daniellansun commented on PR #2845:
URL: https://github.com/apache/groovy/pull/2845#issuecomment-5479443071
@paulk-asert Thanks, Paul — this was the right list to walk through before
merge. We have decided each row as below; the well-formedness checks stay on
**every** compilation unit (dynamic Groovy and scripts included), with no
opt-out.
### Team call 1 — `new T[n]` / `new T[]{…}`
We will **reject** it, with no carve-out in `isReifiable`.
A type variable is not reifiable (JLS 4.7 / 15.10.1). What Groovy 4/5
compiled was `Object[]` (or the bound) typed as `T[]` — Java’s `(T[]) new
Object[n]`, without the cast in the source. Treating `T` as reifiable would
also be the wrong predicate for `instanceof T`.
The Java idiom remains the workaround, in both dynamic and `@CompileStatic`
code:
```groovy
items = (T[]) new Object[capacity] // unbounded T
items = (T[]) new Bound[capacity] // T extends Bound
items = (T[]) Array.newInstance(token, n) // when a Class<T> is at hand
```
`new List<String>[n]` stays rejected; `new List<?>[n]` stays legal.
### Team call 2 — generic class extending `Throwable`
We will **reject** it as well, for JLS 8.1.2 / javac parity. Groovy’s
`catch` is erased, so the class would still run on the JVM — but this PR’s
charter is well-formedness that javac already enforces, and Groovy 6 is the
window.
Workaround: keep the exception non-generic and move the type parameter onto
an accessor (or a factory). Parameterized `catch` is already impossible in the
grammar (`catchType` has no type arguments).
### Remaining rows
Agreed: **break and document** for all of them, including `List<int>`, `new
T()` / `T.class`, `implements X<? extends …>`, `new ArrayList<?>()` , a class
type as an additional bound, `Foo<String>.class`, and `Outer.Inner<String>`
with a raw generic `Outer`.
A table in that shape is now in `core-object-orientation.adoc` §Generics
(`[[generics-well-formedness]]`), with the two workarounds above as executable
examples. I would still welcome a matching table in the 6.0 release notes if
you would like to take that, as you offered.
### Message nits
Both fixed:
- `new T[n]` now reports `generic array creation of T` (the type variable,
not the erasure).
- `Foo<String>.class` now reports `Cannot select from a parameterized type`
(JLS 15.8.2). `Cell<String>.ID` / `.id()` keep the 4.5.2 “static member through
a parameterization” wording. `value.class` / `value*.class` are unchanged —
those are `getClass()`, not class literals.
### `"outer.class"` metadata
Noted. The enclosing type lives on the `ClassNode` field
(`getOuterClassType()` / `@since 6.0.0`); we will not restore a metadata
fallback. Transform authors who still read the GROOVY-10646-era key will see
`null`.
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