Decoupling rtc_base from Obj-C code

webrtc/rtc_base/BUILD.gn

Index: webrtc/rtc_base/BUILD.gn
diff --git a/webrtc/rtc_base/BUILD.gn b/webrtc/rtc_base/BUILD.gn
index 925f915aca4efd600f1d7adca70b55e8ca99a08c..7d83bfe2c666bce6b512fecd04eed054b2999d37 100644
--- a/webrtc/rtc_base/BUILD.gn
+++ b/webrtc/rtc_base/BUILD.gn
@@ -399,6 +399,43 @@ rtc_source_set("rtc_json") {
 }
 
 rtc_static_library("rtc_base") {

[kwiberg-webrtc, 2017/08/31 20:46:14]

If you made this a source set, would the need for no-op file go away?

[mbonadei, 2017/09/01 09:24:35]

In the next patch set I have switched to rtc_source_set. Please note that
there are some differences (especially regarding how the linker works on
them):

source_set:
https://chromium.googlesource.com/chromium/src/tools/gn/+/HEAD/docs/reference...
static_library:
https://chromium.googlesource.com/chromium/src/tools/gn/+/HEAD/docs/reference...

If you confirm that a source_set is a good to have I am happy to avoid noop
files (and I will review other CLs too).

[kwiberg-webrtc, 2017/09/01 11:23:44]

The default Chromium advice is to use a source set unless you know you need a
static library. And in this case in particular, almost all the "weight" of this
target is in rtc_base_generic, which is already a static library, so I think a
source set is a good fit.

+  if (is_ios || is_mac) {
+    # In order to build a static_library targeting macOS or iOS
+    # we have to provide at least one source file to avoid a build
+    # error.
+    sources = [
+      "noop.mm",
+    ]
+    public_deps = [
+      ":rtc_base_objc",
+    ]
+  } else {
+    # In order to build a static_library targeting macOS or iOS
+    # we have to provide at least one source file to avoid a build
+    # error.
+    sources = [
+      "noop.cc",
+    ]

[kwiberg-webrtc, 2017/08/31 20:46:14]

I'm confused. In the else clause, we *aren't* on macOS or iOS, so why add a
no-op source file? And why have different types of no-op files for the two
cases?

[mbonadei, 2017/09/01 09:24:35]

Oh wait... Yes you are right! In similar CLs I avoided to add the noop file if
we are
not targeting iOS or macOS. This is probably a leftover that I copy/pasted and 
refactored to look symmetric. :/

Good catch! Thanks!

In the next patch set I switched rtc_base from rtc_static_library to
rtc_source_set
so probably we can drop both noop.{mm,cc}.

+    public_deps = [
+      ":rtc_base_generic",
+    ]

[kwiberg-webrtc, 2017/08/31 20:46:14]

This one could be lifted out of the if-else, right? (And if you did, could
rtc_base_objc have a regular dep instead of a public dep on rtc_base_generic?)

[mbonadei, 2017/09/01 09:24:36]

This is the right thing to do. I was too focused on breaking the circular
dependency
that I overlooked this. It is included in the next patch set. Thanks!

+  }
+}
+
+if (is_ios || is_mac) {
+  rtc_static_library("rtc_base_objc") {
+    sources = [
+      "applefilesystem.mm",
+      "thread_darwin.mm",
+    ]
+    public_deps = [
+      ":rtc_base_generic",
+    ]
+    visibility = [ ":rtc_base" ]
+  }
+}
+
+rtc_static_library("rtc_base_generic") {
   cflags = []
   cflags_cc = []
   libs = []
@@ -414,7 +451,6 @@ rtc_static_library("rtc_base") {
   all_dependent_configs = [ ":rtc_base_all_dependent_config" ]
 
   sources = [
-    "applefilesystem.mm",
     "asyncinvoker-inl.h",
     "asyncinvoker.cc",
     "asyncinvoker.h",
@@ -508,6 +544,11 @@ rtc_static_library("rtc_base") {
     "thread.h",
   ]
 
+  visibility = [
+    ":rtc_base",
+    ":rtc_base_objc",
+  ]
+
   # TODO(henrike): issue 3307, make rtc_base build with the Chromium default
   # compiler settings.
   suppressed_configs += [ "//build/config/compiler:chromium_code" ]
@@ -567,10 +608,7 @@ rtc_static_library("rtc_base") {
   }
 
   if (is_ios || is_mac) {
-    sources += [
-      "macifaddrs_converter.cc",
-      "thread_darwin.mm",
-    ]
+    sources += [ "macifaddrs_converter.cc" ]
   }
 
   if (use_x11) {