Add a Dart runtime for Protovalidate

Makefile

@@ -14,6 +14,9 @@ GOLANGCI_LINT_VERSION := v1.64.7
 BAZELISK_VERSION := v1.27.0
 # Set to use a different compiler. For example, `GO=go1.18rc1 make test`.
 GO ?= go
+DART ?= dart
+# Directory containing the protoc-gen-dart plugin (from `dart pub global activate protoc_plugin`).
+PROTOC_GEN_DART_BIN ?= $(HOME)/.pub-cache/bin
 ARGS ?=
 
 
@@ -65,6 +68,26 @@ lint-protovalidate: | $(BIN)/buf  ## Check invariants of validate.proto
 conformance: ## Build conformance harness
 	$(GO) build -o $(BIN)/protovalidate-conformance ./tools/protovalidate-conformance
 
+.PHONY: test-dart
+test-dart: ## Analyze and unit-test the Dart runtime
+	cd dart && $(DART) pub get
+	cd dart && $(DART) analyze lib bin
+	cd dart && $(DART) test
+
+.PHONY: conformance-dart
+conformance-dart: conformance ## Run conformance tests against the Dart runtime
+	cd dart && $(DART) pub get
+	cd dart && $(DART) compile exe bin/protovalidate_conformance.dart -o $(abspath $(BIN))/protovalidate-conformance-dart
+	$(BIN)/protovalidate-conformance \
+		--expected_failures=dart/conformance/expected_failures.yaml \
+		$(BIN)/protovalidate-conformance-dart
+
+.PHONY: generate-dart
+generate-dart: | $(BIN)/buf ## Regenerate Dart code for the runtime and conformance suite
+	PATH="$(PROTOC_GEN_DART_BIN):$(abspath $(BIN)):$$PATH" \
+		$(BIN)/buf generate --template dart/buf.gen.yaml --include-imports --include-wkt
+	cd dart && $(DART) run tool/gen_conformance_registry.dart
+
 .PHONY: generate
 generate: ## Regenerate code and license headers
 	$(MAKE) generate-bazel

dart/.gitignore

@@ -0,0 +1,3 @@
+# Dart tool cache and build output.
+.dart_tool/
+build/

dart/README.md

@@ -0,0 +1,81 @@
+# protovalidate-dart
+
+A Dart runtime for [Protovalidate](https://protovalidate.com), validating
+Protobuf messages against the standard validation rules declared with
+`buf.validate` field options.
+
+This runtime implements the **standard, CEL-free subset** of Protovalidate. It
+does not evaluate custom [CEL](https://cel.dev) expressions; rules that are only
+expressible through CEL are out of scope (see [Limitations](#limitations)).
+
+## Usage
+
+The validator reads rules and structure from a
+`google.protobuf.FileDescriptorSet` and reads field values from your generated
+messages by reflection. Build a descriptor set for your protos with
+`buf build -o image.binpb`, then:
+
+```dart
+import 'dart:io';
+import 'package:protovalidate/protovalidate.dart';
+import 'package:your_app/gen/user.pb.dart';
+
+void main() {
+  final validator =
+      Validator.fromBuffer(File('image.binpb').readAsBytesSync());
+
+  final user = User()..email = 'not-an-email';
+
+  // Returns the list of violations (empty when valid).
+  final violations = validator.validate(user);
+  for (final v in violations) {
+    print('${v.ruleId}: ${v.message}');
+  }
+
+  // Or throw on the first invalid message.
+  validator.check(user); // throws ValidationException
+}
+```
+
+## Supported rules
+
+| Target | Rules |
+| --- | --- |
+| field | `required`, `ignore` (`IGNORE_UNSPECIFIED` / `IGNORE_IF_ZERO_VALUE` / `IGNORE_ALWAYS`) |
+| numeric | `const`, `lt`, `lte`, `gt`, `gte`, `in`, `not_in`, `finite` (float/double) |
+| `bool` | `const` |
+| `string` | `const`, `len`, `min_len`, `max_len`, `len_bytes`, `min_bytes`, `max_bytes`, `pattern`, `prefix`, `suffix`, `contains`, `not_contains`, `in`, `not_in`, `email`, `uri`, `uuid` |
+| `bytes` | `const`, `len`, `min_len`, `max_len`, `prefix`, `suffix`, `contains`, `in`, `not_in`, `uuid` |
+| `enum` | `const`, `defined_only`, `in`, `not_in` |
+| repeated | `min_items`, `max_items`, `unique`, `items` |
+| map | `min_pairs`, `max_pairs`, `keys`, `values` |
+
+Nested messages are validated recursively. String lengths are counted in Unicode
+code points (`len`/`min_len`/`max_len`) or UTF-8 bytes (`*_bytes`). `pattern` uses
+RE2-style syntax via Dart `RegExp`.
+
+## Limitations
+
+Out of scope for this runtime (and recorded in
+[`conformance/expected_failures.yaml`](conformance/expected_failures.yaml)):
+
+- Custom, predefined, and message-level CEL rules (`cel`, `cel_expression`).
+- Well-known-type rules (`google.protobuf.Any`, `Duration`, `Timestamp`,
+  `FieldMask`, and the wrapper types).
+- Message-level `oneof` rules and `OneofRules`.
+- String/bytes formats beyond `email`, `uri`, and `uuid` (e.g. `hostname`, `ip*`,
+  `address`, `uri_ref`, `tuuid`, `ulid`, `host_and_port`).
+- Protobuf Editions edge cases (some of which `protoc-gen-dart` does not yet
+  generate, such as delimited-encoded message fields).
+
+## Development
+
+```shell
+make test-dart          # dart analyze + dart test
+make conformance-dart   # run the Protovalidate conformance suite
+make generate-dart      # regenerate Dart code from the .proto sources
+```
+
+`make generate-dart` requires `protoc-gen-dart` on `PATH`
+(`dart pub global activate protoc_plugin`). Generated code lives in
+`lib/src/gen/` and `bin/conformance_types.g.dart` and is checked in.

dart/analysis_options.yaml

@@ -0,0 +1,12 @@
+include: package:lints/recommended.yaml
+
+analyzer:
+  exclude:
+    # Generated code carries its own ignore directives; keep analysis focused on
+    # the hand-written runtime.
+    - lib/src/gen/**
+
+linter:
+  rules:
+    - prefer_final_locals
+    - avoid_print