scripts: default to using .go-version's version for tests and builds

Manual cherrypick of e094139

Additionally, provide ability to opt-out of the .go-version and use a
custom one via env vars: FORCE_HOST_GO and GO_VERSION.

Co-authored by: Madhav Jivrajani <[email protected]>
Signed-off-by: joshjms <[email protected]>

Author: joshjms

scripts/test_lib.sh

@@ -52,3 +52,22 @@ function log_info {
   >&2 echo "$@"
   >&2 echo -n -e "${COLOR_NONE}"
 }
+
+function determine_go_version {
+  # Borrowing from how Kubernetes does this:
+  #  https://github.com/kubernetes/kubernetes/blob/17854f0e0a153b06f9d0db096e2cd8ab2fa89c11/hack/lib/golang.sh#L510-L520
+  #
+  # default GO_VERSION to content of .go-version
+  GO_VERSION="${GO_VERSION:-"$(cat "./.go-version")"}"
+  if [ "${GOTOOLCHAIN:-auto}" != 'auto' ]; then
+    # no-op, just respect GOTOOLCHAIN
+    :
+  elif [ -n "${FORCE_HOST_GO:-}" ]; then
+    export GOTOOLCHAIN='local'
+  else
+    GOTOOLCHAIN="go${GO_VERSION}"
+    export GOTOOLCHAIN
+  fi
+}
+
+determine_go_version