RFR: Simplify jextract backend pipeline

[Jorn Vernee]

On Thu, 30 Nov 2023 19:19:17 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

> Now that we have mutable attributes, we can make the jextract pipeline a little simpler, by making sure that each step in the jextract pipeline doesn't destroy the information contained in the jextract model and, additionally, by making sure that each step can only add attributes to the IR (which are acted upon later on).
> 
> To do this, I had to do some foundational changes to TreeMaker, to make sure that all declaration nodes were being correctly de-duplicated: since declarations are referenced back by types, if a declaration is re-created multiple times, the types pointing to that declaration end up being out of sync, and that's not desirable (because that could lead to a loss of some of the attributes).
> 
> I also removed the `Transformer` interface: altering the model is not something the jextract pipeline should attempt to do. This meant that existing transformers have been reimplemented as side-effecting visitors, as follows:
> 
> * `EnumConstantLifter` adds an attribute to constants which belong to an enum (but no longer drops the enum on the ground);
> * `IncludeFilter` marks several declaration with a `Skip` attribute, to signal `outputFactory` not to generate any code for them;
> * `DuplicateFilter` also uses the `Skip` attribute to drop redundant declarations.
> 
> Additionally, the `NameMangler` has been simplified quite a bit, to the point that now it is just a simple visitor which ends up attaching attributes to declarations (`JavaName`, `JavaParameterNames`, `JavaFunctionalInterfaceName`). These attributes are later inspected (from `OutputFactory`). Since now the attribute is added directly to the relevant declaration, there is no need to have complex keying logic inside `NameMangler`.

src/main/java/org/openjdk/jextract/impl/DuplicateFilter.java line 74:

> 72:         // into the this.decls field.
> 73:         header.members().forEach(fieldTree -> fieldTree.accept(this, null));
> 74:         return header;

The `decls` field seems redundant now? We only add to the list, but never seem to read (and the comment here could be dropped too I think).

src/main/java/org/openjdk/jextract/impl/IncludeFilter.java line 94:

> 92:         if (parent == null && !includeHelper.isIncluded(tree)) {
> 93:             //skip
> 94:             tree.addAttribute(new Skip());

Maybe we could use a singleton instance?

src/main/java/org/openjdk/jextract/impl/NameMangler.java line 163:

> 161:     public Void visitScoped(Declaration.Scoped scoped, Declaration parent) {
> 162:         String name = scoped.name();
> 163:         if (name.isEmpty() && parent != null) {

Can we see a `null` parent here now? The old code doesn't have the null check.

src/main/java/org/openjdk/jextract/impl/TreeMaker.java line 124:

> 122:             declarationCache.put(pos, decl);
> 123:         }
> 124:         return decl;

IIRC we had a cache here before, but removed it because it was faster to re-create trees. That might have inadvertently also created latent issues with inconsistent IR views of the same decl?

Any way, we need the cache to 'canonicalize' IR nodes. Good to know.

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

PR Review Comment: https://git.openjdk.org/jextract/pull/148#discussion_r1411242850
PR Review Comment: https://git.openjdk.org/jextract/pull/148#discussion_r1411280046
PR Review Comment: https://git.openjdk.org/jextract/pull/148#discussion_r1411284691
PR Review Comment: https://git.openjdk.org/jextract/pull/148#discussion_r1411290220