From 4a0aa6eecf10432453c22031c247cf24819f1040 Mon Sep 17 00:00:00 2001
From: daurnimator <quae@daurnimator.com>
Date: Fri, 12 May 2017 14:52:14 +1000
Subject: Add facility for a user provided (state-global) native error handler

---
 README.md     |  6 ++++++
 src/lapi.js   |  7 +++++++
 src/ldo.js    | 26 ++++++++++++++++++++------
 src/lstate.js |  1 +
 src/lua.js    |  1 +
 tests/lapi.js | 40 ++++++++++++++++++++++++++++++++++++++++
 6 files changed, 75 insertions(+), 6 deletions(-)

diff --git a/README.md b/README.md
index a41b94b..0fbfc4e 100644
--- a/README.md
+++ b/README.md
@@ -106,6 +106,12 @@ Alias for `lua_pushcfunction`.
 Alias for `lua_pushcclosure`.
 
 
+### `lua_atnativeerror(L, func)`
+
+Sets a function to be called if a native JavaScript error is thrown across a lua pcall.
+The function will be run as if it were a message handler (see https://www.lua.org/manual/5.3/manual.html#2.3).
+
+
 ### `b = lua_isproxy(p, L)`
 
 Returns a boolean `b` indicating whether `p` is a proxy (See `lua_toproxy`).
diff --git a/src/lapi.js b/src/lapi.js
index f56fc81..c0e619b 100644
--- a/src/lapi.js
+++ b/src/lapi.js
@@ -36,6 +36,12 @@ const lua_atpanic = function(L, panicf) {
     return old;
 };
 
+const lua_atnativeerror = function(L, errorf) {
+    let old = L.l_G.atnativeerror;
+    L.l_G.atnativeerror = errorf;
+    return old;
+};
+
 // Return value for idx on stack
 const index2addr = function(L, idx) {
     let ci = L.ci;
@@ -1104,6 +1110,7 @@ module.exports.index2addr_           = index2addr_;
 module.exports.lua_absindex          = lua_absindex;
 module.exports.lua_arith             = lua_arith;
 module.exports.lua_atpanic           = lua_atpanic;
+module.exports.lua_atnativeerror     = lua_atnativeerror;
 module.exports.lua_call              = lua_call;
 module.exports.lua_callk             = lua_callk;
 module.exports.lua_checkstack        = lua_checkstack;
diff --git a/src/ldo.js b/src/ldo.js
index bb34216..c4619e5 100644
--- a/src/ldo.js
+++ b/src/ldo.js
@@ -273,12 +273,26 @@ const luaD_rawrunprotected = function(L, f, ud) {
     } catch (e) {
         if (lj.status === TS.LUA_OK) {
             /* error was not thrown via luaD_throw, i.e. it is a JS error */
-            lj.status = -1;
-            /* run error handler (if possible) with error object as light userdata */
-            try {
-                lapi.lua_pushlightuserdata(L, e);
-                ldebug.luaG_errormsg(L);
-            } catch (e) {}
+            /* run user error handler (if it exists) */
+            let atnativeerror = L.l_G.atnativeerror;
+            if (atnativeerror) {
+                try {
+                    lj.status = TS.LUA_OK;
+
+                    lapi.lua_pushcfunction(L, atnativeerror);
+                    lapi.lua_pushlightuserdata(L, e);
+                    luaD_callnoyield(L, L.top - 2, 1);
+
+                    lj.status = TS.LUA_ERRRUN;
+                } catch(e2) {
+                    if (lj.status === TS.LUA_OK) {
+                        /* also failed */
+                        lj.status = -1;
+                    }
+                }
+            } else {
+                lj.status = -1;
+            }
         }
     }
 
diff --git a/src/lstate.js b/src/lstate.js
index 7d7ff80..5a65c12 100644
--- a/src/lstate.js
+++ b/src/lstate.js
@@ -66,6 +66,7 @@ class global_State {
         this.mainthread = L;
         this.l_registry = new lobject.TValue(CT.LUA_TNIL, null);
         this.panic = null;
+        this.atnativeerror = null;
         this.version = null;
         this.tmname = new Array(ltm.TMS.TM_N);
         this.mt = new Array(LUA_NUMTAGS);
diff --git a/src/lua.js b/src/lua.js
index 135dadb..94eff3d 100644
--- a/src/lua.js
+++ b/src/lua.js
@@ -95,6 +95,7 @@ module.exports.LUA_DIRSEP              = defs.LUA_DIRSEP;
 module.exports.lua_absindex            = lapi.lua_absindex;
 module.exports.lua_arith               = lapi.lua_arith;
 module.exports.lua_atpanic             = lapi.lua_atpanic;
+module.exports.lua_atnativeerror       = lapi.lua_atnativeerror;
 module.exports.lua_call                = lapi.lua_call;
 module.exports.lua_callk               = lapi.lua_callk;
 module.exports.lua_checkstack          = lapi.lua_checkstack;
diff --git a/tests/lapi.js b/tests/lapi.js
index b739860..1dbdd5c 100644
--- a/tests/lapi.js
+++ b/tests/lapi.js
@@ -481,3 +481,43 @@ test('lua_settable, lua_gettable', function (t) {
         "Correct element(s) on the stack"
     );
 });
+
+test('lua_atnativeerror', function(t) {
+    t.plan(7);
+
+    let L = lauxlib.luaL_newstate();
+    let errob = {};
+
+    lua.lua_pushcfunction(L, function(L) {
+        throw errob;
+    });
+    t.strictEqual(lua.lua_pcall(L, 0, 0, 0), -1, "without a native error handler pcall should be -1");
+    lua.lua_pop(L, 1);
+
+
+    lua.lua_atnativeerror(L, function(L) {
+        let e = lua.lua_touserdata(L, 1);
+        t.strictEqual(e, errob);
+        lua.lua_pushstring(L, lua.to_luastring("runtime error!"));
+        return 1;
+    });
+    lua.lua_pushcfunction(L, function(L) {
+        throw errob;
+    });
+    t.strictEqual(lua.lua_pcall(L, 0, 0, 0), lua.LUA_ERRRUN, "should return lua.LUA_ERRRUN");
+    t.strictEqual(lua.lua_tojsstring(L, -1), "runtime error!");
+    lua.lua_pop(L, 1);
+
+
+    lua.lua_atnativeerror(L, function(L) {
+        let e = lua.lua_touserdata(L, 1);
+        t.strictEqual(e, errob);
+        lauxlib.luaL_error(L, lua.to_luastring("runtime error!"));
+    });
+    lua.lua_pushcfunction(L, function(L) {
+        throw errob;
+    });
+    t.strictEqual(lua.lua_pcall(L, 0, 0, 0), lua.LUA_ERRRUN, "luaL_error from a native error handler should result in LUA_ERRRUN");
+    t.strictEqual(lua.lua_tojsstring(L, -1), "runtime error!");
+    lua.lua_pop(L, 1);
+});
-- 
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