support negative slice index for arrayview and bytesview

builtin/arrayview.mbt

@@ -234,10 +234,11 @@ pub fn op_as_view[T](
   let len = self.length()
   let end = match end {
     None => len
-    Some(end) => end
+    Some(end) => if end < 0 { len + end } else { end }
   }
+  let start = if start < 0 { len + start } else { start }
   guard start >= 0 && start <= end && end <= len else {
-    abort("View start index out of bounds")
+    abort("View index out of bounds")
   }
   ArrayView::{ buf: self.buffer(), start, len: end - start }
 }
@@ -289,10 +290,11 @@ pub fn op_as_view[T](
   let len = self.length()
   let end = match end {
     None => len
-    Some(end) => end
+    Some(end) => if end < 0 { len + end } else { end }
   }
+  let start = if start < 0 { len + start } else { start }
   guard start >= 0 && start <= end && end <= len else {
-    abort("View start index out of bounds")
+    abort("View index out of bounds")
   }
   ArrayView::{ buf: self.buf, start: self.start + start, len: end - start }
 }

builtin/arrayview_test.mbt

@@ -1,4 +1,4 @@
-// Copyright 2024 International Digital Economy Academy
+// Copyright 2025 International Digital Economy Academy
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -120,3 +120,111 @@ test "arrayview_filter" {
   assert_eq!(filtered.length(), 1)
   assert_eq!(filtered[0], 4)
 }
+
+test "negative index1" {
+  let arr = [1, 2, 3]
+  let view = arr[-1:]
+  inspect!(view, content="[3]")
+  let view = arr[-2:]
+  inspect!(view, content="[2, 3]")
+  let view = arr[-3:]
+  inspect!(view, content="[1, 2, 3]")
+  let view = arr[:-1]
+  inspect!(view, content="[1, 2]")
+  let view = arr[:-2]
+  inspect!(view, content="[1]")
+  let view = arr[:-3]
+  inspect!(view, content="[]")
+  let view = arr[-3:-3]
+  inspect!(view, content="[]")
+  let view = arr[-3:-2]
+  inspect!(view, content="[1]")
+  let view = arr[-3:-1]
+  inspect!(view, content="[1, 2]")
+  let view = arr[-3:0]
+  inspect!(view, content="[]")
+  let view = arr[-3:1]
+  inspect!(view, content="[1]")
+  let view = arr[-3:2]
+  inspect!(view, content="[1, 2]")
+  let view = arr[-3:3]
+  inspect!(view, content="[1, 2, 3]")
+}
+
+test "negative index2" {
+  let arr = [0, 1, 2, 3, 4][1:4]
+  let view = arr[-1:]
+  inspect!(view, content="[3]")
+  let view = arr[-2:]
+  inspect!(view, content="[2, 3]")
+  let view = arr[-3:]
+  inspect!(view, content="[1, 2, 3]")
+  let view = arr[:-1]
+  inspect!(view, content="[1, 2]")
+  let view = arr[:-2]
+  inspect!(view, content="[1]")
+  let view = arr[:-3]
+  inspect!(view, content="[]")
+  let view = arr[-3:-3]
+  inspect!(view, content="[]")
+  let view = arr[-3:-2]
+  inspect!(view, content="[1]")
+  let view = arr[-3:-1]
+  inspect!(view, content="[1, 2]")
+  let view = arr[-3:0]
+  inspect!(view, content="[]")
+  let view = arr[-3:1]
+  inspect!(view, content="[1]")
+  let view = arr[-3:2]
+  inspect!(view, content="[1, 2]")
+  let view = arr[-3:3]
+  inspect!(view, content="[1, 2, 3]")
+}
+
+test "panic negative index1" {
+  let arr = [1, 2, 3]
+  let _ = arr[-4:]
+
+}
+
+test "panic negative index2" {
+  let arr = [1, 2, 3]
+  let _ = arr[:-4]
+
+}
+
+test "panic negative index3" {
+  let arr = [1, 2, 3]
+  let _ = arr[-1:-2]
+
+}
+
+test "panic negative index4" {
+  let arr = [1, 2, 3]
+  let _ = arr[-1:-3]
+
+}
+
+test "panic negative index5" {
+  let arr = [1, 2, 3][:]
+  let _ = arr[-4:]
+
+}
+
+test "panic negative index6" {
+  let arr = [1, 2, 3][:]
+  let _ = arr[:-4]
+
+}
+
+test "panic negative index7" {
+  let arr = [1, 2, 3][:]
+  let _ = arr[-1:-2]
+
+}
+
+test "panic negative index8" {
+  let arr = [1, 2, 3][:]
+  let _ = arr[-1:-3]
+
+}

builtin/bytesview.mbt

@@ -71,8 +71,9 @@ pub fn op_as_view(self : Bytes, start~ : Int = 0, end? : Int) -> BytesView {
   let len = self.length()
   let end = match end {
     None => len
-    Some(end) => end
+    Some(end) => if end < 0 { len + end } else { end }
   }
+  let start = if start < 0 { len + start } else { start }
   guard start >= 0 && start <= end && end <= len else {
     abort("Invalid index for BytesView")
   }
@@ -94,8 +95,9 @@ pub fn op_as_view(self : BytesView, start~ : Int = 0, end? : Int) -> BytesView {
   let len = self.length()
   let end = match end {
     None => len
-    Some(end) => end
+    Some(end) => if end < 0 { len + end } else { end }
   }
+  let start = if start < 0 { len + start } else { start }
   guard start >= 0 && start <= end && end <= len else {
     abort("Invalid index for BytesView")
   }

builtin/bytesview_test.mbt

@@ -1,4 +1,4 @@
-// Copyright 2024 International Digital Economy Academy
+// Copyright 2025 International Digital Economy Academy
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -46,7 +46,7 @@ test "basic3" {
 
 test "panic invalid index1" {
   let bs = b"\x00\x01\x02\x03\x04\x05"
-  let _ = bs[-1:]
+  let _ = bs[-7:]
 
 }
 
@@ -64,7 +64,7 @@ test "panic invalid index3" {
 
 test "panic invalid index4" {
   let bs = b"\x00\x01\x02\x03\x04\x05"[:]
-  let _ = bs[-1:]
+  let _ = bs[:-7]
 
 }
 
@@ -88,3 +88,205 @@ test "iter" {
     content="[b'\\x00', b'\\x01', b'\\x02', b'\\x03', b'\\x04', b'\\x05']",
   )
 }
+
+test "negative index1" {
+  let bs = b"\x01\x02\x03"
+  let bv = bs[-1:]
+  inspect!(
+    bv,
+    content=
+      #|b"\x03"
+    ,
+  )
+  let bv = bs[-2:]
+  inspect!(
+    bv,
+    content=
+      #|b"\x02\x03"
+    ,
+  )
+  let bv = bs[-3:]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01\x02\x03"
+    ,
+  )
+  let bv = bs[:-1]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01\x02"
+    ,
+  )
+  let bv = bs[:-2]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01"
+    ,
+  )
+  let bv = bs[:-3]
+  inspect!(
+    bv,
+    content=
+      #|b""
+    ,
+  )
+  let bv = bs[-3:-3]
+  inspect!(
+    bv,
+    content=
+      #|b""
+    ,
+  )
+  let bv = bs[-3:-2]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01"
+    ,
+  )
+  let bv = bs[-3:-1]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01\x02"
+    ,
+  )
+  let bv = bs[-3:0]
+  inspect!(
+    bv,
+    content=
+      #|b""
+    ,
+  )
+  let bv = bs[-3:1]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01"
+    ,
+  )
+  let bv = bs[-3:2]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01\x02"
+    ,
+  )
+  let bv = bs[-3:3]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01\x02\x03"
+    ,
+  )
+}
+
+test "negative index2" {
+  let bs = b"\x00\x01\x02\x03\x04"[1:4]
+  let bv = bs[-1:]
+  inspect!(
+    bv,
+    content=
+      #|b"\x03"
+    ,
+  )
+  let bv = bs[-2:]
+  inspect!(
+    bv,
+    content=
+      #|b"\x02\x03"
+    ,
+  )
+  let bv = bs[-3:]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01\x02\x03"
+    ,
+  )
+  let bv = bs[:-1]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01\x02"
+    ,
+  )
+  let bv = bs[:-2]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01"
+    ,
+  )
+  let bv = bs[:-3]
+  inspect!(
+    bv,
+    content=
+      #|b""
+    ,
+  )
+  let bv = bs[-3:-3]
+  inspect!(
+    bv,
+    content=
+      #|b""
+    ,
+  )
+  let bv = bs[-3:-2]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01"
+    ,
+  )
+  let bv = bs[-3:-1]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01\x02"
+    ,
+  )
+  let bv = bs[-3:0]
+  inspect!(
+    bv,
+    content=
+      #|b""
+    ,
+  )
+  let bv = bs[-3:1]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01"
+    ,
+  )
+  let bv = bs[-3:2]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01\x02"
+    ,
+  )
+  let bv = bs[-3:3]
+  inspect!(
+    bv,
+    content=
+      #|b"\x01\x02\x03"
+    ,
+  )
+}
+
+test "panic negative index1" {
+  let bs = b"\x01\x02\x03"
+  let _ = bs[-1:-2]
+
+}
+
+test "panic negative index2" {
+  let bs = b"\x01\x02\x03"[:]
+  let _ = bs[-1:-2]
+
+}