RFR: JDK-8275308: Add valueOf(Runtime.Version) factory to SourceVersion [v3]

[Jonathan Gibbons]

On Wed, 20 Oct 2021 06:15:41 GMT, Joe Darcy <darcy at openjdk.org> wrote:

>> I wanted to get input on the design of API of the method before writing the tests.
>> 
>> The new factory method maps from a Runtime.Version object, a object which formally modes the version of the JDK, to a corresponding SourceVersion object.
>> 
>> Given the current histories of versioning of the JDK and SourceVersion this amount to mapping "JDK N" to RELEASE_N, for example, JDK 17 to RELEASE_17, etc. As mentioned in the API note, this could potentially change in the future if the release model changes. Runtime.Version has added in JDK 9, but earlier versions can be modeled. Note that no attempt is made to map "1.2" to RELEASE_2 and that since Runtime.Version grammar does not allow a leading 0 term, RELEASE_0 will *not* be returned by the new method.
>> 
>> Another design point: an out-of-range feature version is treated as an error so a Runtime.Version with a feature of 19 mapped in JDK 18 will fail with an IllegalArgumentException rather than saturating at RELEASE_18. If saturating would be more helpful for the envisioned use cases, I'm open to changing the spec accordingly.
>> 
>> CSR to follow once the API is nailed down.
>
> Joe Darcy has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - Add support for reverse conversion.
>  - Merge branch 'master' into JDK-8275308
>  - Fix typo.
>  - JDK-8275308: Add valueOf(Runtime.Version) factory to SourceVersio

src/java.compiler/share/classes/javax/lang/model/SourceVersion.java line 525:

> 523:         if (feature > Runtime.version().feature()) {
> 524:             throw new IllegalArgumentException("No matching SourceVersion for " + rv);
> 525:         } else {

Using `Runtime.version()` as a stand-in for the max `SourceVersion` seems non-obvious. Would it be better to use `SourceVersion.latest().runtimeVersion()` instead?

What about when running this API on JDK N-1?

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PR: https://git.openjdk.java.net/jdk/pull/5973