Add documentation about how to use bot toolchain on Win
Change-Id: I21b1677955c80cd4eff8c5ad660887905a4e1b8a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/244915
Reviewed-by: James Price <jrprice@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
diff --git a/docs/building.md b/docs/building.md
index f269fa6..8387a5a 100644
--- a/docs/building.md
+++ b/docs/building.md
@@ -130,3 +130,20 @@
get via homebrew, `brew install llvm`, and use something like `CC=<path to full
clang> cmake ..` to setup a build using that toolchain.
+### Reproducing bot specific environments on Windows + CMake
+When investigating build issues being seen by CI/CQ it is sometimes necessary
+to replicate the exact environment from a builder/bot for local debugging.
+
+As part of a Dawn checkout the toolchains used by the builders should already be
+checked out in your repo. For Windows, using CMake, to use them instead of the
+system installed toolchain, there is a script supplied to set up the
+environment.
+
+Instead of using the system batch file to set up the environment, i.e.
+```sh
+C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvars64.bat
+```
+use the appropriate script from `third_party\depot_tools\win_toolchain`, i.e.
+```sh
+ C:\src\dawn\third_party\depot_tools\win_toolchain\vs_files\68a20d6dee\Windows Kits\10\bin\SetEnv.cmd
+```
