[External] : RE: Docs generated by Java8 Javadoc are incompatible with "javadoc -source 8"

[Jonathan Gibbons]

On 11/20/22 11:59 PM, Roman Marchenko wrote:
>
> Hi Jon,
>
> Thank you for the answer.
>
> I'm wondering if it's possible to implement support for 'old' form of 
> anchors while generating docs with '-source 8' option to make the docs 
> compatible with Java8 docs. I guess this would make many people (which 
> had issues with docs compatibility before, but didn't say about it) 
> happy. Do you think it is a bad idea? Will it interfere the ongoing 
> work of standardization?
>
It's philosophically wrong to leverage the input language version to 
control the output version. See my earlier example, comparing this to 
javac's `--source` and `--target` option.

If this were to be supported at all, it would have to be done 
differently, such as with new command-line options if so required.  The 
problem is not easy, because it would involve consideration of the form 
of anchors being created for the declarations being documented, and the 
form of anchors being used for the documentation being linked to.  At 
best, it might be reasonable to use the old form of anchors for existing 
documentation that has already been generated by older versions of 
javadoc, but I don't think it is reasonable to use the old form of 
anchors in newly generated documentation.


> There is another question related to this topic. It seems like Javadoc 
> v11...15 cannot generate links to the external 
> docs.oracle.com/javase/8/docs/api at all. So docs generated using 
> ''-source 8' have no links to external documentation. There is 
> JDK-8216497 which, I guess, fixed this for later versions, but I don't 
> understand why it's not backported below. Are there any reasons to 
> block backporting this to lower versions?
>
Not all features (or bug fixes) get backported. Resources are always an 
issue. JDK-8216497 was a significant feature that required non-trivial 
build system changes, to make available the information about the 
platform declarations in earlier releases. That seems like too much to 
backport.


> Of course, the problems above don't seem significant, however Javadoc 
> seems inconsistent for now. So, I think, it'd be good to make it fixed 
> if possible.
>

At a minimum, it should be possible to use generate documentation 
linking to the standard docs at docs.oracle.com/javase/8/docs/api, using 
the `-link` or `linkoffline` options. That would be technically 
independent of the setting of the `--source` option. If that's not 
currently possible, that could be in the grey area
between a bug and an enhancement, and maybe worth investigating.

Is there a reason why you are using a newer version of javadoc, but 
wanting to use `--source 8` and link to older versions of the JDK API?

-- Jon


> Best regards,
>
> Roman
>
> *From:*javadoc-dev <javadoc-dev-retn at openjdk.org> *On Behalf Of 
> *Jonathan Gibbons
> *Sent:* Friday, November 18, 2022 8:30 PM
> *To:* javadoc-dev at openjdk.org
> *Subject:* Re: Docs generated by Java8 Javadoc are incompatible with 
> "javadoc -source 8"
>
> Hi Roman,
>
> TL;DR: The behavior is as expected.
>
> If nothing else, note that `--source` describes the language level of 
> the input source code, and has no relationship whatsoever to HTML 
> version used for the output. This is somewhat similar to javac, where 
> `--source` specifies the version of the input source files, and 
> `--target` specifies the classfile version of the generated class files.
>
> There are other major differences between JDK 8 javadoc and more 
> recent versions.  More obvious than the version of HTML, there is the 
> difference in the page layout: JDK 8 javadoc uses frames and predates 
> the Search facility; later versions do not use frames, and provide the 
> Search mechanism and more in-page links to aid with navigation.
>
> The issue of the form of anchors generated by different versions is an 
> interesting special case, with no easy solution at this time, other 
> than to use compatible versions of javadoc for the API being 
> cross-linked. There is no information available to the `-link` or 
> `-linkoffline` options to know the form of anchors used in the 
> documentation being linked to.
>
> That being said, there is ongoing work to standardize _and specify_ 
> the form of anchors and major structural elements to mitigate against 
> problems going forward.
>
> -- Jon
>
> On 11/18/22 7:32 AM, Roman Marchenko wrote:
>
>     Hi,
>
>     As far as I know, Html4 support was removed from Javadoc a time
>     ago. So now Javadoc generates html5-like anchors even with
>     “-source 8” or “-release 8” option specified. There is JDK-8187521
>     added TestAnchorNames.testHtml5 which checks if Html5-like anchors
>     are generated for “-source 8” option.
>
>     On the other hand, Java8’s Javadoc still supports html4 and
>     doesn’t support html5. So it turns that docs generated by Java8’s
>     Javadoc are not compatible with docs generated by any other (I
>     guess starting from jdk17 and above) “Javadoc -release 8” because
>     they use different types of anchors. So it’s impossible to use
>     cross links in such cases.
>
>     I haven’t found any discussion explaining that, so could anyone
>     explain, please, if it is correct behavior or not?
>
>     - Roman
>
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