Added a job to dry-run the publish_toolstate.py once

.travis.yml

@@ -248,6 +248,15 @@ before_script:
           # Enable core dump on Linux.
           sudo sh -c 'echo "/checkout/obj/cores/core.%p.%E" > /proc/sys/kernel/core_pattern';
       fi
+  - >
+      if [ "$IMAGE" = mingw-check ]; then
+        # verify the publish_toolstate script works.
+        git clone --depth=1 https://github.com/rust-lang-nursery/rust-toolstate.git;
+        cd rust-toolstate;
+        python2.7 "$TRAVIS_BUILD_DIR/src/tools/publish_toolstate.py" "$(git rev-parse HEAD)" "$(git log --format=%s -n1 HEAD)" "" "";
+        cd ..;
+        rm -rf rust-toolstate;
+      fi
 
 # Log time information from this machine and an external machine for insight into possible
 # clock drift. Timezones don't matter since relative deltas give all the necessary info.

src/tools/publish_toolstate.py

@@ -120,6 +120,11 @@ def update_latest(
         sys.exit(0)
 
     print(message)
+
+    if not github_token:
+        print('Dry run only, not committing anything')
+        sys.exit(0)
+
     with open(save_message_to_path, 'w') as f:
         f.write(message)