Default components to static libraries in GN build

build/config/BUILDCONFIG.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # =============================================================================
 # PLATFORM SELECTION
 # =============================================================================
 #
 # There are two main things to set: "os" and "cpu". The "toolchain" is the name
 # of the GN thing that encodes combinations of these things.
@@ skipping 93 matching lines @@
 # - Use a name like "use_foo" or "is_foo" (whatever is more appropriate for
 #   your feature) rather than just "foo".
 #
 # - Write good comments directly above the declaration with no blank line.
 #   These comments will appear as documentation in "gn args --list".
 #
 # - Don't call exec_script inside declare_args. This will execute the script
 #   even if the value is overridden, which is wasteful. See first bullet.
 
 declare_args() {
-  # Component build.
+  # Component build. Setting to true compiles targets declared as "components"
+  # as shared libraries loaded dynamically. This speeds up development time.
+  # When false, components will be linked statically.
   is_component_build = false
 
-  # Debug build.
-  is_debug = true
+  # Set to enable the official build level of optimization. This has nothing
+  # to do with branding, but enables an additional level of optimization above
+  # release (!is_debug). This might be better expressed as a tri-state
+  # (debug, release, official) but for historical reasons there are two
+  # separate flags.
+  is_official_build = false
+
+  # Debug build. Enabling official builds automatically sets is_debug to false.
+  is_debug = !is_official_build
 
   # Whether we're a traditional desktop unix.
   is_desktop_linux = current_os == "linux"
 
   # Set to true when compiling with the Clang compiler. Typically this is used
   # to configure warnings.
   is_clang = current_os == "mac" || current_os == "ios" ||
              current_os == "linux" || current_os == "chromeos"
 
   # Allows the path to a custom target toolchain to be injected as a single
   # argument, and set as the default toolchain.
   custom_toolchain = ""
 
   # This should not normally be set as a build argument.  It's here so that
   # every toolchain can pass through the "global" value via toolchain_args().
   host_toolchain = ""
 
   # DON'T ADD MORE FLAGS HERE. Read the comment above.
 }
 
+assert(!(is_debug && is_official_build), "Can't do official debug builds")
+
 # ==============================================================================
 # TOOLCHAIN SETUP
 # ==============================================================================
 #
 # Here we set the default toolchain, as well as the variable host_toolchain
 # which will identify the toolchain corresponding to the local system when
 # doing cross-compiles. When not cross-compiling, this will be the same as the
 # default toolchain.
 #
 # We do this before anything else to make sure we complain about any
@@ skipping 440 matching lines @@
   } else {
     configs = _executable_configs
   }
 }
 
 # ==============================================================================
 # COMPONENT SETUP
 # ==============================================================================
 
 # Defines a component, which equates to a shared_library when
-# is_component_build == true and a source_set / static_library otherwise.
+# is_component_build == true and a static_library otherwise.
 #
-# Arguments are the same as a normal library with this addition:
-#   component_never_use_source_set: Whether to use static_library instead of
-#       source_set for non-component builds. Some targets (e.g. //base) should
-#       use static_library rather than source_set to avoid linking unused object
-#       files.
+# Use static libraries for the static build rather than source sets because
+# many of of our test binaries link many large dependencies but often don't
+# use large portions of them. The static libraries are much more efficient to
+# link in this situation since only the necessary object files are linked.
+#
+# The invoker can override the type of the target in the non-component-build
+# case by setting static_component_type to either "source_set" or
+# "static_library". If unset, the default will be used.
 template("component") {
-  _never_use_source_set = defined(invoker.component_never_use_source_set) &&
-                          invoker.component_never_use_source_set
-  assert(_never_use_source_set || true)  # Mark as used.
   if (is_component_build) {
     _component_mode = "shared_library"
-  } else if (_never_use_source_set) {
+  } else if (defined(invoker.static_component_type)) {
+    assert(invoker.static_component_type == "static_library" ||
+           invoker.static_component_type == "source_set")
+    _component_mode = invoker.static_component_type
+  } else if (!defined(invoker.sources) || is_mac ||
+             (is_win && is_official_build)) {
+    # When there are no sources defined, use a source set to avoid creating
+    # an empty static library (which generally don't work).
+    #
+    # On Windows official builds, the link time code generation bloats static
+    # libraries to the point where some of them become >32 bits large which
+    # causes lib.exe to fail. Always use source sets for that configuration.
+    #
+    # TODO(brettw) bug 618797: Remove the mac condition. On Mac making these as
+    # static_library causes crashes. Remove the mac condition above when this
+    # is fixed.
+    _component_mode = "source_set"
+  } else {
     _component_mode = "static_library"
-  } else {
-    _component_mode = "source_set"
   }
   target(_component_mode, target_name) {
     # Explicitly forward visibility, implicitly forward everything else.
     # Forwarding "*" doesn't recurse into nested scopes (to avoid copying all
     # globals into each template invocation), so won't pick up file-scoped
     # variables. Normally this isn't too bad, but visibility is commonly
     # defined at the file scope. Explicitly forwarding visibility and then
     # excluding it from the "*" set works around this problem.
     # See http://crbug.com/594610
     forward_variables_from(invoker, [ "visibility" ])
     forward_variables_from(invoker, "*", [ "visibility" ])
 
     # All shared libraries must have the sanitizer deps to properly link in
     # asan mode (this target will be empty in other cases).
     if (!defined(deps)) {
       deps = []
     }
     deps += [ "//build/config/sanitizers:deps" ]
   }
 }