I'm running into an internal compiler error while trying to migrate my project to Kotlin 1.4. I have a Kotlin Multiplatform project (Gradle w/Kotlin dialect) building for two targets (JS and JVM); the JVM target uses Spring Boot 2.2.6. With the project configured to use the 1.3.72 plugin, everything builds fine. Moving to the 1.4.0 plugin (and updating Kotlin library references to 1.4.0) causes the build to fail with the error below:

FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':compileKotlinJvm'.
> Internal compiler error. See log for more details
 . . .
/xxx/xxx/xxx.kt:57
  @PutMapping("/{userId}", consumes = [MediaType.APPLICATION_JSON_VALUE])
                                      ^
e: org.jetbrains.kotlin.util.KotlinFrontEndException: Exception while analyzing expression at (57,39) in /xxx/xxx/xxx.kt
	at org.jetbrains.kotlin.types.expressions.ExpressionTypingVisitorDispatcher.logOrThrowException(ExpressionTypingVisitorDispatcher.java:253)
 . . .
Caused by: java.lang.NoSuchMethodError: kotlin.sequences.SequencesKt.flatMapIterable(Lkotlin/sequences/Sequence;Lkotlin/jvm/functions/Function1;)Lkotlin/sequences/Sequence;
	at org.jetbrains.kotlin.resolve.calls.components.CollectionTypeVariableUsagesInfo.getDependentTypeParameters(ResolutionParts.kt:364)

try adding

extra["kotlin.version"] = "1.4.0"

to your

build.gradle.kts

.

Magic! Thanks very much. Is there documentation anywhere regarding how that value is used?

perfect, thanks!