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Issue metadata

Status: Fixed
Owner: ----
Closed: Nov 20
EstimatedDays: ----
NextAction: ----
OS: Windows
Pri: 2
Type: Bug

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Issue 906559: Change to win_toolchain.json broke external projects using Chromium's build/

Reported by, Nov 19 Project Member

Issue description

Rencently Dawn's standalone Windows builds started failing like this build


Traceback (most recent call last):
  File "e:/b/swarm_slave/w/ir/cache/builder/dawn/build/", line 471, in <module>
  File "e:/b/swarm_slave/w/ir/cache/builder/dawn/build/", line 467, in main
    return commands[sys.argv[1]](*sys.argv[2:])
  File "e:/b/swarm_slave/w/ir/cache/builder/dawn/build/", line 285, in CopyDlls
    x64_runtime, x86_runtime = vs_runtime_dll_dirs
ValueError: too many values to unpack
ERROR at //build/toolchain/win/ Script returned non-zero exit code.

This is because win_toolchain.json gained an extra directory for ARM64. I see that was updated to support it, but the update to happened without us rolling anything into Dawn, which means it is somehow updated out of band.

Shouldn't both win_toolchain.json and be updated at the same time so we don't have breakage because of mismatches?

+CC folks on the CL updating because I don't know how win_toolchain.json is created.

Comment 1 by, Nov 19

Project Member
The following revision refers to this bug:

commit 15d8cb765f748d817e79e3d267806c715100997b
Author: Corentin Wallez <>
Date: Mon Nov 19 10:13:31 2018

Roll Chromium's build system to fix Windows builds

build/win_toolchain.json was updated out of band so we need to roll all
Chromium's build support repos to pick up the respective change to

In the meantime, LASTCHANGE-related functionality changed and requires a
new hook to run before we can call `gn gen`.
BUG= chromium:906559 

Change-Id: Ic5d297b5700193ca72b02874073e6c553f06e04f
Reviewed-by: Corentin Wallez <>
Commit-Queue: Corentin Wallez <>


Comment 2 by, Nov 19

Sorry about this. The asynchrony was known when I made these changes but I forgot how many projects beyond Chromium consume depot_tools.

The basic problem is that depot_tools' win_toolchain\ generates the .json file, and build\ consumes it. Therefore it was important to land the build\ change before landing the depot_tools change. This worked for Chromium, but not for other projects. Merging over the build\ change is the correct fix.

This is a one-time break.

Comment 3 by, Nov 20

Status: Fixed (was: Available)
Thanks for the explanation, if it's a one-time break it is probably ok to close this issue. I'm thinking we should probably have a mailing list for people using Chromium's build system so we can send PSAs for changes like this.

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