corvus-codegen

name

corvus-codegen

description

Generate strongly-typed C# from JSON Schema using the Roslyn source generator or the corvusjson CLI tool. Covers the JsonSchemaTypeGenerator attribute, CLI options, naming heuristics, AdditionalFiles registration, config file format, MSBuild properties, and troubleshooting generated output. USE FOR: generating types from schemas, configuring the source generator or CLI tool, understanding naming heuristics, inspecting generated output, troubleshooting generation issues. DO NOT USE FOR: modifying the generator internals (use corvus-keywords-and-validation), running benchmarks (use corvus-benchmarks).

Code Generation from JSON Schema

Two Code Generation Mechanisms

1. Roslyn Source Generator (build-time)

Add the source generator NuGet package and annotate a partial struct:

[JsonSchemaTypeGenerator("Schemas/person.json")]
public readonly partial struct Person;

Attribute (defined in IncrementalSourceGenerator.cs):

• Constructor: JsonSchemaTypeGeneratorAttribute(string location, bool rebaseToRootPath = false)
• Property: EmitEvaluator (bool) — also emit a standalone schema evaluator
• Must be applied to a partial struct (not class)

All referenced schema files must be registered as <AdditionalFiles>:

<ItemGroup>
  <AdditionalFiles Include="Schemas\**\*.json" />
</ItemGroup>

2. CLI Tool (corvusjson)

# Install the CLI tool
dotnet tool install --global Corvus.Json.Cli

# Generate types
corvusjson jsonschema <schema-path> `
  --rootNamespace MyApp.Models `
  --outputRootTypeName PersonSchema `
  --outputPath Generated/ `
  --engine V5

The command is corvusjson jsonschema (registered in CliAppFactory.cs).

Key CLI options (defined in src/Corvus.Json.Cli.Core/GenerateCommand.cs):

• --rootNamespace — C# namespace for generated types
• --outputRootTypeName — name of the root generated type
• --outputPath — output directory
• --engine — V4 or V5 (default: V5 for corvusjson, V4 for legacy generatejsonschematypes)
• --assertFormat — whether format validation asserts globally (default: true). Takes a value: --assertFormat false gives annotation-only output where the vocabulary treats format as an annotation (e.g. 2020-12)
• --formatMode — format assertion mode overrides as comma-separated entries (mode ∈ assert/disable/warning). format=mode targets one format (e.g. date-time=disable,time=warning); a bare mode (equivalently *=mode) sets the default for all formats across every draft — --formatMode disable is the way to get annotation-only output for draft-04/06/07 (whose vocabulary asserts format, so --assertFormat false alone doesn't). Repeatable; a per-format override beats the * default, --assertFormat, and the vocabulary. warning (string formats only) validates but always succeeds, emitting a WARNING annotation on mismatch
• --codeGenerationMode — TypeGeneration, SchemaEvaluationOnly, or Both
• --nativeEnums — native C# enum emission (V5 engine only, default All): StringEnums emits a nested KnownValues enum for pure string-enum schemas; FlagsObjects emits a nested [Flags] enum for objects whose declared properties are all boolean; All emits both; None emits neither

IMPORTANT: Never invent option names. Verify against GenerateCommand.cs.

Legacy CLI

The generatejsonschematypes command (package: Corvus.Json.CodeGenerator) still works as a shim but defaults to the V4 engine.

MSBuild Properties

All read from the source generator (IncrementalSourceGenerator.cs lines 111-196):

Property	Effect	Default
CorvusTextJsonFallbackVocabulary	Default vocabulary for schemas without $schema	Draft202012
CorvusTextJsonOptionalAsNullable	Set to NullOrUndefined to treat optional as nullable	off
CorvusTextJsonAddExplicitUsings	Add explicit using directives	true
CorvusTextJsonUseImplicitOperatorString	Generate implicit string conversion operators	true
CorvusTextJsonUseOptionalNameHeuristics	Enable optional naming heuristics	true
CorvusTextJsonNativeEnums	Native C# enum emission: None, StringEnums, FlagsObjects, All	All
CorvusTextJsonAlwaysAssertFormat	Assert format validation	true
CorvusTextJsonFormatMode	Per-format mode overrides as ;/,-separated format=mode pairs (assert/disable/warning)	—
CorvusTextJsonDefaultAccessibility	Public or Internal	Public
CorvusTextJsonDisabledNamingHeuristics	Semicolon-separated list of heuristics to disable	—
EmitCompilerGeneratedFiles	Write generated .g.cs to obj/ for inspection	false

Naming Heuristics

The generator uses 15 heuristics (priorities 1–11000) to derive C# type names from JSON Schema. Key ones:

1. title — uses the schema's title keyword
2. $anchor / $id — uses the fragment or filename
3. Property name — derives from the parent property name
4. $ref path — derives from the $ref URI path/fragment

Collisions are resolved by appending a type-kind suffix: Object, Array, String, Number, Boolean.

Optional heuristics can be disabled via CorvusTextJsonDisabledNamingHeuristics.

Config File

For complex generation scenarios, use a config file (corvusjson config):

{
  "typesToGenerate": [
    {
      "schemaFile": "schemas/main.json",
      "rootTypeName": "MainType"
    }
  ],
  "additionalFiles": [
    { "canonicalUri": "https://example.com/shared.json", "contentPath": "schemas/shared.json" }
  ],
  "namedTypes": [
    { "reference": "#/definitions/Foo", "dotnetTypeName": "FooType", "dotnetNamespace": "MyApp.Sub" }
  ],
  "namespaces": {
    "https://example.com/schemas/": "MyApp.ExternalModels"
  }
}

Inspecting Generated Output

# Enable generated file emission in the .csproj
<PropertyGroup>
  <EmitCompilerGeneratedFiles>true</EmitCompilerGeneratedFiles>
</PropertyGroup>

# After building, find generated files at:
# obj\{Config}\{TFM}\generated\Corvus.Text.Json.SourceGenerator\

Common Pitfalls

• Missing <AdditionalFiles>: Referenced schemas not in <AdditionalFiles> are invisible to the source generator.
• Stale generated files: After schema changes, clean and rebuild. Old generated files may cause compilation errors.
• No glob <Compile> items: This repo requires every .cs file to be explicitly listed in the .csproj. CLI-generated output directories need corresponding <Compile Include="..." /> entries.

Cross-References

• For the keyword/vocabulary system that drives generation, see corvus-keywords-and-validation
• For evaluator-only generation, see corvus-standalone-evaluator
• For building and testing generated code, see corvus-build-and-test