From 147335dfd54a831f0fb0440811510abc95a105e9 Mon Sep 17 00:00:00 2001
From: shiron-dev <shiron4710@gmail.com>
Date: Fri, 14 Jun 2024 00:10:47 +0900
Subject: [PATCH] fix error when model property is invalid (#3574)

fix #3504

When unsuitable types are specified in the model property, the invalid
code location is now reported instead of throwing an error.

When compiling the following tsp file, it is reported as follows
```tsp
interface TestInterface1 {
  get1(prop: TestInterface1): TestInterface1;
}
```

```
Diagnostics were reported during compilation:

/projects/typespec/packages/samples/scratch/main.tsp:2:8 - error @typespec/openapi3/invalid-model-property: 'Interface' cannot be specified as a model property.
> 2 |   get1(prop: TestInterface1): TestInterface1;
    |        ^^^^

Found 1 error.
```

---------

Co-authored-by: Timothee Guerin <tiguerin@microsoft.com>
Co-authored-by: Timothee Guerin <timothee.guerin@outlook.com>
---
 .chronus/changes/main-2024-5-13-14-52-31.md | 8 ++++++++
 packages/openapi3/src/lib.ts                | 6 ++++++
 packages/openapi3/src/schema-emitter.ts     | 9 ++++++++-
 3 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 .chronus/changes/main-2024-5-13-14-52-31.md

diff --git a/.chronus/changes/main-2024-5-13-14-52-31.md b/.chronus/changes/main-2024-5-13-14-52-31.md
new file mode 100644
index 0000000000..e5fa0ec174
--- /dev/null
+++ b/.chronus/changes/main-2024-5-13-14-52-31.md
@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: fix
+packages:
+  - "@typespec/openapi3"
+---
+
+Emit diagnostic when an invalid type is used as a property instead of crashing.
diff --git a/packages/openapi3/src/lib.ts b/packages/openapi3/src/lib.ts
index 8b45badd1c..64ef47e267 100644
--- a/packages/openapi3/src/lib.ts
+++ b/packages/openapi3/src/lib.ts
@@ -245,6 +245,12 @@ export const libDef = {
         default: paramMessage`Status code range '${"start"} to '${"end"}' is not supported. OpenAPI 3.0 can only represent range 1XX, 2XX, 3XX, 4XX and 5XX. Example: \`@minValue(400) @maxValue(499)\` for 4XX.`,
       },
     },
+    "invalid-model-property": {
+      severity: "error",
+      messages: {
+        default: paramMessage`'${"type"}' cannot be specified as a model property.`,
+      },
+    },
     "unsupported-auth": {
       severity: "warning",
       messages: {
diff --git a/packages/openapi3/src/schema-emitter.ts b/packages/openapi3/src/schema-emitter.ts
index 44f10ae4a5..3e05cd9978 100644
--- a/packages/openapi3/src/schema-emitter.ts
+++ b/packages/openapi3/src/schema-emitter.ts
@@ -351,7 +351,14 @@ export class OpenAPI3SchemaEmitter extends TypeEmitter<
     });
 
     if (refSchema.kind !== "code") {
-      throw new Error("Unexpected non-code result from emit reference");
+      reportDiagnostic(program, {
+        code: "invalid-model-property",
+        format: {
+          type: prop.type.kind,
+        },
+        target: prop,
+      });
+      return {};
     }
 
     const isRef = refSchema.value instanceof Placeholder || "$ref" in refSchema.value;