RFR: 8346657: Improve out of bounds exception messages for MemorySegments [v8]

[Per Minborg]

On Sun, 16 Nov 2025 14:50:39 GMT, Igor Rudenko <duke at openjdk.org> wrote:

>> Logic for creating IndexOutOfBoundsException in MemorySegment is reworked:
>> - separate logic of checking bounds and constructing exception messages for both `access` and `slice` cases 
>> - idea presented in [JDK-8288534](https://bugs.openjdk.org/browse/JDK-8288534) slightly reworked with preservation of the original approach
>
> Igor Rudenko has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Adjust to TestMergeStoresMemorySegment.java requirements

Previously, AMSI implemented `BiFunction<String, List<Number>, RuntimeException>`, but now that there are two different ways of generating exceptions, we need something else. I think the concept of having the AMSI implement interfaces is a good way of expressing a zero-allocation-on-check invariant in all situations.

Another alternative, compared to the proposed way, would be to create two new private interfaces, perhaps called `RangeCheckingExceptionFormatter` and `SliceCheckingExceptionFormatter`. Here is a sketch which I am certain can be improved:


interface ExceptionFormatter extends BiFunction<String, List<Number>, RuntimeException> {
    MemorySegment segment();
}

interface RangeCheckingExceptionFormatter extends ExceptionFormatter {

    @Override
    default RuntimeException apply(String s, List<Number> numbers) {
        long offset = numbers.get(0).longValue();
        long length = segment().byteSize() - numbers.get(1).longValue() + 1;
        return new IndexOutOfBoundsException(String.format("... <range text> ... on segment %s; new offset = %d; new length = %d",
                segment(), offset, length));
    }
}

interface SliceCheckingExceptionFormatter extends ExceptionFormatter {
    @Override
    default RuntimeException apply(String s, List<Number> numbers) {
        long offset = numbers.get(0).longValue();
        long length = segment().byteSize() - numbers.get(1).longValue() + 1;
        return new IndexOutOfBoundsException(String.format("... <slice text> ... on segment %s; new offset = %d; new length = %d",
                segment(), offset, length));
    }
}


Then we can let AMSI implement these interfaces and trivially implement `ExceptionFormatter::segment` by returning `this`. Then, when we need an exception formatter in the two distinct cases, we just cast `this` to the appropriate formatter type. 

Maybe there is a better way, but I think you get the underlying idea. What do you think?

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PR Comment: https://git.openjdk.org/jdk/pull/28124#issuecomment-3540957760