run-mypy: Move "which mypy" noise into --version, and use in Travis.

Printing the version in Travis builds will help in debugging when we
get different results there from locally.  The new `--version` path
also gives us a handy place to put the "what mypy command are we running"
diagnostic, getting it out of the way of normal interactive use.

tools/run-mypy

@@ -27,7 +27,7 @@ parser = argparse.ArgumentParser(description="Run mypy on files tracked by git."
 parser.add_argument('targets', nargs='*',
                     help="files and directories to check (default: .)")
 parser.add_argument('--version', action='store_true',
-                    help="just run mypy --version")
+                    help="show mypy version information and exit")
 parser.add_argument('--quick', action='store_true',
                     help="pass --quick to mypy")
 parser.add_argument('-m', '--modified', action='store_true',
@@ -64,11 +64,11 @@ VENV_DIR = "/srv/zulip-py3-venv"
 MYPY_VENV_PATH = os.path.join(VENV_DIR, "bin", "mypy")
 if os.path.exists(MYPY_VENV_PATH):
     mypy_command = MYPY_VENV_PATH
-    print("Using mypy from", mypy_command)
 else:
     mypy_command = "mypy"
 
 if args.version:
+    print("mypy command:", mypy_command)
     sys.exit(subprocess.call([mypy_command, "--version"]))
 
 if args.all:

tools/travis/backend

@@ -12,6 +12,7 @@ set -x
 
 # We run mypy after the backend tests so we get output from the
 # backend tests, which tend to uncover more serious problems, first.
+./tools/run-mypy --version
 ./tools/run-mypy --linecoverage-report
 
 ./tools/test-migrations