From b3792cbae57acb12d1262e0de51ca879efaf5624 Mon Sep 17 00:00:00 2001
From: Bobby Grayson <bobbbygrayson+github@gmail.com>
Date: Fri, 9 Oct 2026 08:29:39 -0400
Subject: [PATCH] be-js: report an unconfigured library instead of throwing

`temper run -b js` looked the library up with `getValue` before
checking anything, so a `--library` that names no library, or one
whose config file does not parse, ended in an uncaught Kotlin
exception:

    Exception in thread "main" java.util.NoSuchElementException: Key no-such-library is missing in the map.
        at lang.temper.be.js.RunJsKt.runJsBestEffort(RunJs.kt:69)

The metadata lookup right below it already returns a CliFailure for a
library the build does not know, as py, lua and java do. The
`getValue` threw first. A plain `get` lets that check run; the config
is only read for its library name, which is null-safe already.

Now:

    ## exception.msg: No JS library name for RunLibraryRequest(libraryName=no-such-library, taskName=run)
    Run failed

RunTest.runJsBackendUnknownLibrary runs the `run` input with a
library name it does not have. Before this change it fails with the
NoSuchElementException; after, the run reports failure.

Fixes #611.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Signed-off-by: Bobby Grayson <bobbbygrayson+github@gmail.com>
---
 .../kotlin/lang/temper/be/js/RunJs.kt         |  3 ++-
 .../test/kotlin/lang/temper/cli/RunTest.kt    | 21 +++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/be-js/src/commonMain/kotlin/lang/temper/be/js/RunJs.kt b/be-js/src/commonMain/kotlin/lang/temper/be/js/RunJs.kt
index 978713063..50a682d2e 100644
--- a/be-js/src/commonMain/kotlin/lang/temper/be/js/RunJs.kt
+++ b/be-js/src/commonMain/kotlin/lang/temper/be/js/RunJs.kt
@@ -65,8 +65,9 @@ internal fun runJsBestEffort(
     when (request) {
         is RunBackendSpecificCompilationStepRequest -> error("$request")
         is RunLibraryRequest -> {
+            // Null for a library the build does not know, which the metadata check below reports.
             mainLibraryConfig = dependencies.libraryConfigurations
-                .byLibraryName.getValue(request.libraryName)
+                .byLibraryName[request.libraryName]
             val jsLibraryName = dependencies.metadata[request.libraryName, JsMetadataKey.JsLibraryName]
                 ?: return listOf(
                     ToolchainResult(result = RFailure(CliFailure("No JS library name for $request"))),
diff --git a/cli/src/test/kotlin/lang/temper/cli/RunTest.kt b/cli/src/test/kotlin/lang/temper/cli/RunTest.kt
index 9b192c1bf..e1f2b59fb 100644
--- a/cli/src/test/kotlin/lang/temper/cli/RunTest.kt
+++ b/cli/src/test/kotlin/lang/temper/cli/RunTest.kt
@@ -31,6 +31,7 @@ import kotlin.test.Ignore
 import kotlin.test.Test
 import kotlin.test.assertContains
 import kotlin.test.assertEquals
+import kotlin.test.assertFalse
 import kotlin.test.assertTrue
 
 class RunTest {
@@ -106,6 +107,26 @@ class RunTest {
     @Test
     fun runJsBackend() = runRunTest("run", JsBackend.Factory.backendId)
 
+    @Test
+    fun runJsBackendUnknownLibrary() {
+        val path = resourcePath("/run/input")
+        // Clean up in case someone ran a build in the source tree.
+        removeDirRecursive(path.resolve(TEMPER_OUT_NAME))
+        runWithTemporaryDirCopyOf("RunJsBackendUnknownLibrary", path) { tempDir ->
+            val result = doRun(
+                RunTask(
+                    backends = setOf(JsBackend.Factory.backendId),
+                    request = RunLibraryRequest(
+                        DashedIdentifier.from("no-such-library")!!,
+                        taskName = "RunJsBackendUnknownLibrary",
+                    ),
+                ),
+                workRoot = tempDir,
+            )
+            assertFalse(result.ok)
+        }
+    }
+
     @Ignore("Reexamine how import strategy and run tasks affect running only cherry-picked modules")
     @Test
     fun runJsBackendTop() = runRunTest("runTopLevel", JsBackend.Factory.backendId)