Re: [PATCH v3 1/2] Makefile: use curl-config to determine curl flags

[Junio C Hamano <gitster@pobox.com>]

Dave Borowitz <dborowitz@google.com> writes:

> Use this only when CURLDIR is not explicitly specified, to continue
> supporting older builds. Moreover, if CURL_CONFIG is unset or running
> it returns no results (e.g. because it is missing), default to the old
> behavior of blindly setting -lcurl.
>  	ifdef CURLDIR
> +		CURL_LIBCURL=
>  	else
> +		CURL_CONFIG ?= curl-config
> +		ifeq "$(CURL_CONFIG)" ""
> +			CURL_LIBCURL =
> +		else
> +			CURL_LIBCURL := $(shell $(CURL_CONFIG) --libs)
>  		endif

This "ifeq" is redundant and will never set CURL_LIBCURL to empty
without running the "else" part, I think.  In a Makefile, a variable
explicitly set to empty and a variable that is unset are treated the
same.

	$ cat >Makefile <<EOF
	CURL_CONFIG ?= curl-config
	ifeq "$(CURL_CONFIG)" ""
		X=Empty
	else
		X=NotEmpty
	endif

	ifdef "$(CURL_CONFIG)"
		Z=Defined
	else
		Z=Undefined
	endif

	all::
		@echo "$(X) $(Z)"
	EOF
	$ make -f Makefile CURL_CONFIG=""
	Empty Undefined

That does not mean the patch will give us a broken behaviour,
though.  It just means the ifeq/else part will be redundant.

>  	endif
> +
> +	ifeq "$(CURL_LIBCURL)" ""

This will catch the "$(shell $(CURL_CONFIG) --libs) assigned an
empty string to CURL_LIBCURL" case, so the result is good.

I haven't checked what it would look like if we turn this into an
incremental patch to be applied on top of 'master' (which would give
us a place to document better why we do not rely on the presense of
curl-config), but if we can do so, that would be more preferable
than having to revert the merge of the previous one and then
applying these two patches anew.

Thanks.

> +		ifdef CURLDIR
> +			# Try "-Wl,-rpath=$(CURLDIR)/$(lib)" in such a case.
> +			BASIC_CFLAGS += -I$(CURLDIR)/include
> +			CURL_LIBCURL = -L$(CURLDIR)/$(lib) $(CC_LD_DYNPATH)$(CURLDIR)/$(lib) -lcurl
> +		else
> +			CURL_LIBCURL = -lcurl
> +		endif
> +		ifdef NEEDS_SSL_WITH_CURL
> +			CURL_LIBCURL += -lssl
> +			ifdef NEEDS_CRYPTO_WITH_SSL
> +				CURL_LIBCURL += -lcrypto
> +			endif
> +		endif
> +		ifdef NEEDS_IDN_WITH_CURL
> +			CURL_LIBCURL += -lidn
> +		endif
> +	else
> +		BASIC_CFLAGS += $(shell $(CURL_CONFIG) --cflags)
>  	endif
>  
>  	REMOTE_CURL_PRIMARY = git-remote-http$X