C# record perf + sentinel-based directive assembly

.gitignore

@@ -5,10 +5,11 @@ out/
 */src/main/gen/
 */src/main/antlr/gen
 .idea/*
-# Exception: Include Python module for IntelliJ (needs parent dirs unignored first)
+# Exception: Include Python/C# modules for IntelliJ (needs parent dirs unignored first)
 !.idea/modules/
 .idea/modules/*
 !.idea/modules/rewrite-python-src/
+!.idea/modules/rewrite-csharp-src/
 .project
 .classpath
 .settings/

rewrite-core/src/main/java/org/openrewrite/rpc/RpcReceiveQueue.java

@@ -164,7 +164,10 @@ public <T> List<T> receiveList(@Nullable List<T> before, @Nullable UnaryOperator
                 // Intentional fall-through...
             case CHANGE:
                 msg = take(); // the next message should be a CHANGE with a list of positions
-                assert msg.getState() == RpcObjectData.State.CHANGE;
+                if (msg.getState() != RpcObjectData.State.CHANGE) {
+                    throw new IllegalStateException("Expected CHANGE with positions in receiveList, but got " +
+                        msg.getState() + " (valueType=" + msg.getValueType() + ", value=" + msg.getValue() + ", ref=" + msg.getRef() + ")");
+                }
                 List<Integer> positions = requireNonNull(msg.getValue());
                 List<T> after = new ArrayList<>(positions.size());
                 for (int beforeIdx : positions) {

rewrite-csharp/build.gradle.kts

@@ -0,0 +1,167 @@
+@file:Suppress("UnstableApiUsage")
+
+import java.time.LocalDateTime
+import java.time.format.DateTimeFormatter
+
+plugins {
+    id("org.openrewrite.build.language-library")
+    id("org.openrewrite.build.moderne-source-available-license")
+    id("jvm-test-suite")
+    id("publishing")
+}
+
+dependencies {
+    api(project(":rewrite-core"))
+    api(project(":rewrite-java"))
+
+    api("org.jetbrains:annotations:latest.release")
+    api("com.fasterxml.jackson.core:jackson-annotations")
+
+    implementation("io.moderne:jsonrpc:latest.integration")
+
+    compileOnly(project(":rewrite-test"))
+    compileOnly(project(":rewrite-xml"))
+
+    testImplementation(project(":rewrite-test"))
+    testImplementation(project(":rewrite-xml"))
+    testImplementation("io.moderne:jsonrpc:latest.integration")
+    testRuntimeOnly(project(":rewrite-java-21"))
+}
+
+tasks.withType<Javadoc>().configureEach {
+    (options as StandardJavadocDocletOptions).addStringOption("Xdoclint:none", "-quiet")
+    exclude("**/Cs.java")
+}
+
+// C#-specific build tasks
+val csharpDir = projectDir.resolve("csharp")
+
+// Find dotnet executable
+fun findDotnet(): String {
+    val candidates = listOf("dotnet")
+    for (cmd in candidates) {
+        try {
+            val process = ProcessBuilder(cmd, "--version")
+                .redirectErrorStream(true)
+                .start()
+            if (process.waitFor() == 0) {
+                return cmd
+            }
+        } catch (e: Exception) {
+            // Command not found, try next
+        }
+    }
+    throw GradleException(".NET SDK not found. Please install .NET 8.0+ SDK and ensure 'dotnet' is on your PATH.")
+}
+
+val csharpBuild by tasks.registering(Exec::class) {
+    group = "csharp"
+    description = "Build C# projects"
+
+    workingDir = csharpDir
+    commandLine(findDotnet(), "build")
+
+    doFirst {
+        logger.lifecycle("Building C# projects in ${csharpDir}")
+    }
+}
+
+testing {
+    suites {
+        register<JvmTestSuite>("integTest") {
+            useJUnitJupiter()
+
+            dependencies {
+                implementation(project())
+                implementation(project(":rewrite-java-21"))
+                implementation(project(":rewrite-test"))
+                implementation("org.assertj:assertj-core:latest.release")
+                implementation("org.junit.platform:junit-platform-suite-api")
+                runtimeOnly("org.junit.platform:junit-platform-suite-engine")
+            }
+        }
+    }
+}
+
+// Run tests serially to avoid issues with concurrent C# RPC processes
+tasks.withType<Test> {
+    // Ensure C# is built before running tests
+    dependsOn(csharpBuild)
+
+    maxParallelForks = 1
+    // Add timeout to identify hanging tests
+    systemProperty("junit.jupiter.execution.timeout.default", "30s")
+    // Show test names as they run
+    testLogging {
+        events("started", "passed", "failed", "skipped")
+        showStandardStreams = true
+    }
+}
+
+// ============================================
+// NuGet Publishing Tasks
+// ============================================
+
+// Generate a NuGet-compatible version for CI builds
+// Snapshots use pre-release suffix: 8.73.0-snapshot.20260110143252
+// Releases use clean version: 8.73.0
+val nugetVersion: String = if (System.getenv("CI") != null) {
+    project.version.toString().replace(
+        "-SNAPSHOT",
+        "-snapshot.${LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyyMMddHHmmss"))}"
+    )
+} else {
+    project.version.toString().replace("-SNAPSHOT", "-dev")
+}
+
+// Task to pack the C# project as a NuGet tool package
+// Version is injected via /p:Version so the .csproj is never modified
+val csharpPack by tasks.registering(Exec::class) {
+    group = "csharp"
+    description = "Pack C# project as NuGet package"
+
+    workingDir = csharpDir
+    commandLine(
+        findDotnet(), "pack",
+        "--configuration", "Release",
+        "--output", "dist",
+        "/p:Version=$nugetVersion"
+    )
+
+    inputs.dir(csharpDir.resolve("OpenRewrite"))
+    inputs.property("version", nugetVersion)
+    outputs.dir(csharpDir.resolve("dist"))
+
+    doFirst {
+        csharpDir.resolve("dist").deleteRecursively()
+        logger.lifecycle("Packing C# NuGet package (version: $nugetVersion)")
+    }
+}
+
+// Task to publish NuGet package
+val csharpPublish by tasks.registering(Exec::class) {
+    group = "csharp"
+    description = "Publish C# NuGet package"
+
+    dependsOn(csharpPack)
+
+    workingDir = csharpDir
+    commandLine(
+        findDotnet(), "nuget", "push",
+        "dist/*.nupkg",
+        "--source", "https://api.nuget.org/v3/index.json",
+        "--api-key", project.findProperty("nugetApiKey")?.toString() ?: ""
+    )
+
+    doFirst {
+        if (!project.hasProperty("nugetApiKey")) {
+            throw GradleException("nugetApiKey property is required for NuGet publishing")
+        }
+        logger.lifecycle("Publishing C# NuGet package (version: $nugetVersion)")
+    }
+}
+
+// Wire into the main publish task
+tasks.named("publish") {
+    dependsOn(csharpPublish)
+}

rewrite-csharp/csharp/.gitignore

@@ -0,0 +1,27 @@
+# Build results
+bin/
+obj/
+
+# Visual Studio
+.vs/
+*.user
+*.suo
+*.userosscache
+*.sln.docstates
+
+# JetBrains Rider
+.idea/
+
+# NuGet
+*.nupkg
+*.snupkg
+.nuget/
+packages/
+
+# Test results
+TestResults/
+*.trx
+
+# OS generated
+.DS_Store
+Thumbs.db

rewrite-csharp/csharp/OpenRewrite.sln

@@ -0,0 +1,22 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.0.31903.59
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenRewrite", "OpenRewrite\OpenRewrite.csproj", "{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+EndGlobal