RFR: [15] JDK-8235947: Cleanup/simplify Utils.getBlockTags

Mon Dec 16 19:00:36 UTC 2019

On 12/16/2019 10:44 AM, Pavel Rappo wrote:
> Jon,
>
> The idea of the fix looks reasonable. Since I'm new to javadoc, I have more questions than would
> probably be expected during a typical review.
>
> 1. Could you help me understand the asymmetry in BaseTaglet?
>
>      public boolean accepts(DocTree tree) {
>          return (tree.getKind() == DocTree.Kind.UNKNOWN_BLOCK_TAG
>                      && tagKind == DocTree.Kind.UNKNOWN_BLOCK_TAG)
>                  ? ((UnknownBlockTagTree) tree).getTagName().equals(name)
>                  : tree.getKind() == tagKind;
>      }
>
> Why does this method check the pair (kind, name) for the case of UNKNOWN_BLOCK_TAG, but only checks
> the name in any other case, including the case where kind == UNKNOWN_INLINE_TAG?

The DocTree API has specific nodes, with a specific kind, for all 
"standard" nodes, but the API also
has to cope with additional/unknown/non-standard nodes.  These are (all) 
handled by
UnknownBlockTagTree, which contains the name of the non-standard tag.

Thus, for standard tags, it is sufficient to check the kind; for 
non-standard tags, represented by
instances of UnknownBlockTagTree, you need to check the name stashed in 
the UnknownBlockTagTree
node.

>
> 2. I think we could use contravariant generic parameter in the predicate in Utils:
>
> -    public List<? extends DocTree> getBlockTags(Element element, Predicate<DocTree> filter) {
> +    public List<? extends DocTree> getBlockTags(Element element, Predicate<? super DocTree> filter) {

Since there are no useful/interesting supertypes of the DocTree 
interface, I don't see that it is
necessary or helpful to use super-wildcards.

>
> On a related note. I noticed that com.sun.source.doctree.DocCommentTree uses bounded wildcards in
> the return types of its methods (e.g. List<? extends DocTree>). From a caller's perspective,
> List<DocTree> has the same usability as List<? extends DocTree>, if the caller agrees to only
> consume the elements from the list and to never add them there. Which I think was the intent here.
>
> Unless I'm mistaken, the only reason to use bounded wildcards in the return types is to design for
> covariant returns in subtypes. For example,
>
>      interface MyDocTree extends DocTree {
>          ...
>          List<? extends BlockTagTree> getBlockTags();
>          ...
>      }
>
> We don't seem to have those in javadoc. At the same time we're paying a small boilerplate fee for
> this--unused flexibility--each and every time one of those methods is called. What's worse is that
> this has a ripple effect, causing long generified lines to appear far beyond those methods' call
> sites.
>
> I guess what I'm saying is that we could look into simplifying that on the javadoc side (not the
> javac side).

a) we do use the ability to return lists of subtypes
b) this is a public API that now cannot reasonably be changed
>
> 3. Why did you remove @SuppressWarnings("fallthrough") from CommentHelper.getTagName?
It was not required.  It is a common misconception that multiple 
case-labels are an instance
of fallthrough semantics. It is not.   The fact that javadoc still 
builds, with -Werror, and no
change to the compilation command is additional evidence that the 
annotation was redundant.
Ideally, there ought to be a javac lint warning for unnecessary 
@SuppressWarnings!

>
> 4. Am I right saying that there are no JavaFX-specific taglets? And that is the reason why the
> "propertyDescription" and "defaultValue" tags are processed on the spot. At the same time the
> following constructor was left intact:
>
>      BaseTaglet(String, boolean, Set<Taglet.Location>)

There are no standard JavaFX tags/taglets.  The relationship between 
javadoc and JavaFX is
long and somewhat sad.  Early in the life of JavaFX, ~JDK8, the FX team 
added code to javadoc
to handle their stuff. In 9 the world was improved such that JavaFX was 
bundled/included
with JDK 9. Then, eventually, it got removed again. Sigh.

Arguably, now that the world is getting cleaner in javadoc-impl land, it 
would be reasonable
to have internal taglets for FX stuff, even if we don't include the tags 
in the standard set
supported by the DocTree API.
>
> Is it also for the sake of JavaFX? I wonder if we should spend some time later to hide everything
> JavaFX-related to a neat class rather than having it sprinkled all over the place.

I don't mind sprinkling the code in well-defined uses of well-defined 
abstractions.
But yes, there could be more cleanup in this area.

>
> Thanks for cleaning up the code along the way.

-- Jon

>
> -Pavel
>
>> On 14 Dec 2019, at 02:17, Jonathan Gibbons <jonathan.gibbons at oracle.com> wrote:
>>
>> Please review a moderately simple cleanup to the implementation(s) of Utils.getBlockTags.
>>
>> The existing code is unnecessarily string-oriented, and can be improved by better leveraging DocTree.Kind, especially by updating each subtype of BaseTaglet to know its associated DocTree.Kind.
>>
>> The core of the fix is Utils, with additional support in BaseTaglet and SimpleTaglet. The other changes are derivative changes using the new API.
>>
>> There are more changes possible in this (general) area. For example, there are similar methods such as Utils.hasBlockTag, and methods like CommentHelper.getTagName. At a minimum, it may be reasonable to co-locate all these methods in a new "Tags" utility class, but it is also worth investigating what additional simplifications can be made. But for now, this is a good checkpoint.
>>
>> The old code accidentally covered up a pre-existing bug, which was exposed in the replacement code. The old code did not return @uses and @provides from getBlockTags, and so they did not not to be skipped as part of the main comment in ModuleWriterImpl.  Now they are returned by getBlockTags, and so need to be skipped in TagletWriter.
>>
>> This is all cleanup with no changes in the generated output. There are no new tests and no changes needed to any existing tests. A full comparison against a reference JDK was done with the standard JDK docs (make docs) and with all the output from all the jtreg javadoc tests.
>>
>> -- Jon
>>
>> JBS: https://bugs.openjdk.java.net/browse/JDK-8235947
>> Webrev:  http://cr.openjdk.java.net/~jjg/8235947/webrev.00/
>>