Gofmt error output uses [token/position](http://golang.org/src/pkg/go/token/position.go) to build the string. Consequently, the format is consistent. The only thing that changes is the actual error text. The regular expression translates to:

* Start of line: `^`
* Followed by any text, until `:<digit>:<digit>:<space>` is identified: `(.*?:)(\d*?):(\d*?):\s`
* Followed by any text until end of line: (.*)$

The match groups are:

* [0] Filename
* [1] Line Number
* [2] Char Position
* [3] Error

I should actually move the first colon `:` out of the first match group. That is addressed in 6d5ac5785465b361d406205e2a7dd36078880357.