javac rejects canonical constructor when formal parameter name doesn't match the record component name

[Vicente Romero]

I agree that the spec should be updated, I have created [1] to track 
this issue,

Vicente

[1] https://bugs.openjdk.java.net/browse/JDK-8236599

On 12/25/19 3:28 AM, Tagir Valeev wrote:
> Well, one place where people might dislike it is the established code
> style. Some projects may always use prefixed field names as
> constructor parameters to avoid 'this.' qualifier in assignments.
> Being unable to follow the same style in the records might be
> irritating.
>
> On the other hand, this simplifies things for IDE developers. I'm
> thinking about "make canonical constructor compact" quick-fix
> (available if canonical constructor ends with explicit assignment of
> some record components and has no returns, no custom parameter
> annotations, etc.) I thought it should be quite a difficult problem in
> general as we would need to rename parameters, solve possible name
> conflicts, possibly qualify fields with 'this.', etc. Having the
> restriction that names must be equal, the quick-fix implementation
> will be much simpler.
>
> With best regards,
> Tagir Valeev.
>
> On Wed, Dec 25, 2019 at 12:53 AM Brian Goetz <brian.goetz at oracle.com> wrote:
>> On this one, I agree with the compiler and think the spec should be adjusted.
>>
>> The reasoning is that I am looking down he road at named parameter invocation, and if the record component names mismatch the canonical ctor param names, that will cause trouble for no benefit.
>>
>> Sent from my iPad
>>
>>> On Dec 24, 2019, at 5:50 AM, Tagir Valeev <amaembo at gmail.com> wrote:
>>>
>>> Hello!
>>>
>>> javac 14-ea+28-1366 rejects the following code:
>>>
>>> record R(int x) {
>>>   public R(int _x) { this.x = _x; }
>>> }
>>>
>>> Test.java:2: error: invalid canonical constructor in record R
>>>   public R(int _x) { this.x = _x; }
>>>          ^
>>>   (invalid parameter names in canonical constructor)
>>> Note: Test.java uses preview language features.
>>> Note: Recompile with -Xlint:preview for details.
>>>
>>> However, the spec for the records [1] doesn't prohibit such a
>>>   renaming. It says only that "The types of the formal parameters in the
>>> formal parameter list of the canonical constructor must be identical
>>> to the declared type of the corresponding record component." The
>>> formal parameter names are only mentioned in "derived constructor
>>> signature" definition. However, this definition doesn't prohibit
>>> anything, to my understanding. So either compiler should be updated to
>>> allow such a code or spec should be updated to explicitly prohibit it.
>>>
>>> With best regards,
>>> Tagir Valeev.
>>>
>>> [1] http://cr.openjdk.java.net/~gbierman/jep359/jep359-20191125/specs/records-jls.html#jls-8.10.4