fixed std.array.split_at behavior at right boundary. (#1803)

* fixed IndexedArrayFun behavior at right boundary.

* fixed typo.

* fix code block annotation.

* parameterized IndexedArrayFun contract.

* corrected contract annotation position.

* updated snapshots.

* Fixed doc test due to line number change in std.ncl

---------

Co-authored-by: Ben Yang <ben@ya.ng>

HACKING.md

@@ -66,7 +66,7 @@ nickel-lang-lsp 0.1.0
 
 To only build the main crate `nickel-lang-core`, run:
 
-```console
+```shell
 cargo build -p nickel-lang-core
 ```
 

cli/tests/snapshot/snapshots/snapshot__eval_stderr_array_at_empty_array.ncl.snap

@@ -6,8 +6,8 @@ error: contract broken by the caller of `at`
  invalid array indexing
  ┌─ <stdlib/std.ncl>:162:9
  │
-162 │ | std.contract.unstable.IndexedArrayFun
- │ ------------------------------------- expected type
+162 │ | std.contract.unstable.IndexedArrayFun 'Index
+ │ -------------------------------------------- expected type
  │
  ┌─ [INPUTS_PATH]/errors/array_at_empty_array.ncl:3:16
  │

cli/tests/snapshot/snapshots/snapshot__eval_stderr_array_at_out_of_bound.ncl.snap

@@ -6,8 +6,8 @@ error: contract broken by the caller of `at`
  invalid array indexing
  ┌─ <stdlib/std.ncl>:162:9
  │
-162 │ | std.contract.unstable.IndexedArrayFun
- │ ------------------------------------- expected type
+162 │ | std.contract.unstable.IndexedArrayFun 'Index
+ │ -------------------------------------------- expected type
  │
  ┌─ [INPUTS_PATH]/errors/array_at_out_of_bound.ncl:3:16
  │

core/stdlib/std.ncl

@@ -159,7 +159,7 @@
 
  at
  : forall a. Number -> Array a -> a
- | std.contract.unstable.IndexedArrayFun
+ | std.contract.unstable.IndexedArrayFun 'Index
  | doc m%"
  Retrieves the n-th element from an array, with indices starting at 0.
 
@@ -570,15 +570,15 @@
 
  split_at
  : forall a. Number -> Array a -> { left : Array a, right : Array a }
- | std.contract.unstable.IndexedArrayFun
+ | std.contract.unstable.IndexedArrayFun 'Split
  | doc m%"
  Splits an array in two at a given index and puts all the elements
  to the left of the element at the given index (excluded) in the
  `left` field, and the rest of the array in the `right` field.
 
  # Preconditions
 
- In `split_at inded value`, `index` must be a positive integer such
+ In `split_at index value`, `index` must be a positive integer such
  that `0 <= index <= std.array.length value`.
 
  # Examples
@@ -1325,6 +1325,7 @@
  (fun start => RangeSecond start -> Codomain),
 
  IndexedArrayFun
+ | [| 'Index, 'Split |] -> Dyn -> Dyn
  | doc m%"
  **Warning**: this is an unstable item. It might be renamed,
  modified or deleted in any subsequent minor Nickel version.
@@ -1358,11 +1359,12 @@
  value
  in
 
- let ArrayIndexSecond = fun min_size label value =>
+ let ArrayIndexSecond = fun type min_size label value =>
  if %typeof% min_size == 'Number && %typeof% value == 'Array then
- if min_size >= %length% value then
+ let max_idx = type |> match { 'Index => %length% value - 1, 'Split => %length% value } in
+ if min_size > max_idx then
  let index_as_str = %to_str% min_size in
- let max_as_str = %to_str% (%length% value - 1) in
+ let max_as_str = %to_str% max_idx in
  let note =
  if %length% value == 0 then
  "Can't index into an empty array"
@@ -1378,9 +1380,13 @@
  else
  value
  in
- DependentFun
- ArrayIndexFirst
- (fun index => ArrayIndexSecond index -> Dyn),
+ let contract = fun type label function =>
+ DependentFun
+ ArrayIndexFirst
+ (fun index => ArrayIndexSecond type index -> Dyn)
+ label
+ function
+ in contract,
 
  ArraySliceFun
  | doc m%"

doc/manual/merging.md

@@ -621,9 +621,9 @@ error: missing definition for `required_field2`
  8 │ & { foo.required_field1 = "here" }
  │ ------------------------ in this record
  │
- ┌─ <stdlib/std.ncl>:2991:18
+ ┌─ <stdlib/std.ncl>:2997:18
  │
-2991 │ = fun x y => %deep_seq% x y,
+2997 │ = fun x y => %deep_seq% x y,
  │ ------------ accessed here
 ```