fix(openapi3): use escaped string literals in object values to prevent triple-quote syntax errors

.chronus/changes/copilot-fix-json-interpreter-issue-2025-11-18-15-46-19.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/openapi3"
+---
+
+Fix extension properties with JSON-like strings using escaped string literals to prevent triple-quote syntax issues

packages/openapi3/src/cli/actions/convert/generators/common.ts

@@ -2,7 +2,7 @@
 export function stringLiteral(value: string): string {
   if (value.includes("\n")) {
     // Escape ${...} in multi-line strings to prevent interpolation
-    return `"""\n${value.replaceAll("${", "\\${")}\n"""`;
+    return `"""\n${value.replaceAll("${", "\\${").replaceAll('"""', '\\"""')}\n"""`;
   }
   // Escape both quotes and ${...} in single-line strings to prevent interpolation
   return `"${value.replaceAll('"', '\\"').replaceAll("${", "\\${")}"`;

packages/openapi3/test/tsp-openapi3/convert-openapi3-doc.test.ts

@@ -597,3 +597,64 @@ describe("unixtime format conversion", () => {
     );
   });
 });
+
+describe.each(versions)("Extension with JSON-like string values v%s", (version) => {
+  it("should treat JSON-like string in extension property as an escaped string literal", async () => {
+    const tsp = await convertOpenAPI3Document({
+      openapi: version,
+      info: {
+        title: "Test Service",
+        version: "1.0.0",
+      },
+      paths: {},
+      components: {
+        schemas: {
+          GraderPython: {
+            type: "object",
+            "x-oaiMeta": {
+              name: "Python Grader",
+              group: "graders",
+              example: `{
+  "type": "python",
+  "name": "Example python grader",
+  "image_tag": "2025-05-08",
+  "source": """
+def grade(sample: dict, item: dict) -> float:
+    """
+    Returns 1.0 if \`output_text\` equals \`label\`, otherwise 0.0.
+    """
+    output = sample.get("output_text")
+    label = item.get("label")
+    return 1.0 if output == label else 0.0
+""",
+}`,
+            },
+          },
+        },
+      },
+    } as any);
+
+    // the example should escape the literal syntax contained withing the string value
+    strictEqual(
+      tsp.includes('source": \\"""'),
+      true,
+      "Expected 'example' to be an escaped string literal with newlines represented as \\n, but got: " +
+        tsp,
+    );
+
+    // Should use triple-quoted strings for object literal values
+    strictEqual(
+      tsp.includes('example: """'),
+      true,
+      "Should use triple-quoted strings in object literals as they can break with nested quotes. Got: " +
+        tsp,
+    );
+
+    // Should NOT have nested object structure
+    strictEqual(
+      tsp.includes("example: #{"),
+      false,
+      "Should not parse JSON string as object literal. Got: " + tsp,
+    );
+  });
+});