From a3dd28e923d59ed9afe0e9b17d215d8ce121f1a9 Mon Sep 17 00:00:00 2001
From: yearthmain <yearthmain@gmail.com>
Date: Tue, 4 Aug 2026 11:58:57 +0800
Subject: [PATCH] fix: guard Buffer.from island arguments before bytesNew

---
 .../src/frontend/lowering/lower-containers.ts   | 10 ++++++++--
 .../test/ts7/baselines/order-parity.json        |  6 ++++++
 tests/diagnostics/buffer-from-island/main.ts    |  7 +++++++
 .../node_modules/bytekit/index.d.ts             |  2 ++
 .../node_modules/bytekit/index.js               |  9 +++++++++
 .../node_modules/bytekit/package.json           |  6 ++++++
 .../buffer-from-island/main.ts.txt              | 17 +++++++++++++++++
 7 files changed, 55 insertions(+), 2 deletions(-)
 create mode 100644 tests/diagnostics/buffer-from-island/main.ts
 create mode 100644 tests/diagnostics/buffer-from-island/node_modules/bytekit/index.d.ts
 create mode 100644 tests/diagnostics/buffer-from-island/node_modules/bytekit/index.js
 create mode 100644 tests/diagnostics/buffer-from-island/node_modules/bytekit/package.json
 create mode 100644 tests/harness/__snapshots__/buffer-from-island/main.ts.txt

diff --git a/packages/compiler/src/frontend/lowering/lower-containers.ts b/packages/compiler/src/frontend/lowering/lower-containers.ts
index da557647..b53b3a7c 100644
--- a/packages/compiler/src/frontend/lowering/lower-containers.ts
+++ b/packages/compiler/src/frontend/lowering/lower-containers.ts
@@ -5956,10 +5956,16 @@ const DV_SETTERS: Record<string, { method: IrBytesIntrinsicMethod; le: boolean }
             return { kind: "libCall", fn: "buffer.fromStr", args: [s, enc], type: BYTES_U8, loc };
           }
           if (args.length === 1 && srcIr?.kind === "bytes" && srcIr.elem === "u8") {
-            return { kind: "bytesNew", source: L.lowerExpr(argNode), type: BYTES_U8, loc };
+            const source = L.lowerExpr(argNode);
+            if (source.type.kind === "bytes" && source.type.elem === "u8") {
+              return { kind: "bytesNew", source, type: BYTES_U8, loc };
+            }
           }
           if (args.length === 1 && srcIr?.kind === "array" && srcIr.elem.kind === "f64") {
-            return { kind: "bytesNew", source: L.lowerExpr(argNode), type: BYTES_U8, loc };
+            const source = L.lowerExpr(argNode);
+            if (source.type.kind === "array" && source.type.elem.kind === "f64") {
+              return { kind: "bytesNew", source, type: BYTES_U8, loc };
+            }
           }
         }
       }
diff --git a/packages/compiler/test/ts7/baselines/order-parity.json b/packages/compiler/test/ts7/baselines/order-parity.json
index 2afc3d3e..47e78545 100644
--- a/packages/compiler/test/ts7/baselines/order-parity.json
+++ b/packages/compiler/test/ts7/baselines/order-parity.json
@@ -6483,6 +6483,12 @@
    ],
    "diags": []
   },
+  "<repo>/tests/diagnostics/buffer-from-island/main.ts": {
+   "order": [
+    "<repo>/tests/diagnostics/buffer-from-island/main.ts"
+   ],
+   "diags": []
+  },
   "<repo>/tests/diagnostics/catch-bindings.ts": {
    "order": [
     "<repo>/tests/diagnostics/catch-bindings.ts"
diff --git a/tests/diagnostics/buffer-from-island/main.ts b/tests/diagnostics/buffer-from-island/main.ts
new file mode 100644
index 00000000..4a359c0f
--- /dev/null
+++ b/tests/diagnostics/buffer-from-island/main.ts
@@ -0,0 +1,7 @@
+// @dynamic
+// A package call keeps its value in the island even when its declaration
+// promises a supported container. Buffer.from must fence that boundary.
+import { bytes, numbers } from "bytekit";
+Buffer.from(bytes());
+Buffer.from(numbers());
+void 0;
diff --git a/tests/diagnostics/buffer-from-island/node_modules/bytekit/index.d.ts b/tests/diagnostics/buffer-from-island/node_modules/bytekit/index.d.ts
new file mode 100644
index 00000000..13fbbabe
--- /dev/null
+++ b/tests/diagnostics/buffer-from-island/node_modules/bytekit/index.d.ts
@@ -0,0 +1,2 @@
+export declare function bytes(): Uint8Array;
+export declare function numbers(): number[];
diff --git a/tests/diagnostics/buffer-from-island/node_modules/bytekit/index.js b/tests/diagnostics/buffer-from-island/node_modules/bytekit/index.js
new file mode 100644
index 00000000..5ce107f3
--- /dev/null
+++ b/tests/diagnostics/buffer-from-island/node_modules/bytekit/index.js
@@ -0,0 +1,9 @@
+"use strict";
+
+exports.bytes = function bytes() {
+  return new Uint8Array([1, 2, 3]);
+};
+
+exports.numbers = function numbers() {
+  return [1, 2, 3];
+};
diff --git a/tests/diagnostics/buffer-from-island/node_modules/bytekit/package.json b/tests/diagnostics/buffer-from-island/node_modules/bytekit/package.json
new file mode 100644
index 00000000..ccdfdf94
--- /dev/null
+++ b/tests/diagnostics/buffer-from-island/node_modules/bytekit/package.json
@@ -0,0 +1,6 @@
+{
+  "name": "bytekit",
+  "version": "1.0.0",
+  "main": "index.js",
+  "types": "index.d.ts"
+}
diff --git a/tests/harness/__snapshots__/buffer-from-island/main.ts.txt b/tests/harness/__snapshots__/buffer-from-island/main.ts.txt
new file mode 100644
index 00000000..eb386224
--- /dev/null
+++ b/tests/harness/__snapshots__/buffer-from-island/main.ts.txt
@@ -0,0 +1,17 @@
+buffer-from-island/main.ts:5:1 - error SC2020: 'Buffer.from with this argument shape' is part of the standard library types but has no scriptc lowering yet
+
+  4 | import { bytes, numbers } from "bytekit";
+  5 | Buffer.from(bytes());
+    | ^~~~~~~~~~~~~~~~~~~~
+  6 | Buffer.from(numbers());
+
+  hint: supported: Buffer.from(string, encoding?) with a literal encoding, Buffer.from(u8Array) — a copy — Buffer.from(number[]), or Buffer.from(x.buffer, byteOffset?, length?) — a view sharing x's storage (no free-standing ArrayBuffer value exists; narrow unions first)
+
+buffer-from-island/main.ts:6:1 - error SC2020: 'Buffer.from with this argument shape' is part of the standard library types but has no scriptc lowering yet
+
+  5 | Buffer.from(bytes());
+  6 | Buffer.from(numbers());
+    | ^~~~~~~~~~~~~~~~~~~~~~
+  7 | void 0;
+
+  hint: supported: Buffer.from(string, encoding?) with a literal encoding, Buffer.from(u8Array) — a copy — Buffer.from(number[]), or Buffer.from(x.buffer, byteOffset?, length?) — a view sharing x's storage (no free-standing ArrayBuffer value exists; narrow unions first)
\ No newline at end of file