Auto-update when running brew install/upgrade.

[MikeMcQuaid]

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Follows on from Homebrew/legacy-homebrew#50192.

The main changes from there:

• I've fixed the issue if brew.sh was updated while running
• I've fixed the brew edit workflow for when HOMEBREW_DEVELOPER is set
• Only enable this behaviour if HOMEBREW_AUTO_UPDATE is set (so I can test it locally and see how annoying it is to e.g. run on every command).

CC @UniqMartin @xu-cheng @bfontaine @apjanke on what would be required for this to be merged as-is (disabled by default).

[ilovezfs]

brew update currently gives a summary of what happened. Are we OK with that info now getting spit out at the top of random installations, and quite possibly off screen almost immediately? Should we just suppress it entirely now?

[MikeMcQuaid]

Are we OK with that info now getting spit out at the top of random installations, and quite possibly off screen almost immediately? Should we just suppress it entirely now?

Yes, I'm OK with that. Something I forgot to do is to add an additional header letting people know that we've autoupdated if there are any changes.

[ilovezfs]

Would you save the update summary and dump it at the end of the install or just leave it at the top?

[MikeMcQuaid]

Leave it at the top.

[UniqMartin]

I think it would be a bit cleaner to package this as a function like so:

update-preinstall() {
  [[ -n "$HOMEBREW_AUTO_UPDATE" ]] || return

  if [[ "$HOMEBREW_COMMAND" = install || "$HOMEBREW_COMMAND" = upgrade ]]
  then
    # Hide shellcheck complaint:
    # shellcheck source=/dev/null
    source "$HOMEBREW_LIBRARY/Homebrew/cmd/update.sh"
    homebrew-update --preinstall
  fi
}

Then use that further down below, e.g.:

{ update-preinstall; "homebrew-$HOMEBREW_COMMAND" "$@"; exit $?; }

To me that not only looks cleaner, but also clearer. It also avoids an unquoted variable expansion.

[MikeMcQuaid]

@UniqMartin Sounds good. Does that still avoid the "file updated under it" issue, yeh?

[UniqMartin]

Does that still avoid the "file updated under it" issue, yeh?

Yes, it does. The function has already been completely parsed by the time it is executed.

[MikeMcQuaid]

Addressed comments.

[MikeMcQuaid]

Will merge this tomorrow if there are no objections.

[chdiza]

Just for my own clarity, what is the knob that prevents an auto-update from happening? (In the legacy thread from which this arose, there seemed to be general agreement that such a knob should exist.)

[UniqMartin]

@chdiza The current state of the code is that this is an opt-in feature. Once this is merged, you would have to set HOMEBREW_AUTO_UPDATE=1 in your environment to enable the auto update.

[chdiza]

@UniqMartin Thanks. I had scanned the code looking for the knob, and my eyes must have skipped right over that shellvar.

[MikeMcQuaid]

I'll add HOMEBREW_NO_AUTO_UPDATE in here just so it's one less thing to remove when we ship this.

[MikeMcQuaid]

Added the HOMEBREW_NO_AUTO_UPDATE, 🚢ing.