yeast: Move schema and YAML loader into yeast-schema crate

For type checking rules, we need to be able to load schemas (so we know
what to check against). However, since we can't have yeast-macros
depending on yeast (where the schema-handling code currently lives) as
this would introduce a circular dependency, we instead split the
schema-related code into its own yeast-schema crate.

Author: tausbn

Cargo.lock

@@ -6,6 +6,7 @@ members = [
     "shared/tree-sitter-extractor",
     "shared/yeast",
     "shared/yeast-macros",
+    "shared/yeast-schema",
     "ruby/extractor",
     "unified/extractor",
     "unified/extractor/tree-sitter-swift",

Cargo.toml

@@ -0,0 +1,12 @@
+load("@rules_rust//rust:defs.bzl", "rust_library")
+load("//misc/bazel/3rdparty/tree_sitter_extractors_deps:defs.bzl", "aliases", "all_crate_deps")
+
+exports_files(["Cargo.toml"])
+
+rust_library(
+    name = "yeast-schema",
+    srcs = glob(["src/**/*.rs"]),
+    aliases = aliases(),
+    visibility = ["//visibility:public"],
+    deps = all_crate_deps(),
+)

misc/bazel/3rdparty/tree_sitter_extractors_deps/defs.bzl

@@ -0,0 +1,9 @@
+[package]
+name = "yeast-schema"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+serde_yaml = "0.9"

shared/yeast-schema/BUILD.bazel

@@ -0,0 +1,33 @@
+//! Schema definitions and YAML/JSON node-types loaders for YEAST.
+//!
+//! This crate carries the parts of the YEAST framework that don't need
+//! `tree-sitter`: the [`schema::Schema`] type and its associated
+//! [`schema::NodeType`] / [`schema::FieldCardinality`] helpers, plus the
+//! YAML and JSON conversion helpers in [`node_types_yaml`].
+//!
+//! It exists so that both the runtime crate (`yeast`) and the
+//! compile-time `rules!` proc macro (`yeast-macros`) can build against a
+//! single source of truth without dragging tree-sitter (a heavy C-backed
+//! dep) into the proc-macro toolchain.
+//!
+//! Tree-sitter-aware adapters — building a `Schema` from a
+//! `tree_sitter::Language`, or loading a YAML schema on top of one —
+//! live in `yeast::schema` and `yeast::node_types_yaml` respectively.
+
+pub mod node_types_yaml;
+pub mod schema;
+
+/// Field IDs are stable `u16`s, matching tree-sitter's representation so a
+/// schema built from a tree-sitter language can preserve the language's
+/// existing IDs.
+pub type FieldId = u16;
+
+/// Kind IDs are stable `u16`s. Like `FieldId`, this matches tree-sitter's
+/// representation.
+pub type KindId = u16;
+
+/// Sentinel field id used to mean "the implicit unfielded slot" (what the
+/// tree-sitter docs call `children` and what YEAST surfaces in queries as
+/// the bare `child:` field). Reserved to avoid clashing with real field
+/// IDs allocated by `Schema::register_field`.
+pub const CHILD_FIELD: u16 = u16::MAX;