-
-The tracking issue for this feature is: [#53485]
-
-[#53485]: https://github.com/rust-lang/rust/issues/53485
-
-------------------------
-
 Add the methods `is_sorted`, `is_sorted_by` and `is_sorted_by_key` to `[T]`;
 add the methods `is_sorted`, `is_sorted_by` and `is_sorted_by_key` to
 `Iterator`.

src/doc/unstable-book/src/library-features/core-private-bignum.md

@@ -1,9 +1,3 @@
-# `test`
-
-The tracking issue for this feature is: None.
-
-------------------------
-
 The internals of the `test` crate are unstable, behind the `test` flag.  The
 most widely used part of the `test` crate are benchmark tests, which can test
 the performance of your code.  Let's make our `src/lib.rs` look like this

src/doc/unstable-book/src/library-features/core-private-diy-float.md

@@ -1,11 +1,3 @@
-# `trace_macros`
-
-The tracking issue for this feature is [#29598].
-
-[#29598]: https://github.com/rust-lang/rust/issues/29598
-
-------------------------
-
 With `trace_macros` you can trace the expansion of macros in your code.
 
 ## Examples

src/doc/unstable-book/src/library-features/dec2flt.md

@@ -7,6 +7,11 @@ edition = "2021"
 [dependencies]
 tidy = { path = "../tidy" }
 
+
+serde_json = "1"
+rustdoc-json-types = { path = "../../rustdoc-json-types" }
+syn = { version = "1", features = ["full"] }
+
 # not actually needed but required for now to unify the feature selection of
 # `num-traits` between this and `rustbook`
 num-traits = "0.2"

src/doc/unstable-book/src/library-features/default-free-fn.md

@@ -0,0 +1,9 @@
+# `{name}`
+
+The tracking issue for this feature is: [#{issue}]
+{items}
+[#{issue}]: https://github.com/rust-lang/rust/issues/{issue}
+
+------------------------
+
+{notes}