From f18a0939e24fa3ef8a7035efc2186e380580d002 Mon Sep 17 00:00:00 2001
From: Dan Gohman <dev@sunfishcode.online>
Date: Tue, 22 Jul 2025 17:59:03 -0700
Subject: [PATCH] Add an `already-called` error to `run` for wasip3.

Define a `run` error type and use it in the `run` function, to allow
programs to report an error instead of trapping if their `run` function
is called more than once.
---
 wit-0.3.0-draft/run.wit | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/wit-0.3.0-draft/run.wit b/wit-0.3.0-draft/run.wit
index 6dd8b68..602ddca 100644
--- a/wit-0.3.0-draft/run.wit
+++ b/wit-0.3.0-draft/run.wit
@@ -1,6 +1,23 @@
 @since(version = 0.3.0)
 interface run {
-  /// Run the program.
-  @since(version = 0.3.0)
-  run: func() -> result;
+    /// Run the program.
+    ///
+    /// This function is only meant to be called once per Wasm instance. If it
+    /// is called more, it will immediately fail with `error.already-called`.
+    ///
+    /// If a program wishes to exit with a specific exit status value, it should
+    /// use the `exit.exit-with-code` function to exit rather than returning
+    /// from `run`.
+    @since(version = 0.3.0)
+    run: func() -> result<_, error>;
+
+    /// An error code returned by `run`.
+    @since(version = 0.3.0)
+    enum error {
+        /// The program did not complete successfully.
+        error,
+
+        /// The `run` function has already been called in the callee's instance.
+        already-called
+    }
 }