curl-7.54.0 introduced GNU make dependency

[0-wiz-0]

curl is usually buildable with BSD make, but in 7.54.0 it started using "$<" again, which in BSD make is only defined in implied rules, not in explicit ones.
Fix: in src/Makefile.am use $(MANPAGE) instead of $&lt; (three places) and update the comment.

[bagder]

thanks!

[dfandrich]

This reverts b1dc45a which is going to break out-of-tree tar ball builds again.

[dfandrich]

https://curl.haxx.se/dev/log.cgi?id=20170420004847-7533#prob1

[bagder]

Tricky. Why does it break the out-of-tree build? I've successfully run my own test builds out-of-tree locally... Can you reproduce that error manually and see if you can understand it?

Or how exactly is $< different than $(MANPAGE) there that explains this?

[bagder]

The problem is building from a tarball where there's a prebuilt docs/curl.1 already so the modified (commit 5b4cbcf) approach doesn't properly rebuild curl.1 in the build tree but still refers to the build tree path in the src/Makefile that builds the curl --manual feature...

[ptor]

Or how exactly is $&lt; different than $(MANPAGE) there that explains this?
I think it's because $&lt; points to the prerequisite (that is, the dependency), which is searched via VPATH, while the $(MANPAGE) variable, when used directly in the rule, is not searched by VPATH - it's just replaced with its value.
A simple test:
--
$ cat Makefile
dep1 = dep1
dep2 = dep2
VPATH = dir
target: $(dep1) $(dep2)
@echo $&lt; and $(dep1) and $(dep2)
--
$ mkdir dir
$ touch dir/dep1
$ touch dep2
--
$ make
dir/dep1 and dep1 and dep2

[dfandrich]

It's only a problem on builds from the tar ball. The issue has to do with rebuilding the curl.1 file. In the tar ball, the time stamps are such that make does not actually rebuild the file, so the only copy is $(top_srcdir)/docs/curl.1. On git checkouts, the file must be rebuilt (because it's not available from the tar ball) so the only copy is in $(top_builddir)/docs/curl.1. $&lt; uses the VPATH to find the right location of the file, whereas $(MANPAGE) hard-codes it. Yes, it's tricky and it took me a while to come up with b1dc45a. I thought I also verified that $< was standard make syntax before checking it in.

[bagder]

Ok, so let's start over. I've revered this change for now since it wasn't the right thing.

[dfandrich]

w.r.t. standard make syntax, $< is used all over the place in the curl automakefiles.

[0-wiz-0]

To clarify, $< is fine in implied rules, silly example:

.c.o:
    $(CC) -c $<

However, in this case it is an explicit rule:

foo.c:
    $(CC) -c $<

In this case, $< is not defined, at least in FreeBSD's and NetBSD's make.

[dfandrich]

It's used at an explicit rule at least once, too: in the ca-bundle in the root Makefile.am