Add workflow graph validation checks (#27106)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/core/workflow/entities/__init__.py

@@ -1,3 +1,5 @@
+from ..runtime.graph_runtime_state import GraphRuntimeState
+from ..runtime.variable_pool import VariablePool
 from .agent import AgentNodeStrategyInit
 from .graph_init_params import GraphInitParams
 from .workflow_execution import WorkflowExecution
@@ -6,6 +8,8 @@ from .workflow_node_execution import WorkflowNodeExecution
 __all__ = [
     "AgentNodeStrategyInit",
     "GraphInitParams",
+    "GraphRuntimeState",
+    "VariablePool",
     "WorkflowExecution",
     "WorkflowNodeExecution",
 ]

api/core/workflow/graph/graph.py

@@ -3,11 +3,12 @@ from collections import defaultdict
 from collections.abc import Mapping, Sequence
 from typing import Protocol, cast, final
 
-from core.workflow.enums import NodeExecutionType, NodeState, NodeType
+from core.workflow.enums import ErrorStrategy, NodeExecutionType, NodeState, NodeType
 from core.workflow.nodes.base.node import Node
 from libs.typing import is_str, is_str_dict
 
 from .edge import Edge
+from .validation import get_graph_validator
 
 logger = logging.getLogger(__name__)
 
@@ -201,6 +202,17 @@ class Graph:
 
         return GraphBuilder(graph_cls=cls)
 
+    @classmethod
+    def _promote_fail_branch_nodes(cls, nodes: dict[str, Node]) -> None:
+        """
+        Promote nodes configured with FAIL_BRANCH error strategy to branch execution type.
+
+        :param nodes: mapping of node ID to node instance
+        """
+        for node in nodes.values():
+            if node.error_strategy == ErrorStrategy.FAIL_BRANCH:
+                node.execution_type = NodeExecutionType.BRANCH
+
     @classmethod
     def _mark_inactive_root_branches(
         cls,
@@ -307,6 +319,9 @@ class Graph:
         # Create node instances
         nodes = cls._create_node_instances(node_configs_map, node_factory)
 
+        # Promote fail-branch nodes to branch execution type at graph level
+        cls._promote_fail_branch_nodes(nodes)
+
         # Get root node instance
         root_node = nodes[root_node_id]
 
@@ -314,7 +329,7 @@ class Graph:
         cls._mark_inactive_root_branches(nodes, edges, in_edges, out_edges, root_node_id)
 
         # Create and return the graph
-        return cls(
+        graph = cls(
             nodes=nodes,
             edges=edges,
             in_edges=in_edges,
@@ -322,6 +337,11 @@ class Graph:
             root_node=root_node,
         )
 
+        # Validate the graph structure using built-in validators
+        get_graph_validator().validate(graph)
+
+        return graph
+
     @property
     def node_ids(self) -> list[str]:
         """

api/core/workflow/graph/validation.py

@@ -0,0 +1,125 @@
+from __future__ import annotations
+
+from collections.abc import Sequence
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, Protocol
+
+from core.workflow.enums import NodeExecutionType, NodeType
+
+if TYPE_CHECKING:
+    from .graph import Graph
+
+
+@dataclass(frozen=True, slots=True)
+class GraphValidationIssue:
+    """Immutable value object describing a single validation issue."""
+
+    code: str
+    message: str
+    node_id: str | None = None
+
+
+class GraphValidationError(ValueError):
+    """Raised when graph validation fails."""
+
+    def __init__(self, issues: Sequence[GraphValidationIssue]) -> None:
+        if not issues:
+            raise ValueError("GraphValidationError requires at least one issue.")
+        self.issues: tuple[GraphValidationIssue, ...] = tuple(issues)
+        message = "; ".join(f"[{issue.code}] {issue.message}" for issue in self.issues)
+        super().__init__(message)
+
+
+class GraphValidationRule(Protocol):
+    """Protocol that individual validation rules must satisfy."""
+
+    def validate(self, graph: Graph) -> Sequence[GraphValidationIssue]:
+        """Validate the provided graph and return any discovered issues."""
+        ...
+
+
+@dataclass(frozen=True, slots=True)
+class _EdgeEndpointValidator:
+    """Ensures all edges reference existing nodes."""
+
+    missing_node_code: str = "MISSING_NODE"
+
+    def validate(self, graph: Graph) -> Sequence[GraphValidationIssue]:
+        issues: list[GraphValidationIssue] = []
+        for edge in graph.edges.values():
+            if edge.tail not in graph.nodes:
+                issues.append(
+                    GraphValidationIssue(
+                        code=self.missing_node_code,
+                        message=f"Edge {edge.id} references unknown source node '{edge.tail}'.",
+                        node_id=edge.tail,
+                    )
+                )
+            if edge.head not in graph.nodes:
+                issues.append(
+                    GraphValidationIssue(
+                        code=self.missing_node_code,
+                        message=f"Edge {edge.id} references unknown target node '{edge.head}'.",
+                        node_id=edge.head,
+                    )
+                )
+        return issues
+
+
+@dataclass(frozen=True, slots=True)
+class _RootNodeValidator:
+    """Validates root node invariants."""
+
+    invalid_root_code: str = "INVALID_ROOT"
+    container_entry_types: tuple[NodeType, ...] = (NodeType.ITERATION_START, NodeType.LOOP_START)
+
+    def validate(self, graph: Graph) -> Sequence[GraphValidationIssue]:
+        root_node = graph.root_node
+        issues: list[GraphValidationIssue] = []
+        if root_node.id not in graph.nodes:
+            issues.append(
+                GraphValidationIssue(
+                    code=self.invalid_root_code,
+                    message=f"Root node '{root_node.id}' is missing from the node registry.",
+                    node_id=root_node.id,
+                )
+            )
+            return issues
+
+        node_type = getattr(root_node, "node_type", None)
+        if root_node.execution_type != NodeExecutionType.ROOT and node_type not in self.container_entry_types:
+            issues.append(
+                GraphValidationIssue(
+                    code=self.invalid_root_code,
+                    message=f"Root node '{root_node.id}' must declare execution type 'root'.",
+                    node_id=root_node.id,
+                )
+            )
+        return issues
+
+
+@dataclass(frozen=True, slots=True)
+class GraphValidator:
+    """Coordinates execution of graph validation rules."""
+
+    rules: tuple[GraphValidationRule, ...]
+
+    def validate(self, graph: Graph) -> None:
+        """Validate the graph against all configured rules."""
+        issues: list[GraphValidationIssue] = []
+        for rule in self.rules:
+            issues.extend(rule.validate(graph))
+
+        if issues:
+            raise GraphValidationError(issues)
+
+
+_DEFAULT_RULES: tuple[GraphValidationRule, ...] = (
+    _EdgeEndpointValidator(),
+    _RootNodeValidator(),
+)
+
+
+def get_graph_validator() -> GraphValidator:
+    """Construct the validator composed of default rules."""
+    return GraphValidator(_DEFAULT_RULES)

api/core/workflow/nodes/node_factory.py

@@ -2,7 +2,7 @@ from typing import TYPE_CHECKING, final
 
 from typing_extensions import override
 
-from core.workflow.enums import ErrorStrategy, NodeExecutionType, NodeType
+from core.workflow.enums import NodeType
 from core.workflow.graph import NodeFactory
 from core.workflow.nodes.base.node import Node
 from libs.typing import is_str, is_str_dict
@@ -82,8 +82,4 @@ class DifyNodeFactory(NodeFactory):
             raise ValueError(f"Node {node_id} missing data information")
         node_instance.init_node_data(node_data)
 
-        # If node has fail branch, change execution type to branch
-        if node_instance.error_strategy == ErrorStrategy.FAIL_BRANCH:
-            node_instance.execution_type = NodeExecutionType.BRANCH
-
         return node_instance