Make GN use_custom_libcxx work properly with sanitizers. Its default value depended on a previous flag, but the value of that flag wasn't getting set until the end of the declare_args block. The solution is to add a new declare_args block. Added documentation for this since it can be surprising. Review URL: https://codereview.chromium.org/1386713002 Cr-Original-Commit-Position: refs/heads/master@{#352109} Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src Cr-Mirrored-Commit: cc637eee86e6041ac9df3ad7d3160ceb2a88cddd
diff --git a/tools/gn/functions.cc b/tools/gn/functions.cc index 86043f0..01d0aeb 100644 --- a/tools/gn/functions.cc +++ b/tools/gn/functions.cc
@@ -344,7 +344,46 @@ "\n" " See also \"gn help buildargs\" for an overview.\n" "\n" - "Example:\n" + " The precise behavior of declare args is:\n" + "\n" + " 1. The declare_arg block executes. Any variables in the enclosing\n" + " scope are available for reading.\n" + "\n" + " 2. At the end of executing the block, any variables set within that\n" + " scope are saved globally as build arguments, with their current\n" + " values being saved as the \"default value\" for that argument.\n" + "\n" + " 3. User-defined overrides are applied. Anything set in \"gn args\"\n" + " now overrides any default values. The resulting set of variables\n" + " is promoted to be readable from the following code in the file.\n" + "\n" + " This has some ramifications that may not be obvious:\n" + "\n" + " - You should not perform difficult work inside a declare_args block\n" + " since this only sets a default value that may be discarded. In\n" + " particular, don't use the result of exec_script() to set the\n" + " default value. If you want to have a script-defined default, set\n" + " some default \"undefined\" value like [], \"\", or -1, and after\n" + " the declare_args block, call exec_script if the value is unset by\n" + " the user.\n" + "\n" + " - Any code inside of the declare_args block will see the default\n" + " values of previous variables defined in the block rather than\n" + " the user-overridden value. This can be surprising because you will\n" + " be used to seeing the overridden value. If you need to make the\n" + " default value of one arg dependent on the possibly-overridden\n" + " value of another, write two separate declare_args blocks:\n" + "\n" + " declare_args() {\n" + " enable_foo = true\n" + " }\n" + " declare_args() {\n" + " # Bar defaults to same user-overridden state as foo.\n" + " enable_bar = enable_foo\n" + " }\n" + "\n" + "Example\n" + "\n" " declare_args() {\n" " enable_teleporter = true\n" " enable_doom_melon = false\n"