Re-export moved proto types under deprecated paths

The proto-models extraction moved the prost-generated types from
`datafusion_proto::generated::*` into `datafusion_proto_models::generated::*`.
cargo-semver-checks flagged ~200 paths as removed, even though my
`pub use datafusion_proto_models::protobuf::*` wildcard re-export should
have covered them — turns out wildcard-of-wildcard re-exports aren't
followed by every static-analysis tool.

Two fixes:

1. `pub mod protobuf` now re-exports directly from
   `datafusion_proto_models::generated::datafusion::*` (the leaf module
   where the types are originally declared) instead of going through
   `datafusion_proto_models::protobuf::*` (itself a `pub use ::*`). One
   level of indirection avoided.

2. New `pub mod generated` re-exports the legacy `generated::datafusion::*`
   and `generated::datafusion_common` paths, with `#[deprecated]` pointing
   downstream callers at `datafusion_proto::protobuf` /
   `datafusion_proto_common::protobuf_common`.

Together: every `datafusion_proto::generated::*` and
`datafusion_proto::protobuf::*` path that compiled on `main` continues
to compile, with deprecation warnings on the legacy `generated::*`
paths.

The other API breaks (`PhysicalPlanNodeExt` trait import for inherent-
looking methods, `from_proto`/`try_from_proto` over `From`/`TryFrom` for
foreign-foreign pairs) can't be made backwards-compatible without
re-introducing the orphan rule problem; they're flagged in the PR
description.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: adriangb

datafusion/proto/src/lib.rs

@@ -137,7 +137,40 @@ pub mod protobuf {
         ScalarValue, Schema,
     };
     pub use datafusion_proto_common::{FromProtoError, ToProtoError};
-    pub use datafusion_proto_models::protobuf::*;
+    // Re-export every type from `datafusion-proto-models`'s generated module
+    // so the existing `datafusion_proto::protobuf::Foo` paths keep resolving.
+    // Going through the deeper `generated::datafusion` path (rather than
+    // `datafusion_proto_models::protobuf`, which is itself a `pub use ::*`)
+    // avoids a double wildcard re-export that some tools (cargo-semver-checks)
+    // don't follow.
+    pub use datafusion_proto_models::generated::datafusion::*;
+}
+
+/// Backwards-compatible re-export of the moved generated types.
+///
+/// The prost-generated structs now live in `datafusion-proto-models`;
+/// this module preserves the legacy `datafusion_proto::generated::*` paths
+/// for downstream callers. Prefer the [`protobuf`] module (or
+/// [`datafusion_proto_models`] directly) in new code.
+#[deprecated(
+    since = "53.1.0",
+    note = "use `datafusion_proto::protobuf` (or `datafusion_proto_models::protobuf`) instead"
+)]
+pub mod generated {
+    /// Re-export of the prost-generated types defined in `datafusion.proto`.
+    #[deprecated(
+        since = "53.1.0",
+        note = "use `datafusion_proto::protobuf` (or `datafusion_proto_models::protobuf`) instead"
+    )]
+    pub use datafusion_proto_models::generated::datafusion;
+
+    /// Re-export of the prost-generated common types defined in
+    /// `datafusion_common.proto`.
+    #[deprecated(
+        since = "53.1.0",
+        note = "use `datafusion_proto_common::protobuf_common` instead"
+    )]
+    pub use datafusion_proto_models::generated::datafusion_common;
 }
 
 #[cfg(doctest)]