Makefiles: add "shared.mak", move ".DELETE_ON_ERROR" to it

We have various behavior that's shared across our Makefiles, or that
really should be (e.g. via defined templates). Let's create a
top-level "shared.mak" to house those sorts of things, and start by
adding the ".DELETE_ON_ERROR" flag to it.

See my own 7b76d6bf221 (Makefile: add and use the ".DELETE_ON_ERROR"
flag, 2021-06-29) and db10fc6c09f (doc: simplify Makefile using
.DELETE_ON_ERROR, 2021-05-21) for the addition and use of the
".DELETE_ON_ERROR" flag.

I.e. this changes the behavior of existing rules in the altered
Makefiles (except "Makefile" & "Documentation/Makefile"). I'm
confident that this is safe having read the relevant rules in those
Makfiles, and as the GNU make manual notes that it isn't the default
behavior is out of an abundance of backwards compatibility
caution. From edition 0.75 of its manual, covering GNU make 4.3:

    [Enabling '.DELETE_ON_ERROR' is] almost always what you want
    'make' to do, but it is not historical practice; so for
    compatibility, you must explicitly request it.

This doesn't introduce a bug by e.g. having this
".DELETE_ON_ERROR" flag only apply to this new shared.mak, Makefiles
have no such scoping semantics.

It does increase the danger that any Makefile without an explicit "The
default target of this Makefile is..." snippet to define the default
target as "all" could have its default rule changed if our new
shared.mak ever defines a "real" rule. In subsequent commits we'll be
careful not to do that, and such breakage would be obvious e.g. in the
case of "make -C t".

We might want to make that less fragile still (e.g. by using
".DEFAULT_GOAL" as noted in the preceding commit), but for now let's
simply include "shared.mak" without adding that boilerplate to all the
Makefiles that don't have it already. Most of those are already
exposed to that potential caveat e.g. due to including "config.mak*".

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

9 files changed, 33 insertions, 13 deletions

diff --git a/Documentation/Makefile b/Documentation/Makefile
index ed656db2ae..ba27456c86 100644
--- a/Documentation/Makefile
+++ b/Documentation/Makefile
@@ -1,3 +1,6 @@
+# Import tree-wide shared Makefile behavior and libraries
+include ../shared.mak
+
 # Guard against environment variables
 MAN1_TXT =
 MAN5_TXT =
@@ -524,7 +527,4 @@ doc-l10n install-l10n::
 	$(MAKE) -C po $@
 endif
 
-# Delete the target file on error
-.DELETE_ON_ERROR:
-
 .PHONY: FORCE
diff --git a/Makefile b/Makefile
index 6f0b4b775f..aa5ff001b6 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,9 @@
 # The default target of this Makefile is...
 all::
 
+# Import tree-wide shared Makefile behavior and libraries
+include shared.mak
+
 # Define V=1 to have a more verbose compile.
 #
 # Define SHELL_PATH to a POSIX shell if your /bin/sh is broken.
@@ -2194,16 +2197,6 @@ shell_compatibility_test: please_set_SHELL_PATH_to_a_more_modern_shell
 strip: $(PROGRAMS) git$X
 	$(STRIP) $(STRIP_OPTS) $^
 
-### Flags affecting all rules
-
-# A GNU make extension since gmake 3.72 (released in late 1994) to
-# remove the target of rules if commands in those rules fail. The
-# default is to only do that if make itself receives a signal. Affects
-# all targets, see:
-#
-#    info make --index-search=.DELETE_ON_ERROR
-.DELETE_ON_ERROR:
-
 ### Target-specific flags and dependencies
 
 # The generic compilation pattern rule and automatically
diff --git a/contrib/scalar/Makefile b/contrib/scalar/Makefile
index 1e9b969f3d..d585b319ed 100644
--- a/contrib/scalar/Makefile
+++ b/contrib/scalar/Makefile
@@ -1,6 +1,9 @@
 # The default target of this Makefile is...
 all::
 
+# Import tree-wide shared Makefile behavior and libraries
+include ../../shared.mak
+
 include ../../config.mak.uname
 -include ../../config.mak.autogen
 -include ../../config.mak
diff --git a/contrib/scalar/t/Makefile b/contrib/scalar/t/Makefile
index 6170672bb3..01e82e56d1 100644
--- a/contrib/scalar/t/Makefile
+++ b/contrib/scalar/t/Makefile
@@ -1,3 +1,6 @@
+# Import tree-wide shared Makefile behavior and libraries
+include ../../../shared.mak
+
 # Run scalar tests
 #
 # Copyright (c) 2005,2021 Junio C Hamano, Johannes Schindelin
diff --git a/shared.mak b/shared.mak
new file mode 100644
index 0000000000..0170bb397a
--- /dev/null
+++ b/shared.mak
@@ -0,0 +1,9 @@
+### Flags affecting all rules
+
+# A GNU make extension since gmake 3.72 (released in late 1994) to
+# remove the target of rules if commands in those rules fail. The
+# default is to only do that if make itself receives a signal. Affects
+# all targets, see:
+#
+#    info make --index-search=.DELETE_ON_ERROR
+.DELETE_ON_ERROR:
diff --git a/t/Makefile b/t/Makefile
index 46cd5fc527..056ce55dcc 100644
--- a/t/Makefile
+++ b/t/Makefile
@@ -1,3 +1,6 @@
+# Import tree-wide shared Makefile behavior and libraries
+include ../shared.mak
+
 # Run tests
 #
 # Copyright (c) 2005 Junio C Hamano
diff --git a/t/interop/Makefile b/t/interop/Makefile
index 31a4bbc716..6911c2915a 100644
--- a/t/interop/Makefile
+++ b/t/interop/Makefile
@@ -1,3 +1,6 @@
+# Import tree-wide shared Makefile behavior and libraries
+include ../../shared.mak
+
 -include ../../config.mak
 export GIT_TEST_OPTIONS
 
diff --git a/t/perf/Makefile b/t/perf/Makefile
index 2465770a78..e4808aebed 100644
--- a/t/perf/Makefile
+++ b/t/perf/Makefile
@@ -1,3 +1,6 @@
+# Import tree-wide shared Makefile behavior and libraries
+include ../../shared.mak
+
 -include ../../config.mak
 export GIT_TEST_OPTIONS
 
diff --git a/templates/Makefile b/templates/Makefile
index d22a71a399..636cee52f5 100644
--- a/templates/Makefile
+++ b/templates/Makefile
@@ -1,3 +1,6 @@
+# Import tree-wide shared Makefile behavior and libraries
+include ../shared.mak
+
 # make and install sample templates
 
 ifndef V