[Investigation] Use pattern matching for instanceof at module jdk.compiler

[Guoxiong Li]

Hi Brian,

Thank you for your reply. My confusion is solved.

If nobody announces that the same work is in progress, I will start the
work.

----
Best Regards,
Guoxiong.

On Thu, Apr 22, 2021 at 1:08 AM Brian Goetz <brian.goetz at oracle.com> wrote:

> Just like keeping the JDK codebase up to "modern Java" standards (an
> ongoing task!), we should do the same with the compiler codebase.  There is
> one constraint; we must wait one extra version to use new (permanent)
> language features in the compiler, because the compiler must be compiled
> with a boot JDK which is of the previous version.  So if pattern matching
> became permanent in 16, we can start to use it in the compiler in 17.
>
> In the JDK, we've set the following guidelines for these sort of
> refactoring patches:
>
>  - Each patch should focus on _one_ refactoring (e.g., replace traditional
> instanceof with pattern).  This reduces the cognitive load on reviewers.
>  - Each patch should have a single review domain.  This is not an issue
> for the compiler, but is an issue for the JDK, where `java.base` has
> generic library code, security code, UI code, each of which requires review
> by separate skillsets.
>  - Patches shouldn't be "too big".  This argues for breaking down by
> groups of related packages if the whole thing is too big.
>  - No API changes.
>  - Patches should be, to the degree possible, produced entirely by
> automated refactoring tools.  Resist the urge to make small manual tweaks
> to make the code look better.  Again, this makes it much easier for
> reviewers to conclude "nothing to see here."
>
>
> On 4/21/2021 12:51 PM, Guoxiong Li wrote:
>
> Hi all,
>
> The JEP-394[1] implemented the `Pattern matching for instanceof` at JDK
> 16. It is a good specification. Many packages or modules of the JDK begin
> to use it, such as package `java.time`[2][3]. I think it is good for the
> javac compiler to use it, too.
>
> Here are some issues we need to consider or something I want to confirm.
>
> 1. What's your opinion about this idea? Is it necessary?
> 2. Is somebody doing the same thing locally? If not, I would like to do
> that.
> 3. Is it good to revise the whole module `jdk.compiler` by submitting a
> big patch? Or, should we separate it into several sub-tasks according to
> different packages?
> 4. Do the related modules, such as `java.compiler`, also need to be
> revised?
>
> Any idea is appreciated.
>
> [1] https://openjdk.java.net/jeps/394
> [2] https://bugs.openjdk.java.net/browse/JDK-8263668
> [3] https://github.com/openjdk/jdk/pull/3170
>
> ----
> Best Regards,
> Guoxiong
>
>
>
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