[bazel] Check Bazel version when found in PATH

The `bazelisk.sh` script will try to use a real Bazel from the `PATH` if
it can find it, but doesn't check its value against `.bazelversion`.

This change checks the version and falls back to downloading `bazelisk`
if it doesn't match.

Signed-off-by: James Wainwright <[email protected]>

Author: jwnrt

bazelisk.sh

@@ -110,6 +110,14 @@ function main() {
     local file="${BAZEL_BIN:-${bindir}/bazelisk}"
     local lockfile="${bindir}/bazelisk.lock"
 
+    # If the user has Bazel in their PATH, check its version.
+    # Fallback to bazelisk if it doesn't match.
+    if [ -x "$BAZEL_BIN" ]; then
+        if [ "$("$BAZEL_BIN" --version)" != "bazel $(cat .bazelversion)" ]; then
+            file="${bindir}/bazelisk"
+        fi
+    fi
+
     # Are we using bazel from the user's PATH or using bazelisk?
     if expr match "${file}" ".*bazelisk$" >/dev/null; then
         if ! up_to_date "$file"; then