Rollup merge of #144498 - Noratrieb:rustc-json-schema, r=jieyouxu,davidtwco

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.

I was motivated to do this because I saw someone write their own version of this schema by hand, so demand for this clearly exists. It's not a lot of effort to implement, so I thought it would make sense.

MCP: https://github.com/rust-lang/compiler-team/issues/905

I think it would also be useful to put this in the sysroot in `etc` so people can link it directly in their editors.

I would have loved to add a test that validates the JSON schema against the spec JSON of every builtin target, but I don't want to do it as the JSON schema validation crates have incredible amounts of dependencies because JSON schema supports a ton of random features. I don't want to add that, even as a dev dependency.

1 files changed, 34 insertions, 4 deletions

diff --git a/compiler/rustc_target/src/spec/json.rs b/compiler/rustc_target/src/spec/json.rs
index e9ae5734d5b..f236be92b3b 100644
--- a/compiler/rustc_target/src/spec/json.rs
+++ b/compiler/rustc_target/src/spec/json.rs
@@ -408,12 +408,12 @@ impl ToJson for Target {
     }
 }
 
-#[derive(serde_derive::Deserialize)]
+#[derive(serde_derive::Deserialize, schemars::JsonSchema)]
 struct LinkSelfContainedComponentsWrapper {
     components: Vec<LinkSelfContainedComponents>,
 }
 
-#[derive(serde_derive::Deserialize)]
+#[derive(serde_derive::Deserialize, schemars::JsonSchema)]
 #[serde(untagged)]
 enum TargetFamiliesJson {
     Array(StaticCow<[StaticCow<str>]>),
@@ -429,6 +429,18 @@ impl FromStr for EndianWrapper {
     }
 }
 crate::json::serde_deserialize_from_str!(EndianWrapper);
+impl schemars::JsonSchema for EndianWrapper {
+    fn schema_name() -> std::borrow::Cow<'static, str> {
+        "Endian".into()
+    }
+    fn json_schema(_: &mut schemars::SchemaGenerator) -> schemars::Schema {
+        schemars::json_schema! ({
+            "type": "string",
+            "enum": ["big", "little"]
+        })
+        .into()
+    }
+}
 
 /// `ExternAbi` is in `rustc_abi`, which doesn't have access to the macro and serde.
 struct ExternAbiWrapper(rustc_abi::ExternAbi);
@@ -441,8 +453,22 @@ impl FromStr for ExternAbiWrapper {
     }
 }
 crate::json::serde_deserialize_from_str!(ExternAbiWrapper);
+impl schemars::JsonSchema for ExternAbiWrapper {
+    fn schema_name() -> std::borrow::Cow<'static, str> {
+        "ExternAbi".into()
+    }
+    fn json_schema(_: &mut schemars::SchemaGenerator) -> schemars::Schema {
+        let all =
+            rustc_abi::ExternAbi::ALL_VARIANTS.iter().map(|abi| abi.as_str()).collect::<Vec<_>>();
+        schemars::json_schema! ({
+            "type": "string",
+            "enum": all,
+        })
+        .into()
+    }
+}
 
-#[derive(serde_derive::Deserialize)]
+#[derive(serde_derive::Deserialize, schemars::JsonSchema)]
 struct TargetSpecJsonMetadata {
     description: Option<StaticCow<str>>,
     tier: Option<u64>,
@@ -450,7 +476,7 @@ struct TargetSpecJsonMetadata {
     std: Option<bool>,
 }
 
-#[derive(serde_derive::Deserialize)]
+#[derive(serde_derive::Deserialize, schemars::JsonSchema)]
 #[serde(rename_all = "kebab-case")]
 // Ensure that all unexpected fields get turned into errors.
 // This helps users stay up to date when the schema changes instead of silently
@@ -593,3 +619,7 @@ struct TargetSpecJson {
     supports_xray: Option<bool>,
     entry_abi: Option<ExternAbiWrapper>,
 }
+
+pub fn json_schema() -> schemars::Schema {
+    schemars::schema_for!(TargetSpecJson)
+}