RFR: 8282823: javac should constrain more uses of preview APIs [v2]

[Maurizio Cimadamore]

On Mon, 14 Mar 2022 20:19:16 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> Consider a class or interface with a method marked as preview. Subclassing the class or implementing the interface by itself should not cause a preview error/warning (as that would be problematic for Loom), but overriding the method should produce a preview error/warning.
>> 
>> This patch adds the error/warning in case a preview method is overridden.
>
> Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Only produce preview warnings for immediate overriders of preview methods.

Logic looks good. Note that `membersClosure` is memory hungry - although here you are only (correctly) only calling it when there is some preview method around, so I think that's acceptable.

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Check.java line 1912:

> 1910:             if (m.owner != origin ||
> 1911:                 //performance - only do the expensive checks when the overridden method is a Preview API:
> 1912:                 (other.flags() & PREVIEW_API) == 0) {

indentation seems off here - e.g. I'd expect double "tab" in the second line of the `if` condition?

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Check.java line 1918:

> 1916:             for (Symbol s : types.membersClosure(origin.type, false).getSymbolsByName(m.name)) {
> 1917:                 if (m != s && m.overrides(s, origin, types, false)) {
> 1918:                     //only check if the preview only if "m" immediatelly overrides "other"

This comments seems to be off

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Marked as reviewed by mcimadamore (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/7774