RFR: JDK-8300914: Allow `@` as an escape in documentation comments [v2]

[Jonathan Gibbons]

On Thu, 2 Feb 2023 10:41:27 GMT, Pavel Rappo <prappo at openjdk.org> wrote:

>> Jonathan Gibbons has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:
>> 
>>  - Merge with upstream/master
>>  - JDK-8301294: Allow `@` as an escape in documentation comments
>
> src/jdk.compiler/share/classes/com/sun/source/doctree/EscapeTree.java line 37:
> 
>> 35:  * <ul>
>> 36:  *     <li>{@code @@}, representing {@code @}, where it would otherwise be treated as introducing a block or inline tag,
>> 37:  *     <li>{@code @/}, representing {@code /}, as part of {@code *@/} to represent <code>*/</code>, and
> 
> For other reviewers. Interpret that middle bullet literally: `@` escapes `/` only if it is preceded by `*`. In other words, it's a triple `*@/`, not a pair `@/`.
> 
> `@/` without preceding `*` causes errors if it can be confused for a start of a tag.
> 
> For a block tag:
> 
>     error: no tag name after '@'
>          @/
>           ^
> 
> For an inline tag:
> 
>     error: no tag name after '@'
>          {@/
>           ^
> 
> (FWIW, @jonathan-gibbons, note that the caret positions differ: the former points to `/` while the latter points to `@`. )
> 
> `*` is a sort of looked-behind and not consumed, which can be seen from the fact that
> 
>     /**
>      @*@/
>      */
> 
> is translated to this in documentation
> 
>     */
> 
> Given all of the above, I'm not sure if `@/` can be technically qualified as an ordinary escape sequence.

'/' cannot be part of a tag name.

A tag name starts with a character for which `isUnicodeIdentifierStart` is true, followed by zero or more characters for which `isUnicodeIdentifierPart` is true or is one of `.`, `-`, `:`.  See `DocCommentParser.readTagName` for verification. (We should update the Doc Comment Spec for that as well.)

So, the text of error messages above are correct, even if the positions require tweaking.

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PR: https://git.openjdk.org/jdk/pull/12372