Omit FETCH_THIS in closures

Non-static closures are guaranteed to have $this. The existing comment
highlights this, but fails to handle it correctly.

Zend/zend_compile.c

@@ -316,6 +316,7 @@ static bool zend_is_not_imported(zend_string *name) {
 void zend_oparray_context_begin(zend_oparray_context *prev_context) /* {{{ */
 {
 	*prev_context = CG(context);
+	CG(context).prev = CG(context).op_array ? prev_context : NULL;
 	CG(context).opcodes_size = INITIAL_OP_ARRAY_SIZE;
 	CG(context).vars_size = 0;
 	CG(context).literals_size = 0;
@@ -2920,11 +2921,21 @@ static bool is_global_var_fetch(zend_ast *ast)
 
 static bool this_guaranteed_exists(void) /* {{{ */
 {
-	zend_op_array *op_array = CG(active_op_array);
-	/* Instance methods always have a $this.
-	 * This also includes closures that have a scope and use $this. */
-	return op_array->scope != NULL
-		&& (op_array->fn_flags & ZEND_ACC_STATIC) == 0;
+	zend_oparray_context *ctx = &CG(context);
+	while (ctx) {
+		/* Instance methods always have a $this.
+		 * This also includes closures that have a scope and use $this. */
+		zend_op_array *op_array = ctx->op_array;
+		if (op_array->fn_flags & ZEND_ACC_STATIC) {
+			return false;
+		} else if (op_array->scope) {
+			return true;
+		} else if (!(op_array->fn_flags & ZEND_ACC_CLOSURE)) {
+			return false;
+		}
+		ctx = ctx->prev;
+	}
+	return false;
 }
 /* }}} */
 
@@ -7870,6 +7881,7 @@ static void zend_compile_func_decl(znode *result, zend_ast *ast, bool toplevel)
 	}
 
 	zend_oparray_context_begin(&orig_oparray_context);
+	CG(context).op_array = op_array;
 
 	{
 		/* Push a separator to the loop variable stack */

Zend/zend_compile.h

@@ -190,6 +190,8 @@ typedef struct _zend_live_range {
 
 /* Compilation context that is different for each op array. */
 typedef struct _zend_oparray_context {
+	struct _zend_oparray_context *prev;
+	zend_op_array *op_array;
 	uint32_t   opcodes_size;
 	int        vars_size;
 	int        literals_size;

Zend/zend_language_scanner.l

@@ -615,6 +615,7 @@ static zend_op_array *zend_compile(int type)
 
 		zend_file_context_begin(&original_file_context);
 		zend_oparray_context_begin(&original_oparray_context);
+		CG(context).op_array = op_array;
 		zend_compile_top_stmt(CG(ast));
 		CG(zend_lineno) = last_lineno;
 		zend_emit_final_return(type == ZEND_USER_FUNCTION);