Fixed #23702 -- Fixed adding an explicit id field on SQLite.

Thanks gavinwahl for the report.

django/db/backends/sqlite3/schema.py

@@ -75,8 +75,8 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                 )
         # Add in any altered fields
         for (old_field, new_field) in alter_fields:
-            del body[old_field.name]
+            body.pop(old_field.name, None)
-            del mapping[old_field.column]
+            mapping.pop(old_field.column, None)
             body[new_field.name] = new_field
             if old_field.null and not new_field.null:
                 case_sql = "coalesce(%(col)s, %(default)s)" % {

docs/releases/1.7.2.txt

@@ -11,3 +11,6 @@ Bugfixes
 
 * Fixed migration's renaming of auto-created many-to-many tables when changing
   :attr:`Meta.db_table <django.db.models.Options.db_table>` (:ticket:`23630`).
+
+* Fixed a migration crash when adding an explicit ``id`` field to a model on
+  SQLite (:ticket:`23702`).

tests/schema/tests.py

@@ -490,6 +490,25 @@ class SchemaTests(TransactionTestCase):
         else:
             self.fail("No FK constraint for author_id found")
 
+    def test_alter_implicit_id_to_explict(self):
+        """
+        Should be able to convert an implicit "id" field to an explicit "id"
+        primary key field.
+        """
+        with connection.schema_editor() as editor:
+            editor.create_model(Author)
+
+        new_field = IntegerField(primary_key=True)
+        new_field.set_attributes_from_name("id")
+        new_field.model = Author
+        with connection.schema_editor() as editor:
+            editor.alter_field(
+                Author,
+                Author._meta.get_field_by_name("id")[0],
+                new_field,
+                strict=True,
+            )
+
     def test_rename(self):
         """
         Tests simple altering of fields