[gn build] Add a flag to provide the path to zlib on Windows.

[sebmarchand]

Summary

This allows Windows developer to provide the path to zlib.lib when
setting llvm_enable_zlib=true.

[sebmarchand]

Hey Nico,

PTAL. This is my first CL on Phabricator so I might have made some mistakes in the config.

[thakis]

Thanks for the patch! The way I thought this would look is to have the arg in http://llvm-cs.pcc.me.uk/utils/gn/build/libs/zlib/enable.gni#3 and then change the lower declare_args block to have llvm_enable_zlib = host_os != "win" || zlib_path != "". Does that make sense?

[sebmarchand]

Address Nico's comments.

[sebmarchand]

In D80042#2042904, @thakis wrote:

Thanks for the patch! The way I thought this would look is to have the arg in http://llvm-cs.pcc.me.uk/utils/gn/build/libs/zlib/enable.gni#3 and then change the lower declare_args block to have llvm_enable_zlib = host_os != "win" || zlib_path != "". Does that make sense?

Thanks, that makes sense. The new arg is already in utils/gn/build/libs/zlib/enable.gni , did you simply meant to put it in a new declare_args block before the existing one?

[sebmarchand]

Thanks! I don't think that I can commit this though, the doc says "If you do not have commit access, someone has to commit the change for you (with attribution)" , could you please do that? Thanks!

[thakis]

f8e833a50183ce2048e3cf5929afa672caea0df5

[thakis]

Looks like this breaks the build on Windows: http://45.33.8.238/win/15588/step_4.txt

…because the assert is in zlib_config, and while we only add the dep on that if llvm_enable_zlib, the config is evaluated at the top level.

[thakis]

landed a fix attempt in f8cccd126b4780a4

[sebmarchand]

Ha shoot, looks like you're fixing this in https://github.com/llvm/llvm-project/commit/f8cccd126b4780a42c00ba84848a66a1c8567183 ?

[sebmarchand]

Looks like we need something like this:

if (host_os == "win" && zlib_path != "") {

  include_dirs = [ zlib_path ]
  libs = [ "$zlib_path/zlib.lib" ]
}

?

llvm/utils/gn/build/libs/zlib/BUILD.gn

 import("//llvm/utils/gn/build/libs/zlib/enable.gni")
 
 config("zlib_config") {
   visibility = [ ":zlib" ]
+  if (host_os == "win") {
+    assert(zlib_path != "", "Please provide the path to zlib")
+    include_dirs = [ zlib_path ]
+    libs = [ "$zlib_path/zlib.lib" ]
+  } else {
     libs = [ "z" ]
   }
+}
 
 group("zlib") {
   if (llvm_enable_zlib) {
     public_configs = [ ":zlib_config" ]
   }
 }

llvm/utils/gn/build/libs/zlib/enable.gni

 declare_args() {
+  # Enabling zlib on Windows requires to provide the path to the .lib and
+  # its header files.
+  if (host_os == "win") {
+    # The path to zlib.lib and its corresponding header files.
+    zlib_path = ""
+  }
+}
+
+declare_args() {
   # Whether to include code that links against zlib.
-  llvm_enable_zlib = host_os != "win"
+  llvm_enable_zlib = host_os != "win" || zlib_path != ""
 }