more test fixes

Signed-off-by: Jesse Hodges <hodges.jesse@gmail.com>

Author: gjesse

sqlmesh/core/plan/builder.py

@@ -152,6 +152,7 @@ def __init__(
             allow_additive_models if allow_additive_models is not None else []
         )
         self._enable_preview = enable_preview
+        self._preview_start_provided = preview_start is not None
         self._preview_start = preview_start
         self._preview_min_intervals = preview_min_intervals
         self._end_bounded = end_bounded
@@ -241,6 +242,8 @@ def execution_time(self) -> TimeLike:
 
     def set_start(self, new_start: TimeLike) -> PlanBuilder:
         self._start = new_start
+        if not self._preview_start_provided and self._forward_only_preview_needed:
+            self._preview_start = new_start
         self.override_start = True
         self._latest_plan = None
         return self
@@ -262,6 +265,8 @@ def set_effective_from(self, effective_from: t.Optional[TimeLike]) -> PlanBuilde
         self._effective_from = effective_from
         if effective_from and self._is_dev and not self.override_start:
             self._start = effective_from
+            if not self._preview_start_provided and self._forward_only_preview_needed:
+                self._preview_start = effective_from
         self._latest_plan = None
         return self
 

tests/core/test_plan.py

@@ -3043,6 +3043,40 @@ def test_forward_only_preview_start_does_not_override_implicit_backfill_start(ma
     ]
 
 
+def test_forward_only_preview_start_follows_implicit_plan_start_updates(make_snapshot):
+    context_diff, new_snapshot = _make_forward_only_preview_context_diff(make_snapshot)
+
+    plan_builder = PlanBuilder(
+        context_diff,
+        default_start="2025-01-03",
+        end="2025-01-04",
+        is_dev=True,
+        forward_only=True,
+        enable_preview=True,
+    )
+
+    assert plan_builder.build().restatements == {
+        new_snapshot.snapshot_id: (
+            to_timestamp("2025-01-03"),
+            to_timestamp("2025-01-05"),
+        )
+    }
+
+    assert plan_builder.set_effective_from("2025-01-01").build().restatements == {
+        new_snapshot.snapshot_id: (
+            to_timestamp("2025-01-01"),
+            to_timestamp("2025-01-05"),
+        )
+    }
+
+    assert plan_builder.set_start("2025-01-02").build().restatements == {
+        new_snapshot.snapshot_id: (
+            to_timestamp("2025-01-02"),
+            to_timestamp("2025-01-05"),
+        )
+    }
+
+
 def test_forward_only_preview_start_does_not_limit_regular_backfill(make_snapshot):
     context_diff, preview_new_snapshot = _make_forward_only_preview_context_diff(make_snapshot)