[SCons] Simplify building cmake libraries.

Add an extra "CMakeBuild" method to reduce configuration needed by each
library.

tools/cmake.py

@@ -101,6 +101,18 @@ def cmake_generator(target, source, env, for_signature):
     ]
 
 
+def cmake_build(env, target_dir, source_dir, cmake_outputs=[], cmake_targets=[], cmake_options=[], dependencies=[]):
+    cmake_env = env.Clone()
+    target = env.Dir("{}/{}/{}".format(target_dir, env["platform"], env["arch"]))
+    source = env.Dir(source_dir)
+    builder_targets = [target] + [str(target) + "/" + f for f in cmake_outputs]
+    builder_sources = [source] + dependencies
+    cmake_env.Append(CMAKECONFFLAGS=["-D%s=%s" % it for it in cmake_options.items()])
+    if len(cmake_targets) > 0:
+        cmake_env.Append(CMAKEBUILDFLAGS=["-t"] + [t for t in cmake_targets])
+    return cmake_env.CMake(builder_targets, builder_sources)
+
+
 def options(opts):
     opts.Add("cmake_default_flags", "Default CMake platform flags override, will be autodetected if not specified.", "")
 
@@ -120,3 +132,4 @@ def generate(env):
     env["CMAKEBUILDFLAGS"] = SCons.Util.CLVar("")
     env["CMAKEBUILDCOM"] = "$CMAKE --build ${TARGET.dir} $CMAKEBUILDFLAGS -j$CMAKEBUILDJOBS"
     env["BUILDERS"]["CMake"] = SCons.Builder.Builder(generator=cmake_generator, emitter=cmake_emitter)
+    env.AddMethod(cmake_build, "CMakeBuild")

tools/rtc.py

@@ -1,8 +1,8 @@
 import os
 
 
-def rtc_cmake_config(env):
-    config = {
+def build_library(env, ssl):
+    rtc_config = {
         "CMAKE_BUILD_TYPE": "RelWithDebInfo" if env["debug_symbols"] else "Release",
         "USE_NICE": 0,
         "NO_WEBSOCKET": 1,
@@ -15,21 +15,31 @@ def rtc_cmake_config(env):
         "OPENSSL_CRYPTO_LIBRARY": env["SSL_CRYPTO_LIBRARY"],
         "OPENSSL_ROOT_DIR": env["SSL_INSTALL"],
     }
-    return config
+    is_msvc = env.get("is_msvc", False)
+    lib_ext = ".lib" if is_msvc else ".a"
+    lib_prefix = "" if is_msvc else "lib"
+    rtc_libs = [
+        "{}datachannel-static{}".format(lib_prefix, lib_ext),
+        "deps/libjuice/{}juice-static{}".format(lib_prefix, lib_ext),
+        "deps/libsrtp/{}srtp2{}".format(lib_prefix, lib_ext),
+        "deps/usrsctp/usrsctplib/{}usrsctp{}".format(lib_prefix, lib_ext),
+    ]
+    # Build libdatachannel
+    rtc = env.CMakeBuild(
+        "#bin/thirdparty/libdatachannel/",
+        "#thirdparty/libdatachannel",
+        cmake_options=rtc_config,
+        cmake_outputs=rtc_libs,
+        cmake_targets=["datachannel-static"],
+        dependencies=ssl,
+    )
 
-
-def build_library(env, ssl):
+    # Configure env.
     if env["platform"] == "windows":
         env.PrependUnique(LIBS=["iphlpapi", "bcrypt"])
+    env.Prepend(LIBS=list(filter(lambda f: str(f).endswith(lib_ext), rtc)))
+    env.Append(CPPPATH=["#thirdparty/libdatachannel/include"])
 
-    env.Prepend(LIBS=env["RTC_LIBS"])
-
-    rtc_env = env.Clone()
-    rtc_targets = [env.Dir(env["RTC_BUILD"])] + env["RTC_LIBS"]
-    rtc_sources = [env.Dir(env["RTC_SOURCE"])] + ssl
-    rtc_env.Append(CMAKECONFFLAGS=["-D%s=%s" % it for it in rtc_cmake_config(env).items()])
-    rtc_env.Append(CMAKEBUILDFLAGS=["-t", "datachannel-static"])
-    rtc = rtc_env.CMake(rtc_targets, rtc_sources)
     return rtc
 
 
@@ -38,23 +48,4 @@ def exists(env):
 
 
 def generate(env):
-    env["RTC_SOURCE"] = env.Dir("#thirdparty/libdatachannel").abspath
-    env["RTC_BUILD"] = env.Dir("#bin/thirdparty/libdatachannel/{}/{}".format(env["platform"], env["arch"])).abspath
-    env["RTC_INCLUDE"] = env["RTC_SOURCE"] + "/include"
-    lib_ext = ".a"
-    lib_prefix = "lib"
-    if env.get("is_msvc", False):
-        lib_ext = ".lib"
-        lib_prefix = ""
-    env["RTC_LIBS"] = [
-        env.File(env["RTC_BUILD"] + "/" + lib)
-        for lib in [
-            "{}datachannel-static{}".format(lib_prefix, lib_ext),
-            "deps/libjuice/{}juice-static{}".format(lib_prefix, lib_ext),
-            "deps/libsrtp/{}srtp2{}".format(lib_prefix, lib_ext),
-            "deps/usrsctp/usrsctplib/{}usrsctp{}".format(lib_prefix, lib_ext),
-        ]
-    ]
     env.AddMethod(build_library, "BuildLibDataChannel")
-    env.Append(LIBPATH=[env["RTC_BUILD"]])
-    env.Append(CPPPATH=[env["RTC_INCLUDE"]])