bootstrap: Make the automatic sync more resilient.

Reported by Paul Eggert in
<https://lists.gnu.org/archive/html/bug-gnulib/2022-07/msg00060.html>.

* top/bootstrap (bootstrap_sync): Set to true when bootstrap-funclib.sh
is not present.
* top/gen-bootstrap.sed: Insert a couple of comment lines.
* build-aux/bootstrap: Regenerated using "make build-aux/bootstrap".

2 files changed, 17 insertions, 8 deletions

diff --git a/top/bootstrap b/top/bootstrap
index b7216d20fe..e9d8ad82aa 100755
--- a/top/bootstrap
+++ b/top/bootstrap
@@ -153,14 +153,7 @@ do
   --bootstrap-sync)
     bootstrap_sync=true;;
   --no-bootstrap-sync)
-    if test -f "$medir"/bootstrap-funclib.sh; then
-      bootstrap_sync=false
-    else
-      # We have only completed the first phase of an upgrade from a bootstrap
-      # version < 2022-07-24. Need to do the second phase now.
-      bootstrap_sync=true
-    fi
-    ;;
+    bootstrap_sync=false;;
   --no-git)
     use_git=false;;
   *)
@@ -179,6 +172,12 @@ fi
 
 check_build_prerequisites $use_git
 
+if ! test -f "$medir"/bootstrap-funclib.sh; then
+  # We have only completed the first phase of an upgrade from a bootstrap
+  # version < 2022-07-24. Need to do the second phase now.
+  bootstrap_sync=true
+fi
+
 if $bootstrap_sync; then
   prepare_GNULIB_SRCDIR
   upgrade_bootstrap
diff --git a/top/gen-bootstrap.sed b/top/gen-bootstrap.sed
index 2851db5eaf..c182abfa50 100644
--- a/top/gen-bootstrap.sed
+++ b/top/gen-bootstrap.sed
@@ -1,3 +1,13 @@
+1{
+a\
+# DO NOT EDIT! GENERATED AUTOMATICALLY!
+a\
+# This script is only a trampoline that fetches the companion scripts
+a\
+# (bootstrap-funclib.sh, autopull.sh, autogen.sh).
+a\
+
+}
 /^[.] "[$]medir"[/]bootstrap-funclib.sh/{
   s/^.*$//
   r top/bootstrap-funclib.sh