RFR: 8348611: Eliminate DeferredLintHandler and emit warnings after attribution [v6]

[Maurizio Cimadamore]

On Tue, 29 Jul 2025 21:39:47 GMT, Archie Cobbs <acobbs at openjdk.org> wrote:

>> This is a cleanup/refactoring of how lint warnings are logged and `@SuppressWarnings` annotations applied.
>> 
>> A central challenge with lint warnings is that warnings can be generated during any compiler phase, but whether a particular lint warning is suppressed via `@SuppressWarnings` can't be known until after attribution. For example, the parser doesn't have enough information to interpret and apply `@SuppressWarnings("text-blocks")` to text blocks, or `@SuppressWarnings("preview")` to preview lexical features; instead, the `DeferredLintHandler` is used to workaround this limitation.
>> 
>> In addition, several other factors complicate things:
>> * Knowing the current applicable `Lint` instance requires manually tracking it with each declaration visited and applying/removing the `@SuppressWarnings` annotation there, if any
>> * Some warnings are "suppressibly mandatory" (i.e., they are _emitted if not suppressed_ instead of _emitted if enabled_)
>> * Some warnings are "unsuppressibly mandatory" (e.g., the "internal proprietary API" warning)
>> * Some mandatory warnings are _aggregated_ into notes that are emitted at the end of compilation when not enabled
>> * Some warnings are _lint_ warnings, with a corresponding lint category, while others are just "plain" warnings
>> * Some lint warnings are suppressible via `@SuppressWarnings`, while others are only suppressible via `-Xlint:-foo` flags
>> * Speculative compilation requires holding log messages in purgatory until the speculation resolves, after which they are then either discarded or emitted. But this creates a tricky interaction with `DeferredLintHandler` because even after speculation is complete, we may still not yet know whether a warning should be suppressed.
>> 
>> Previously the logic to get all of this right was non-obviously woven around the code base. In particular, you needed to know somehow whether or not to use `DeferredLintHandler`, and in what "mode".
>> 
>> The overall goal of this PR is to simplify usage so that **no matter where you are in the compiler, you can just invoke `log.warning()` to log a warning** and (mostly) forget about all of the details listed above.
>
> Archie Cobbs has updated the pull request incrementally with one additional commit since the last revision:
> 
>   More refactoring to simplify LintMapper per review.

src/jdk.compiler/share/classes/com/sun/tools/javac/code/LintMapper.java line 356:

> 354: 
> 355:             // If this declaration is not "interesting", we don't need to create a MappedDecl for it
> 356:             if (lint == previousLint && parent.parent != null) {

Does this mean we create a mapped decl for all toplevel decls in a file (even if their `lint` is not interesting) ? Why?

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/24584#discussion_r2242392260