Closes the migration tracked in #23043.
The new builder API (methods on the AST types themselves) has been in place for a while, all Oxc crates are migrated, and every crate which uses `AstBuilder` already enables `disable_old_builder` in its tests. The module docs said "after a few weeks, we will remove `AstBuilder`'s own methods entirely" — this does that.
## What's removed
- `crates/oxc_ast/src/generated/ast_builder.rs` and `builder/methods.rs` — `AstBuilder`'s own node and primitive constructors.
- `AstBuilderGenerator`, which produced the former.
- The `disable_old_builder` Cargo feature, plus the dev-dependency hacks it required across 33 manifests. Eight crates depended on `oxc_ast` *purely* to turn the feature on; those deps and their `cargo-shear` ignore entries are gone too.
## One thing worth reviewing
`AstBuilderGenerator` owned the `#[builder(default)]` / `#[builder(skip)]` attr registration that `BuilderMethodsGenerator` only *reads* — its doc comment said as much. Deleting it naively would have silently dropped `skip`/`default` handling for the 12 AST types using those attrs, so `attrs()` and `parse_attr()` move to `BuilderMethodsGenerator`.
The evidence this was faithful: after regenerating, `builder_methods.rs` and every other generated file are **byte-identical**. The only generated change in the diff is the deletion.
## Breaking changes
- `AstBuilder`'s own methods are gone. Use the AST type methods: `Statement::new_expression_statement(span, expr, &builder)` instead of `builder.statement_expression(span, expr)`.
- `AstBuilder` is no longer `Copy`/`Clone`, and its `allocator` field is private — use the `allocator` method from `GetAllocator`.
- `AstBuilder` and `NONE` are no longer re-exported from the crate root; import them from `oxc_ast::builder`. (The `disable_old_builder` feature already gated these off, so nothing in-tree used the root path.)
- The `disable_old_builder` feature no longer exists — remove it from any manifest that sets it.
A migration note covering all of the above is in `crates/oxc_ast/src/builder/mod.rs`.
---
Implemented with AI assistance (Claude Code); design, review, and verification driven by the author per the repo AI-usage policy.
Part of #23043.
We don't enable `oxc_ast`'s `disable_old_builder` Cargo feature in any of our published crates, or crates that are depended on by published crates.
Tasks are private to the repo, so enable this feature on them, to ensure no usage of legacy `AstBuilder` methods sneak in during the transition period before we delete these methods.
For historical reasons, `oxc_span` crate was re-exporting string types which now live in `oxc_str` crate.
Remove these re-exports, and import these types directly from `oxc_str`.
Main motivation is just that it makes sense, but it should also have a minor positive effect on compile times - `oxc_span` and `oxc_str` crates can now be compiled in parallel.
Move post-transform checker into a `tasks` crate. It doesn't feel like it belongs in `oxc_semantic`. It also feels like too heavy a lump of code to put in `tasks/common`.
Boshen