From 39818c169a5ed23d4a69c255da4cca0708e36ed7 Mon Sep 17 00:00:00 2001
From: Eric Myhre <hash@exultant.us>
Date: Wed, 14 Dec 2022 04:02:44 +0100
Subject: [PATCH] Add a SchemaConcatenate operation.

This stops one step shy of introducing an "include" features to th
IPLD Schema syntax... but can easily be used to produce such behavior.
---
 schema/dmt/operations.go | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
 create mode 100644 schema/dmt/operations.go

diff --git a/schema/dmt/operations.go b/schema/dmt/operations.go
new file mode 100644
index 00000000..0f83e5da
--- /dev/null
+++ b/schema/dmt/operations.go
@@ -0,0 +1,27 @@
+package schemadmt
+
+import (
+	"github.com/ipld/go-ipld-prime/datamodel"
+	"github.com/ipld/go-ipld-prime/node/bindnode"
+)
+
+// ConcatenateSchemas returns a new schema DMT object containing the
+// type declarations from both.
+//
+// As is usual for DMT form data, there is no check about the validity
+// of the result yet; you'll need to apply `Compile` on the produced value
+// to produce a usable compiled typesystem or to become certain that
+// all references in the DMT are satisfied, etc.
+func ConcatenateSchemas(a, b *Schema) *Schema {
+	// The joy of having an intermediate form that's just regular data model:
+	// we can implement this by simply using data model "copy" operations,
+	// and the result is correct.
+	nb := Type.Schema.NewBuilder()
+	if err := datamodel.Copy(bindnode.Wrap(a, Type.Schema.Type()), nb); err != nil {
+		panic(err)
+	}
+	if err := datamodel.Copy(bindnode.Wrap(b, Type.Schema.Type()), nb); err != nil {
+		panic(err)
+	}
+	return bindnode.Unwrap(nb.Build()).(*Schema)
+}