Feat: allow supplying dialect in diff, conditionally copy ASTs (#4208)

sqlglot/diff.py

@@ -14,6 +14,9 @@
 from sqlglot import Dialect, expressions as exp
 from sqlglot.helper import ensure_list
 
+if t.TYPE_CHECKING:
+ from sqlglot.dialects.dialect import DialectType
+
 
 @dataclass(frozen=True)
 class Insert:
@@ -63,6 +66,7 @@ def diff(
  target: exp.Expression,
  matchings: t.List[t.Tuple[exp.Expression, exp.Expression]] | None = None,
  delta_only: bool = False,
+ copy: bool = True,
  **kwargs: t.Any,
 ) -> t.List[Edit]:
  """
@@ -91,6 +95,9 @@ def diff(
  Note: expression references in this list must refer to the same node objects that are
  referenced in source / target trees.
  delta_only: excludes all `Keep` nodes from the diff.
+ copy: whether to copy the input expressions.
+ Note: if this is set to false, the caller must ensure that there are no shared references
+ in the two ASTs, otherwise the diffing algorithm may produce unexpected behavior.
  kwargs: additional arguments to pass to the ChangeDistiller instance.
 
  Returns:
@@ -110,8 +117,8 @@ def compute_node_mappings(
  if id(old_node) in matching_ids
  }
 
- source_copy = source.copy()
- target_copy = target.copy()
+ source_copy = source.copy() if copy else source
+ target_copy = target.copy() if copy else target
 
  node_mappings = {
  **compute_node_mappings(source, source_copy),
@@ -149,10 +156,10 @@ class ChangeDistiller:
  Chawathe et al. described in http://ilpubs.stanford.edu:8090/115/1/1995-46.pdf.
  """
 
- def __init__(self, f: float = 0.6, t: float = 0.6) -> None:
+ def __init__(self, f: float = 0.6, t: float = 0.6, dialect: DialectType = None) -> None:
  self.f = f
  self.t = t
- self._sql_generator = Dialect().generator()
+ self._sql_generator = Dialect.get_or_raise(dialect).generator()
 
  def diff(
  self,

tests/test_diff.py

@@ -225,5 +225,20 @@ def test_identifier(self):
  ],
  )
 
+ def test_dialect_aware_diff(self):
+ from sqlglot.generator import logger
+
+ with self.assertLogs(logger) as cm:
+ # We want to assert there are no warnings, but the 'assertLogs' method does not support that.
+ # Therefore, we are adding a dummy warning, and then we will assert it is the only warning.
+ logger.warning("Dummy warning")
+
+ expression = parse_one("SELECT foo FROM bar FOR UPDATE", dialect="oracle")
+ self._validate_delta_only(
+ diff_delta_only(expression, expression.copy(), dialect="oracle"), []
+ )
+
+ self.assertEqual(["WARNING:sqlglot:Dummy warning"], cm.output)
+
  def _validate_delta_only(self, actual_delta, expected_delta):
  self.assertEqual(set(actual_delta), set(expected_delta))