html/template: data race with concurrent ExecuteTemplate calls [1.15 backport]

[gopherbot]

@josharian requested issue #47040 to be considered for backport to the next 1.15 minor release.

496d7c6 is the fix.

@gopherbot, please open backport issues.

[mknyszek]

Data race in what is documented to be a concurrent-safe context with no workaround. Approved.

[josharian]

Thanks, @mknyszek.

@ianlancetaylor as the original author of the fix, I think the next step is for you to mail a cherry-pick change. Ditto for #47042.

[ianlancetaylor]

I have twice had to revert CLs that fix this problem. The current CL has not yet been in any release, so it may just be pending another revert. I think it would be very premature to backport the CL to the 1.15 and 1.16 branches before the 1.17 release is out.

[mknyszek]

@ianlancetaylor Sounds good, I'll un-approve then.

[dmitshur]

Go 1.17 has been released, and so Go 1.15 is no longer supported per the release policy. Closing.