[Mac/iOS/GN] Place a version in the command of toolchain tools implemented using scripts.

build/toolchain/mac/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.
 
 # TODO(brettw) Use "gcc_toolchain.gni" like the Linux toolchains. This requires
 # some enhancements since the commands on Mac are slightly different than on
 # Linux.
 
 import("../goma.gni")
 import("//build/config/ios/ios_sdk.gni")
@@ skipping 41 matching lines @@
 
     # concurrent_links is picked up from the declare_arg().
 
     # 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
     ld = invoker.ld
 
+    # When implementing tools using Python scripts, a TOOL_VERSION=N env
+    # variable is placed in front of the command. The N should be incremented
+    # whenever the script is changed, so that the build system rebuilds all
+    # edges that utilize the script. Ideally this should be changed to use
+    # proper input-dirty checking, but that could be expensive. Instead, use a
+    # script to get the tool scripts' modification time to use as the version.
+    # This won't cause a re-generation of GN files when the tool script changes
+    # but it will cause edges to be marked as dirty if the ninja files are
+    # regenerated. See https://crbug.com/619083 for details. A proper fix
+    # would be to have inputs to tools (https://crbug.com/621119).
+    tool_versions =
+        exec_script("get_tool_mtime.py",

[brettw, 2016/06/17 20:43:30]

Can you move this up above the template() definition? This is still getting
called more than once for inputs that are constant.

[Robert Sesek, 2016/06/17 20:53:32]

Done.

+                    rebase_path([
+                                  "//build/toolchain/mac/compile_xcassets.py",
+                                  "//build/toolchain/mac/copy_bundle_data.py",
+                                  "//build/toolchain/mac/filter_libtool.py",
+                                  "//build/toolchain/mac/linker_driver.py",
+                                ],
+                                root_build_dir),
+                    "trim scope")
+
     linker_driver =
+        "TOOL_VERSION=${tool_versions.linker_driver} " +
         rebase_path("//build/toolchain/mac/linker_driver.py", root_build_dir)
 
     # Make these apply to all tools below.
     lib_switch = "-l"
     lib_dir_switch = "-L"
 
     # Object files go in this directory. Use label_name instead of
     # target_output_name since labels will generally have no spaces and will be
     # unique in the directory.
     object_subdir = "{{target_out_dir}}/{{label_name}}"
@@ skipping 56 matching lines @@
       depsformat = "gcc"
       description = "OBJCXX {{output}}"
       outputs = [
         "$object_subdir/{{source_name_part}}.o",
       ]
     }
 
     tool("alink") {
       script =
           rebase_path("//build/toolchain/mac/filter_libtool.py", root_build_dir)
-      command = "rm -f {{output}} && python $script libtool -static {{arflags}} -o {{output}} {{inputs}}"
+      command = "rm -f {{output}} && TOOL_VERSION=${tool_versions.filter_libtool} python $script libtool -static {{arflags}} -o {{output}} {{inputs}}"
       description = "LIBTOOL-STATIC {{output}}"
       outputs = [
         "{{output_dir}}/{{target_output_name}}{{output_extension}}",
       ]
       default_output_dir = "{{target_out_dir}}"
       default_output_extension = ".a"
       output_prefix = "lib"
     }
 
     tool("solink") {
@@ skipping 126 matching lines @@
     }
 
     tool("copy_bundle_data") {
       if (is_ios) {
         _extra_args = "--strings-format=binary1"
       } else {
         _extra_args = ""
       }
       _tool = rebase_path("//build/toolchain/mac/copy_bundle_data.py",
                           root_build_dir)
-      command = "python $_tool ${_extra_args} {{source}} {{output}}"
+      command = "TOOL_VERSION=${tool_versions.copy_bundle_data} python $_tool ${_extra_args} {{source}} {{output}}"
       description = "COPY_BUNDLE_DATA {{source}} {{output}}"
       pool = ":bundle_pool($default_toolchain)"
     }
     tool("compile_xcassets") {
       _tool = rebase_path("//build/toolchain/mac/compile_xcassets.py",
                           root_build_dir)
       if (is_ios) {
         _sdk_name = ios_sdk_name
         _min_deployment_target = ios_deployment_target
       } else {
         _sdk_name = mac_sdk_name
         _min_deployment_target = mac_deployment_target
       }
       command = "rm -f {{output}} && " +
+                "TOOL_VERSION=${tool_versions.compile_xcassets} " +
                 "python $_tool -p $_sdk_name -t $_min_deployment_target " +
                 "-o {{output}} {{inputs}}"
 
       description = "COMPILE_XCASSETS {{output}}"
       pool = ":bundle_pool($default_toolchain)"
     }
 
     toolchain_args() {
       current_cpu = invoker.toolchain_cpu
       current_os = invoker.toolchain_os
@@ skipping 84 matching lines @@
 }
 
 mac_toolchain("x64") {
   toolchain_cpu = "x64"
   toolchain_os = "mac"
   cc = "${goma_prefix}/gcc"
   cxx = "${goma_prefix}/g++"
   ld = cxx
   is_clang = false
 }