Teach build.py to cross-compile go-based packages.

go/bootstrap.py

 #!/usr/bin/env python
 # Copyright 2014 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.
 
 """Prepares a local hermetic Go installation.
 
 - Downloads and unpacks the Go toolset in ../../golang.
 - Downloads and installs Glide (used by deps.py).
 - Fetches code dependencies via deps.py.
@@ skipping 402 matching lines @@
 
   Supposed to be called at the beginning of some script (it modifies logger).
 
   Args:
     go_paths: list of paths to search for deps.lock, for each path deps.py
         will install all dependencies in <path>/.vendor/src/*.
     logging_level: logging level of bootstrap process.
   """
   logging.basicConfig()
   LOGGER.setLevel(logging_level)
-  updated = ensure_toolset_installed(TOOLSET_ROOT)
-  ensure_glide_installed(TOOLSET_ROOT)
-  for p in go_paths:
-    update_vendor_packages(p, force=updated)
-  if updated:
-    # GOPATH/pkg may have binaries generated with previous version of toolset,
-    # they may not be compatible and "go build" isn't smart enough to rebuild
-    # them.
+
+  # We need to build and run some Go binaries during bootstrap (e.g. glide), so
+  # make sure cross-compilation mode is disabled during bootstrap. Restore it
+  # back once bootstrap is finished.
+  prev_environ = {}
+  for k in ('GOOS', 'GOARCH', 'GOARM'):
+    prev_environ[k] = os.environ.pop(k, None)
+
+  try:
+    updated = ensure_toolset_installed(TOOLSET_ROOT)
+    ensure_glide_installed(TOOLSET_ROOT)
     for p in go_paths:
-      remove_directory([p, 'pkg'])
+      update_vendor_packages(p, force=updated)
+    if updated:
+      # GOPATH/pkg may have binaries generated with previous version of toolset,
+      # they may not be compatible and "go build" isn't smart enough to rebuild
+      # them.
+      for p in go_paths:
+        remove_directory([p, 'pkg'])
+  finally:
+    # Restore os.environ back. Have to do it key-by-key to actually modify the
+    # process environment (replacing os.environ object as a whole does nothing).
+    for k, v in prev_environ.iteritems():
+      if v is not None:
+        os.environ[k] = v
 
 
 def prepare_go_environ():
   """Returns dict with environment variables to set to use Go toolset.
 
   Installs or updates the toolset and vendored dependencies if necessary.
   """
   bootstrap([WORKSPACE], logging.INFO)
   return get_go_environ(
-    toolset_root=TOOLSET_ROOT,
-    workspace=WORKSPACE,       # primary GOPATH with source code
-    vendor_paths=[WORKSPACE],  # where to look for deps.yaml and .vendor dirs
-    go_appengine_path=GO_APPENGINE)
+      toolset_root=TOOLSET_ROOT,
+      workspace=WORKSPACE,       # primary GOPATH with source code
+      vendor_paths=[WORKSPACE],  # where to look for deps.yaml and .vendor dirs
+      go_appengine_path=GO_APPENGINE)
 
 
 def find_executable(name, workspaces):
   """Returns full path to an executable in some bin/ (in GOROOT or GOBIN)."""
   basename = name
   if EXE_SFX and basename.endswith(EXE_SFX):
     basename = basename[:-len(EXE_SFX)]
   roots = [os.path.join(TOOLSET_ROOT, 'go', 'bin')]
   for path in workspaces:
     roots.extend([
       os.path.join(path, '.vendor', 'bin'),
       os.path.join(path, 'bin'),
     ])
   for root in roots:
     full_path = os.path.join(root, basename + EXE_SFX)
     if os.path.exists(full_path):
       return full_path
   return name
 
 
 def main():
   bootstrap([WORKSPACE], logging.DEBUG)
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())