RFR: JEP 359-Records: compiler code

Maurizio Cimadamore maurizio.cimadamore at oracle.com
Mon Oct 21 20:44:19 UTC 2019

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 

- 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 

* test/langtools/tools/javac/AnonymousClass/AnonymousClassFlags.java -  
why the change from @run to @compile?

- 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, 
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.


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


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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