chore: generate code on the fly without storing in repo (#1704)

Part of #1701.

automation/code-generator/build.gradle.kts

@@ -2,19 +2,11 @@ plugins {
     buildsrc.convention.`kotlin-jvm`
 
     kotlin("plugin.serialization")
-
-    application
 }
 
 dependencies {
+    implementation("com.google.devtools.ksp:symbol-processing-api:2.0.21-1.0.26")
     implementation("com.squareup:kotlinpoet:2.0.0")
+    implementation("com.squareup:kotlinpoet-ksp:2.0.0")
     implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.7.3")
 }
-
-application {
-    mainClass.set("io.github.typesafegithub.workflows.codegenerator.GenerationEntryPointKt")
-}
-
-tasks.run.configure {
-    workingDir(rootProject.layout.projectDirectory)
-}

automation/code-generator/src/main/kotlin/io/github/typesafegithub/workflows/codegenerator/KspGenerator.kt

@@ -0,0 +1,21 @@
+package io.github.typesafegithub.workflows.codegenerator
+
+import com.google.devtools.ksp.processing.CodeGenerator
+import com.google.devtools.ksp.processing.Resolver
+import com.google.devtools.ksp.processing.SymbolProcessor
+import com.google.devtools.ksp.symbol.KSAnnotated
+import io.github.typesafegithub.workflows.dsl.expressions.generateEventPayloads
+
+class KspGenerator(
+    private val codeGenerator: CodeGenerator,
+) : SymbolProcessor {
+    private var wasRun = false
+
+    override fun process(resolver: Resolver): List<KSAnnotated> {
+        if (!wasRun) {
+            generateEventPayloads(codeGenerator = codeGenerator)
+            wasRun = true
+        }
+        return emptyList()
+    }
+}

automation/code-generator/src/main/kotlin/io/github/typesafegithub/workflows/codegenerator/KspGeneratorProvider.kt

@@ -0,0 +1,12 @@
+package io.github.typesafegithub.workflows.codegenerator
+
+import com.google.devtools.ksp.processing.SymbolProcessor
+import com.google.devtools.ksp.processing.SymbolProcessorEnvironment
+import com.google.devtools.ksp.processing.SymbolProcessorProvider
+
+class KspGeneratorProvider : SymbolProcessorProvider {
+    override fun create(environment: SymbolProcessorEnvironment): SymbolProcessor =
+        KspGenerator(
+            codeGenerator = environment.codeGenerator,
+        )
+}

automation/code-generator/src/main/kotlin/io/github/typesafegithub/workflows/dsl/expressions/GenerateEventPayloads.kt

@@ -1,5 +1,6 @@
 package io.github.typesafegithub.workflows.dsl.expressions
 
+import com.google.devtools.ksp.processing.CodeGenerator
 import com.squareup.kotlinpoet.AnnotationSpec
 import com.squareup.kotlinpoet.ClassName
 import com.squareup.kotlinpoet.FileSpec
@@ -8,30 +9,26 @@ import com.squareup.kotlinpoet.ParameterizedTypeName.Companion.parameterizedBy
 import com.squareup.kotlinpoet.PropertySpec
 import com.squareup.kotlinpoet.TypeSpec
 import com.squareup.kotlinpoet.asClassName
+import com.squareup.kotlinpoet.ksp.writeTo
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.JsonArray
 import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.json.JsonObject
 import kotlinx.serialization.json.JsonPrimitive
-import java.io.File
+import kotlin.io.path.Path
+import kotlin.io.path.invariantSeparatorsPathString
 
-fun main() {
-    generateEventPayloads()
-}
-
-/*
+/**
  * Generate type-safe accessors for GitHub Event payloads
  * The payloads depend on the kind of the event: pull request, push, ...
  *
  * We read event payloads from binding-generate/src/test/resources/payloads
- * We generate it inside       github-workflows-kt/src/main/kotlin/io/github/typesafegithub/workflows/expressions/contexts
+ * The generated files are added using KSP's [codeGenerator].
  *
  * The JSONs come from https://docs.github.com/en/developers/webhooks-and-events/webhooks/webhook-events-and-payloads
  * Feel free to add any payload you might need from that page
- * */
-fun generateEventPayloads() {
-    println("== generateEventPayloads()")
-    println("GitHubContext subclass  will be generated in ${kotlinGenDir.absolutePath}")
+ */
+fun generateEventPayloads(codeGenerator: CodeGenerator) {
     val params =
         listOf(
             PayloadEventParams("PushEvent", "event-push.json"),
@@ -41,15 +38,14 @@ fun generateEventPayloads() {
         )
     params
         .map { it.generateTypesafePayload() }
-        .forEach { fileSpec -> fileSpec.writeTo(kotlinGenDir) }
-    println("\n")
+        .forEach { fileSpec ->
+            fileSpec.writeTo(codeGenerator = codeGenerator, aggregating = false)
+        }
 }
 
 private val EXPRESSIONS = "io.github.typesafegithub.workflows.dsl.expressions"
 private val PACKAGE = "$EXPRESSIONS.contexts"
-private val resourcesDir = File("automation/code-generator/src/main/resources/payloads")
-
-private val kotlinGenDir = File("github-workflows-kt/src/gen/kotlin")
+private val resourcesDir = Path("/payloads")
 
 // ClassNames
 private val fakeList = ClassName(EXPRESSIONS, "FakeList")
@@ -61,23 +57,22 @@ private val annotationFileSuppress =
         .addMember("%S", "ObjectPropertyNaming")
         .build()
 
-private val fileComment = "File auto-generated by :gradlew code-generator:run"
+private val fileComment = "File auto-generated by KSP"
 
 data class PayloadEventParams(
     val className: String,
     val path: String,
 ) {
-    val jsonFile = resourcesDir.resolve(path)
+    val jsonFile = resourcesDir.resolve(path).invariantSeparatorsPathString
 
     init {
         check(className == className.toPascalCase())
-        check(jsonFile.canRead()) { "Can't read ${jsonFile.canonicalPath}" }
     }
 }
 
 fun PayloadEventParams.generateTypesafePayload(): FileSpec {
-    println("Parsing ${jsonFile.canonicalPath}")
-    val element: JsonObject = Json.parseToJsonElement(jsonFile.readText()) as JsonObject
+    val jsonFileContent = this::class.java.getResource(jsonFile)?.readText() ?: error("Cannot read $jsonFile!")
+    val element: JsonObject = Json.parseToJsonElement(jsonFileContent) as JsonObject
     val objects: Map<String, JsonObject> = findAllObjects(element, "event")
     val fileSpec = generateObjectTypes(objects, className)
     return fileSpec
@@ -133,7 +128,6 @@ fun JsonObject.generateObjectType(
     key: String,
     filename: String,
 ): TypeSpec {
-    println("Generating class ${payloadClassName(key, filename)} : ExpressionContext(\"github.$key\")")
     val properties = mapNotNull { it.generatePropertySpec(key, filename) }
     return TypeSpec
         .objectBuilder(payloadClassName(key, filename))
@@ -167,7 +161,6 @@ fun Map.Entry<String, JsonElement>.generatePropertySpec(
                 .build()
         }
         else -> {
-            println("Warning: unhandled $child")
             null
         }
     }

automation/code-generator/src/main/resources/META-INF/services/com.google.devtools.ksp.processing.SymbolProcessorProvider

@@ -0,0 +1 @@
+io.github.typesafegithub.workflows.codegenerator.KspGeneratorProvider

github-workflows-kt/build.gradle.kts

@@ -7,6 +7,7 @@ plugins {
     buildsrc.convention.`duplicate-versions`
 
     kotlin("plugin.serialization")
+    id("com.google.devtools.ksp") version "2.0.21-1.0.26"
 
     // Code quality.
     id("io.gitlab.arturbosch.detekt")
@@ -24,6 +25,7 @@ dependencies {
     implementation("org.jetbrains.kotlinx:kotlinx-serialization-core:1.7.3")
     implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.7.3")
     implementation(projects.sharedInternal)
+    ksp(projects.automation.codeGenerator)
 
     testImplementation("dev.zacsweers.kctfork:core:0.5.1")
     // Needed to use the right version of the compiler for the libraries that depend on it.
@@ -38,14 +40,6 @@ dependencies {
     testImplementation("EndBug:add-and-commit:v9")
 }
 
-sourceSets {
-    main {
-        java {
-            setSrcDirs(listOf("src/gen/kotlin"))
-        }
-    }
-}
-
 tasks.withType<KotlinCompile> {
     compilerOptions {
         freeCompilerArgs.addAll(
@@ -68,7 +62,7 @@ kotlin {
 }
 
 fun ConfigurableKtLintTask.kotlinterConfig() {
-    exclude { it.file.invariantSeparatorsPath.contains("/gen/") }
+    exclude { it.file.invariantSeparatorsPath.contains("/generated/") }
 }
 
 tasks.lintKotlinMain {