JDK 13 RFR of JDK-8221264: Refactor SourceVersion#latestSupported

[Jonathan Gibbons]

Looks good to me.

-- Jon


On 03/25/2019 09:41 AM, Joe Darcy wrote:
> Hello,
>
> Hopefully the final iteration of this patch; updated materials:
>
>     8221264 Refactor and update SourceVersion.latestSupported
>     http://cr.openjdk.java.net/~darcy/8221264.2/
>     NEW! CSR https://bugs.openjdk.java.net/browse/JDK-8221415
>
> I added a comment citing JEP 322: "Time-Based Release Versioning" to 
> justify the new implementation.
>
> A CSR is needed because of the update to the minimum version returned, 
> just an @apiNote would not necessarily need a CSR as the changes would 
> be informative rather than normative.
>
> The particular implementation below would only work on JDK 10 and 
> higher as it uses a method added in JDK 10. However, the lower-bound 
> of latest supported is raised to JDK *9* rather than JDK 10 since an 
> independent implementation of the API could be written to run and 
> compile against 9.
>
> A few additional comments. The most common way of using the 
> javax.lang.model API is expected to be the version bundled in the JDK. 
> There is one particular other use case that has always intended to be 
> supported by JSR 269, namely running the API from JDK N on JDK (N-1) 
> assuming the user had their own compilation of the API. If other 
> mix-and-match use cases work that is fine - and the new implementation 
> should accurately support a larger number of reasonable combinations - 
> but it is a non-goal to impose any additional engineering constraints 
> on the evolution of the API to maximize the range of JDKs it can be 
> run on.
>
> Patch below.
>
> Thanks,
>
> -Joe
>
> --- 
> old/src/java.compiler/share/classes/javax/lang/model/SourceVersion.java 
> 2019-03-25 08:53:35.544735632 -0700
> +++ 
> new/src/java.compiler/share/classes/javax/lang/model/SourceVersion.java 
> 2019-03-25 08:53:35.220573632 -0700
> @@ -58,7 +58,7 @@
>       *   9: modules, small cleanups to 1.7 and 1.8 changes
>       *  10: local-variable type inference (var)
>       *  11: local-variable syntax for lambda parameters
> -     *  12: TBD
> +     *  12: no changes (switch expressions in preview)
>       *  13: TBD
>       */
>
> @@ -208,38 +208,36 @@
>
>      private static final SourceVersion latestSupported = 
> getLatestSupported();
>
> +    /*
> +     * The integer to release enum constant implemented by this method
> +     * assumes the JEP 322: "Time-Based Release Versioning" scheme is
> +     * in effect. This scheme began in JDK 10. If the JDK versioning
> +     * scheme is revised, this method may need to be updated
> +     * accordingly.
> +     */
>      private static SourceVersion getLatestSupported() {
> -        try {
> -            String specVersion = 
> System.getProperty("java.specification.version");
> -
> -            switch (specVersion) {
> -                case "13":
> -                    return RELEASE_13;
> -                case "12":
> -                    return RELEASE_12;
> -                case "11":
> -                    return RELEASE_11;
> -                case "10":
> -                    return RELEASE_10;
> -                case "9":
> -                    return RELEASE_9;
> -                case "1.8":
> -                    return RELEASE_8;
> -                case "1.7":
> -                    return RELEASE_7;
> -                case "1.6":
> -                    return RELEASE_6;
> -            }
> -        } catch (SecurityException se) {}
> -
> -        return RELEASE_5;
> +        int intVersion = Runtime.version().feature();
> +        return (intVersion >= 11) ?
> +            valueOf("RELEASE_" + Math.min(13, intVersion)):
> +            RELEASE_10;
>      }
>
>      /**
>       * Returns the latest source version fully supported by the
> -     * current execution environment.  {@code RELEASE_5} or later must
> +     * current execution environment.  {@code RELEASE_9} or later must
>       * be returned.
>       *
> +     * @apiNote This method is included alongside {@link latest} to
> +     * allow situations where the language model API is running on a
> +     * platform version different than the latest version modeled by
> +     * the API to be identified. One way that sort of situation can
> +     * occur is if a IDE or similar tool is using the API to model
> +     * source version <i>N</i> while running on platform version
> +     * (<i>N</i> - 1). Running in this configuration is
> +     * supported by the API. Running an API on platform versions
> +     * earlier than (<i>N</i> - 1) or later than <i>N</i>
> +     * may or may not work as an implementation detail.
> +     *
>       * @return the latest source version that is fully supported
>       */
>      public static SourceVersion latestSupported() {
>
>