Add support for threading compiler flag to Rust target

org.lflang/src/org/lflang/generator/rust/RustGenerator.kt

@@ -71,7 +71,7 @@ class RustGenerator(
 
         Files.createDirectories(fileConfig.srcGenPath)
 
-        val gen = RustModelBuilder.makeGenerationInfo(targetConfig, reactors)
+        val gen = RustModelBuilder.makeGenerationInfo(targetConfig, reactors, errorReporter)
         val codeMaps: Map<Path, CodeMap> = RustEmitter.generateRustProject(fileConfig, gen)
 
         if (targetConfig.noCompile || errorsOccurred()) {

org.lflang/src/org/lflang/generator/rust/RustModel.kt

@@ -35,6 +35,7 @@ import java.nio.file.Path
 import java.util.*
 
 private typealias Ident = String
+const val PARALLEL_RT_FEATURE = "parallel-runtime"
 
 /** Root model class for the entire generation. */
 data class GenerationInfo(
@@ -416,15 +417,15 @@ object RustModelBuilder {
     /**
      * Given the input to the generator, produce the model classes.
      */
-    fun makeGenerationInfo(targetConfig: TargetConfig, reactors: List<Reactor>): GenerationInfo {
+    fun makeGenerationInfo(targetConfig: TargetConfig, reactors: List<Reactor>, errorReporter: ErrorReporter): GenerationInfo {
         val reactorsInfos = makeReactorInfos(reactors)
         // todo how do we pick the main reactor? it seems like super.doGenerate sets that field...
         val mainReactor = reactorsInfos.lastOrNull { it.isMain } ?: reactorsInfos.last()
 
 
         val dependencies = targetConfig.rust.cargoDependencies.toMutableMap()
         dependencies.compute(RustEmitterBase.runtimeCrateFullName) { _, spec ->
-            computeDefaultRuntimeConfiguration(spec, targetConfig)
+            computeDefaultRuntimeConfiguration(spec, targetConfig, errorReporter)
         }
 
         return GenerationInfo(
@@ -452,20 +453,28 @@ object RustModelBuilder {
     private fun computeDefaultRuntimeConfiguration(
         userSpec: CargoDependencySpec?,
         targetConfig: TargetConfig,
+        errorReporter: ErrorReporter
     ): CargoDependencySpec {
-
-        val userRtVersion: String? = targetConfig.runtimeVersion
-
         if (userSpec == null) {
             // default configuration for the runtime crate
-            return if (targetConfig.externalRuntimePath != null) newCargoSpec(
-                gitTag = userRtVersion?.let { "v$it" },
-                localPath = targetConfig.externalRuntimePath,
-            ) else newCargoSpec(
-                gitRepo = RustEmitterBase.runtimeGitUrl,
+
+            val userRtVersion: String? = targetConfig.runtimeVersion
+            // enable parallel feature if asked
+            val parallelFeature = listOf(PARALLEL_RT_FEATURE).takeIf { targetConfig.threading }
+
+            val spec = newCargoSpec(
                 gitTag = userRtVersion?.let { "v$it" },
-                rev = runtimeGitRevision.takeIf { userRtVersion == null },
+                features = parallelFeature,
             )
+
+            if (targetConfig.externalRuntimePath != null) {
+                spec.localPath = targetConfig.externalRuntimePath
+            } else {
+                spec.gitRepo = RustEmitterBase.runtimeGitUrl
+                spec.rev = runtimeGitRevision.takeIf { userRtVersion == null }
+            }
+
+            return spec
         } else {
             if (userSpec.localPath == null && userSpec.gitRepo == null) {
                 // default the location
@@ -481,6 +490,15 @@ object RustModelBuilder {
                 userSpec.localPath = targetConfig.externalRuntimePath
             }
 
+            // enable parallel feature if asked
+            if (targetConfig.threading && PARALLEL_RT_FEATURE !in userSpec.features) {
+                userSpec.features += PARALLEL_RT_FEATURE
+            }
+
+            if (!targetConfig.threading && PARALLEL_RT_FEATURE in userSpec.features) {
+                errorReporter.reportWarning("Threading cannot be disabled as it was enabled manually as a runtime feature.")
+            }
+
             return userSpec
         }
     }

org.lflang/src/org/lflang/generator/rust/rust-runtime-version.txt

@@ -1 +1 @@
-f35bcc79a5422eae256e9082314a05e9b4530bc4
+0100686e1d0fcf648f7979e0fca2017e6b33a9a6

test/Rust/src-gen/Cargo.toml

@@ -16,7 +16,7 @@
 # If it causes problems, we can throw it away or hide it.
 [workspace]
 members = ["*"]
-exclude = ["target", "multiport", "generics"]
+exclude = ["concurrent", "target", "multiport", "generics"]
 
 [profile.release-with-min-size] # use `build-type: MinSizeRel`
 inherits = "release"

test/Rust/src/concurrent/Workers.lf

@@ -0,0 +1,10 @@
+target Rust { workers: 16 };
+main reactor {
+    reaction(startup) {=
+        if (ctx.num_workers() != 16) {
+            panic!("Expected to have 16 workers.");
+        } else {
+            println!("Using 16 workers.");
+        }
+    =}
+}