all: attempt to make method for shadow checks consistent with 1.12 and 1.13

govet.sh

@@ -8,16 +8,24 @@ printf "Running go vet shadow...\n"
 command -v shadow >/dev/null 2>&1 || (
   dir=$(mktemp -d)
   pushd $dir
-  go mod init tool
-  go get golang.org/x/tools/go/analysis/passes/shadow/cmd/shadow
+  go mod init shadow
+  # The go vet -vettool option was added in 1.12, and broken in the initial
+  # 1.13 release for any vettool that doesn't support the unsafeptr flag. The
+  # shadow tool doesn't support the unsafeptr flag.  Until either support for
+  # unsafeptr is added to shadow or passing through that flag is removed from
+  # go vet we can use the anazlyer by wrapping it in our own main that ignores
+  # unsafeptr. This temporary work around was suggested here:
+  # https://github.com/golang/go/issues/34053
+  gofmt > main.go <<-EOF
+    package main
+    import "flag"
+    import "golang.org/x/tools/go/analysis/passes/shadow"
+    import "golang.org/x/tools/go/analysis/singlechecker"
+    func init() { flag.String("unsafeptr", "", "") }
+    func main() { singlechecker.Main(shadow.Analyzer) }
+EOF
+  go install
   popd
 )
 
-# The go vet -vettool option was added in 1.12, and broken in the initial 1.13
-# release. Until it is fixed we must call vettool's directly as a work around.
-# https://github.com/golang/go/issues/34053
-if [[ $GOLANG_VERSION = 1.12.* ]]; then
-  go vet -vettool=$(which shadow) ./...
-else
-  shadow ./...
-fi
+go vet -vettool=$(which shadow) ./...