jamplus: link command line too long for osx - macos

Question

I'm using jamplus to build a vendor's cross-platform project. On osx, the C tool's command line (fed via clang to ld) is too long.
Response files are the classic answer to command lines that are too long: jamplus states in the manual that one can generate them on the fly.
The example in the manual looks like this:
actions response C++
{
$(C++) ##(-filelist #($(2)))
}
Almost there! If I specifically blow out the C.Link command, like this:
actions response C.Link
{
"$(C.LINK)" $(LINKFLAGS) -o $(<[1]:C) -Wl,-filelist,#($(2:TC)) $(NEEDLIBS:TC) $(LINKLIBS:TC))
}
in my jamfile, I get the command line I need that passes through to the linker, but the response file isn't newline terminated, so link fails (osx ld requires newline-separated entries).
Is there a way to expand a jamplus list joined with newlines? I've tried using the join expansion $(LIST:TCJ=\n) without luck. $(LIST:TCJ=#(\n)) doesn't work either. If I can do this, the generated file would hopefully be correct.
If not, what jamplus code can I use to override the link command for clang, and generate the contents on the fly from a list? I'm looking for the least invasive way of handling this - ideally, modifying/overriding the tool directly, instead of adding new indirect targets wherever a link is required - since it's our vendor's codebase, as little edit as possible is desired.

Answer 1

The syntax you are looking for is:
newLine = "
" ;
actions response C.Link
{
"$(C.LINK)" $(LINKFLAGS) -o $(<[1]:C) -Wl,-filelist,#($(2:TCJ=$(newLine))) $(NEEDLIBS:TC) $(LINKLIBS:TC))
}
To be clear (I'm not sure how StackOverflow will format the above), the newLine variable should be defined by typing:
newLine = "" ;
And then placing the carat between the two quotes and hitting enter. You can use this same technique for certain other characters, i.e.
tab = " " ;
Again, start with newLine = "" and then place carat between the quotes and hit tab. In the above it is actually 4 spaces which is wrong, but hopefully you get the idea. Another useful one to have is:
dollar = "$" ;
The last one is useful as $ is used to specify variables typically, so having a dollar variable is useful when you actually want to specify a dollar literal. For what it is worth, the Jambase I am using (the one that ships with the JamPlus I am using), has this:
SPACE = " " ;
TAB = " " ;
NEWLINE = "
" ;
Around line 28...

Answer 2

I gave up on trying to use escaped newlines and other language-specific characters within string joins. Maybe there's an awesome way to do that, that was too thorny to discover.
Use a multi-step shell command with multiple temp files.
For jamplus (and maybe other jam variants), the section of the actions response {} between the curly braces becomes an inline shell script. And the response file syntax #(<value>) returns a filename that can be assigned within the shell script, with the contents set to <value>.
Thus, code like:
actions response C.Link
{
_RESP1=#($(2:TCJ=#)#$(NEEDLIBS:TCJ=#)#$(LINKLIBS:TCJ=#))
_RESP2=#()
perl -pe "s/[#]/\n/g" < $_RESP1 > $_RESP2
"$(C.LINK)" $(LINKFLAGS) -o $(<[1]:C) -Wl,-filelist,$_RESP2
}
creates a pair of temp files, assigned to shell variable names _RESP1 and _RESP2. File at path _RESP1 is assigned the contents of the expanded sequence joined with a # character. Search and replace is done with a perl one liner into _RESP2. And link proceeds as planned, and jamplus cleans up the intermediate files.
I wasn't able to do this with characters like :;\n, but # worked as long as it had no adjacent whitespace. Not completely satisfied, but moving on.