Move goma/ccache logic to //build/toolchain/gcc_toolchain.gni

build/toolchain/gcc_toolchain.gni

Index: build/toolchain/gcc_toolchain.gni
diff --git a/build/toolchain/gcc_toolchain.gni b/build/toolchain/gcc_toolchain.gni
index 41766ce920985f529a5312ef61122ce389739593..ca5560bc8c33cf94a683bd4d45a6859ae7ac0225 100644
--- a/build/toolchain/gcc_toolchain.gni
+++ b/build/toolchain/gcc_toolchain.gni
@@ -4,6 +4,8 @@
 
 import("//build/config/nacl/config.gni")
 import("//build/config/sanitizers/sanitizers.gni")
+import("//build/toolchain/ccache.gni")
+import("//build/toolchain/goma.gni")
 import("//build/toolchain/toolchain.gni")
 
 # This value will be inherited in the toolchain below.
@@ -84,6 +86,22 @@ template("gcc_toolchain") {
     assert(defined(invoker.toolchain_os),
            "gcc_toolchain() must specify a \"toolchain_os\"")
 
+    # Allow toolchains to avoid ccache/goma explicitly

[brettw, 2015/09/24 19:35:56]

The phrasing of this comment seems weird to me, since I don't really see it as
opt-out. I'd say we don't need a comment here, but you should document the new
use_ccache and use_goma variables in the comment above the template above.

[Dirk Pranke, 2015/09/24 19:41:08]

I'm not sure I understand you; we still want the command line arg use_goma to
override 
things for the default toolchains; are you suggesting that we should modify,
e.g., clang_x64's toolchain_args
to say use_goma = use_goma ?

[tsniatowski, 2015/09/24 19:48:26]

This wouldn't do anything. As I understand it the setting would simply be better
documented as "Set to false to avoid using ccache/goma even if requested
globally" near where other invoker-settable variables are listed.

+    if (defined(invoker.use_ccache)) {
+      use_ccache = invoker.use_ccache
+    }
+    if (defined(invoker.use_goma)) {
+      use_goma = invoker.use_goma
+    }
+    if (use_goma) {
+      assert(!use_ccache, "Goma and ccache can't be used together.")
+      compiler_prefix = "$goma_dir/gomacc "
+    } else if (use_ccache) {
+      compiler_prefix = "ccache "
+    } else {
+      compiler_prefix = ""
+    }
+
     # This define changes when the toolchain changes, forcing a rebuild.
     # Nothing should ever use this define.
     if (defined(invoker.rebuild_define)) {
@@ -92,11 +110,8 @@ template("gcc_toolchain") {
       rebuild_string = ""
     }
 
-    # We can't do string interpolation ($ in strings) on things with dots in
-    # them. To allow us to use $cc below, for example, we create copies of
-    # these values in our scope.
-    cc = invoker.cc
-    cxx = invoker.cxx
+    cc = compiler_prefix + invoker.cc
+    cxx = compiler_prefix + invoker.cxx
     ar = invoker.ar
     ld = invoker.ld
     if (defined(invoker.readelf)) {