Suggest using a newer JDK for unavailable options in -java-output-version

[BalmungSan]

Compiler version

3.3.3

Minimized code

cs launch scala:3.3.3 -- -java-output-version 21

Output

21 is not a valid choice for -java-output-version

Expectation

According to the JDK compatibility page: https://docs.scala-lang.org/overviews/jdk-compatibility/overview.html
Scala 3 supports Java 21 since 3.3.1.
Yet, despite that, the compiler rejects 21 as a valid Java output version. Furthermore, printing the -help of the compiler and looking for -java-output-version only lists up to Java 17 as supported targets.

I would expect to be able to use 21 as a valid Java output version. This, in turn, should allow me to:

• Access Java stdlib methods added since Java 21; like Character.isEmoji: https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/Character.html#isEmoji(int)
• Generate Java class files whose bytecode version is 65.0: https://javaalmanac.io/bytecode/versions/
• Parse Java sources that use Java 21 language features; like pattern matching: https://docs.oracle.com/en/java/javase/21/language/pattern-matching-switch-expressions-and-statements.html

[BalmungSan]

False alarm, it does accept 21 as long as your JDK is also at least 21; which makes total sense.
I was running on a 17 JDK when I tested this, which explains why it only shown 17 as the maximum supported target.

Having said that, IMHO, the error message was really misleading.
Something along the lines of

While 21 is supported by the compiler, your current environment is running in version 17, thus 21 is an invalid target.

Or something similar (English is not my first language, so the redaction can probably be improved).

---

This issue is no longer a "Bug report" but rather a "Error/Warning message report".

[SethTisue]

I was fooled by this as well. I agree the error message is worth improving.

[som-snytt]

also -java-output-version:help is not supported