JDK 15 RFR of JDK-8240130: Improve and update discussion of visitor evolution warnings

Wed Mar 11 05:09:05 UTC 2020

Hello,

Updated and expanded version of the webrev:

     http://cr.openjdk.java.net/~darcy/8240130.1

A few notes on reviewing:

     * The delta for each FooVisitor$N utility visitor family should be 
the same. I confirmed this visually by aligning up the udiffs of each 
family and switching between tabs.

     * To highlight the text differences, I did *not* reflow the 
paragraphs in this webrev. I'll do that before a push.

     * Some visitors had a tip

> Note that annotating methods in concrete
> subclasses with {@link java.lang.Override @Override} will help
>  ensure that methods are overridden as intended.

     While this may have been useful back in JDK 6, I don't think it is 
needed in JDK 15 and I'm proposing to remove these notes.

     * The wording in TypeKindVisitor$N was updated to explicitly 
mention the possibility of new enum values being added, aligning with 
the wording already in use in ElementKindVisitor$N.

Thanks,

-Joe

On 3/5/2020 12:18 PM, Jonathan Gibbons wrote:
>
> Looks good to me.
>
> Consider using a ':' instead of ',' on this line in the first file:
>
> 66 * visitUnknown}, behavior that will be overridden in concrete
> -- Jon
>
> On 2/26/20 10:00 PM, Joe Darcy wrote:
>> Hello,
>>
>> Please review the documentation changes for
>>
>>     JDK-8240130: Improve and update discussion of visitor evolution 
>> warnings
>> http://cr.openjdk.java.net/~darcy/8240130.0/
>>
>> Patch below. Some discussion of and rationale for the changes, the 
>> original javax.lang.model visitor interfaces and concrete visitor 
>> types had various warning about the unusual compatibility policies 
>> those types would use. Unlike other post-Java SE 6 era types, it was 
>> anticipated methods would be added to interfaces. Prior to default 
>> methods in JDK 8, such additions were a highly unusual occurrence for 
>> public types in the JDK. After default methods were used commonly in 
>> jDK 8, such additions are of less concern. The risk of a true source 
>> compatibility is also low for a new "visitFoo" method since it will 
>> have a parameter of type Foo, which is new to the release, and thus 
>> not have an overloading conflict with a method in an existing visitor 
>> outside of the JDK.
>>
>> The warnings are thus toned down and adjusted to note that the 
>> envisioned additions have already occurred for prior language 
>> additions. For example, the current policy is only to deprecate the 
>> constructors of obsolete visitor classes rather than the whole class. 
>> The "directly or indirectly call" visitUnknown is to accurately 
>> describe, but not limit to, the current policy of the visitFoo 
>> methods in affected concrete visitors calling the visitFoo default 
>> method on the *interface*, which in turn calls visitUnknown.
>>
>> The warning text is pulled into an apiNote to avoid getting 
>> inherit-doc-ed for any subclasses. Once the shape of the changes for 
>> the interface and visitor classes are agree to, I'll replicated the 
>> changes for the other types.
>>
>> Thanks,
>>
>> -Joe
>>
>> --- 
>> old/src/java.compiler/share/classes/javax/lang/model/element/ElementVisitor.java 
>> 2020-02-26 13:13:00.848880601 -0800
>> +++ 
>> new/src/java.compiler/share/classes/javax/lang/model/element/ElementVisitor.java 
>> 2020-02-26 13:13:00.512880601 -0800
>> @@ -40,10 +40,17 @@
>>   * is {@code null}; see documentation of the implementing class for
>>   * details.
>>   *
>> - * <p> <b>WARNING:</b> It is possible that methods will be added to
>> + * @apiNote
>> + *
>> + * WARNING: It is possible that methods will be added to
>>   * this interface to accommodate new, currently unknown, language
>>   * structures added to future versions of the Java™ programming
>> - * language.  Therefore, visitor classes directly implementing this
>> + * language.
>> + *
>> + * Such additions have already occurred to support language features
>> + * added after this API was introduced.
>> + *
>> + * Visitor classes directly implementing this
>>   * interface may be source incompatible with future versions of the
>>   * platform.  To avoid this source incompatibility, visitor
>>   * implementations are encouraged to instead extend the appropriate
>> @@ -52,21 +59,15 @@
>>   * parameters, return type, etc. rather than one of the abstract
>>   * classes.
>>   *
>> - * <p>Note that methods to accommodate new language constructs could
>> - * be added in a source <em>compatible</em> way if they were added as
>> - * <em>default methods</em>.  However, default methods are only
>> - * available on Java SE 8 and higher releases and the {@code
>> - * javax.lang.model.*} packages bundled in Java SE 8 were required to
>> - * also be runnable on Java SE 7.  Therefore, default methods
>> - * were <em>not</em> used when extending {@code javax.lang.model.*}
>> - * to cover Java SE 8 language features.  However, default methods
>> - * are used in subsequent revisions of the {@code javax.lang.model.*}
>> - * packages that are only required to run on Java SE 8 and higher
>> - * platform versions.
>> - *
>> - * @apiNote
>> + * <p>Methods to accommodate new language constructs are expected to
>> + * be added as default methods to provide strong source compatibility,
>> + * as done for {@link visitModule visitModule}. The implementations of
>> + * the default methods will in turn call {@link visitUnknown
>> + * visitUnknown}, behavior that will be overridden in concrete
>> + * visitors supporting the source version with the new language
>> + * construct.
>>   *
>> - * There are several families of classes implementing this visitor
>> + * <p>There are several families of classes implementing this visitor
>>   * interface in the {@linkplain javax.lang.model.util util
>>   * package}. The families follow a naming pattern along the lines of
>>   * {@code FooVisitor}<i>N</i> where <i>N</i> indicates the
>> --- 
>> old/src/java.compiler/share/classes/javax/lang/model/util/AbstractElementVisitor6.java 
>> 2020-02-26 13:13:01.560880601 -0800
>> +++ 
>> new/src/java.compiler/share/classes/javax/lang/model/util/AbstractElementVisitor6.java 
>> 2020-02-26 13:13:01.196880601 -0800
>> @@ -36,7 +36,9 @@
>>   * appropriate for the {@link SourceVersion#RELEASE_6 RELEASE_6}
>>   * source version.
>>   *
>> - * <p> <b>WARNING:</b> The {@code ElementVisitor} interface
>> + * @apiNote
>> + *
>> + * <strong>WARNING:</strong> The {@code ElementVisitor} interface
>>   * implemented by this class may have methods added to it in the
>>   * future to accommodate new, currently unknown, language structures
>>   * added to future versions of the Java™ programming language.
>> @@ -46,12 +48,12 @@
>>   * methods with names beginning with {@code "visit"}.
>>   *
>>   * <p>When such a new visit method is added, the default
>> - * implementation in this class will be to call the {@link
>> + * implementation in this class will be to directly or indirectly 
>> call the {@link
>>   * #visitUnknown visitUnknown} method.  A new abstract element visitor
>>   * class will also be introduced to correspond to the new language
>>   * level; this visitor will have different default behavior for the
>> - * visit method in question.  When the new visitor is introduced, all
>> - * or portions of this visitor may be deprecated.
>> + * visit method in question.  When a new visitor is introduced,
>> + * portions of this visitor class may be deprecated, including its 
>> constructors.
>>   *
>>   * @param <R> the return type of this visitor's methods. Use {@link
>>   *            Void} for visitors that do not need to return results.
>>
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