Fix arrow function with never return type

Zend/tests/gh7900.phpt

@@ -0,0 +1,26 @@
+--TEST--
+GH-7900: Arrow function with never return type compile-time errors
+--INI--
+zend.assertions=1
+assert.exception=1
+--FILE--
+<?php
+
+$x = fn(): never => throw new \Exception('Here');
+
+try {
+    var_dump($x());
+} catch (\Exception $e) {
+    echo $e->getMessage(), "\n";
+}
+
+try {
+    assert((fn(): never => 42) && false);
+} catch (\Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+?>
+--EXPECT--
+Here
+assert(fn(): never => 42 && false)

Zend/zend_ast.c

@@ -1761,9 +1761,12 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 			}
 			if (decl->child[2]) {
 				if (decl->kind == ZEND_AST_ARROW_FUNC) {
-					ZEND_ASSERT(decl->child[2]->kind == ZEND_AST_RETURN);
+					zend_ast *body = decl->child[2];
+					if (body->kind == ZEND_AST_RETURN) {
+						body = body->child[0];
+					}
 					smart_str_appends(str, " => ");
-					zend_ast_export_ex(str, decl->child[2]->child[0], 0, indent);
+					zend_ast_export_ex(str, body, 0, indent);
 					break;
 				}
 

Zend/zend_compile.c

@@ -7349,6 +7349,19 @@ static void zend_compile_func_decl(znode *result, zend_ast *ast, bool toplevel)
 	} else if (uses_ast) {
 		zend_compile_closure_uses(uses_ast);
 	}
+
+	if (ast->kind == ZEND_AST_ARROW_FUNC) {
+		bool needs_return = true;
+		if (op_array->fn_flags & ZEND_ACC_HAS_RETURN_TYPE) {
+			zend_arg_info *return_info = CG(active_op_array)->arg_info - 1;
+			needs_return = !ZEND_TYPE_CONTAINS_CODE(return_info->type, IS_NEVER);
+		}
+		if (needs_return) {
+			stmt_ast = zend_ast_create(ZEND_AST_RETURN, stmt_ast);
+			decl->child[2] = stmt_ast;
+		}
+	}
+
 	zend_compile_stmt(stmt_ast);
 
 	if (is_method) {

Zend/zend_language_parser.y

@@ -1222,8 +1222,7 @@ inline_function:
 	|	fn returns_ref backup_doc_comment '(' parameter_list ')' return_type
 		T_DOUBLE_ARROW backup_fn_flags backup_lex_pos expr backup_fn_flags
 			{ $$ = zend_ast_create_decl(ZEND_AST_ARROW_FUNC, $2 | $12, $1, $3,
-				  zend_string_init("{closure}", sizeof("{closure}") - 1, 0), $5, NULL,
-				  zend_ast_create(ZEND_AST_RETURN, $11), $7, NULL);
+				  zend_string_init("{closure}", sizeof("{closure}") - 1, 0), $5, NULL, $11, $7, NULL);
 				  ((zend_ast_decl *) $$)->lex_pos = $10;
 				  CG(extra_fn_flags) = $9; }
 ;