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

[Dave Borowitz <dborowitz@google.com>]

curl-config is usually installed alongside a curl distribution, and
its purpose is to provide flags for building against libcurl, so use
it instead of guessing flags and dependent libraries.

Allow overriding CURL_CONFIG to a custom path to curl-config, to
compile against a curl installation other than the first in PATH.

Depending on the set of features curl is compiled with, there may be
more libraries required than the previous two options of -lssl and
-lidn. For example, with a vanilla build of libcurl-7.36.0 on Mac OS X
10.9:

$ ~/d/curl-out-7.36.0/lib/curl-config --libs
-L/Users/dborowitz/d/curl-out-7.36.0/lib -lcurl -lgssapi_krb5 -lresolv -lldap -lz

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.

Signed-off-by: Dave Borowitz <dborowitz@google.com>
---
 Makefile | 51 +++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 37 insertions(+), 14 deletions(-)

diff --git a/Makefile b/Makefile
index 2128ce3..cb4ee37 100644
--- a/Makefile
+++ b/Makefile
@@ -34,8 +34,14 @@ all::
 # git-http-push are not built, and you cannot use http:// and https://
 # transports (neither smart nor dumb).
 #
+# Define CURL_CONFIG to the path to a curl-config binary other than the
+# default 'curl-config'. If CURL_CONFIG is unset or points to a binary that
+# is not found, defaults to the CURLDIR behavior, or if CURLDIR is not set,
+# uses -lcurl with no additional library detection.
+#
 # Define CURLDIR=/foo/bar if your curl header and library files are in
-# /foo/bar/include and /foo/bar/lib directories.
+# /foo/bar/include and /foo/bar/lib directories.  This overrides CURL_CONFIG,
+# but is less robust.
 #
 # Define NO_EXPAT if you do not have expat installed.  git-http-push is
 # not built, and you cannot push using http:// and https:// transports (dumb).
@@ -143,9 +149,11 @@ all::
 #
 # Define NEEDS_SSL_WITH_CRYPTO if you need -lssl when using -lcrypto (Darwin).
 #
-# Define NEEDS_SSL_WITH_CURL if you need -lssl with -lcurl (Minix).
+# Define NEEDS_SSL_WITH_CURL if you need -lssl with -lcurl (Minix).  Only used
+# if CURLDIR is set.
 #
-# Define NEEDS_IDN_WITH_CURL if you need -lidn when using -lcurl (Minix).
+# Define NEEDS_IDN_WITH_CURL if you need -lidn when using -lcurl (Minix).  Only
+# used if CURLDIR is set.
 #
 # Define NEEDS_LIBICONV if linking with libc is not enough (Darwin).
 #
@@ -1118,20 +1126,35 @@ ifdef NO_CURL
 	REMOTE_CURL_NAMES =
 else
 	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)/$(lib) -lcurl
+		CURL_LIBCURL=
 	else
-		CURL_LIBCURL = -lcurl
-	endif
-	ifdef NEEDS_SSL_WITH_CURL
-		CURL_LIBCURL += -lssl
-		ifdef NEEDS_CRYPTO_WITH_SSL
-			CURL_LIBCURL += -lcrypto
+		CURL_CONFIG ?= curl-config
+		ifeq "$(CURL_CONFIG)" ""
+			CURL_LIBCURL =
+		else
+			CURL_LIBCURL := $(shell $(CURL_CONFIG) --libs)
 		endif
 	endif
-	ifdef NEEDS_IDN_WITH_CURL
-		CURL_LIBCURL += -lidn
+
+	ifeq "$(CURL_LIBCURL)" ""
+		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
-- 
1.9.1.423.g4596e3a