add to ndjson and to jsonl to the standard library (nushell#10519)

follow up to
- nushell#10283

# Description
even though it appears defining `to foo` does not allow to do `save
x.foo` for free (see nushell#10429),
because nushell#10283 did add `from ndjson` and `from jsonl` to the standard
library, i thought adding their `to ...` counterpart would make sense
:yum:

# User-Facing Changes
users can now convert structured data back to NDJSON and JSONL :ok_hand:

# Tests + Formatting
this PR adds the exact same tests as for the `from ...` commands
- structured data is in `result` and the string is now the expected
- the two invalid `from ...` tests cannot be reproduced for `to ...`
afaik

# After Submitting

crates/nu-std/std/formats.nu

@@ -9,12 +9,22 @@
 # These functions help `open` the files with unsupported extensions such as ndjson.
 #
 
-# Convert from ndjson to structured data.
+# Convert from [NDJSON](http://ndjson.org/) to structured data.
 export def "from ndjson" []: string -> any {
  from json --objects
 }
 
-# Convert from jsonl to structured data.
+# Convert from [JSONL](https://jsonlines.org/) to structured data.
 export def "from jsonl" []: string -> any {
  from json --objects
 }
+
+# Convert structured data to [NDJSON](http://ndjson.org/).
+export def "to ndjson" []: any -> string {
+ each { to json --raw } | to text
+}
+
+# Convert structured data to [JSONL](https://jsonlines.org/).
+export def "to jsonl" []: any -> string {
+ each { to json --raw } | to text
+}

crates/nu-std/tests/test_formats.nu

@@ -1,26 +1,34 @@
 use std assert
 
-def ndjson_test_data1 [] {
- '{"a":1}
-{"a":2}
-{"a":3}
-{"a":4}
-{"a":5}
-{"a":6}'
+def test_data_multiline [] {
+ let lines = [
+ "{\"a\": 1}",
+ "{\"a\": 2}",
+ "{\"a\": 3}",
+ "{\"a\": 4}",
+ "{\"a\": 5}",
+ "{\"a\": 6}",
+ ]
+
+ if $nu.os-info.name == "windows" {
+ $lines | str join "\r\n"
+ } else {
+ $lines | str join "\n"
+ }
 }
 
 #[test]
 def from_ndjson_multiple_objects [] {
  use std formats *
- let result = ndjson_test_data1 | from ndjson
+ let result = test_data_multiline | from ndjson
  let expect = [{a:1},{a:2},{a:3},{a:4},{a:5},{a:6}]
  assert equal $result $expect "could not convert from NDJSON"
 }
 
 #[test]
 def from_ndjson_single_object [] {
  use std formats *
- let result = '{"a":1}' | from ndjson
+ let result = '{"a": 1}' | from ndjson
  let expect = [{a:1}]
  assert equal $result $expect "could not convert from NDJSON"
 }
@@ -34,15 +42,15 @@ def from_ndjson_invalid_object [] {
 #[test]
 def from_jsonl_multiple_objects [] {
  use std formats *
- let result = ndjson_test_data1 | from jsonl
+ let result = test_data_multiline | from jsonl
  let expect = [{a:1},{a:2},{a:3},{a:4},{a:5},{a:6}]
  assert equal $result $expect "could not convert from JSONL"
 }
 
 #[test]
 def from_jsonl_single_object [] {
  use std formats *
- let result = '{"a":1}' | from jsonl
+ let result = '{"a": 1}' | from jsonl
  let expect = [{a:1}]
  assert equal $result $expect "could not convert from JSONL"
 }
@@ -52,3 +60,35 @@ def from_jsonl_invalid_object [] {
  use std formats *
  assert error { '{"a":1' | from jsonl }
 }
+
+#[test]
+def to_ndjson_multiple_objects [] {
+ use std formats *
+ let result = [{a:1},{a:2},{a:3},{a:4},{a:5},{a:6}] | to ndjson | str trim
+ let expect = test_data_multiline
+ assert equal $result $expect "could not convert to NDJSON"
+}
+
+#[test]
+def to_ndjson_single_object [] {
+ use std formats *
+ let result = [{a:1}] | to ndjson | str trim
+ let expect = "{\"a\": 1}"
+ assert equal $result $expect "could not convert to NDJSON"
+}
+
+#[test]
+def to_jsonl_multiple_objects [] {
+ use std formats *
+ let result = [{a:1},{a:2},{a:3},{a:4},{a:5},{a:6}] | to jsonl | str trim
+ let expect = test_data_multiline
+ assert equal $result $expect "could not convert to JSONL"
+}
+
+#[test]
+def to_jsonl_single_object [] {
+ use std formats *
+ let result = [{a:1}] | to jsonl | str trim
+ let expect = "{\"a\": 1}"
+ assert equal $result $expect "could not convert to JSONL"
+}