Merging upstream version 15.0.0.

Signed-off-by: Daniel Baumann <daniel@debian.org>

sqlglot/optimizer/normalize_identifiers.py

@@ -0,0 +1,36 @@
+from sqlglot import exp
+from sqlglot._typing import E
+from sqlglot.dialects.dialect import RESOLVES_IDENTIFIERS_AS_UPPERCASE, DialectType
+
+
+def normalize_identifiers(expression: E, dialect: DialectType = None) -> E:
+    """
+    Normalize all unquoted identifiers to either lower or upper case, depending on
+    the dialect. This essentially makes those identifiers case-insensitive.
+
+    Example:
+        >>> import sqlglot
+        >>> expression = sqlglot.parse_one('SELECT Bar.A AS A FROM "Foo".Bar')
+        >>> normalize_identifiers(expression).sql()
+        'SELECT bar.a AS a FROM "Foo".bar'
+
+    Args:
+        expression: The expression to transform.
+        dialect: The dialect to use in order to decide how to normalize identifiers.
+
+    Returns:
+        The transformed expression.
+    """
+    return expression.transform(_normalize, dialect, copy=False)
+
+
+def _normalize(node: exp.Expression, dialect: DialectType = None) -> exp.Expression:
+    if isinstance(node, exp.Identifier) and not node.quoted:
+        node.set(
+            "this",
+            node.this.upper()
+            if dialect in RESOLVES_IDENTIFIERS_AS_UPPERCASE
+            else node.this.lower(),
+        )
+
+    return node