Handle non-printable control characters when escaping JSON

[mediremi]

When the VS Code extension calls rescript-editor-analysis, it replies with JSON serialised by analysis/vendor/json/Json.ml.

While Json.escape escapes printable characters correctly, it did not handle non-printable control characters (i.e. characters with a char code < 0x20). This meant that JSON sent to VS code was not always escaped properly and prevented code actions from being available in certain situations.

For example, opening up https://github.com/rescript-lang/rescript-lang.org/blob/master/src/bindings/RescriptCompilerApi.res in VS Code currently results in SyntaxError: Bad control character in string literal in JSON at position 1319 (line 15 column 751):

In the example above, this is caused by Warning.toCompactErrorLine containing a string with control character 0x27.

With the escaping logic I've added, this issue no longer occurs.

Changes I've made

• Handled control characters in analysis/vendor/json/Json.ml
• Renamed tests/ounit_tests/ounit_json_tests.ml to tests/ounit_tests/ounit_ext_json_tests.ml
• Created a tests/ounit_tests/ounit_json_tests.ml test suite for analysis/vendor/json/Json.ml
• Handled control characters in compiler/ext/ext_json_noloc.ml, which is used by the bsb watcher

Future work

• analysis/vendor/json/Json.ml and compiler/ext/ext_json should probably be eventually replaced with Yojson

[mediremi]

The existing Ext_json tests were moved to tests/ounit_tests/ounit_ext_json_tests.ml

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commit: 3c376bc

[zth]

This is looking good to me, thank you! @cristianoc any thoughts?

[cristianoc]

This is looking good to me, thank you! @cristianoc any thoughts?

Looks great!