Add --print target-spec-json-schema

This schema is helpful for people writing custom target spec JSON. It
can provide autocomplete in the editor, and also serves as documentation
when there are documentation comments on the structs, as `schemars` will
put them in the schema.

4 files changed, 46 insertions, 0 deletions

diff --git a/src/bootstrap/src/core/build_steps/dist.rs b/src/bootstrap/src/core/build_steps/dist.rs
index a5f0718bc01..99a1062109a 100644
--- a/src/bootstrap/src/core/build_steps/dist.rs
+++ b/src/bootstrap/src/core/build_steps/dist.rs
@@ -590,6 +590,8 @@ impl Step for Rustc {
             // Debugger scripts
             builder.ensure(DebuggerScripts { sysroot: image.to_owned(), target });
 
+            generate_target_spec_json_schema(builder, image);
+
             // HTML copyright files
             let file_list = builder.ensure(super::run::GenerateCopyright);
             for file in file_list {
@@ -618,6 +620,28 @@ impl Step for Rustc {
     }
 }
 
+fn generate_target_spec_json_schema(builder: &Builder<'_>, sysroot: &Path) {
+    // Since we run rustc in bootstrap, we need to ensure that we use the host compiler.
+    // We do this by using the stage 1 compiler, which is always compiled for the host,
+    // even in a cross build.
+    let stage1_host = builder.compiler(1, builder.host_target);
+    let mut rustc = command(builder.rustc(stage1_host)).fail_fast();
+    rustc
+        .env("RUSTC_BOOTSTRAP", "1")
+        .args(["--print=target-spec-json-schema", "-Zunstable-options"]);
+    let schema = rustc.run_capture(builder).stdout();
+
+    let schema_dir = tmpdir(builder);
+    t!(fs::create_dir_all(&schema_dir));
+    let schema_file = schema_dir.join("target-spec-json-schema.json");
+    t!(std::fs::write(&schema_file, schema));
+
+    let dst = sysroot.join("etc");
+    t!(fs::create_dir_all(&dst));
+
+    builder.install(&schema_file, &dst, FileType::Regular);
+}
+
 /// Copies debugger scripts for `target` into the given compiler `sysroot`.
 #[derive(Debug, Clone, Hash, PartialEq, Eq)]
 pub struct DebuggerScripts {
diff --git a/src/bootstrap/src/utils/proc_macro_deps.rs b/src/bootstrap/src/utils/proc_macro_deps.rs
index 777c8601aa1..db2369097d6 100644
--- a/src/bootstrap/src/utils/proc_macro_deps.rs
+++ b/src/bootstrap/src/utils/proc_macro_deps.rs
@@ -43,6 +43,7 @@ pub static CRATES: &[&str] = &[
     "rustc-hash",
     "self_cell",
     "serde",
+    "serde_derive_internals",
     "sha2",
     "smallvec",
     "stable_deref_trait",
diff --git a/src/doc/rustc/src/targets/custom.md b/src/doc/rustc/src/targets/custom.md
index 6c1494186a4..e1750e27f0b 100644
--- a/src/doc/rustc/src/targets/custom.md
+++ b/src/doc/rustc/src/targets/custom.md
@@ -16,6 +16,21 @@ rustc +nightly -Z unstable-options --target=wasm32-unknown-unknown --print targe
 
 To use a custom target, see the (unstable) [`build-std` feature](../../cargo/reference/unstable.html#build-std) of `cargo`.
 
+<div class="warning">
+
+The target JSON properties are not stable and subject to change.
+Always pin your compiler version when using custom targets!
+
+</div>
+
+## JSON Schema
+
+`rustc` provides a JSON schema for the custom target JSON specification.
+Because the schema is subject to change, you should always use the schema from the version of rustc which you are passing the target to.
+
+It can be found in `etc/target-spec-json-schema.json` in the sysroot (`rustc --print sysroot`) or printed with `rustc +nightly -Zunstable-options --print target-spec-json-schema`.
+The existence and name of this schema is, just like the properties of the JSON specification, not stable and subject to change.
+
 ## Custom Target Lookup Path
 
 When `rustc` is given an option `--target=TARGET` (where `TARGET` is any string), it uses the following logic:
diff --git a/src/tools/tidy/src/deps.rs b/src/tools/tidy/src/deps.rs
index 60347b2ea64..a9804761400 100644
--- a/src/tools/tidy/src/deps.rs
+++ b/src/tools/tidy/src/deps.rs
@@ -267,6 +267,7 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "digest",
     "displaydoc",
     "dissimilar",
+    "dyn-clone",
     "either",
     "elsa",
     "ena",
@@ -346,6 +347,8 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "rand_xorshift", // dependency for doc-tests in rustc_thread_pool
     "rand_xoshiro",
     "redox_syscall",
+    "ref-cast",
+    "ref-cast-impl",
     "regex",
     "regex-automata",
     "regex-syntax",
@@ -357,11 +360,14 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "rustix",
     "ruzstd", // via object in thorin-dwp
     "ryu",
+    "schemars",
+    "schemars_derive",
     "scoped-tls",
     "scopeguard",
     "self_cell",
     "serde",
     "serde_derive",
+    "serde_derive_internals",
     "serde_json",
     "serde_path_to_error",
     "sha1",