RFR: JDK-8250768: javac should be adapted to changes in JEP 12

[Hannes Wallnöfer]

On Fri, 16 Oct 2020 15:20:03 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

> This is an update to javac and javadoc, to introduce support for Preview APIs, and generally improve javac and javadoc
> behavior to more closely adhere to JEP 12.
> The notable changes are:
> 
>  * adding support for Preview APIs (javac until now supported primarily only preview language features, and APIs
>    associated with preview language features). This includes:
>      * the @PreviewFeature annotation has boolean attribute "reflective", which should be true for reflective Preview APIs,
>        false otherwise. This replaces the existing "essentialAPI" attribute with roughly inverted meaning.
>      * the preview warnings for preview APIs are auto-suppressed as described in the JEP 12. E.g. the module that declares the
>        preview API is free to use it without warnings
>  * improving error/warning messages. Please see [1] for a list of cases/examples.
>  * class files are only marked as preview if they are using a preview feature. [1] also shows if a class file is marked as
>    preview or not.
>  * the PreviewFeature annotation has been moved to jdk.internal.javac package (originally was in the jdk.internal package).
>  * Preview API in JDK's javadoc no longer needs to specify @preview tag in the source files. javadoc will auto-generate a
>    note for @PreviewFeature elements, see e.g. [2] and [3] (non-reflective and reflective API, respectively). A summary of
>    preview elements is also provided [4]. Existing uses of @preview have been updated/removed.
>  * non-JDK javadoc is also enhanced to auto-generate preview notes for uses of Preview elements, and for declaring
>    elements using preview language features [5].
>  
>  Please also see the CSR [6] for more information.
>  
>  [1] http://cr.openjdk.java.net/~jlahoda/8250768/JEP12-errors-warnings-v6.html
>  [2] http://cr.openjdk.java.net/~jlahoda/8250768/jdk.javadoc.00/api/java.base/java/lang/Record.html
>  [3]
>  http://cr.openjdk.java.net/~jlahoda/8250768/jdk.javadoc.00/api/java.compiler/javax/lang/model/element/RecordComponentElement.html
>  [4] http://cr.openjdk.java.net/~jlahoda/8250768/jdk.javadoc.00/api/preview-list.html [5]
>  http://cr.openjdk.java.net/~jlahoda/8250768/test.javadoc.00/ [6] https://bugs.openjdk.java.net/browse/JDK-8250769

src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/HtmlDocletWriter.java line 2238:

> 2236:             if (previewTree != null) {
> 2237:                 previewDiv.add(new HtmlTree(TagName.A).put(HtmlAttr.ID, "preview")
> 2238:                                                       .add(new
> RawHtml(utils.getPreviewTreeSummaryOrDetails(previewTree, false))));

The `id` attribute needs to be unique within the page, so in addition to make the value not a valid java identifier (as
@jonathan-gibbons pointed out in a comment elsewhere) we need to support multiple preview ids per page. One way to do
this would be to add the element name to the id value, e.g. `preview-<element name>`.

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PR: https://git.openjdk.java.net/jdk/pull/703