Write updated loaddefs to a temporary file and rename into place.

In a parallel build, byte compilation can be running at the same times
as loaddefs.el is being regenerated.  However, in a CANNOT_DUMP build,
loaddefs.el is read at startup and must always be in a usable state.

* lisp/Makefile.in ($(lisp)/loaddefs.el): Write generated output to
loaddefs.el.new and then rename it to loaddefs.el.

1 files changed, 5 insertions, 1 deletions

diff --git a/lisp/Makefile.in b/lisp/Makefile.in
index 185554ca63a..63d593c7e68 100644
--- a/lisp/Makefile.in
+++ b/lisp/Makefile.in
@@ -179,14 +179,18 @@ $(lisp)/finder-inf.el:
 # Note that we set no-update-autoloads in _generated_ leim files.
 # If you want to allow autoloads in such files, remove that,
 # and make this depend on leim.
+#
+# Write to a temporary file in case we're doing a parallel build and a
+# CANNOT_DUMP-mode Emacs needs to read loaddefs at startup.
 autoloads .PHONY: $(lisp)/loaddefs.el
 $(lisp)/loaddefs.el: $(LOADDEFS)
         @echo Directories for loaddefs: ${SUBDIRS_ALMOST}
         $(AM_V_GEN)$(emacs) -l autoload \
             --eval '(setq autoload-ensure-writable t)' \
             --eval '(setq autoload-builtin-package-versions t)' \
-            --eval '(setq generated-autoload-file (expand-file-name (unmsys--file-name "$@")))' \
+            --eval '(setq generated-autoload-file (expand-file-name (unmsys--file-name "$(lisp)/loaddefs.tmp")))' \
             -f batch-update-autoloads ${SUBDIRS_ALMOST}
+        mv -f $(lisp)/loaddefs.tmp $@
 
 # autoloads only runs when loaddefs.el is nonexistent, although it
 # generates a number of different files. Provide a force option to enable