Binary number literals with underscores appear as error blocks

[shabbyrobe]

What did you do? (required: The issue will be closed when not provided)

I created a source file with a binary number that contained underscores (i.e. 0b0000_0000)

What did you expect to happen?

I expected it to have the same colour as a binary number without underscores.

What happened instead?

It was a very different colour - a huge red error block!

Configuration (MUST fill this out):

vim-go version:

Current master (b7c7109)

vimrc you used to reproduce (use a minimal vimrc with other plugins disabled; do not link to a 2,000 line vimrc):

This isn't needed - I've attached the change I believe solves the issue below.

Vim version (first three lines from :version):

8.1.1368

Go version (go version):

1.3

Go environment

This isn't needed - I've attached the change I believe solves the issue below.

---

The syntax file invim-go is classifying binary number literals with underscores as goBinaryError instead of goBinaryInt.

I think the minimal change required is this, but I'm not sure and I'm not confident with complex vim regex nests that I'm not breaking something someone else relies on, hence an issue report rather than a PR:

-syn match       goBinaryInt         "\<-\=0[bB][01]\+\>"
-syn match       goBinaryError       "\<-\=0[bB][01]*[^ \t01]\S*\>"
+syn match       goBinaryInt         "\<-\=0[bB][_01]\+\>"
+syn match       goBinaryError       "\<-\=0[bB][_01]*[^ \t_01]\S*\>"

It looks like goHexadecimalInt and goOctalInt have the same problem, but similar minimal interventions like the above did not produce the desired outcome for me (octal ints and hex ints were no longer classified).

[bhcleek]

fiexed by #2584