scripts/bootstrap-prefix: fix endless loop with Gentoo bootstrap

When we try to use turbo-boost bootstrap, we end up in an endless loop.
Reason is the code that was added to ensure individual stage calls would
have a properly inited environment.  However that contained not just a
bug, but also would cause stage_host_gentoo to be called over and over
again.

Now just exit from bootstrap_interactive once we set all the vars we
need.  Ensure we don't run any bootstrapping code before that point.

Thanks Leonardo Hernández Hernández for pointing this out.

Closes: https://bugs.gentoo.org/914261
Signed-off-by: Fabian Groffen <grobian@gentoo.org>

scripts/bootstrap-prefix.sh

@@ -2811,8 +2811,7 @@ EOF
 	done
 	export PATH="$EPREFIX/usr/bin:$EPREFIX/bin:$EPREFIX/tmp/usr/bin:$EPREFIX/tmp/bin:$EPREFIX/tmp/usr/local/bin:${PATH}"
 
-	if [[ -z ${PARTIAL_BOOTSTRAP} ]]; then
-		cat << EOF
+	cat << EOF
 
 OK!  I'm going to give it a try, this is what I have collected sofar:
   EPREFIX=${EPREFIX}
@@ -2826,15 +2825,23 @@ Prefix.  In short, I'm going to run stage1, stage2, stage3, followed by
 emerge -e system.  If any of these stages fail, both you and me are in
 deep trouble.  So let's hope that doesn't happen.
 EOF
-		echo
-		[[ ${TODO} == 'noninteractive' ]] && ans="" ||
-		read -p "Type here what you want to wish me [luck] " ans
-		if [[ -n ${ans} && ${ans} != "luck" ]] ; then
-			echo "Huh?  You're not serious, are you?"
-			sleep 3
-		fi
-		echo
-  fi
+	echo
+	[[ ${TODO} == 'noninteractive' ]] && ans="" ||
+	read -p "Type here what you want to wish me [luck] " ans
+	if [[ -n ${ans} && ${ans} != "luck" ]] ; then
+		echo "Huh?  You're not serious, are you?"
+		sleep 3
+	fi
+	echo
+
+	# because we unset ROOT from environment above, and we didn't set
+	# ROOT as argument in the script, we set ROOT here to the EPREFIX we
+	# just harvested
+	ROOT="${EPREFIX}"
+	set_helper_vars
+
+	# stop here if all we wanted was the env to be setup correctly
+	[[ -n ${SETUP_ENV_ONLY} ]] && return 0
 
 	if [[ -d ${HOST_GENTOO_EROOT} ]]; then
 		if ! [[ -x ${EPREFIX}/tmp/usr/lib/portage/bin/emerge ]] && ! ${BASH} ${BASH_SOURCE[0]} "${EPREFIX}" stage_host_gentoo ; then
@@ -2855,25 +2862,6 @@ EOF
 		fi
 	fi
 
-	# because we unset ROOT from environment above, and we didn't set
-	# ROOT as argument in the script, we set ROOT here to the EPREFIX we
-	# just harvested
-	ROOT="${EPREFIX}"
-	set_helper_vars
-
-	if [[ -n ${PARTIAL_BOOTSTRAP} ]]; then
-	cat << EOF
-
-OK! All necessary tools and ENV variables were installed:
-  EPREFIX=${EPREFIX}
-  CHOST=${CHOST}
-  PATH=${PATH}
-  MAKEOPTS=${MAKEOPTS}
-Now I'm going to  run an <action> you asked me to.
-EOF
-		return 0;
-	fi
-
 	if ! [[ -e ${EPREFIX}/.stage1-finished ]] && ! bootstrap_stage1_log ; then
 		# stage 1 fail
 		cat << EOF
@@ -3308,17 +3296,19 @@ fi
 
 einfo "ready to bootstrap ${TODO}"
 
-# part of bootstrap_interactive should be executed before any bootstrap_${TODO}
-# to properly setup environment variables and guarantee that bootstrap_${TODO}
-# executes inside a prefix
-if [[ ${TODO} != "noninteractive" && $(type -t bootstrap_${TODO} == "function") ]]; then
-	PARTIAL_BOOTSTRAP=true
-	TODO='noninteractive' bootstrap_interactive || exit 1
-	bootstrap_${TODO} || exit 1
-	exit 0
+# When we call individual stages separately (e.g. not from
+# bootstrap_interactive) we might need some env to be setup in order to
+# function properly.  Basically do a non-interactive call for each stage
+# that will only set whatever needs to be set.
+if [[ ${TODO} != "interactive" && ${TODO} != "noninteractive" ]] ; then
+	# squelch the output, we've seen it already when running from
+	# interactive proper
+	SETUP_ENV_ONLY=true TODO=noninteractive \
+		bootstrap_interactive > /dev/null || exit 1
 fi
 
-# bootstrap_interactive proceeds with guessed defaults when TODO=noninteractive
+# call the appropriate function,
+# beware noninteractive is just a mode of interactive
 bootstrap_${TODO#non} || exit 1
 
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