It seems to be a frequent occurrence that non-versioned github urls with line numbers are included in issues. These links make investigations more time consuming when code inevitably changes.

The problematic pattern is: https://github.com/<repo>/blob/master.+#L\d+
Example: https://github.com/golang/go/blob/master/src/mime/multipart/formdata.go#L78

I would guess that a quarter of these match that pattern.

Let's say there are 3 primary categories of non-versioned code urls with line number(s):

1. non-Go (mostly on github.com)
2. Go on github.com
3. Go on golang.org

3 is very much in our control and is discussed in #14062.
1 and 2 are harder to control. A solution could be gopherbot replying to new issues that match the pattern with a permalink that included the latest commit when the issue was created. (Another solution is to have the new issue template suggest a versioned url for any non-playground code.)

To avoid spam, maybe this would only respond to the body of a new issue - not any comments.

The message could be something like:

• https://github.com/golang/go/blob/master/src/run.bash#L21 is currently

  go/src/run.bash

  Line 21 in 47be3d4

  unset CDPATH # in case user has it set

• https://github.com/moby/moby/blob/master/poule.yml#L36 is currently https://github.com/moby/moby/blob/f4ebcb42ac527b24ab54525d5824478fcd2960c0/poule.yml#L36

@andybons @bradfitz