From 79e306f11d934383a6915ab7a7c28be33a5ab363 Mon Sep 17 00:00:00 2001
From: Miles Ziemer <mziemer@amazon.com>
Date: Tue, 26 Mar 2024 10:55:57 -0400
Subject: [PATCH] Load other shapes when a mixin can't be resolved

Found this when working on the language server - if you have a model
like:
```
$version: "2"

namespace com.foo

string Foo

@mixin
structure Bar {}

structure Baz with [Unknown] {}
```
loading it will result in `Foo` and `Bar` also not being loaded.
It seems like the reason for this was that if TopologicalShapeSort
failed, we wouldn't build _any_ shapes into the model, despite
TopologicalShapeSort being able to resolve some shapes.

Practically speaking I'm not sure if this means much in general,
but for the language server its big because without it, you
can't have mixin completions unless you either don't reload the
model on changes (which means you can't type a mixin, then get
completions to use it), or don't update the server's version
of the model if the new version is broken (which reduces the
quality of diagnostics, and has the same issue as the other way).
---
 .../smithy/model/loader/LoaderShapeMap.java   |  2 +-
 .../model/loader/ModelAssemblerTest.java      | 25 +++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/smithy-model/src/main/java/software/amazon/smithy/model/loader/LoaderShapeMap.java b/smithy-model/src/main/java/software/amazon/smithy/model/loader/LoaderShapeMap.java
index 669b88f6338..122bd5cd20c 100644
--- a/smithy-model/src/main/java/software/amazon/smithy/model/loader/LoaderShapeMap.java
+++ b/smithy-model/src/main/java/software/amazon/smithy/model/loader/LoaderShapeMap.java
@@ -229,7 +229,7 @@ private List<ShapeId> sort() {
                     emitUnresolved(shape, e.getUnresolved(), e.getResolved());
                 }
             }
-            return Collections.emptyList();
+            return e.getResolved();
         }
     }
 
diff --git a/smithy-model/src/test/java/software/amazon/smithy/model/loader/ModelAssemblerTest.java b/smithy-model/src/test/java/software/amazon/smithy/model/loader/ModelAssemblerTest.java
index 4067b70662c..3c542b41f9d 100644
--- a/smithy-model/src/test/java/software/amazon/smithy/model/loader/ModelAssemblerTest.java
+++ b/smithy-model/src/test/java/software/amazon/smithy/model/loader/ModelAssemblerTest.java
@@ -49,6 +49,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
+import java.util.Set;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import org.junit.jupiter.api.AfterEach;
@@ -1391,4 +1392,28 @@ public void handlesMultipleInheritanceForMixinMembers() {
         String actualPattern = shape.expectTrait(PatternTrait.class).getValue();
         assertThat(actualPattern, equalTo("baz"));
     }
+
+    @Test
+    public void loadsShapesWhenThereAreUnresolvedMixins() {
+        String modelText = "$version: \"2\"\n"
+                       + "namespace com.foo\n"
+                       + "\n"
+                       + "string Foo\n"
+                       + "@mixin\n"
+                       + "structure Bar {}\n"
+                       + "structure Baz with [Unknown] {}\n";
+        ValidatedResult<Model> result = Model.assembler()
+                .addUnparsedModel("foo.smithy", modelText)
+                .assemble();
+
+        assertThat(result.isBroken(), is(true));
+        assertThat(result.getResult().isPresent(), is(true));
+        Set<ShapeId> fooShapes = result.getResult().get().getShapeIds().stream()
+                .filter(id -> id.getNamespace().equals("com.foo"))
+                .collect(Collectors.toSet());
+        assertThat(fooShapes, containsInAnyOrder(
+                ShapeId.from("com.foo#Foo"),
+                ShapeId.from("com.foo#Bar")
+        ));
+    }
 }