Re: src/Makefile unhelpful

[Gregory Heytings <gregory@heytings.org>]

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Complete patch attached, comments welcome.

I added a (minimal) sanity check, too.  I remember at least one case when 
make "failed to fail", it returned 0 even though the build did in fact not 
succeed.

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From 8cab514b4499b99f3c2ae07fa345b54c4ecc5823 Mon Sep 17 00:00:00 2001
From: Gregory Heytings <gregory@heytings.org>
Date: Sat, 17 Sep 2022 10:39:03 +0000
Subject: [PATCH] Display a help message when building Emacs failed.

* Makefile.in (actual-all): New target, replacing the former all target.
(advice-on-failure, sanity-check): New targets.
(all): Use the new targets.
---
 Makefile.in | 42 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/Makefile.in b/Makefile.in
index 3f811ea60f..2e518de348 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -366,7 +366,47 @@ ELN_DESTDIR =
 
 gsettings_SCHEMAS = etc/org.gnu.emacs.defaults.gschema.xml
 
-all: ${SUBDIR} info $(gsettings_SCHEMAS:.xml=.valid) src-depending-on-lisp
+all:
+	$(MAKE) actual-all || $(MAKE) advice-on-failure exit-status=$$?
+	$(MAKE) sanity-check
+
+.PHONY: actual-all advice-on-failure sanity-check
+
+actual-all: ${SUBDIR} info $(gsettings_SCHEMAS:.xml=.valid) src-depending-on-lisp
+
+advice-on-failure:
+	@echo
+	@echo "  Make failed with exit status ${exit-status}."
+	@cat Makefile | \
+	  sed -n '/^# ADVICE-ON-FAILURE-BEGIN/,$${p;/^# ADVICE-ON-FAILURE-END/q};' | \
+	  sed 's/^# //' | grep -v '^ADVICE-ON-FAILURE-'
+	@echo
+	@exit ${exit-status}
+
+# ADVICE-ON-FAILURE-BEGIN
+#   You might consider to:
+#   - run "make bootstrap", which might fix the problem
+#   - run "git clean -fdx" and run "make" again, which might fix
+#     the problem if it was not fixed by "make bootstrap"
+#     !BEWARE! "git clean -fdx" restores the local repository in its
+#     !BEWARE! pristine state, it deletes all local changes and all
+#     !BEWARE! untracked files
+#   - run "make V=1", which displays the full commandes invoked by
+#     make, to further investigate the problem
+# ADVICE-ON-FAILURE-END
+
+sanity-check:
+	@v=$$(src/emacs${EXEEXT} --batch --eval \
+	  '(progn (defun f (n) (if (= 0 n) 1 (* n (f (- n 1))))) (princ (f 10)))' \
+	  2> /dev/null); \
+	[ "X$$v" == "X3628800" ] && exit 0; \
+	echo; \
+	echo "  Make succeeded, but Emacs is not functional."; \
+	cat Makefile | \
+	  sed -n '/^# ADVICE-ON-FAILURE-BEGIN/,$${p;/^# ADVICE-ON-FAILURE-END/q};' | \
+	  sed 's/^# //' | grep -v '^ADVICE-ON-FAILURE-'; \
+	echo; \
+	exit 1
 
 .PHONY: all ${SUBDIR} blessmail epaths-force epaths-force-w32 epaths-force-ns-self-contained etc-emacsver
 
-- 
2.35.1