ensuring getmetatable exists during evals

Author: tomblind

debugger/debugger.ts

@@ -363,6 +363,8 @@ export namespace Debugger {
         return mappedExpression;
     }
 
+    const metatableAccessor: LuaDebug.MetatableAccessor = "lldbg_getmetatable";
+
     function execute(
         statement: string,
         level: number,
@@ -384,12 +386,14 @@ export namespace Debugger {
             {},
             {
                 __index(this: unknown, name: string) {
+                    if (name === metatableAccessor) {
+                        return getmetatable;
+                    }
                     const variable = locs.vars[name] ?? ups.vars[name];
                     if (variable !== undefined) {
                         return variable.val;
-                    } else {
-                        return fenv[name];
                     }
+                    return fenv[name];
                 },
                 __newindex(this: unknown, name: string, val: unknown) {
                     const variable = locs.vars[name] ?? ups.vars[name];

debugger/protocol.d.ts

@@ -111,6 +111,8 @@ declare namespace LuaDebug {
     type StartToken = "@lldbg|";
     type EndToken = "|lldbg@";
 
+    type MetatableAccessor = "lldbg_getmetatable";
+
     type ScriptRootsEnv = "LOCAL_LUA_DEBUGGER_SCRIPT_ROOTS";
     type BreakInCoroutinesEnv = "LOCAL_LUA_DEBUGGER_BREAK_IN_COROUTINES";
     type StepUnmappedLinesEnv = "LOCAL_LUA_DEBUGGER_STEP_UNMAPPED_LINES";

extension/luaDebugSession.ts

@@ -68,6 +68,7 @@ const enum OutputCategory {
 const maxStackCount = 100;
 const metatableDisplayName = "[[metatable]]";
 const tableLengthDisplayName = "[[length]]";
+const metatableAccessor: LuaDebug.MetatableAccessor = "lldbg_getmetatable";
 const envVariable = "LOCAL_LUA_DEBUGGER_VSCODE";
 const filePathEnvVariable = "LOCAL_LUA_DEBUGGER_FILEPATH";
 const scriptRootsEnvVariable: LuaDebug.ScriptRootsEnv = "LOCAL_LUA_DEBUGGER_SCRIPT_ROOTS";
@@ -520,7 +521,9 @@ export class LuaDebugSession extends LoggingDebugSession {
             }
 
             if (typeof vars.metatable !== "undefined" && typeof baseName !== "undefined") {
-                variables.push(this.buildVariable(vars.metatable, `getmetatable(${baseName})`, metatableDisplayName));
+                variables.push(
+                    this.buildVariable(vars.metatable, `${metatableAccessor}(${baseName})`, metatableDisplayName)
+                );
             }
 
             if (typeof vars.length !== "undefined" && !isMultiResult) {