Add support for yielding keys

Keys are yielded using the

    yield $key => $value

syntax. Currently this is implemented as a statement only and not as an
expression, because conflicts arise considering nesting and use in arrays:

    yield yield $a => $b;
    // could be either
    yield (yield $a) => $b;
    // or
    yield (yield $a => $b);

Once I find some way to resolve these conflicts this should be available
as an expression too.

Also the key yielding code is rather copy-and-past-y for the value yielding
code, so that should be factored out.

Zend/tests/generators/generator_with_keys.phpt

@@ -0,0 +1,26 @@
+--TEST--
+Generators can also yield keys
+--FILE--
+<?php
+
+function *reverse(array $array) {
+    end($array);
+    while (null !== $key = key($array)) {
+        yield $key => current($array);
+        prev($array);
+    }
+}
+
+$array = [
+    'foo' => 'bar',
+    'bar' => 'foo',
+];
+
+foreach (reverse($array) as $key => $value) {
+    echo $key, ' => ', $value, "\n";
+}
+
+?>
+--EXPECT--
+bar => foo
+foo => bar

Zend/zend_compile.c

@@ -2662,7 +2662,7 @@ void zend_do_return(znode *expr, int do_end_vparse TSRMLS_DC) /* {{{ */
 }
 /* }}} */
 
-void zend_do_yield(znode *result, const znode *expr TSRMLS_DC) /* {{{ */
+void zend_do_yield(znode *result, const znode *value, const znode *key TSRMLS_DC) /* {{{ */
 {
 	zend_op *opline;
 
@@ -2674,8 +2674,14 @@ void zend_do_yield(znode *result, const znode *expr TSRMLS_DC) /* {{{ */
 
 	opline->opcode = ZEND_YIELD;
 
-	if (expr) {
-		SET_NODE(opline->op1, expr);
+	if (value) {
+		SET_NODE(opline->op1, value);
+	} else {
+		SET_UNUSED(opline->op1);
+	}
+
+	if (key) {
+		SET_NODE(opline->op2, key);
 	} else {
 		SET_UNUSED(opline->op2);
 	}

Zend/zend_compile.h

@@ -490,7 +490,7 @@ void zend_do_build_full_name(znode *result, znode *prefix, znode *name, int is_c
 int zend_do_begin_class_member_function_call(znode *class_name, znode *method_name TSRMLS_DC);
 void zend_do_end_function_call(znode *function_name, znode *result, const znode *argument_list, int is_method, int is_dynamic_fcall TSRMLS_DC);
 void zend_do_return(znode *expr, int do_end_vparse TSRMLS_DC);
-void zend_do_yield(znode *result, const znode *expr TSRMLS_DC);
+void zend_do_yield(znode *result, const znode *value, const znode *key TSRMLS_DC);
 void zend_do_suspend_if_generator(TSRMLS_D);
 void zend_do_handle_exception(TSRMLS_D);
 

Zend/zend_generators.c

@@ -92,6 +92,10 @@ void zend_generator_close(zend_generator *generator, zend_bool finished_executio
 		generator->value = NULL;
 	}
 
+	if (generator->key) {
+		zval_ptr_dtor(&generator->key);
+		generator->key = NULL;
+	}
 }
 /* }}} */
 
@@ -269,6 +273,10 @@ ZEND_METHOD(Generator, key)
 	generator = (zend_generator *) zend_object_store_get_object(object TSRMLS_CC);
 
 	zend_generator_ensure_initialized(object, generator TSRMLS_CC);
+
+	if (generator->key) {
+		RETURN_ZVAL(generator->key, 1, 0);
+	}
 }
 /* }}} */
 

Zend/zend_generators.h

@@ -30,6 +30,8 @@ typedef struct _zend_generator {
 	zend_execute_data *execute_data;
 	/* Current value */
 	zval *value;
+	/* Current key */
+	zval *key;
 	/* Variable to put sent value into */
 	temp_variable *send_target;
 } zend_generator;

Zend/zend_language_parser.y

@@ -299,6 +299,7 @@ unticked_statement:
 	|	T_RETURN ';'						{ zend_do_return(NULL, 0 TSRMLS_CC); }
 	|	T_RETURN expr_without_variable ';'	{ zend_do_return(&$2, 0 TSRMLS_CC); }
 	|	T_RETURN variable ';'				{ zend_do_return(&$2, 1 TSRMLS_CC); }
+	|	T_YIELD expr T_DOUBLE_ARROW expr ';' { zend_do_yield(&$$, &$4, &$2 TSRMLS_CC); }
 	|	T_GLOBAL global_var_list ';'
 	|	T_STATIC static_var_list ';'
 	|	T_ECHO echo_expr_list ';'
@@ -801,8 +802,8 @@ expr_without_variable:
 	|	combined_scalar { $$ = $1; }
 	|	'`' backticks_expr '`' { zend_do_shell_exec(&$$, &$2 TSRMLS_CC); }
 	|	T_PRINT expr  { zend_do_print(&$$, &$2 TSRMLS_CC); }
-	|	T_YIELD { zend_do_yield(&$$, NULL TSRMLS_CC); }
-	|	T_YIELD expr { zend_do_yield(&$$, &$2 TSRMLS_CC); }
+	|	T_YIELD { zend_do_yield(&$$, NULL, NULL TSRMLS_CC); }
+	|	T_YIELD expr { zend_do_yield(&$$, &$2, NULL TSRMLS_CC); }
 	|	function is_generator is_reference { zend_do_begin_lambda_function_declaration(&$$, &$1, $2.op_type, $3.op_type, 0 TSRMLS_CC); }
 		'(' parameter_list ')' lexical_vars { zend_do_suspend_if_generator(TSRMLS_C); }
 		'{' inner_statement_list '}' { zend_do_end_function_declaration(&$1 TSRMLS_CC); $$ = $4; }

Zend/zend_vm_def.h

@@ -5258,7 +5258,7 @@ ZEND_VM_HANDLER(159, ZEND_SUSPEND_AND_RETURN_GENERATOR, ANY, ANY)
 	ZEND_VM_RETURN();
 }
 
-ZEND_VM_HANDLER(160, ZEND_YIELD, CONST|TMP|VAR|CV|UNUSED, ANY)
+ZEND_VM_HANDLER(160, ZEND_YIELD, CONST|TMP|VAR|CV|UNUSED, CONST|TMP|VAR|CV|UNUSED)
 {
 	USE_OPLINE
 
@@ -5270,6 +5270,11 @@ ZEND_VM_HANDLER(160, ZEND_YIELD, CONST|TMP|VAR|CV|UNUSED, ANY)
 		zval_ptr_dtor(&generator->value);
 	}
 
+	/* Destroy the previously yielded key */
+	if (generator->key) {
+		zval_ptr_dtor(&generator->key);
+	}
+
 	/* Set the new yielded value */
 	if (OP1_TYPE != IS_UNUSED) {
 		zend_free_op free_op1;
@@ -5297,11 +5302,43 @@ ZEND_VM_HANDLER(160, ZEND_YIELD, CONST|TMP|VAR|CV|UNUSED, ANY)
 
 		FREE_OP1_IF_VAR();
 	} else {
-		/* If no value way specified yield null */
+		/* If no value was specified yield null */
 		Z_ADDREF(EG(uninitialized_zval));
 		generator->value = &EG(uninitialized_zval);
 	}
 
+	/* Set the new yielded key */
+	if (OP2_TYPE != IS_UNUSED) {
+		zend_free_op free_op2;
+		zval *key = GET_OP2_ZVAL_PTR(BP_VAR_R);
+
+		/* Consts, temporary variables and references need copying */
+		if (OP2_TYPE == IS_CONST || OP2_TYPE == IS_TMP_VAR
+			|| (PZVAL_IS_REF(key) && Z_REFCOUNT_P(key) > 0)
+		) {
+			zval *copy;
+
+			ALLOC_ZVAL(copy);
+			INIT_PZVAL_COPY(copy, key);
+
+			/* Temporary variables don't need ctor copying */
+			if (!IS_OP1_TMP_FREE()) {
+				zval_copy_ctor(copy);
+			}
+
+			generator->key = copy;
+		} else {
+			Z_ADDREF_P(key);
+			generator->key = key;
+		}
+
+		FREE_OP2_IF_VAR();
+	} else {
+		/* Setting the key to NULL signals that the auto-increment key
+		 * generation should be used */
+		generator->key = NULL;
+	}
+
 	/* If a value is sent it should go into the result var */
 	generator->send_target = &EX_T(opline->result.var);