Error checking to clarify SYSTEMROOT errors

Occasionally developers hit this cryptic error:

Exception: Environment variable "SYSTEMROOT" required to be set to valid path

The error message is well intentioned but inevitably misleading. The problem is
rarely if ever caused by SYSTEMROOT not being set. In the most recent case it
was caused by the "SetEnv.cmd && set" command failing.

This change adds two bits of error checking - checking the error code of the
Popen command, and ensuring that the results coming in to
_ExtractImportantEnvironment are plausible. Both of these checks can detect this
particular error, and one or both of them should detect future problems.

This was initially done for gyp in crrev.com/1501673004, this makes the same fix
for gn builds.

R=jam@chromium.org

Review URL: https://codereview.chromium.org/1502183004

Cr-Commit-Position: refs/heads/master@{#363930}

1 files changed, 6 insertions, 0 deletions

diff --git a/build/toolchain/win/setup_toolchain.py b/build/toolchain/win/setup_toolchain.py
index f395044..4e79cd9 100644
--- a/build/toolchain/win/setup_toolchain.py
+++ b/build/toolchain/win/setup_toolchain.py
@@ -32,6 +32,10 @@ def _ExtractImportantEnvironment(output_of_set):
       'tmp',
       )
   env = {}
+  # This occasionally happens and leads to misleading SYSTEMROOT error messages
+  # if not caught here.
+  if output_of_set.count('=') == 0:
+    raise Exception('Invalid output_of_set. Value is:\n%s' % output_of_set)
   for line in output_of_set.splitlines():
     for envvar in envvars_to_save:
       if re.match(envvar + '=', line.lower()):
@@ -123,6 +127,8 @@ def main():
     popen = subprocess.Popen(
         args, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
     variables, _ = popen.communicate()
+    if popen.returncode != 0:
+      raise Exception('"%s" failed with error %d' % (args, popen.returncode))
     env = _ExtractImportantEnvironment(variables)
     env['PATH'] = runtime_dirs + ';' + env['PATH']