I ran the tests on Ubuntu 14.04 and it looks good. Please make the formatting and style changes that I mentioned above, and I'll merge.

Can confirm that this makes the build work on Arch as well.

I can confirm that this makes the build work on Fedora 23 as well.

Updated the commit:

• Fixed indentation
• Consistently quoting ${input}
• Removed now unused custom command target 'copy_glibc_module'
• Used CMAKE_LIBRARY_ARCHITECTURE as suggested by @estan

Nice work. A question though: What happened to the creation of the output directory now? It seems it's gone. Is it created implicitly somehow, or have we all had the directory already created when we tested this?

Also, and this is just a suggestion, but couldn't the CMakeLists.txt now be simplified to something like (untested):

set(sources
  Glibc.swift
)

set(output_dir "${SWIFTLIB_DIR}/glibc")

file(MAKE_DIRECTORY "${output_dir}")

# Set correct paths to glibc headers
set(GLIBC_INCLUDE_PATH "/usr/include")
if(CMAKE_LIBRARY_ARCHITECTURE)
  set(GLIBC_ARCH_INCLUDE_PATH "${GLIBC_INCLUDE_PATH}/${CMAKE_LIBRARY_ARCHITECTURE}")
else()
  set(GLIBC_ARCH_INCLUDE_PATH "${GLIBC_INCLUDE_PATH}")
endif()
if (NOT EXISTS "${GLIBC_ARCH_INCLUDE_PATH}/sys")
  message(FATAL_ERROR "Glibc headers were not found.")
endif()

configure_file(module.map.in "${output_dir}/module.map" @ONLY)

swift_install_in_component(stdlib
    FILES "${output_dir}/module.map"
    DESTINATION "lib/swift/glibc")

add_swift_library(swiftGlibc IS_SDK_OVERLAY
    ${sources}
    FILE_DEPENDS "${output_dir}/module.map" "${SWIFTLIB_DIR}/glibc"
    INSTALL_IN_COMPONENT stdlib-experimental)

What I did was:

• Add file(MAKE_DIRECTORY "${output_dir}")
• Let sources be the list of Swift sources
• Handle module.map.in / module.map as a special case (not likely there will be many?), so no loop / regex substitutions needed.

I'll let someone from the Swift project comment on what they think of that.

I also realized now that with the custom command target gone, I get

CMake Warning (dev):
  Policy CMP0058 is not set: Ninja requires custom command byproducts to be
  explicit.  Run "cmake --help-policy CMP0058" for policy details.  Use the
  cmake_policy command to set the policy and suppress this warning.

  This project specifies custom command DEPENDS on files in the build tree
  that are not specified as the OUTPUT or BYPRODUCTS of any
  add_custom_command or add_custom_target:

   lib/swift/glibc
   lib/swift/glibc/module.map

  For compatibility with versions of CMake that did not have the BYPRODUCTS
  option, CMake is generating phony rules for such files to convince 'ninja'
  to build.

  Project authors should add the missing BYPRODUCTS or OUTPUT options to the
  custom commands that produce these files.
This warning is for project developers.  Use -Wno-dev to suppress it.

with CMake 3.4.0. The custom command DEPENDS it speaks of is that added by add_swift_library. Not sure what the best way to handle this is, or if it should just be ignored for now. The cmake --help-policy CMP0058 is quite lengthy...

Could always do cmake_policy(SET CMP0058 OLD) in the top-level CMakeLists.txt to suppress it on CMake 3.4+. But I think that could be done in a separate pull request, if at all.

It's verified with a clean build that the directory is created, so that works fine.

I didn't want to rewrite too much of the file, because I'm new to CMake, but I agree that it can be simplified. And indeed, it might be best to have a look at that another time.

Regarding the warning, I didn't catch that, but just adding the custom command target back in seems pointless to me, since it's not really doing anything anymore. I would expect that it's possible to depend on a generated configuration file, but I can have another look at it tomorrow. In the meantime, if someone with more CMake experience has an easy solution, let me know.

Alright. Good that the mkdir is not needed.

Yes, any possible simplifications can be another PR. Just wanted to throw it out there :)

I agree it's a little silly to have a "dummy" custom command. And the warning will only appear on CMake 3.4.0+, which are very new versions. So let's postpone that as well. I get truckloads of such policy warnings about other things anyway.

To me this can go in as is.

👍

Was considering doing similar things.

Tested it on Fedora 23, works well.

Final update (hopefully). I'm becoming a CMake expert now, so I dared to rewrite a bit more ;)

• Now creating module.map in the default location: ${CMAKE_CURRENT_BINARY_DIR}
• Added custom command target to copy it to ${output_dir}
• Cleaned up based on proposal by @estan

This seems to be the only solution to prevent the CMP0058 policy warning. I think normally you don't directly depend on generated configuration, but have an automatic dependency. For example with config.h. In this case we want to depend on module.map explicitly and it seems we need a custom command target for that.

There are other solutions, like generating a script for doing the substitutions, or generating a CMake file that is used during build, but I didn't want to move away too far from the working solution. If required, we can improve later.

Only drawback I see is the extra file we create, furthermore this solution works fine:

• When just touching module.map.in, module.map is regenerated, but unchanged, so it's not copied to ${output_dir}.
• When changing module.map.in, module.map is regenerated and copied, so it will trigger a rebuild.

Thanks for this. I'd like to test this fix on Scientific Linux 7.1, but I'm having trouble applying the patch. I replaced stdlib/public/Glibc/CMakeLists.txt with the version from this commit, and likewise removed stdlib/public/Glibc/module.map and added the stdlib/public/Glibc/module.map.in from this commit.

But after doing so, the build doesn't know how to create stdlib/public/Glibc/module.map:

• /home/lanes/cmake-3.4.1-Linux-x86_64.binary_distribution/bin/cmake --build /home/lanes/swift/build/Ninja-DebugAssert/swift-linux-x86_64 -- all swift-stdlib-linux-x86_64
  ninja: error: '/home/lanes/swift/swift/stdlib/public/Glibc/module.map', needed by 'lib/swift/glibc', missing and no known rule to make it

How should this fix be applied? Sorry for such a simple question - I'm fairly new to cmake and don't know ninja at all.

The changed build configuration should be detected. Did you try to run the build-script, or are you running cmake manually?

I forgot to switch to the appropriate branch. Once I did that, I was able to build successfully on Scientific Linux 7.1

Ok 👍

I tested on Ubuntu 14.04 and it works.