Validation not working on Map keys in RestController

Question

Using Spring Boot 2.2.6, given this Controller:

@RestController
@Validated
class MyController {
    @GetMapping("foo")
    fun getFirmwareVersionDifference(
        @RequestParam @Valid versions: @Valid Map<
            @Pattern(regexp = "a|b|c")
            String, String>
    ): String {
       // …
    }
}

I would expect the request foo?d=any to throw a ConstraintViolationException, but the controller is called normally.

I have a MethodValidationPostProcessor in my context and it works for other validations. If I change the RequestParam to @RequestParam @Valid @Length(min=3) installedFirmwareVersion: String it works as expected fine.

What am I missing?

Answer 1

This is a kotlin compiler bug / missing feature: https://youtrack.jetbrains.com/issue/KT-13228

As documented in https://youtrack.jetbrains.com/issue/KT-35843 this is partially solved in kotlin 1.3.70.

Here's how you can set the compiler flag in build.gradle.kts

tasks.withType<KotlinCompile> {
    kotlinOptions {
        freeCompilerArgs = listOf("-Xemit-jvm-type-annotations")
        jvmTarget = "11" // at least 8 should work, I only tested 11
    }
}