build(error-reporting): gate json wire shape behind a default-off json feature (bd-egcyeym9)

The json.rs wire shape (JsonDiagnostic etc.) carries `schemars` and Quarto's
`quarto.org` schema URLs — both Quarto policy. Make it opt-in so the
soon-to-be-published quarto-error-reporting is lean for non-Quarto consumers:

- `schemars` becomes `optional = true`; new `[features] json = ["dep:schemars"]`.
- `lib.rs`: `pub mod json` + its re-export gated behind `#[cfg(feature = "json")]`.
- `tests/schema_drift.rs`: `#![cfg(feature = "json")]` (empty test binary when off).
- The 4 crates that use the wire symbols (quarto, quarto-core, quarto-preview,
  wasm-quarto-hub-client) enable `features = ["json"]`.

`cargo tree` confirms `schemars` is absent under default features and present with
`--features json`. `to_json` (uses serde_json::json!, not the module) and
coalesce.rs stay unconditional. In the q2 workspace json is on via feature
unification, so the wire shape and schema_drift test build as before.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: cscheid

crates/quarto-core/Cargo.toml

@@ -38,7 +38,7 @@ quarto-system-runtime.workspace = true
 quarto-pandoc-types.workspace = true
 quarto-source-map.workspace = true
 quarto-doctemplate.workspace = true
-quarto-error-reporting.workspace = true
+quarto-error-reporting = { workspace = true, features = ["json"] }
 quarto-config.workspace = true
 quarto-yaml.workspace = true
 quarto-ast-reconcile.workspace = true

crates/quarto-error-reporting/Cargo.toml

@@ -20,17 +20,25 @@ serde = { workspace = true }
 serde_json = { workspace = true }
 
 # JSON Schema generation for the wire format (bd-iey8o). Scoped to
-# this crate: `schemars` documents machine-to-machine JSON shapes
-# emitted by Quarto. Do NOT add it to other crates for the purpose
-# of validating user-authored YAML config — that's the job of
-# `quarto-yaml-validation`, which speaks Quarto's own dialect. See
-# `claude-notes/plans/2026-05-22-q2-render-json-errors.md` §
-# "Coexistence with quarto-yaml-validation".
-schemars = { workspace = true }
+# this crate AND to the `json` feature: `schemars` documents the
+# machine-to-machine JSON shapes in `json.rs`. Do NOT add it to other
+# crates for the purpose of validating user-authored YAML config —
+# that's the job of `quarto-yaml-validation`, which speaks Quarto's own
+# dialect. See `claude-notes/plans/2026-05-22-q2-render-json-errors.md`
+# § "Coexistence with quarto-yaml-validation".
+schemars = { workspace = true, optional = true }
 
 # URL handling for file:// hyperlinks
 url = "2.5"
 
+[features]
+# The `json.rs` wire shape (JsonDiagnostic etc.) and its `schemars`
+# dependency are opt-in: the q2 consumers (quarto, quarto-core,
+# quarto-preview, wasm-quarto-hub-client) enable `json`, while a
+# standalone non-Quarto consumer gets a leaner build with no schemars.
+# Default-off so the published crate stays minimal.
+json = ["dep:schemars"]
+
 [dev-dependencies]
 # No dev dependencies yet
 

crates/quarto-error-reporting/src/lib.rs

@@ -62,7 +62,10 @@ pub mod builder;
 // (WASM render bridge) and quarto-preview (server-side diagnostics
 // endpoint). Lifted from wasm-quarto-hub-client under bd-b9kzg so
 // the q2-preview SPA can consume both feeds without a translation
-// layer.
+// layer. Behind the default-off `json` feature (carries `schemars`
+// and Quarto's `quarto.org` schema URLs) so the published crate stays
+// minimal for non-Quarto consumers.
+#[cfg(feature = "json")]
 pub mod json;
 
 // Macros for convenient error creation
@@ -85,6 +88,7 @@ pub use coalesce::{CoalescedDiagnostic, coalesce_by_source};
 pub use diagnostic::{
     DetailItem, DetailKind, DiagnosticKind, DiagnosticMessage, MessageContent, TextRenderOptions,
 };
+#[cfg(feature = "json")]
 pub use json::{
     JsonDiagnostic, JsonDiagnosticDetail, JsonPass1Failure, diagnostic_to_json, with_source_file,
 };

crates/quarto-error-reporting/tests/schema_drift.rs

@@ -25,6 +25,11 @@
 //! # Regenerate after editing JsonDiagnostic / JsonPass1Failure:
 //! QUARTO_REGEN_SCHEMAS=1 cargo nextest run -p quarto-error-reporting --test schema_drift
 //! ```
+//!
+//! Gated on the `json` feature (the wire shapes live behind it); compiles to an
+//! empty test binary when `json` is off. In the q2 workspace the feature is on
+//! (enabled by `quarto`/`quarto-core`/… via unification).
+#![cfg(feature = "json")]
 
 use std::path::PathBuf;
 

crates/quarto-preview/Cargo.toml

@@ -26,7 +26,7 @@ automerge = { version = "0.8.0", features = ["utf16-indexing"] }
 samod = { version = "0.9.0", git = "https://github.com/quarto-dev/samod.git", branch = "q2", features = ["tokio"] }
 
 quarto-core.workspace = true
-quarto-error-reporting.workspace = true
+quarto-error-reporting = { workspace = true, features = ["json"] }
 quarto-hub.workspace = true
 quarto-pandoc-types.workspace = true
 quarto-source-map.workspace = true

crates/quarto/Cargo.toml

@@ -24,7 +24,7 @@ tokio.workspace = true
 
 quarto-core = { workspace = true, features = ["clap"] }
 quarto-error-catalog.workspace = true
-quarto-error-reporting.workspace = true
+quarto-error-reporting = { workspace = true, features = ["json"] }
 quarto-source-map.workspace = true
 quarto-trace.workspace = true
 quarto-trace-server.workspace = true

crates/wasm-quarto-hub-client/Cargo.toml

@@ -16,7 +16,7 @@ quarto-core = { path = "../quarto-core" }
 # NOTE: `quarto-error-catalog` is intentionally NOT a dependency here — the WASM
 # bridge never surfaces docs URLs, so installing the catalog would only bloat the
 # bundle past the PWA precache limit. See the comment in `init()` in src/lib.rs.
-quarto-error-reporting = { path = "../quarto-error-reporting" }
+quarto-error-reporting = { path = "../quarto-error-reporting", features = ["json"] }
 # Direct dep so the test-only `quarto_highlight_for_test` export can
 # call the Registry-backed highlight path. Same crate quarto-core uses
 # via CodeHighlightStage — ensuring WASM tests exercise the same code