RFR: 8374633: Bang in signatures should go before the type

[Vicente Romero]

On Tue, 6 Jan 2026 18:12:56 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

> This PR tweaks signature generation so that bangs are added before the type being restricted, not after.
> 
> After fixing this I realized that no test was failing :-) so I added a separate compilation test to test `ClassReader`.
> The test revealed some gaps in parsing of generic type test patterns with null-restriction, which I have fixed.
> 
> Also, the test revealed issues with type substitution, as type substitution was not preserving the null-restrictions in the "from" types. This is also now fixed.

lgtm

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Marked as reviewed by vromero (Committer).

PR Review: https://git.openjdk.org/valhalla/pull/1860#pullrequestreview-3631994103