RFR: 8268850: AST model for 'var' variables should more closely adhere to the source code [v2]

[Vicente Romero]

On Wed, 25 Feb 2026 11:11:53 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> Currently, if a local variable is declared using `var`, or if a lambda parameter has an inferred (missing) type, the AST model is a bit weird. The variable starts with `null` type, and the type is then replaced with a synthetic AST representing the real type. This (draft) PR is attempting to clean this up a little:
>> - variables declared with `var` have `VarTypeTree` as the type. This is a new AST node that represents `var`. Positions are expected to be exact w.r.t. what is in the source code.
>> - lambda parameters with inferred type would have `null` as the type. This is consistent with majority of the places in the AST where something is not part of the source code
>> - for explicit parameters, the type is the real type, as before
>> 
>> This is not a compatible change, but I tried to partially write two clients, and it feels it wasn't too bad, and (hopefully) the new state is cleaner/more consistent.
>> 
>> There are some consistency comments:
>> 
>> - when the inferred types are inaccessible, javac (currently) sometimes produces a compile-time error, and sometimes does not; after reading the JLS, the error is indeed mandated in some cases, and not in others. `test/langtools/tools/javac/lvti/VarAccessibility.java` shows the cases
>> - when the inferred types have potential for various types of warnings, javac (currently) sometimes produces those warnings, and sometimes not. The decision here is mostly implementation driven. I looked at the possibility to always produce the warnings, but there's https://bugs.openjdk.org/browse/JDK-8013222, from which it seems the original intent was to not produce the warnings. So, this PR currently will not produce warnings on the inferred types.
>> 
>> I was considering adding something similar to get JCVarDecl.DeclKind, but (based on the experience from the clients), it didn't feel strongly needed, as the type is determinable from `getType()`.
>> 
>> Any insights?
>> 
>> CC @cushon
>> 
>> Please also review:
>> - CSR: https://bugs.openjdk.org/browse/JDK-8376736
>> - release note: https://bugs.openjdk.org/browse/JDK-8377951
>
> Jan Lahoda has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 29 commits:
> 
>  - Merge remote-tracking branch 'upstream-ssh/master' into JDK-8268850-vartype-ast
>  - Cleanup
>  - Adjusting tests.
>  - Merge branch 'JDK-8371683' into JDK-8268850-vartype-ast+JDK-8371683
>  - Updating header years.
>  - Fixing parsing with flags.
>  - Cleanup.
>  - Fixing parsing.
>  - Adding source-level restriction.
>  - 8371683: TYPE_USE annotation on var lambda parameter should be rejected
>  - ... and 19 more: https://git.openjdk.org/jdk/compare/6c39d1bb...d22966a5

Marked as reviewed by vromero (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/29369#pullrequestreview-3854330029