Replace the rust-toolchain if a local build failed

A missing VERSION should not cause update_rust.py to throw an
exception.

Change-Id: I7345954c8167c7568d5f5d86271402a360f2ef6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4355884
Auto-Submit: danakj <[email protected]>
Reviewed-by: Collin Baker <[email protected]>
Commit-Queue: Collin Baker <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1120824}
NOKEYCHECK=True
GitOrigin-RevId: c718137ac1a105efc62da400a09206bd1a34a078

Author: danakj

package_rust.py

@@ -14,8 +14,7 @@
 sys.path.append(
     os.path.join(os.path.dirname(THIS_DIR), '..', 'clang', 'scripts'))
 
-from build_rust import (RUST_TOOLCHAIN_OUT_DIR, THIRD_PARTY_DIR,
-                        VERSION_STAMP_PATH)
+from build_rust import (RUST_TOOLCHAIN_OUT_DIR, THIRD_PARTY_DIR)
 from update_rust import (GetPackageVersionForBuild)
 from package import (MaybeUpload, TeeCmd)
 from update import (CHROMIUM_DIR)

update_rust.py

@@ -98,7 +98,7 @@ def GetDownloadPackageVersion():
 
 # Get the version of the toolchain package we already have.
 def GetStampVersion():
-    if os.path.exists(RUST_TOOLCHAIN_OUT_DIR):
+    if os.path.exists(VERSION_STAMP_PATH):
         with open(VERSION_STAMP_PATH) as version_file:
             existing_stamp = version_file.readline().rstrip()
         version_re = re.compile(r'rustc [0-9.]+ [0-9a-f]+ \((.+?) chromium\)')