arrow2-convert migration 4: support serde-based types in codegen (#3902)

This introduces the `rust.attr.serde_type` attribute, allowing you to
use any `serde`-compatible Rust types in our IDL.
```
table ViewportLayout (
  "attr.rust.derive": "PartialEq",
  "attr.rust.override_crate": "re_viewport"
) {
  space_view_keys: [ubyte] (order: 100, "attr.rust.serde_type": "std::collections::BTreeSet<re_viewer_context::SpaceViewId>");

  tree: [ubyte] (order: 101, "attr.rust.serde_type": "egui_tiles::Tree<re_viewer_context::SpaceViewId>");

  auto_layout: bool (order: 102);
}
```

This unblocks further blueprint experimentations, and is the last
blocker to sunset `arrow2-convert`.

- `SpaceViewComponent`, `SpaceViewMaximized` & `ViewportLayout` are now
all implemented that way.
- `re_viewport` is now free of `arrow2-convert`.

---

`arrow2-convert` migration PR series:
- #3853 
- #3855
- #3897
- #3902
- #3917

Author: teh-cmc

Cargo.lock

@@ -1,2 +1,5 @@
 include "./blueprint/auto_space_views.fbs";
 include "./blueprint/panel_view.fbs";
+include "./blueprint/space_view_component.fbs";
+include "./blueprint/space_view_maximized.fbs";
+include "./blueprint/viewport_layout.fbs";

crates/re_types/definitions/rerun/blueprint.fbs

@@ -0,0 +1,20 @@
+include "arrow/attributes.fbs";
+include "python/attributes.fbs";
+include "rust/attributes.fbs";
+
+include "rerun/datatypes.fbs";
+include "rerun/attributes.fbs";
+
+namespace rerun.blueprint;
+
+// ---
+
+/// A view of a space.
+///
+/// Unstable. Used for the ongoing blueprint experimentations.
+table SpaceViewComponent (
+  "attr.rust.derive_only": "Clone",
+  "attr.rust.override_crate": "re_viewport"
+) {
+  space_view: [ubyte] (order: 100, "attr.rust.serde_type": "crate::SpaceViewBlueprint");
+}

crates/re_types/definitions/rerun/blueprint/space_view_component.fbs

@@ -0,0 +1,24 @@
+include "arrow/attributes.fbs";
+include "python/attributes.fbs";
+include "rust/attributes.fbs";
+
+include "rerun/datatypes.fbs";
+include "rerun/attributes.fbs";
+
+namespace rerun.blueprint;
+
+// ---
+
+/// Whether a space view is maximized.
+///
+/// Unstable. Used for the ongoing blueprint experimentations.
+table SpaceViewMaximized (
+  "attr.arrow.transparent",
+  "attr.rust.derive": "Copy, Default, PartialEq, Eq",
+  "attr.rust.override_crate": "re_viewport",
+  "attr.rust.repr": "transparent",
+  "attr.rust.tuple_struct"
+) {
+  id: [ubyte] (order: 100, nullable, "attr.rust.serde_type": "re_viewer_context::SpaceViewId");
+}
+

crates/re_types/definitions/rerun/blueprint/space_view_maximized.fbs

@@ -0,0 +1,27 @@
+include "arrow/attributes.fbs";
+include "python/attributes.fbs";
+include "rust/attributes.fbs";
+
+include "rerun/datatypes.fbs";
+include "rerun/attributes.fbs";
+
+namespace rerun.blueprint;
+
+// ---
+
+/// A view of a space.
+///
+/// Unstable. Used for the ongoing blueprint experimentations.
+table ViewportLayout (
+  "attr.rust.derive": "PartialEq",
+  "attr.rust.override_crate": "re_viewport"
+) {
+  /// space_view_keys
+  space_view_keys: [ubyte] (order: 100, "attr.rust.serde_type": "std::collections::BTreeSet<re_viewer_context::SpaceViewId>");
+
+  /// tree
+  tree: [ubyte] (order: 101, "attr.rust.serde_type": "egui_tiles::Tree<re_viewer_context::SpaceViewId>");
+
+  /// auto_layout
+  auto_layout: bool (order: 102);
+}

crates/re_types/definitions/rerun/blueprint/viewport_layout.fbs

@@ -41,3 +41,11 @@ attribute "attr.rust.new_pub_crate";
 /// an object of kind `Blueprint` with `attr.rust.override_crate=re_viewport`, the final
 /// object will be generated in `crates/re_viewport/src/blueprint`.
 attribute "attr.rust.override_crate";
+
+/// Specify on an object field of type `[ubyte]` in order to (de)serialize using a pre-existing
+/// `serde` implementation.
+///
+/// Everything else works the same, include how module names are derived: e.g. if you define
+/// an object of kind `Blueprint` with `attr.rust.override_crate=re_viewport`, the final
+/// object will be generated in `crates/re_viewport/src/blueprint`.
+attribute "attr.rust.serde_type";