Support function flags in script EVAL via shebang header (#10126)

In #10025 we added a mechanism for flagging certain properties for Redis Functions.
This lead us to think we'd like to "port" this mechanism to Redis Scripts (`EVAL`) as well. 

One good reason for this, other than the added functionality is because it addresses the
poor behavior we currently have in `EVAL` in case the script performs a (non DENY_OOM) write operation
during OOM state. See #8478 (And a previous attempt to handle it via #10093) for details.
Note that in Redis Functions **all** write operations (including DEL) will return an error during OOM state
unless the function is flagged as `allow-oom` in which case no OOM checking is performed at all.

This PR:
- Enables setting `EVAL` (and `SCRIPT LOAD`) script flags as defined in #10025.
- Provides a syntactical framework via [shebang](https://en.wikipedia.org/wiki/Shebang_(Unix)) for
  additional script annotations and even engine selection (instead of just lua) for scripts.
- Provides backwards compatibility so scripts without the new annotations will behave as they did before.
- Appropriate tests.
- Changes `EVAL[SHA]/_RO` to be flagged as `STALE` commands. This makes it possible to flag individual
  scripts as `allow-stale` or not flag them as such. In backwards compatibility mode these commands will
  return the `MASTERDOWN` error as before.
- Changes `SCRIPT LOAD` to be flagged as a `STALE` command. This is mainly to make it logically
  compatible with the change to `EVAL` in the previous point. It enables loading a script on a stale server
  which is technically okay it doesn't relate directly to the server's dataset. Running the script does, but that
  won't work unless the script is explicitly marked as `allow-stale`.

Note that even though the LUA syntax doesn't support hash tag comments `.lua` files do support a shebang
tag on the top so they can be executed on Unix systems like any shell script. LUA's `luaL_loadfile` handles
this as part of the LUA library. In the case of `luaL_loadbuffer`, which is what Redis uses, I needed to fix the
input script in case of a shebang manually. I did this the same way `luaL_loadfile` does, by replacing the
first line with a single line feed character.

1 files changed, 11 insertions, 1 deletions

diff --git a/tests/cluster/tests/00-base.tcl b/tests/cluster/tests/00-base.tcl
index ff5044496..656128e53 100644
--- a/tests/cluster/tests/00-base.tcl
+++ b/tests/cluster/tests/00-base.tcl
@@ -68,5 +68,15 @@ test "Function no-cluster flag" {
         redis.register_function{function_name='f1', callback=function() return 'hello' end, flags={'no-cluster'}}
     }
     catch {R 1 fcall f1 0} e
-    assert_match {*Can not run function on cluster, 'no-cluster' flag is set*} $e
+    assert_match {*Can not run script on cluster, 'no-cluster' flag is set*} $e
+}
+
+test "Script no-cluster flag" {
+    catch {
+        R 1 eval {#!lua flags=no-cluster
+            return 1
+        } 0
+    } e
+    
+    assert_match {*Can not run script on cluster, 'no-cluster' flag is set*} $e
 }