Allow disabling warnings as errors in GN

build/config/compiler/BUILD.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.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/ccache.gni")
 
 if (current_cpu == "arm") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
   import("//build/config/mips.gni")
 }
 if (is_posix) {
   import("//build/config/gcc/gcc_version.gni")
 }
 if (is_win) {
   import("//build/config/win/visual_studio_version.gni")
 }
 
 declare_args() {
+  # Default to warnings as errors for default workflow, where we catch
+  # warnings with known toolchains. Allow overriding this e.g. for Chromium
+  # builds on Linux that could use a different version of the compiler.
+  treat_warnings_as_errors = true
+
   # Normally, Android builds are lightly optimized, even for debug builds, to
   # keep binary size down. Setting this flag to true disables such optimization
   android_full_debug = false
 
   # Whether to use the binary binutils checked into third_party/binutils.
   # These are not multi-arch so cannot be used except on x86 and x86-64 (the
   # only two architectures that are currently checked in). Turn this off when
   # you are using a custom toolchain and need to control -B in cflags.
   linux_use_bundled_binutils = is_linux && current_cpu == "x64"
   binutils_path = rebase_path("//third_party/binutils/Linux_x64/Release/bin",
@@ skipping 559 matching lines @@
 # default_warnings ------------------------------------------------------------
 #
 # Collects all warning flags that are used by default.  This is used as a
 # subconfig of both chromium_code and no_chromium_code.  This way these
 # flags are guaranteed to appear on the compile command line after -Wall.
 config("default_warnings") {
   cflags = []
   cflags_cc = []
 
   if (is_win) {
+    if (treat_warnings_as_errors) {
+      cflags += [ "/WX" ]
+    }
+
     cflags += [
-      # Treat warnings as errors.
-      "/WX",
-
       # Warnings permanently disabled:
 
       # C4127: conditional expression is constant
       # This warning can in theory catch dead code and other problems, but
       # triggers in far too many desirable cases where the conditional
       # expression is either set by macros or corresponds some legitimate
       # compile-time constant expression (due to constant template args,
       # conditionals comparing the sizes of different types, etc.).  Some of
       # these can be worked around, but it's not worth it.
       "/wd4127",
@@ skipping 79 matching lines @@
         # Disable unused-value (crbug.com/505318) except -Wunused-result.
         "-Wno-unused-value",
         "-Wunused-result",
       ]
     }
   } else {
     # Common GCC warning setup.
     cflags += [
       # Enables.
       "-Wendif-labels",  # Weird old-style text after an #endif.
-      "-Werror",  # Warnings as errors.
 
       # Disables.
       "-Wno-missing-field-initializers",  # "struct foo f = {0};"
       "-Wno-unused-parameter",  # Unused function parameters.
     ]
 
+    if (treat_warnings_as_errors) {
+      cflags += [ "-Werror" ]
+    }
+
     if (is_mac) {
       cflags += [ "-Wnewline-eof" ]
       if (!is_nacl) {
         # When compiling Objective-C, warns if a method is used whose
         # availability is newer than the deployment target. This is not
         # required when compiling Chrome for iOS.
         cflags += [ "-Wpartial-availability" ]
       }
     }
 
@@ skipping 503 matching lines @@
   if (symbol_level == 0) {
     configs = [ ":no_symbols" ]
   } else if (symbol_level == 1) {
     configs = [ ":minimal_symbols" ]
   } else if (symbol_level == 2) {
     configs = [ ":symbols" ]
   } else {
     assert(false)
   }
 }