8314213: DocLint should warn about unknown standard tags

[pavelrappo]

This PR is primarily informational: aside from adding a few code comments and assert statements, it acts as a place to record observations on unknown JavaDoc tag reporting mechanics. Because it's a PR, this text will be automatically sent to the javadoc-dev mailing list and archived for future reference.

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DocLint can be run in three modes:

• from javac (i.e. javac -Xdoclint)
• from javadoc (i.e. javadoc -Xdoclint)
• as a standalone test tool (i.e. test/langtools/tools/doclint/DocLintTester.java)

While the core of all these modes is the same, jdk.javadoc.internal.doclint.DocLint, and is capable of reporting on unknown tags, whether an unknown tag will be reported, depends on the core configuration, which differs significantly among these modes.

The latter mode is for testing only and can be configured flexibly, but it's of little interest to us. The former two modes are important as they face end user, but are limited in their configuration and, additionally, each has own peculiarities.

In javac mode, DocLint cannot be passed with a list of custom tags: the required wiring is missing. So, when a potentially unknown tag is detected, the error is not raised because env.customTags == null:

private void checkUnknownTag(DocTree tree, String tagName) {
    if (env.customTags != null && !env.customTags.contains(tagName))
        ^^^^^^^^^^^^^^^^^^^^^^
        env.messages.error(SYNTAX, tree, "dc.tag.unknown", tagName);
}

This is why we don't see errors for JDK-specific tags (e.g. @implSpec, @implNote, @apiNote, @jls) when make images, during which DocLint is run from javac.

In javadoc mode DocLint is passed with a list of custom tags, containing tags captured from -tag and -taglet options. Because make docs runs javadoc with such options for each of the JDK-specific tags, all tags are known, and no errors are reported.

Here's a twist though: javadoc has its own machinery for reporting unknown tags. So why don't we see doubling of diagnostics? There should be an error from DocLint and a warning [sic!] from javadoc, but there's only an error. Here's why:

public void checkTags(Element element, Iterable<? extends DocTree> trees) {
    CommentHelper ch = utils.getCommentHelper(element);
    for (DocTree tag : trees) {
        String name = tag.getKind().tagName;
                          ^^^^^^^^^^^^^^^^^
        if (name == null) {
            continue;
        }
        if (!name.isEmpty() && name.charAt(0) == '@') {
            name = name.substring(1);
        }
        if (! (standardTags.contains(name) || allTaglets.containsKey(name))) {
            if (standardTagsLowercase.contains(Utils.toLowerCase(name))) {
                messages.warning(ch.getDocTreePath(tag), "doclet.UnknownTagLowercase", ch.getTagName(tag));
                continue;
            } else {
                messages.warning(ch.getDocTreePath(tag), "doclet.UnknownTag", ch.getTagName(tag));
                continue;
            }
        }

Unknown tags are modelled by two DocTree subinterfaces, UnknownInlineTagTree and UnknownBlockTagTree, each of which return the name of the captured tag from getTagName(), not from getKind().tagName, which (unsurprisingly) returns null for those two kinds. That means that the body of this if block is dead code (i.e. DocLint or not, it's never reached for an unknown tag):

        if (! (standardTags.contains(name) || allTaglets.containsKey(name))) {

Here's another twist: DocLint can be disabled for a javadoc run: -Xdoclint:none. When coupled with defunct javadoc reporting, disabled DocLint means that no unknown tags are reported.

I don't know which of the above is by mistake and which by design, but it's how it works today. We could address (some of) that in a later PR. Personally, I wouldn't provide missing wiring in javac, given that javac mode has been recently somewhat de-emphasized. That said, I think we should repair javadoc reporting and make sure that either DocLint or javadoc, but not both, report on unknown tags at all times (i.e. whatever the javadoc configuration might be).

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Progress

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Issue

• JDK-8314213: DocLint should warn about unknown standard tags (Bug - P4)

Reviewers

• Jonathan Gibbons (@jonathan-gibbons - Reviewer)

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[pavelrappo]

I forgot to add one important point. tier1 now also does make docs: if there are doc errors, including unknown tags, they will be caught early. Whether doc build succeeds or fails, can be seen, for example, in PR checks (Pre-submit tests - docs / build - Build / test).

[pavelrappo]

Filed a follow-up bug: https://bugs.openjdk.org/browse/JDK-8314448

[openjdk]

@pavelrappo This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8314213: DocLint should warn about unknown standard tags

Reviewed-by: jjg

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At the time when this comment was updated there had been 5 new commits pushed to the master branch:

• 6b396da: 8062795: (fs) Files.setPermissions requires read access when NOFOLLOW_LINKS specified
• 7b28d36: 8314330: java/foreign tests should respect vm flags when start new processes
• b32d641: 8311943: Cleanup usages of toLowerCase() and toUpperCase() in java.base
• 13f6450: 8313765: Invalid CEN header (invalid zip64 extra data field size)
• 24e896d: 8310275: Bug in assignment operator of ReservedMemoryRegion

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As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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[jonathan-gibbons]

we could/should have more tests for some of these situations

[pavelrappo]

/integrate

[openjdk]

Going to push as commit 6f1071f.
Since your change was applied there have been 11 commits pushed to the master branch:

• 4331193: 8314423: Multiple patterns without unnamed variables
• 249dc37: 8314321: Remove unused field jdk.internal.util.xml.impl.Attrs.mAttrIdx
• b78f5a1: 8314076: ICC_ColorSpace#minVal/maxVal have the opposite description
• 2a1176b: 8314276: Improve PtrQueue API around size/capacity
• 0c3bc71: 8281169: Expand discussion of elements and types
• f143380: 8314240: test/jdk/sun/security/pkcs/pkcs7/SignerOrder.java fails to compile
• 6b396da: 8062795: (fs) Files.setPermissions requires read access when NOFOLLOW_LINKS specified
• 7b28d36: 8314330: java/foreign tests should respect vm flags when start new processes
• b32d641: 8311943: Cleanup usages of toLowerCase() and toUpperCase() in java.base
• 13f6450: 8313765: Invalid CEN header (invalid zip64 extra data field size)
• ... and 1 more: https://git.openjdk.org/jdk/compare/1925508425cf1b2d46173754077a588290253430...master

Your commit was automatically rebased without conflicts.

[openjdk]

@pavelrappo Pushed as commit 6f1071f.

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