Re: [PATCH v3 11/34] fsmonitor-fs-listen-win32: stub in backend for Windows

Ævar Arnfjörð Bjarmason [off-list ref] writes:

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Why put this in an ifdef?

...

Why does the FSMONITOR_DAEMON_BACKEND option require a nonexistent line
as opposed to an empty one?

I do not quite get the question.

#!/bin/sh
cat >make.file <<\EOF
all::
ifeq ($(FSMONITOR_DAEMON_BACKEND),)
	echo it is empty
endif
ifndef FSMONITOR_DAEMON_BACKEND
	echo it is undefined
endif
EOF

echo "unset???"
make -f make.file

echo "set to empty???"
make -f make.file FSMONITOR_DAEMON_BACKEND=

These two make invocations will give us the same result, showing
that "is it set to empty" and "is it unset" are the same.

Indeed, which is why I'm pointing out that wrapping it in an ifdef is
pointless, which is why we don't do it for the other ones.

We do have a bunch of ifdef'd things there for perf etc., I'm not sure
if it matters or not for those.

Sorry, but I still do not get the question.  There are bunch of
ifndef in Makefile in addition to ifeq/ifneq and your question

    FSMONITOR_DAEMON_BACKEND option require a nonexistent line as
    opposed to an empty one?

is asking "why is it X" when X is not quite true.  I presume that
your "wrapping it in an ifdef" refers to a construct like this:

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+ifdef FSMONITOR_DAEMON_BACKEND
+	COMPAT_CFLAGS += -DHAVE_FSMONITOR_DAEMON_BACKEND
+	COMPAT_OBJS += compat/fsmonitor/fsmonitor-fs-listen-$(FSMONITOR_DAEMON_BACKEND).o
+endif

but is your suggestion that it should be written like this instead?

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+ifneq ($(FSMONITOR_DAEMON_BACKEND),)
+	COMPAT_CFLAGS += -DHAVE_FSMONITOR_DAEMON_BACKEND
+	COMPAT_OBJS += compat/fsmonitor/fsmonitor-fs-listen-$(FSMONITOR_DAEMON_BACKEND).o
+endif

I do not think the latter is any easier to follow (and we have many
ifdef and ifndef in our Makefile already).  Perhaps I will see what
you mean when I see your "better alternative", but so far, I am not
successfully guessing what it is.