fix(stdlib): Prevent addBytesSlice throwing error on empty buffer (#1394

)

compiler/test/stdlib/buffer.test.gr

@@ -189,6 +189,10 @@ Buffer.addBytesSlice(0, 0, bytes, buf)
 assert Buffer.toBytes(buf) == Bytes.empty
 Buffer.addBytesSlice(0, Bytes.length(bytes), bytes, buf)
 assert Buffer.toBytes(buf) == bytes
+let emptyBytes = Bytes.make(0)
+let emptyBuffer = Buffer.make(0)
+Buffer.addBytesSlice(0, 0, emptyBytes, emptyBuffer)
+assert emptyBuffer == Buffer.make(0)
 
 // addString / toString
 let str = "Let's get this 🍞"
@@ -268,7 +272,9 @@ Buffer.addString("✨", buf2)
 Buffer.addBuffer(buf1, buf0)
 Buffer.addBuffer(buf2, buf0)
 assert Buffer.toString(buf0) == "✨🍩✨"
-
+let emptyBuffer = Buffer.make(0)
+Buffer.addBuffer(Buffer.make(0), emptyBuffer)
+assert emptyBuffer == Buffer.make(0)
 // addBufferSlice
 let buf0 = Buffer.make(0)
 let buf1 = Buffer.make(0)

stdlib/buffer.gr

@@ -339,32 +339,34 @@ export let addBytesSlice =
     bytes: Bytes,
     buffer: Buffer,
   ) => {
-  let (-) = WasmI32.sub
-  let (<) = WasmI32.ltS
-  let (>) = WasmI32.gtS
-  let (>=) = WasmI32.geS
-
-  // bounds check start
-  let bytelen = WasmI32.load(WasmI32.fromGrain(bytes), 4n)
-  let srcOff = coerceNumberToWasmI32(start)
-  if (srcOff < 0n || srcOff >= bytelen) {
-    throw Exception.IndexOutOfBounds
-  }
+  if (length != 0) {
+    let (-) = WasmI32.sub
+    let (<) = WasmI32.ltS
+    let (>) = WasmI32.gtS
+    let (>=) = WasmI32.geS
+
+    // bounds check start
+    let bytelen = WasmI32.load(WasmI32.fromGrain(bytes), 4n)
+    let srcOff = coerceNumberToWasmI32(start)
+    if (srcOff < 0n || srcOff >= bytelen) {
+      throw Exception.IndexOutOfBounds
+    }
 
-  // bounds check length
-  let len = coerceNumberToWasmI32(length)
-  if (len < 0n || len > bytelen - srcOff) {
-    throw Exception.IndexOutOfBounds
-  }
+    // bounds check length
+    let len = coerceNumberToWasmI32(length)
+    if (len < 0n || len > bytelen - srcOff) {
+      throw Exception.IndexOutOfBounds
+    }
 
-  autogrow(length, buffer)
+    autogrow(length, buffer)
 
-  let dstOff = coerceNumberToWasmI32(buffer.len)
-  let src = WasmI32.fromGrain(bytes)
-  let dst = WasmI32.fromGrain(buffer.data)
-  appendBytes(srcOff, dstOff, len, src, dst)
+    let dstOff = coerceNumberToWasmI32(buffer.len)
+    let src = WasmI32.fromGrain(bytes)
+    let dst = WasmI32.fromGrain(buffer.data)
+    appendBytes(srcOff, dstOff, len, src, dst)
 
-  buffer.len += length
+    buffer.len += length
+  }
 }
 
 /**