I think this was an intentional change.

CC @griesemer

any rationale or reference for the change? dueling gofmt across releases makes for unhappy CI and contributors. If the benefit is significant, changes make sense, but I'm not seeing it here.

Correct. This was done on purpose. We do the same for prefixes, e.g. 0X123 becomes 0x123. The reason is that now that we allow 0O123, the form 0o123` is easier to read. We simply make the change everywhere, and didn't stop with exponents either (but we leave hexadecimal digits alone).

Closing as working as intended.

@liggitt My apologies. With the proliferation of new number formats that are permitted, we (I mean several people in the Go team) felt that it would be good for gofmt to enforce a preferred, uniform style of capitalization.

I understand the unhappy CI - but that would be the case for any gofmt change, woulnd't it? If there's anything more "substantial" (I don't mean to disqualify your complaint) where this is causing problems, please feel free to re-open.

that would be the case for any gofmt change, woulnd't it?

Yes, though usually the cost is easier to bear given the improved readability. The benefit here wasn't as obvious (we only had exponents in our codebase)

Digging into the change, it looks like this is normalizing where no normalization previously occurred, so the output of 1.13 will still be acceptable to 1.12, which reduces my concern (versions of gofmt flipping opinions about the "right" formatting makes backports to branches built with different go versions painful)

Correct. The new gofmt is now stricter. It has not changed its opinion.