From f6392b1cfaa132896ccd697fa29d64d0b1201a83 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 5 Aug 2026 16:30:14 +0000
Subject: [PATCH 1/3] Initial plan


From ed63dbe2fdf8d858982dd5454e3d81f8444e7604 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Fri, 7 Aug 2026 12:19:20 +0000
Subject: [PATCH 2/3] fix(compiler): reject spreads that add properties to
 array models

Co-authored-by: timotheeguerin <1031227+timotheeguerin@users.noreply.github.com>
---
 packages/compiler/src/core/checker.ts        | 13 +++++++++
 packages/compiler/test/checker/model.test.ts | 28 ++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/packages/compiler/src/core/checker.ts b/packages/compiler/src/core/checker.ts
index 8d2203984d9..75624e55a98 100644
--- a/packages/compiler/src/core/checker.ts
+++ b/packages/compiler/src/core/checker.ts
@@ -5254,6 +5254,19 @@ export function createChecker(program: Program, resolver: NameResolver): Checker
           parentModel,
         );
 
+        if (
+          parentModel.indexer?.key.name === "integer" &&
+          (newProperties.length > 0 || additionalIndexer !== undefined)
+        ) {
+          reportCheckerDiagnostic(
+            createDiagnostic({
+              code: "no-array-properties",
+              target: prop.target,
+            }),
+          );
+          continue;
+        }
+
         if (additionalIndexer) {
           if (spreadIndexers) {
             spreadIndexers.push(additionalIndexer);
diff --git a/packages/compiler/test/checker/model.test.ts b/packages/compiler/test/checker/model.test.ts
index 5555a516397..2ba67205e5f 100644
--- a/packages/compiler/test/checker/model.test.ts
+++ b/packages/compiler/test/checker/model.test.ts
@@ -704,6 +704,34 @@ describe("with is", () => {
     });
   });
 
+  it("model is array cannot spread record properties", async () => {
+    const diagnostics = await Tester.diagnose(`
+        model A is Array<string> {
+          ...Record<int32>;
+        }
+        `);
+    expectDiagnostics(diagnostics, {
+      code: "no-array-properties",
+      message: "Array models cannot have any properties.",
+    });
+  });
+
+  it("model extends array cannot spread model properties", async () => {
+    const diagnostics = await Tester.diagnose(`
+        model Source {
+          name: string;
+        }
+
+        model A extends Array<string> {
+          ...Source;
+        }
+        `);
+    expectDiagnostics(diagnostics, {
+      code: "no-array-properties",
+      message: "Array models cannot have any properties.",
+    });
+  });
+
   it("doesn't allow duplicate properties", async () => {
     const diagnostics = await Tester.diagnose(`
         model A { x: int32 }

From 4e2fe195d97742e6691718da88339fcde899e9f2 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Fri, 7 Aug 2026 12:20:16 +0000
Subject: [PATCH 3/3] fix(compiler): use array-model check for spread
 validation

Co-authored-by: timotheeguerin <1031227+timotheeguerin@users.noreply.github.com>
---
 packages/compiler/src/core/checker.ts | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/packages/compiler/src/core/checker.ts b/packages/compiler/src/core/checker.ts
index 75624e55a98..eadd4c977bb 100644
--- a/packages/compiler/src/core/checker.ts
+++ b/packages/compiler/src/core/checker.ts
@@ -5254,10 +5254,7 @@ export function createChecker(program: Program, resolver: NameResolver): Checker
           parentModel,
         );
 
-        if (
-          parentModel.indexer?.key.name === "integer" &&
-          (newProperties.length > 0 || additionalIndexer !== undefined)
-        ) {
+        if (isArrayModelType(parentModel) && (newProperties.length > 0 || additionalIndexer !== undefined)) {
           reportCheckerDiagnostic(
             createDiagnostic({
               code: "no-array-properties",