Updated MSVC toolchain to 2017, and further refactored GN

'windk' is no longer a thing. There are two separate variables to point
at your compiler (win_vc), and SDK (win_sdk).

'msvc' is no longer a thing, either. By default, we look for 2017 and
then 2015 (in the default locations). If neither is located, use an
assert to let users know they should set win_vc. Then, detect if win_vc
points at a 2017 or 2015 installation, and configure it automatically.

Because the toolchain is now 2017, update the GN files to handle building
x86 in that configuration. In fact, we only support x86 builds (with 2017
or 2015) using the toolchain assets. Keep a 2015 toolchain around as a
new asset, so we can add bot coverage.

Docs-Preview: https://skia.org/?cl=81841
Bug: skia:
Change-Id: I8c68a6f949e54c0e798a219450bbb9406f8dc6ac
Reviewed-on: https://skia-review.googlesource.com/81841
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Brian Osman <brianosman@google.com>

22 files changed, 124 insertions, 53 deletions

diff --git a/gn/BUILD.gn b/gn/BUILD.gn
index cf94889a70..4819ee151a 100644
--- a/gn/BUILD.gn
+++ b/gn/BUILD.gn
@@ -55,9 +55,9 @@ config("default") {
     ]
 
     if (msvc == 2015) {
-      _include_dirs = [ "$windk/VC/include" ]
+      _include_dirs = [ "$win_vc/include" ]
     } else {  # 2017
-      _include_dirs = [ "$windk/VC/Tools/MSVC/$win_toolchain_version/include" ]
+      _include_dirs = [ "$win_vc/Tools/MSVC/$win_toolchain_version/include" ]
     }
     _include_dirs += [
       "$win_sdk/Include/$win_sdk_version/shared",
@@ -83,13 +83,13 @@ config("default") {
     ]
     if (msvc == 2015) {
       if (target_cpu == "x86") {
-        lib_dirs += [ "$windk/VC/lib" ]
+        lib_dirs += [ "$win_vc/lib" ]
       } else {
-        lib_dirs += [ "$windk/VC/lib/amd64" ]
+        lib_dirs += [ "$win_vc/lib/amd64" ]
       }
     } else {  # 2017
       lib_dirs +=
-          [ "$windk/VC/Tools/MSVC/$win_toolchain_version/lib/$target_cpu" ]
+          [ "$win_vc/Tools/MSVC/$win_toolchain_version/lib/$target_cpu" ]
     }
   } else {
     cflags += [
diff --git a/gn/BUILDCONFIG.gn b/gn/BUILDCONFIG.gn
index e9912e2c26..80cc0986cc 100644
--- a/gn/BUILDCONFIG.gn
+++ b/gn/BUILDCONFIG.gn
@@ -25,20 +25,16 @@ declare_args() {
   cc = "cc"
   cxx = "c++"
 
-  msvc = 2015
+  win_sdk = "C:/Program Files (x86)/Windows Kits/10"
+  win_sdk_version = ""
+
+  win_vc = ""
+  win_toolchain_version = ""
+
   clang_win = ""
 }
 declare_args() {
   is_debug = !is_official_build
-
-  if (msvc == 2015) {
-    windk = "C:/Program Files (x86)/Microsoft Visual Studio 14.0"
-  } else {
-    windk = "C:/Program Files (x86)/Microsoft Visual Studio/2017/Professional"
-    win_toolchain_version = ""
-  }
-  win_sdk = "C:/Program Files (x86)/Windows Kits/10"
-  win_sdk_version = ""
 }
 
 assert(!(is_debug && is_official_build))
@@ -133,10 +129,42 @@ if (is_android) {
   }
 }
 
+msvc = ""
+if (target_os == "win") {
+  # By default we look for 2017, then 2015. If MSVC is installed in a non-default
+  # location, you can set win_vc to inform us where it is.
+  vc_2017_default =
+      "C:/Program Files (x86)/Microsoft Visual Studio/2017/Professional/VC"
+  vc_2015_default = "C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC"
+
+  if (win_vc == "") {
+    if ("True" ==
+        exec_script("//gn/checkdir.py", [ "$vc_2017_default" ], "trim string")) {
+      win_vc = vc_2017_default
+      msvc = 2017
+    } else if ("True" == exec_script("//gn/checkdir.py",
+                                     [ "$vc_2015_default" ],
+                                     "trim string")) {
+      win_vc = vc_2015_default
+      msvc = 2015
+    }
+  }
+  assert(win_vc != "")  # Could not find VC installation. Set win_vc to your VC directory.
+
+  if (msvc == "") {
+    if ("True" ==
+        exec_script("//gn/checkdir.py", [ "$win_vc/Tools" ], "trim string")) {
+      msvc = 2017
+    } else {
+      msvc = 2015
+    }
+  }
+}
+
 if (target_os == "win") {
   if (msvc == 2017 && win_toolchain_version == "") {
     win_toolchain_version = exec_script("//gn/highest_version_dir.py",
-                                        [ "$windk/VC/Tools/MSVC" ],
+                                        [ "$win_vc/Tools/MSVC" ],
                                         "trim string")
   }
   if (win_sdk_version == "") {
diff --git a/gn/toolchain/BUILD.gn b/gn/toolchain/BUILD.gn
index 7497bcb690..76de226530 100644
--- a/gn/toolchain/BUILD.gn
+++ b/gn/toolchain/BUILD.gn
@@ -34,20 +34,16 @@ toolchain("msvc") {
   lib_dir_switch = "/LIBPATH:"
 
   if (msvc == 2015) {
-    bin = "$windk/VC/bin/amd64"
-    env_setup = ""
-    if (target_cpu == "x86") {
-      bin += "_x86"
-      env_setup = "cmd /c $windk/win_sdk/bin/SetEnv.cmd /x86 && "
-    }
+    bin = "$win_vc/bin/amd64"
   } else {
-    bin = "$windk/VC/Tools/MSVC/$win_toolchain_version/bin/HostX64/$target_cpu"
-    env_setup = ""
-    if (target_cpu == "x86") {
-      print("Be sure to run")
-      print("\"$windk/VC/Auxiliary/Build/vcvarsall.bat\" amd64_x86")
-      print("to set up your environment before running ninja.")
-    }
+    bin = "$win_vc/Tools/MSVC/$win_toolchain_version/bin/HostX64/$target_cpu"
+  }
+
+  env_setup = ""
+  if (target_cpu == "x86") {
+    # Toolchain asset includes a script that configures for x86 building.
+    # We don't support x86 builds with local MSVC installations.
+    env_setup = "cmd /c $win_sdk/bin/SetEnv.cmd /x86 && "
   }
 
   if (clang_win != "") {
diff --git a/infra/bots/assets/win_toolchain/VERSION b/infra/bots/assets/win_toolchain/VERSION
index 62f9457511..c7930257df 100644
--- a/infra/bots/assets/win_toolchain/VERSION
+++ b/infra/bots/assets/win_toolchain/VERSION
@@ -1 +1 @@
-6
\ No newline at end of file
+7
\ No newline at end of file
diff --git a/infra/bots/assets/win_toolchain_2015/VERSION b/infra/bots/assets/win_toolchain_2015/VERSION
new file mode 100644
index 0000000000..1e8b314962
--- /dev/null
+++ b/infra/bots/assets/win_toolchain_2015/VERSION
@@ -0,0 +1 @@
+6
diff --git a/infra/bots/assets/win_toolchain_2015/common.py b/infra/bots/assets/win_toolchain_2015/common.py
new file mode 100755
index 0000000000..4920c9b4fb
--- /dev/null
+++ b/infra/bots/assets/win_toolchain_2015/common.py
@@ -0,0 +1,26 @@
+#!/usr/bin/env python
+#
+# Copyright 2016 Google Inc.
+#
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+
+"""Common vars used by scripts in this directory."""
+
+
+import os
+import sys
+
+FILE_DIR = os.path.dirname(os.path.abspath(__file__))
+INFRA_BOTS_DIR = os.path.realpath(os.path.join(FILE_DIR, os.pardir, os.pardir))
+
+sys.path.insert(0, INFRA_BOTS_DIR)
+from assets import assets
+
+ASSET_NAME = os.path.basename(FILE_DIR)
+
+
+def run(cmd):
+  """Run a command, eg. "upload" or "download". """
+  assets.main([cmd, ASSET_NAME] + sys.argv[1:])
diff --git a/infra/bots/assets/win_toolchain_2015/download.py b/infra/bots/assets/win_toolchain_2015/download.py
new file mode 100755
index 0000000000..96cc87d43f
--- /dev/null
+++ b/infra/bots/assets/win_toolchain_2015/download.py
@@ -0,0 +1,16 @@
+#!/usr/bin/env python
+#
+# Copyright 2016 Google Inc.
+#
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+
+"""Download the current version of the asset."""
+
+
+import common
+
+
+if __name__ == '__main__':
+  common.run('download')
diff --git a/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-Clang-x86_64-Debug-GDI.json b/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-Clang-x86_64-Debug-GDI.json
index be03a35e07..609fa0796e 100644
--- a/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-Clang-x86_64-Debug-GDI.json
+++ b/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-Clang-x86_64-Debug-GDI.json
@@ -20,7 +20,7 @@
       "[CUSTOM_C:\\_B_WORK]/skia/bin/gn.exe",
       "gen",
       "[CUSTOM_C:\\_B_WORK]/skia/out/Build-Win-Clang-x86_64-Debug-GDI/Debug_x64",
-      "--args=cc=\"clang\" clang_win=\"[START_DIR]/clang_win\" cxx=\"clang++\" extra_cflags=[\"-O1\"] target_cpu=\"x86_64\" win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616/win_sdk\" windk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616\""
+      "--args=cc=\"clang\" clang_win=\"[START_DIR]/clang_win\" cxx=\"clang++\" extra_cflags=[\"-O1\"] target_cpu=\"x86_64\" win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/win_sdk\" win_vc=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/VC\""
     ],
     "cwd": "[CUSTOM_C:\\_B_WORK]/skia",
     "env": {
diff --git a/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-Clang-x86_64-Release-Vulkan.json b/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-Clang-x86_64-Release-Vulkan.json
index 9827284c47..038be54a44 100644
--- a/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-Clang-x86_64-Release-Vulkan.json
+++ b/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-Clang-x86_64-Release-Vulkan.json
@@ -20,7 +20,7 @@
       "[CUSTOM_C:\\_B_WORK]/skia/bin/gn.exe",
       "gen",
       "[CUSTOM_C:\\_B_WORK]/skia/out/Build-Win-Clang-x86_64-Release-Vulkan/Release_x64",
-      "--args=cc=\"clang\" clang_win=\"[START_DIR]/clang_win\" cxx=\"clang++\" is_debug=false skia_enable_vulkan_debug_layers=false skia_vulkan_sdk=\"[START_DIR]/win_vulkan_sdk\" target_cpu=\"x86_64\" win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616/win_sdk\" windk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616\""
+      "--args=cc=\"clang\" clang_win=\"[START_DIR]/clang_win\" cxx=\"clang++\" is_debug=false skia_enable_vulkan_debug_layers=false skia_vulkan_sdk=\"[START_DIR]/win_vulkan_sdk\" target_cpu=\"x86_64\" win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/win_sdk\" win_vc=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/VC\""
     ],
     "cwd": "[CUSTOM_C:\\_B_WORK]/skia",
     "env": {
diff --git a/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-Clang-x86_64-Release.json b/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-Clang-x86_64-Release.json
index 5ce58bafe5..28ec945aa8 100644
--- a/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-Clang-x86_64-Release.json
+++ b/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-Clang-x86_64-Release.json
@@ -20,7 +20,7 @@
       "[CUSTOM_C:\\_B_WORK]/skia/bin/gn.exe",
       "gen",
       "[CUSTOM_C:\\_B_WORK]/skia/out/Build-Win-Clang-x86_64-Release/Release_x64",
-      "--args=cc=\"clang\" clang_win=\"[START_DIR]/clang_win\" cxx=\"clang++\" is_debug=false target_cpu=\"x86_64\" win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616/win_sdk\" windk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616\""
+      "--args=cc=\"clang\" clang_win=\"[START_DIR]/clang_win\" cxx=\"clang++\" is_debug=false target_cpu=\"x86_64\" win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/win_sdk\" win_vc=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/VC\""
     ],
     "cwd": "[CUSTOM_C:\\_B_WORK]/skia",
     "env": {
diff --git a/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-MSVC-x86-Debug-Exceptions.json b/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-MSVC-x86-Debug-Exceptions.json
index 6fa401d1b3..bf08caa1a5 100644
--- a/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-MSVC-x86-Debug-Exceptions.json
+++ b/infra/bots/recipe_modules/flavor/examples/full.expected/Build-Win-MSVC-x86-Debug-Exceptions.json
@@ -20,7 +20,7 @@
       "[CUSTOM_C:\\_B_WORK]/skia/bin/gn.exe",
       "gen",
       "[CUSTOM_C:\\_B_WORK]/skia/out/Build-Win-MSVC-x86-Debug-Exceptions/Debug",
-      "--args=extra_cflags=[\"/EHsc\"] target_cpu=\"x86\" win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616/win_sdk\" windk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616\""
+      "--args=extra_cflags=[\"/EHsc\"] target_cpu=\"x86\" win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/win_sdk\" win_vc=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/VC\""
     ],
     "cwd": "[CUSTOM_C:\\_B_WORK]/skia",
     "env": {
diff --git a/infra/bots/recipe_modules/flavor/examples/full.expected/Test-Win10-MSVC-ShuttleA-GPU-GTX660-x86_64-Debug-All.json b/infra/bots/recipe_modules/flavor/examples/full.expected/Test-Win10-MSVC-ShuttleA-GPU-GTX660-x86_64-Debug-All.json
index 472f328828..301fcd2878 100644
--- a/infra/bots/recipe_modules/flavor/examples/full.expected/Test-Win10-MSVC-ShuttleA-GPU-GTX660-x86_64-Debug-All.json
+++ b/infra/bots/recipe_modules/flavor/examples/full.expected/Test-Win10-MSVC-ShuttleA-GPU-GTX660-x86_64-Debug-All.json
@@ -20,7 +20,7 @@
       "[START_DIR]/skia/bin/gn.exe",
       "gen",
       "[START_DIR]/out/Debug_x64",
-      "--args=win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616/win_sdk\" windk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616\""
+      "--args=win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/win_sdk\" win_vc=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/VC\""
     ],
     "cwd": "[START_DIR]/skia",
     "env": {
diff --git a/infra/bots/recipe_modules/flavor/gn_flavor.py b/infra/bots/recipe_modules/flavor/gn_flavor.py
index f018094929..62eb15ffa5 100644
--- a/infra/bots/recipe_modules/flavor/gn_flavor.py
+++ b/infra/bots/recipe_modules/flavor/gn_flavor.py
@@ -35,7 +35,7 @@ class GNFlavorUtils(default_flavor.DefaultFlavorUtils):
     linux_vulkan_sdk   = str(self.m.vars.slave_dir.join('linux_vulkan_sdk'))
     win_toolchain = str(self.m.vars.slave_dir.join(
       't', 'depot_tools', 'win_toolchain', 'vs_files',
-      'd3cb0e37bdd120ad0ac4650b674b09e81be45616'))
+      'a9e1098bba66d2acccc377d5ee81265910f29272'))
     win_vulkan_sdk = str(self.m.vars.slave_dir.join('win_vulkan_sdk'))
 
     cc, cxx = None, None
@@ -143,8 +143,8 @@ class GNFlavorUtils(default_flavor.DefaultFlavorUtils):
       'sanitize': sanitize,
       'target_cpu': target_arch,
       'target_os': 'ios' if 'iOS' in extra_config else '',
-      'windk': win_toolchain if 'Win' in os else '',
       'win_sdk': win_toolchain + '/win_sdk' if 'Win' in os else '',
+      'win_vc': win_toolchain + '/VC' if 'Win' in os else '',
     }.iteritems():
       if v:
         args[k] = '"%s"' % v
diff --git a/infra/bots/recipes/compile.expected/Build-Win-Clang-x86_64-Release-Vulkan.json b/infra/bots/recipes/compile.expected/Build-Win-Clang-x86_64-Release-Vulkan.json
index ce22786f86..bc261e8990 100644
--- a/infra/bots/recipes/compile.expected/Build-Win-Clang-x86_64-Release-Vulkan.json
+++ b/infra/bots/recipes/compile.expected/Build-Win-Clang-x86_64-Release-Vulkan.json
@@ -114,7 +114,7 @@
       "[CUSTOM_C:\\_B_WORK]\\skia\\bin\\gn.exe",
       "gen",
       "[CUSTOM_C:\\_B_WORK]\\skia\\out\\Build-Win-Clang-x86_64-Release-Vulkan\\Release_x64",
-      "--args=cc=\"clang\" clang_win=\"[START_DIR]\\clang_win\" cxx=\"clang++\" is_debug=false skia_enable_vulkan_debug_layers=false skia_vulkan_sdk=\"[START_DIR]\\win_vulkan_sdk\" target_cpu=\"x86_64\" win_sdk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\d3cb0e37bdd120ad0ac4650b674b09e81be45616/win_sdk\" windk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\d3cb0e37bdd120ad0ac4650b674b09e81be45616\""
+      "--args=cc=\"clang\" clang_win=\"[START_DIR]\\clang_win\" cxx=\"clang++\" is_debug=false skia_enable_vulkan_debug_layers=false skia_vulkan_sdk=\"[START_DIR]\\win_vulkan_sdk\" target_cpu=\"x86_64\" win_sdk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\a9e1098bba66d2acccc377d5ee81265910f29272/win_sdk\" win_vc=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\a9e1098bba66d2acccc377d5ee81265910f29272/VC\""
     ],
     "cwd": "[CUSTOM_C:\\_B_WORK]\\skia",
     "env": {
diff --git a/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Debug-ANGLE.json b/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Debug-ANGLE.json
index 413228a481..37d2f5e99e 100644
--- a/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Debug-ANGLE.json
+++ b/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Debug-ANGLE.json
@@ -112,7 +112,7 @@
       "[CUSTOM_C:\\_B_WORK]\\skia\\bin\\gn.exe",
       "gen",
       "[CUSTOM_C:\\_B_WORK]\\skia\\out\\Build-Win-MSVC-x86-Debug-ANGLE\\Debug",
-      "--args=skia_use_angle=true target_cpu=\"x86\" win_sdk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\d3cb0e37bdd120ad0ac4650b674b09e81be45616/win_sdk\" windk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\d3cb0e37bdd120ad0ac4650b674b09e81be45616\""
+      "--args=skia_use_angle=true target_cpu=\"x86\" win_sdk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\a9e1098bba66d2acccc377d5ee81265910f29272/win_sdk\" win_vc=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\a9e1098bba66d2acccc377d5ee81265910f29272/VC\""
     ],
     "cwd": "[CUSTOM_C:\\_B_WORK]\\skia",
     "env": {
diff --git a/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Debug-Exceptions.json b/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Debug-Exceptions.json
index e0a64ffeb9..0f86d1c853 100644
--- a/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Debug-Exceptions.json
+++ b/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Debug-Exceptions.json
@@ -112,7 +112,7 @@
       "[CUSTOM_C:\\_B_WORK]\\skia\\bin\\gn.exe",
       "gen",
       "[CUSTOM_C:\\_B_WORK]\\skia\\out\\Build-Win-MSVC-x86-Debug-Exceptions\\Debug",
-      "--args=extra_cflags=[\"/EHsc\"] target_cpu=\"x86\" win_sdk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\d3cb0e37bdd120ad0ac4650b674b09e81be45616/win_sdk\" windk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\d3cb0e37bdd120ad0ac4650b674b09e81be45616\""
+      "--args=extra_cflags=[\"/EHsc\"] target_cpu=\"x86\" win_sdk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\a9e1098bba66d2acccc377d5ee81265910f29272/win_sdk\" win_vc=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\a9e1098bba66d2acccc377d5ee81265910f29272/VC\""
     ],
     "cwd": "[CUSTOM_C:\\_B_WORK]\\skia",
     "env": {
diff --git a/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Debug.json b/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Debug.json
index e8103ff424..ed4c248660 100644
--- a/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Debug.json
+++ b/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Debug.json
@@ -112,7 +112,7 @@
       "[CUSTOM_C:\\_B_WORK]\\skia\\bin\\gn.exe",
       "gen",
       "[CUSTOM_C:\\_B_WORK]\\skia\\out\\Build-Win-MSVC-x86-Debug\\Debug",
-      "--args=target_cpu=\"x86\" win_sdk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\d3cb0e37bdd120ad0ac4650b674b09e81be45616/win_sdk\" windk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\d3cb0e37bdd120ad0ac4650b674b09e81be45616\""
+      "--args=target_cpu=\"x86\" win_sdk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\a9e1098bba66d2acccc377d5ee81265910f29272/win_sdk\" win_vc=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\a9e1098bba66d2acccc377d5ee81265910f29272/VC\""
     ],
     "cwd": "[CUSTOM_C:\\_B_WORK]\\skia",
     "env": {
diff --git a/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Release-GDI.json b/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Release-GDI.json
index 7c1661589e..e3f51f7e5a 100644
--- a/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Release-GDI.json
+++ b/infra/bots/recipes/compile.expected/Build-Win-MSVC-x86-Release-GDI.json
@@ -112,7 +112,7 @@
       "[CUSTOM_C:\\_B_WORK]\\skia\\bin\\gn.exe",
       "gen",
       "[CUSTOM_C:\\_B_WORK]\\skia\\out\\Build-Win-MSVC-x86-Release-GDI\\Release",
-      "--args=is_debug=false target_cpu=\"x86\" win_sdk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\d3cb0e37bdd120ad0ac4650b674b09e81be45616/win_sdk\" windk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\d3cb0e37bdd120ad0ac4650b674b09e81be45616\""
+      "--args=is_debug=false target_cpu=\"x86\" win_sdk=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\a9e1098bba66d2acccc377d5ee81265910f29272/win_sdk\" win_vc=\"[START_DIR]\\t\\depot_tools\\win_toolchain\\vs_files\\a9e1098bba66d2acccc377d5ee81265910f29272/VC\""
     ],
     "cwd": "[CUSTOM_C:\\_B_WORK]\\skia",
     "env": {
diff --git a/infra/bots/recipes/compile.expected/alternate_repo.json b/infra/bots/recipes/compile.expected/alternate_repo.json
index 6732f130e5..0600437238 100644
--- a/infra/bots/recipes/compile.expected/alternate_repo.json
+++ b/infra/bots/recipes/compile.expected/alternate_repo.json
@@ -114,7 +114,7 @@
       "[CUSTOM_C:\\_B_WORK]/skia/bin/gn.exe",
       "gen",
       "[CUSTOM_C:\\_B_WORK]/skia/out/Build-Win-Clang-x86_64-Release-Vulkan/Release_x64",
-      "--args=cc=\"clang\" clang_win=\"[START_DIR]/clang_win\" cxx=\"clang++\" is_debug=false skia_enable_vulkan_debug_layers=false skia_vulkan_sdk=\"[START_DIR]/win_vulkan_sdk\" target_cpu=\"x86_64\" win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616/win_sdk\" windk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616\""
+      "--args=cc=\"clang\" clang_win=\"[START_DIR]/clang_win\" cxx=\"clang++\" is_debug=false skia_enable_vulkan_debug_layers=false skia_vulkan_sdk=\"[START_DIR]/win_vulkan_sdk\" target_cpu=\"x86_64\" win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/win_sdk\" win_vc=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/VC\""
     ],
     "cwd": "[CUSTOM_C:\\_B_WORK]/skia",
     "env": {
diff --git a/infra/bots/recipes/compile.expected/trybot.json b/infra/bots/recipes/compile.expected/trybot.json
index 62055412b1..cbdb832243 100644
--- a/infra/bots/recipes/compile.expected/trybot.json
+++ b/infra/bots/recipes/compile.expected/trybot.json
@@ -118,7 +118,7 @@
       "[CUSTOM_C:\\_B_WORK]/skia/bin/gn.exe",
       "gen",
       "[CUSTOM_C:\\_B_WORK]/skia/out/Build-Win-Clang-x86_64-Release-Vulkan/Release_x64",
-      "--args=cc=\"clang\" clang_win=\"[START_DIR]/clang_win\" cxx=\"clang++\" is_debug=false skia_enable_vulkan_debug_layers=false skia_vulkan_sdk=\"[START_DIR]/win_vulkan_sdk\" target_cpu=\"x86_64\" win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616/win_sdk\" windk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/d3cb0e37bdd120ad0ac4650b674b09e81be45616\""
+      "--args=cc=\"clang\" clang_win=\"[START_DIR]/clang_win\" cxx=\"clang++\" is_debug=false skia_enable_vulkan_debug_layers=false skia_vulkan_sdk=\"[START_DIR]/win_vulkan_sdk\" target_cpu=\"x86_64\" win_sdk=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/win_sdk\" win_vc=\"[START_DIR]/t/depot_tools/win_toolchain/vs_files/a9e1098bba66d2acccc377d5ee81265910f29272/VC\""
     ],
     "cwd": "[CUSTOM_C:\\_B_WORK]/skia",
     "env": {
diff --git a/infra/bots/tasks.json b/infra/bots/tasks.json
index 6c2a3aca00..ee7c0b3360 100644
--- a/infra/bots/tasks.json
+++ b/infra/bots/tasks.json
@@ -5364,7 +5364,7 @@
         {
           "name": "skia/bots/win_toolchain",
           "path": "t",
-          "version": "version:6"
+          "version": "version:7"
         }
       ],
       "dimensions": [
diff --git a/site/user/build.md b/site/user/build.md
index 4d5600579f..0cdf322b22 100644
--- a/site/user/build.md
+++ b/site/user/build.md
@@ -228,17 +228,21 @@ to the desired OS version.
 Windows
 -------
 
-Skia can build on Windows with Visual Studio 2015 Update 3, or Visual Studio
-2017 by setting `msvc = 2017` in GN.  No older versions are supported. The bots
-use a packaged 2015 toolchain, which Googlers can download like this:
+Skia can build on Windows with Visual Studio 2017 or Visual Studio 2015 Update 3.
+If GN is unable to locate either of those, it will print an error message. In that
+case, you can pass your `VC` path to GN via `win_vc`.
+
+The bots use a packaged 2017 toolchain, which Googlers can download like this:
 
     python infra/bots/assets/win_toolchain/download.py -t C:/toolchain
 
-If you pass that downloaded path to GN via `windk`, you can build using that
-toolchain instead of your own from Visual Studio.  This toolchain is the only
-way we support 32-bit builds with 2015, by also setting `target_cpu="x86"`.
-32-bit builds should work with the default 2017 install if you follow the
-directions GN prints to set up your environment.
+You can then pass the VC and SDK paths to GN by setting your GN args:
+
+    win_vc = "C:\toolchain\depot_tools\win_toolchain\vs_files\a9e1098bba66d2acccc377d5ee81265910f29272\VC"
+    win_sdk = "C:\toolchain\depot_tools\win_toolchain\vs_files\a9e1098bba66d2acccc377d5ee81265910f29272\win_sdk"
+
+This toolchain is the only way we support 32-bit builds, by also setting `target_cpu="x86"`.
+There is also a corresponding 2015 toolchain, downloaded via `infra/bots/assets/win_toolchain_2015`.
 
 ### Visual Studio Solutions