From 47cce5f1f54b86483f6f745c9625722d8ca576ac Mon Sep 17 00:00:00 2001
From: Jordon Phillips <JordonPhillips@users.noreply.github.com>
Date: Tue, 7 Nov 2023 15:26:36 +0100
Subject: [PATCH] Generate union docs

---
 .../smithy/docgen/core/DirectedDocGen.java       |  2 +-
 .../smithy/docgen/core/DocSymbolProvider.java    |  8 ++++++++
 smithy-docgen-test/model/main.smithy             | 16 ++++++++++++++++
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/smithy-docgen-core/src/main/java/software/amazon/smithy/docgen/core/DirectedDocGen.java b/smithy-docgen-core/src/main/java/software/amazon/smithy/docgen/core/DirectedDocGen.java
index 17a19ed..87a8217 100644
--- a/smithy-docgen-core/src/main/java/software/amazon/smithy/docgen/core/DirectedDocGen.java
+++ b/smithy-docgen-core/src/main/java/software/amazon/smithy/docgen/core/DirectedDocGen.java
@@ -74,7 +74,7 @@ public void generateError(GenerateErrorDirective<DocGenerationContext, DocSettin
 
     @Override
     public void generateUnion(GenerateUnionDirective<DocGenerationContext, DocSettings> directive) {
-        // no-op for now
+        new StructuredShapeGenerator(directive.context()).accept(directive.shape(), MemberListingType.OPTIONS);
     }
 
     @Override
diff --git a/smithy-docgen-core/src/main/java/software/amazon/smithy/docgen/core/DocSymbolProvider.java b/smithy-docgen-core/src/main/java/software/amazon/smithy/docgen/core/DocSymbolProvider.java
index e3affa4..f66cb0d 100644
--- a/smithy-docgen-core/src/main/java/software/amazon/smithy/docgen/core/DocSymbolProvider.java
+++ b/smithy-docgen-core/src/main/java/software/amazon/smithy/docgen/core/DocSymbolProvider.java
@@ -26,6 +26,7 @@
 import software.amazon.smithy.model.shapes.ShapeId;
 import software.amazon.smithy.model.shapes.ShapeVisitor;
 import software.amazon.smithy.model.shapes.StructureShape;
+import software.amazon.smithy.model.shapes.UnionShape;
 import software.amazon.smithy.model.traits.InputTrait;
 import software.amazon.smithy.model.traits.OutputTrait;
 import software.amazon.smithy.model.traits.StringTrait;
@@ -215,6 +216,13 @@ public Symbol intEnumShape(IntEnumShape shape) {
                 .build();
     }
 
+    @Override
+    public Symbol unionShape(UnionShape shape) {
+        return getSymbolBuilder(shape)
+                .definitionFile(getDefinitionFile(serviceShape, shape))
+                .build();
+    }
+
     @Override
     public Symbol memberShape(MemberShape shape) {
         var builder = getSymbolBuilder(shape)
diff --git a/smithy-docgen-test/model/main.smithy b/smithy-docgen-test/model/main.smithy
index 383eb26..157fee5 100644
--- a/smithy-docgen-test/model/main.smithy
+++ b/smithy-docgen-test/model/main.smithy
@@ -77,6 +77,8 @@ structure DocumentedStructure {
 
     /// This is a self-referential member. This is a thing that should be possible.
     self: DocumentedStructure
+
+    union: DocumentedUnion
 }
 
 /// This in an enum that can have one of the following values:
@@ -133,3 +135,17 @@ structure ServiceError with [ErrorMixin] {}
 
 /// This error is only returned by DocumentedOperation
 structure DocumentedOperationError with [ErrorMixin] {}
+
+/// Unions can only have one member set. The member name is used as a tag to
+/// determine which member is intended at runtime.
+union DocumentedUnion {
+    /// Union members for the most part look like structure members, with the exception
+    /// that exactly one must be set.
+    string: String
+
+    /// It doesn't matter that multiple members target the same type, since the type
+    /// isn't the discriminator, the tag (member name) is.
+    otherString: String
+
+    struct: DocumentedStructure
+}