RFR: 8303374: Implement JEP 455: Primitive Types in Patterns, instanceof, and switch (Preview) [v57]

[Luca Kellermann]

On Wed, 31 Jan 2024 10:03:23 GMT, Aggelos Biboudis <abimpoudis at openjdk.org> wrote:

>> This is the proposed patch for Primitive types in patterns, instanceof, and switch (Preview).
>> 
>> Draft spec here: https://cr.openjdk.org/~abimpoudis/instanceof/latest/
>
> Aggelos Biboudis has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 78 commits:
> 
>  - Merge branch 'master' into primitive-patterns
>  - Update summary in ExactnessConversionsSupportTest
>  - Address review by Jan
>  - Remove redundant null check  and introduce a const boolean for unconditionally exact pairs
>  - Small fix in Javadoc
>  - Tidy up Javadoc of Lower.visitTypeTest
>  - Tidy up Javadoc of IllegalArgumentException in typeSwitch
>  - Improve readability in SwitchBootstraps
>  - Update year
>  - Cleanup redundant clone
>  - ... and 68 more: https://git.openjdk.org/jdk/compare/ec56c72b...f68748b1

src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java line 676:

> 674:         }
> 675:         else if (selectorType.equals(targetType) ||
> 676:                 ((selectorType.equals(byte.class) && !targetType.equals(char.class)) ||

Suggestion:

                ((selectorType.equals(byte.class) && targetType.isPrimitve() && !targetType.equals(boolean.class) && !targetType.equals(char.class)) ||

Otherwise, `SwitchBootstraps.typeSwitch` produces wrong results for `byte`:

var l = MethodHandles.lookup();
var shortType = MethodType.methodType(int.class, short.class, int.class);
var byteType = MethodType.methodType(int.class, byte.class, int.class);

CallSite shortSwitch = SwitchBootstraps.typeSwitch(l, "", shortType, String.class);
CallSite byteSwitch = SwitchBootstraps.typeSwitch(l, "", byteType, String.class);

int shortIndex = (int) shortSwitch.getTarget().invokeExact((short) 1, 0);
int byteIndex = (int) byteSwitch.getTarget().invokeExact((byte) 1, 0);

System.out.println(shortIndex == 1); // true
System.out.println(byteIndex == 1); // false
System.out.println(byteIndex); // 0

This would cause this code to misbehave (if it would compile, which it doesn't):

byte b = 1;
switch (b) {
    case String s -> System.out.println("How did we get here? byte is " + s.getClass());
}

So it isn't really a problem with `javac` but could cause problems for other users of `SwitchBootstraps`.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/15638#discussion_r2030113548