Reverted "Fixed #28646 -- Prevented duplicate index when unique is set to True on PostgreSQL."

This reverts commit 9cf9c796be8dd53bc3b11355ff39d65c81d7be6d due to a crash on Oracle
as it didn't allow multiple indexes on the same field.

2 files changed, 10 insertions, 32 deletions

diff --git a/django/db/backends/base/schema.py b/django/db/backends/base/schema.py
index f6b675339a..3e38c56d50 100644
--- a/django/db/backends/base/schema.py
+++ b/django/db/backends/base/schema.py
@@ -964,7 +964,9 @@ class BaseDatabaseSchemaEditor:
                 fks_dropped.add((old_field.column,))
                 self.execute(self._delete_fk_sql(model, fk_name))
         # Has unique been removed?
-        if old_field.unique and not old_field.primary_key and not new_field.unique:
+        if old_field.unique and (
+            not new_field.unique or self._field_became_primary_key(old_field, new_field)
+        ):
             # Find the unique constraint for this field
             meta_constraint_names = {
                 constraint.name for constraint in model._meta.constraints
diff --git a/django/db/backends/postgresql/schema.py b/django/db/backends/postgresql/schema.py
index c0a785c7e1..0c8548a5d6 100644
--- a/django/db/backends/postgresql/schema.py
+++ b/django/db/backends/postgresql/schema.py
@@ -140,13 +140,6 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                     return sequence["name"]
         return None
 
-    def _is_changing_type_of_indexed_text_column(self, old_field, old_type, new_type):
-        return (old_field.db_index or old_field.unique) and (
-            (old_type.startswith("varchar") and not new_type.startswith("varchar"))
-            or (old_type.startswith("text") and not new_type.startswith("text"))
-            or (old_type.startswith("citext") and not new_type.startswith("citext"))
-        )
-
     def _alter_column_type_sql(
         self, model, old_field, new_field, new_type, old_collation, new_collation
     ):
@@ -154,7 +147,11 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         # different type.
         old_db_params = old_field.db_parameters(connection=self.connection)
         old_type = old_db_params["type"]
-        if self._is_changing_type_of_indexed_text_column(old_field, old_type, new_type):
+        if (old_field.db_index or old_field.unique) and (
+            (old_type.startswith("varchar") and not new_type.startswith("varchar"))
+            or (old_type.startswith("text") and not new_type.startswith("text"))
+            or (old_type.startswith("citext") and not new_type.startswith("citext"))
+        ):
             index_name = self._create_index_name(
                 model._meta.db_table, [old_field.column], suffix="_like"
             )
@@ -258,25 +255,6 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                 model, old_field, new_field, new_type, old_collation, new_collation
             )
 
-    def _new_index_should_be_added(self, old_field, new_field):
-        return not (old_field.db_index or old_field.unique) and (
-            new_field.db_index or new_field.unique
-        )
-
-    def _deleted_index_should_be_recreated(
-        self, old_field, new_field, old_type, new_type
-    ):
-        if (
-            not old_field.unique
-            and (
-                not new_field.db_index
-                or (new_field.unique and not new_field.primary_key)
-            )
-        ) or (
-            self._is_changing_type_of_indexed_text_column(old_field, old_type, new_type)
-        ):
-            return True
-
     def _alter_field(
         self,
         model,
@@ -299,10 +277,8 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             strict,
         )
         # Added an index? Create any PostgreSQL-specific indexes.
-        if self._new_index_should_be_added(
-            old_field, new_field
-        ) or self._deleted_index_should_be_recreated(
-            old_field, new_field, old_type, new_type
+        if (not (old_field.db_index or old_field.unique) and new_field.db_index) or (
+            not old_field.unique and new_field.unique
         ):
             like_index_statement = self._create_like_index_sql(model, new_field)
             if like_index_statement is not None: