From a5c941139c8b623eb7dc0e9ccdc4133e1c45048f Mon Sep 17 00:00:00 2001
From: Arne Welzel <arne.welzel@corelight.com>
Date: Tue, 6 Feb 2024 14:17:39 +0100
Subject: [PATCH] Stmt: Introduce STMT_EXTERN

It's currently possible for plugin's to implement their own statement
subclasses and override the Exec() implementation. This has been leveraged
by ZeekJS [1] and zeek-perf-support [2] as well as a private WASM plugin.
All of these used STMT_ANY as the tag of their own statement subclasses.

With STMT_EXTERN, we make the possibility to add external code into the AST
somewhat more supported. It's all in detail space and plugin authors have
no guarantee for stability, but it seems such a powerful extension point
that IMO we should keep it.

I'm conscious there's the broader topic how this interacts with ZAM
optimization like in-lining or rewriting of statements. However, this
already applies to the STMT_ANY usage of the mentioned plugins.

[1] https://github.com/corelight/zeekjs
[2] https://github.com/zeek/zeek-perf-support
---
 src/Stmt.cc     | 1 +
 src/StmtEnums.h | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/Stmt.cc b/src/Stmt.cc
index cf455c44ed..6041e16e8a 100644
--- a/src/Stmt.cc
+++ b/src/Stmt.cc
@@ -52,6 +52,7 @@ const char* stmt_name(StmtTag t) {
         "ZAM",
         "null",
         "assert",
+        "extern",
     };
 
     return stmt_names[int(t)];
diff --git a/src/StmtEnums.h b/src/StmtEnums.h
index 3eb463eab9..7a237cb043 100644
--- a/src/StmtEnums.h
+++ b/src/StmtEnums.h
@@ -31,7 +31,8 @@ enum StmtTag {
     STMT_ZAM,           // a ZAM function body
     STMT_NULL,
     STMT_ASSERT,
-#define NUM_STMTS (int(STMT_ASSERT) + 1)
+    STMT_EXTERN, // for custom Stmt subclasses provided by plugins
+#define NUM_STMTS (int(STMT_EXTERN) + 1)
 };
 
 enum StmtFlowType {