feat: Persist Variables for Enhanced Debugging Workflow (#20699)

This pull request introduces a feature aimed at improving the debugging experience during workflow editing. With the addition of variable persistence, the system will automatically retain the output variables from previously executed nodes. These persisted variables can then be reused when debugging subsequent nodes, eliminating the need for repetitive manual input.

By streamlining this aspect of the workflow, the feature minimizes user errors and significantly reduces debugging effort, offering a smoother and more efficient experience.

Key highlights of this change:

- Automatic persistence of output variables for executed nodes.
- Reuse of persisted variables to simplify input steps for nodes requiring them (e.g., `code`, `template`, `variable_assigner`).
- Enhanced debugging experience with reduced friction.

Closes #19735.

api/core/variables/segments.py

@@ -75,6 +75,20 @@ class StringSegment(Segment):
 class FloatSegment(Segment):
     value_type: SegmentType = SegmentType.NUMBER
     value: float
+    # NOTE(QuantumGhost): seems that the equality for FloatSegment with `NaN` value has some problems.
+    # The following tests cannot pass.
+    #
+    #     def test_float_segment_and_nan():
+    #         nan = float("nan")
+    #         assert nan != nan
+    #
+    #         f1 = FloatSegment(value=float("nan"))
+    #         f2 = FloatSegment(value=float("nan"))
+    #         assert f1 != f2
+    #
+    #         f3 = FloatSegment(value=nan)
+    #         f4 = FloatSegment(value=nan)
+    #         assert f3 != f4
 
 
 class IntegerSegment(Segment):

api/core/variables/types.py

@@ -18,3 +18,17 @@ class SegmentType(StrEnum):
     NONE = "none"
 
     GROUP = "group"
+
+    def is_array_type(self):
+        return self in _ARRAY_TYPES
+
+
+_ARRAY_TYPES = frozenset(
+    [
+        SegmentType.ARRAY_ANY,
+        SegmentType.ARRAY_STRING,
+        SegmentType.ARRAY_NUMBER,
+        SegmentType.ARRAY_OBJECT,
+        SegmentType.ARRAY_FILE,
+    ]
+)

api/core/variables/utils.py

@@ -1,8 +1,26 @@
+import json
 from collections.abc import Iterable, Sequence
 
+from .segment_group import SegmentGroup
+from .segments import ArrayFileSegment, FileSegment, Segment
+
 
 def to_selector(node_id: str, name: str, paths: Iterable[str] = ()) -> Sequence[str]:
     selectors = [node_id, name]
     if paths:
         selectors.extend(paths)
     return selectors
+
+
+class SegmentJSONEncoder(json.JSONEncoder):
+    def default(self, o):
+        if isinstance(o, ArrayFileSegment):
+            return [v.model_dump() for v in o.value]
+        elif isinstance(o, FileSegment):
+            return o.value.model_dump()
+        elif isinstance(o, SegmentGroup):
+            return [self.default(seg) for seg in o.value]
+        elif isinstance(o, Segment):
+            return o.value
+        else:
+            super().default(o)