Integers with leading zeros displaying as strings

[mattkerlogue]

Describe the bug

When editing lists in YAML if the integers 8 and 9 have leading zeros (i.e. 08 or 09 code highlighting displays them as if they were strings. When the YAML extension is disabled the values are highlighted correctly as numerics.

I first discovered this when amending some YAML where dates are encoded separately as the day, month and year (hence the leading zeros).

Expected Behavior

Bare values of 08 and 09 (or with more leading zeros, or with following digits) should be highlighted as numeric values. As per VS Code when the extension is disabled.

YAML code highlighting when extension disabled:

Current Behavior

Bare values of 08 and 09 (or with more leading zeros, or with following digits) are highlighted as if a string.

YAML code highlighting when extension enabled:

Steps to Reproduce

1. Open a new file, set language to YAML
2. Create a list/array of numeric values including some with 08 and 09

Environment

• Windows
• Mac
• Linux
• other (please specify)

Screenshots are with the Nord theme, but also occurs with other colour themes enabled.

[datho7561]

Can you try using the prerelease version of the extension and double check if that fixes it? As far as I can tell, that should fix it. It was a buggy regular expression that should have been resolved by #1182.

[mattkerlogue]

Do you mean the version via 'install pre-release' in VS Code itself? Because, if so, that's still coming up with the same problem.

Version: 1.20.2026011308

Or do I need to download and compile the extension from source?

[datho7561]

That's what I meant. Dang, I'll check it out again.

[datho7561]

I don't know what's going on, this is what I have with 1.20.2026011308:

[datho7561]

AHHHH I see, 08 and 09 are labelled as timestamps, it just doesn't show up with any of the themes that I have. I need to see if that's the correct behaviour

[datho7561]

I can't find anything in the YAML spec that describes what will be treated as a timestamp and what won't. I don't know if it's helpful to try and syntax highlight it specially. I think the right course of action is to remove that (unless it's helpful for someone) or modify it so that if it's also a normal number then it shouldn't be a timestamp.

[datho7561]

While removing that, I realized that 08 wasn't being highlighted as an integer, because for some reason the "canonical form" regex supplied in the spec was being used instead of the one under 10.3.2

[datho7561]

Some implementations of YAML 1.1 treat 08 as a string 😞 and pyyaml seems to not support YAML 1.2 yet.