RFR: JEP 359-Records: compiler code
Jan Lahoda
jan.lahoda at oracle.com
Tue Oct 22 15:21:19 UTC 2019
Hi,
In addition to Maurizio's comments, a few more comments:
-for tests, "--enable-preview -source 14" is used on many places. This
will cause issues when JDK 15 is started (and --enable-preview -source
14 will be replaced with --enable-preview -source 15). On all places
where that is possible, "--enable-preview -source ${jdk.version}" should
be used, or a programmatic equivalent.
-for code like this:
---$ cat R.java
public record R(int i) {}
---
compiling without --enable-preview:
--- $ javac R.java
/tmp/R.java:1: error: class, interface, or enum expected
public record R(int i) {}
^
1 error
---
it would be nice if we could provide some helpful note that to get
support for records, --enable-preview needs to be used. It may not be
possible to embed that into the error esp. for nested records, but at
least a warning. Just so that the user would get a hint what they are
doing wrong if records don't work for them.
-in Flags, it would be nice to document on which Symbols given flag may
appear. That would be useful in order to partition the Flags into
separate Symbol-kind specific sub-sets.
-in Lower, there is method "recordVars, which looks at the superclasses
of a record, to see if these have a state component - is a record
superclass of a record allowed? (I thought it isn't.)
-there seem to be commented debugs in Check, like:
+ //System.out.println("at Check.validateAnnotation: flags: " +
Flags.toString(s.flags_field) + ", declaration tree " + declarationTree);
Ideally, these would be removed
-in:
test/langtools/tools/javac/launcher/SourceLauncherTest.javathere are
changes like:
- file + ":1: error: class, interface, or enum expected\n" +
+ file + ":1: error: class, interface, enum expected\n" +
are these intentional? These seem suspicious to me.
-in:
test/langtools/tools/javac/processing/model/element/TestRecord.java
and:
test/langtools/tools/javac/processing/model/element/TestRecordDesugar.java
there is @bug 8888888 - that seems like a placeholder number.
Thanks,
Jan
On 21. 10. 19 22:44, Maurizio Cimadamore wrote:
> And here are some comments on Lower
>
> - findMethodOrFailSilently doesn't seem to be used anywhere; this
> should be removed and associated changes in Resolve reverted
>
> - findUserDefinedAccessors - this seems to have to do with setting the
> record component symbol straight - this should happen well before Lower,
> otherwise I'm not even sure what annotations processor will see? This
> code should go in TypeEnter, where you already look up for existing
> accessor.
>
> - related; not 100% as to why in visitRecordDef you protect against
> accessor not being there - which means you need to do a lookup. You need
> to get to this part of the code where all accessors have been set. Then
> the code can be simplified.
>
> - As pointed out previously, getting rid of the Pair<Kind, Symbol>
> accessor will result in cascading simplification in few methods in Lower
> too
>
> - both the signature generator and the indy machinery are shared between
> LambdaToMethod and Lower - so we should probably put them somewhere in a
> common superclass which can be used by the various backend steps
>
> - I guess the main translation strategy for record members is to
> generate an indy - where the runtime gives you back some constant
> callsite which wraps a method handle with the right signature. If so,
> some comments should be sprinkled around to clarify that this is indeed
> the case.
>
> - I also guess that the if/else in generateRecordMethod is to avoid
> generating a tree if an explicit member has been declared by the user -
> again, correct, but some comments please ;-)
>
>
> Also some comments on tests:
>
> * test/langtools/tools/javac/6402516/CheckLocalElements.java - why the
> change?
>
> * test/langtools/tools/javac/AnonymousClass/AnonymousClassFlags.java -
> why the change from @run to @compile?
>
> *
> test/langtools/tools/javac/annotations/repeatingAnnotations/combo/TargetAnnoCombo.java
> - who is using the new target?
>
> * diags/** in general, for all new diagnostics added it would be nice to
> have an html of the output (I have a script for doing that, let me know
> if you need it)
>
> * examples-not-yet - why no test for local records? That should be easy
> to add (I hope)?
>
> * test/langtools/tools/javac/parser/JavacParserTest.java - here I wonder
> if we should have different messages depending on the version (eg. we
> don't want to say 'expected records' if compiling with -source 12?)
>
> * test/langtools/tools/javac/tree/JavacTreeScannerTest.java,
> test/langtools/tools/javac/tree/SourceTreeScannerTest.java,
> src/jdk.compiler/share/classes/com/sun/tools/javac/code/Accessors.java -
> seems like these probably depend on the accessor pairs being in the AST?
>
> * test/langtools/tools/javac/doctree/AccessorsTest.java - not sure about
> this, does it even belong to this patch? I'd be surprised if DocTree
> does anything special with accessors?
>
> * test/langtools/tools/javac/doctree/AccessorsTest.java - this tests
> that ElementFilter and getAccessor() agree, but doesn't test that they
> actually yield the correct result
>
> * more generally, certain tests (e.g. signature mismatches, record
> component names order mismatches, reflection tests, serialization tests)
> have a certain ad-hoc nature to them - in the sense that they test one
> record shape or two and that's it. E.g.
>
> test/langtools/tools/javac/records/mandated_members/read_resolve_method/CheckReadResolveMethodTest.java
>
>
> I'd like to see a more combinatorial-oriented approach to such tests,
> where at least we tests all primitive types plus a reference type of
> choice, with varying degrees of arity (and w/, w/o varargs).
>
>
> That's all for now
>
> Thanks
> Maurizio
>
> On 21/10/2019 19:01, Maurizio Cimadamore wrote:
>> Hi Vicente,
>> I did a pretty thorough pass on most of the code. I didn't look at
>> tests, and I also didn't look at Lower. Comments below:
>>
>> * Flags.java - VARARGS flag for records components; I wonder, instead
>> of a new flag, can we use the internal VARARGS flag we have for
>> methods, and attach that to the record symbol? That should also lead
>> to more direct code in TypeHelper
>>
>> * Symbol.java - I think the override for 'erasure' is redundant -
>> isn't that the impl from supertype?
>>
>> * Symbol.java (and others) in general this webrev shuld be updated as
>> soon as Jan push the @Preview work, as I see that methods implementing
>> preview API are using the 'deprecate for removal' annotation
>>
>> * Symbol.java - I wonder if accessor list with Pair<Kind, Symbol>
>> isn't a premature generalization; we should just add a getter symbol
>> and that's it
>>
>> * Attr.java - I think we might want to leave the door open for a check
>> which forces all constructors of a record to go through the canonical
>> one (depending on where the spec lands)
>>
>> * Check.java - understanding checkpoint: when we see an annotation on
>> a record component, first we check it's one of the kinds which are
>> allowed (if not, error), and, if it's allowed, we add all record
>> component annotations to record component elements, and we also filter
>> away all annotations that have nothing to do with the element in which
>> they appear. If my understanding is correct, I think this logic should
>> be documented more clearly; I found the comment after the "if
>> (isRecordField)" to be a bit obscure.
>>
>> * Enter.java - why are you removing the static flag on records? I
>> don't see anything similar around for enums.
>>
>> * Flow.java - not sure I get the changes to checkInit; typically
>> checkInit is called at the use-site of DA/DU variables. Here it seems
>> you suppress some of the errors emitted for accessing record fields
>> inside the canonical constructor - but I hope that code like this
>>
>> record Foo(int x) {
>> Foo(int x) {
>> print(this.x);
>> }
>> }
>>
>> Still give errors? If this works correctly, which errors does the
>> 'guard' around the error generation is supposed to protect against?
>>
>> * MemberEnter.java - why the filter for HYPOTHETICAL ? It's only used
>> here...
>>
>> * TypeEnter.java - implicit super calls are added in Attr::visitMethod
>> for regular calls; we should do the same for records (or add all in
>> TypeEnter - that is records and class should be consistent)
>>
>> * TypeEnter.java - on finishClass - you are calling memberEnter on
>> record fields, which I think you already did in the new RecordsPhase
>>
>> * TypeEnter.java - (stylistic) addRecordsMemberIfNeeded should deal
>> with _all_ record members (e.g. including accessors), not just some?
>>
>> * TypeEnter.java - checkForSerializationMember should probably be
>> moved to MemberEnter::visitVar, or even to Attr (note that the code
>> for the check is doing a little visit :-))
>>
>> * TypeEnter.java - again on check timings; while it's ok for the code
>> in here to add new synthetic members, I think it's less ok to add more
>> global error checks (such as make sure that the canonical declaration
>> whose parameter names match the record components in order); these
>> should live in Attr. More generally, I think that we should only check
>> stuff here if we think that the check will add any value to annotation
>> processing. Every other check can be deferred, and take place in a
>> more 'deterministic' part of javac.
>>
>> * TypeEnter.java - I think finishClass should be a bit better at
>> determining as to whether default constructor is needed or not - for
>> instance, this check:
>>
>> if ((sym.flags() & INTERFACE) == 0 &&
>> 928 !TreeInfo.hasConstructors(tree.defs)) {
>>
>> Should be generalized to something that works for both classes and
>> records; for classes you need to check if there's no other
>> constructor; for records you need to check if there's no other
>> constructor _with same signature_ as the canonical one. Then you can
>> simplify addRecordMembers and remove the dependency on the boolean
>> 'generatedConstructor' parameter. In other words the code should:
>>
>> 1) check if default/canonical constructor generation is required
>> 2) if so, use the appropriate helper to generate the code
>> 3) at the end, add the remaining record members (under the assumption
>> that the canonical constructor has already been added in (1), if that
>> was missing)
>>
>> *TypeEnter.java - addAccessor can be simplified if we only worry about
>> getters. Again, the checks in here feel more Attr check than
>> MemberEnter checks.
>>
>> *TypeEnter.java - in addRecordMembersIfNeeded, I don't get why we
>> create a tree for a member, and then we visit the member tree with
>> memberEnter, just to add it to the scope. I understand that, currently
>> addEnumMembers does the same, but this looks very roundabout; I wonder
>> if there's a way to make all this process a bit simpler - create a
>> symbol and add that to the scope. Or are there important checks in
>> MemberEnter that we would lose?
>>
>> *JCTree.java/TreeMaker.java - I don't think there's any need to store
>> accessors in the field AST; these are only used from TypeEnter, and
>> TypeEnter can do whatever it does by looking at which record
>> components there are in the record class, and add a getter for each.
>> Let's make the code simpler and more direct
>>
>> * ClassReader.java - should we just silently ignore record attributes
>> when not in preview mode - or should we issue classfile errors?
>>
>> * ClassReader.java - what kind of validation should we do on record
>> attributes? Currently javac does nothing. Should we check that we have
>> (i) getters (ii) toString/hashCode/equals implementations and (iii) a
>> canonical constructor (ad fail if we don't) ? At the very least I
>> would add code to _parse_ the attribute, even if we do nothing with
>> it, so that at least we throw a classfile error if the attribute is
>> badly broken
>>
>> * Tokens.java - for "var", "yields" and other context-dependent
>> keywords we never added a token. We just handled that in JavacParser.
>> Why the difference here? I think it's best to stick to current style
>> and maybe fix all of them (assuming that's what we want to do) in a
>> followup cleanup. Actually, after looking at parser, it seems like you
>> already handle that manually, so I just suggest to revert the changed
>> to Tokens
>>
>> * TreeInfo.java - how is 'isCanonicalConstructor' not returning 'true'
>> for all constructors inside a record, as opposed to only return true
>> for the canonical one?
>>
>> * TreeInfo.java - There is some code reuse possible between
>> "recordFieldTypes" and "recordFields"
>>
>> * Names.java - what is 'oldEquals' ?
>>
>> * JavacParser.java - timing of checks; I don't think we should check
>> for illegal record component names in here
>>
>> * JavacParser.java - code can be simplified somewhat by getting rid of
>> accessors in VarDef AST.
>>
>>
>>
>>
>>
>> On 21/10/2019 13:31, Vicente Romero wrote:
>>> Hi,
>>>
>>> Please review the compiler code for JEP 359 (Records) [1]
>>>
>>> Thanks in advance for the feedback,
>>> Vicente
>>>
>>> [1]
>>> http://cr.openjdk.java.net/~vromero/records.review/compiler/webrev.00/
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