When a HEAD build fails, output an instruction to raise PRs not issues

[issyl0]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?

---

- I didn't originally intend to go into too much detail here about raising PRs rather than issues, as it doesn't feel like something people will read, but I couldn't think of a better place to put that extra detail, so here we are.

- If there are better places for this then I'll gladly hear them!

• This has to be in multiple places, hence a new method. A patch failing
  to apply, which is a common occurrence with HEAD builds because the
  patch is already upstream, raises a different exception to another,
  "normal" build failure.

Tested with:

╭─issyl0@rigel /home/linuxbrew/.linuxbrew/Homebrew ‹head-builds-arent-officially-supported*›
╰─ $ brew install --HEAD mtr
==> Cloning https://github.com/traviscross/mtr.git
Updating /home/issyl0/.cache/Homebrew/mtr--git
==> Checking out branch master
Already on 'master'
Your branch is up to date with 'origin/master'.
HEAD is now at 155f76a Merge pull request #340 from Sea-n/master
==> Downloading traviscross/mtr#315
Already downloaded: /home/issyl0/.cache/Homebrew/downloads/82d9d939303d8fceb7a3ae071ecd49a5f075e0fb451b308653b555ffbae74336--315.patch
==> Patching
==> Applying 315.patch
patching file packet/probe.c
Hunk #1 FAILED at 323.
Hunk #2 FAILED at 364.
2 out of 2 hunks FAILED -- saving rejects to file packet/probe.c.rej
Error: Failure while executing; `patch -g 0 -f -p1 -i /tmp/mtr--patch-20200330-10734-avjmyy/315.patch` exited with 1.
HEAD builds are unsupported by maintainers - please file pull requests instead of issues.

and

╭─issyl0@rigel /home/linuxbrew/.linuxbrew/Homebrew ‹head-builds-arent-officially-supported*›
╰─ $ brew install --HEAD zookeeper
==> Cloning https://gitbox.apache.org/repos/asf/zookeeper.git
Updating /home/issyl0/.cache/Homebrew/zookeeper--git
==> Checking out branch master
Already on 'master'
Your branch is up to date with 'origin/master'.
HEAD is now at 1ff1b779 ZOOKEEPER-3755: Use maven to create fatjar
==> ant compile_jute
Last 15 lines from /home/issyl0/.cache/Homebrew/Logs/zookeeper/01.ant:
2020-03-30 21:45:10 +0100

ant
compile_jute

Picked up _JAVA_OPTIONS: -Duser.home=/home/issyl0/.cache/Homebrew/java_cache
Buildfile: build.xml does not exist!
Build failed

READ THIS: https://docs.brew.sh/Troubleshooting

HEAD builds are unsupported by maintainers - please file pull requests instead of issues.

• This came about because I feel like I've done a lot of telling people that HEAD builds are unsupported when they raise issues about patches that don't apply, or broken builds.

[MikeMcQuaid]

• but I couldn't think of a better place to put that extra detail, so here we are.

How about somewhere like:

brew/Library/Homebrew/brew.rb

Lines 163 to 164 in 38c7128

	$stderr.puts "#{Tty.bold}Please report this issue:#{Tty.reset}"
	$stderr.puts " #{Formatter.url(OS::ISSUES_URL)}"

or the BuildError handled above? Should be able to special-case the output based on --HEAD.

[issyl0]

Thanks, @MikeMcQuaid! I've done that, accounting for the different exceptions I encountered along the way between patches failing to apply and normal build failures. There's a bit of duplication still... 🤔

[MikeMcQuaid]

Thanks again @issyl0!