feat(mappers): Stream name can now be accessed in __alias__ context of stream maps

docs/stream_maps.md

@@ -266,6 +266,14 @@ The `Faker` class.
 The `Faker` class was deprecated in favor of instance methods on the `fake` object.
 :::
 
+#### Built-in Alias Variable Names
+
+- `__stream_name__` - the existing stream name
+
+:::{versionadded} TODO
+The `__stream_name__` variable.
+:::
+
 #### Automatic Schema Detection
 
 For performance reasons, type detection is performed at runtime using text analysis
@@ -640,6 +648,36 @@ stream_maps:
 Support for stream glob expressions.
 :::
 
+### Aliasing two or more streams
+
+The `__alias__` operation evaluates simple python expressions.
+
+You can combine this with glob expressions to rename more than one stream:
+
+````{tab} meltano.yml
+```yaml
+stream_maps:
+  "*":
+    __alias__: "__stream_name__ + '_v2'"
+```
+````
+
+````{tab} JSON
+```json
+{
+    "stream_maps": {
+        "*": {
+            "__alias__": "__stream_name__ + '_v2'"
+        }
+    }
+}
+```
+````
+
+:::{versionadded} TODO
+Support for `__alias__` expression evaluation.
+:::
+
 ### Understanding Filters' Affects on Parent-Child Streams
 
 Nested child streams iterations will be skipped if their parent stream has a record-level

singer_sdk/mapper.py

@@ -779,6 +779,7 @@ def register_raw_stream_schema(  # noqa: PLR0912, C901
                 elif MAPPER_ALIAS_OPTION in stream_def:
                     # <source>: __alias__: <alias>
                     stream_alias = stream_def.pop(MAPPER_ALIAS_OPTION)
+                    stream_alias = PluginMapper._eval_stream(stream_alias, stream_name)
 
             if stream_name == source_stream:
                 # Exact match
@@ -831,3 +832,40 @@ def register_raw_stream_schema(  # noqa: PLR0912, C901
             else:
                 # Additional mappers for aliasing and multi-projection:
                 self.stream_maps[source_stream].append(mapper)
+
+    @staticmethod
+    def _eval_stream(expr: str, stream_name: str) -> str:
+        """Solve an alias expression.
+
+        Args:
+            expr: String expression to evaluate.
+            stream_name: Name of stream to transform.
+
+        Returns:
+            Evaluated expression.
+
+        Raises:
+            MapExpressionError: If the mapping expression failed to evaluate.
+        """
+        # Allow stream name access within alias transform
+        names = {"__stream_name__": stream_name}
+
+        result: str
+
+        try:
+            expr_evaluator = simpleeval.EvalWithCompoundTypes(names=names)
+            result = expr_evaluator.eval(expr)
+        except simpleeval.NameNotDefined:
+            logging.debug(
+                "Failed to evaluate simpleeval expression %(expr) - "
+                "falling back to original expression",
+                extra={"expr": expr},
+            )
+            result = expr
+        except (simpleeval.InvalidExpression, SyntaxError) as ex:
+            msg = f"Failed to evaluate simpleeval expressions {expr}."
+            raise MapExpressionError(msg) from ex
+
+        logging.debug("Stream eval result: %s = %s", expr, result)
+
+        return result

tests/core/test_mapper.py

@@ -768,6 +768,30 @@ def discover_streams(self):
             "aliased_stream_batch.jsonl",
             id="aliased_stream_batch",
         ),
+        pytest.param(
+            {"mystream": {"__alias__": "aliased.stream"}},
+            {"flattening_enabled": False, "flattening_max_depth": 0},
+            "aliased_stream_not_expr.jsonl",
+            id="aliased_stream_not_expr",
+        ),
+        pytest.param(
+            {"mystream": {"__alias__": "'__stream_name__'"}},
+            {"flattening_enabled": False, "flattening_max_depth": 0},
+            "aliased_stream_quoted.jsonl",
+            id="aliased_stream_quoted",
+        ),
+        pytest.param(
+            {"mystream": {"__alias__": "'aliased_' + __stream_name__"}},
+            {"flattening_enabled": False, "flattening_max_depth": 0},
+            "builtin_variable_stream_name_alias.jsonl",
+            id="builtin_variable_stream_name_alias",
+        ),
+        pytest.param(
+            {"mystream": {"__alias__": "__stream_name__.upper()"}},
+            {"flattening_enabled": False, "flattening_max_depth": 0},
+            "builtin_variable_stream_name_alias_expr.jsonl",
+            id="builtin_variable_stream_name_alias_expr",
+        ),
         pytest.param(
             {},
             {"flattening_enabled": True, "flattening_max_depth": 0},

tests/snapshots/mapped_stream/aliased_stream_not_expr.jsonl

@@ -0,0 +1,6 @@
+{"type":"STATE","value":{}}
+{"type":"SCHEMA","stream":"aliased.stream","schema":{"properties":{"email":{"type":["string"]},"count":{"type":["integer","null"]},"user":{"properties":{"id":{"type":["integer","null"]},"sub":{"properties":{"num":{"type":["integer","null"]},"custom_obj":{"type":["string","null"]}},"type":["object","null"]},"some_numbers":{"items":{"type":["number"]},"type":["array","null"]}},"type":["object","null"]}},"type":"object","required":["email"]},"key_properties":[]}
+{"type":"RECORD","stream":"aliased.stream","record":{"email":"alice@example.com","count":21,"user":{"id":1,"sub":{"num":1,"custom_obj":"obj-hello"},"some_numbers":[3.14,2.718]}},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"aliased.stream","record":{"email":"bob@example.com","count":13,"user":{"id":2,"sub":{"num":2,"custom_obj":"obj-world"},"some_numbers":[10.32,1.618]}},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"aliased.stream","record":{"email":"charlie@example.com","count":19,"user":{"id":3,"sub":{"num":3,"custom_obj":"obj-hello"},"some_numbers":[1.414,1.732]}},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"STATE","value":{"bookmarks":{"mystream":{}}}}

tests/snapshots/mapped_stream/aliased_stream_quoted.jsonl

@@ -0,0 +1,6 @@
+{"type":"STATE","value":{}}
+{"type":"SCHEMA","stream":"__stream_name__","schema":{"properties":{"email":{"type":["string"]},"count":{"type":["integer","null"]},"user":{"properties":{"id":{"type":["integer","null"]},"sub":{"properties":{"num":{"type":["integer","null"]},"custom_obj":{"type":["string","null"]}},"type":["object","null"]},"some_numbers":{"items":{"type":["number"]},"type":["array","null"]}},"type":["object","null"]}},"type":"object","required":["email"]},"key_properties":[]}
+{"type":"RECORD","stream":"__stream_name__","record":{"email":"alice@example.com","count":21,"user":{"id":1,"sub":{"num":1,"custom_obj":"obj-hello"},"some_numbers":[3.14,2.718]}},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"__stream_name__","record":{"email":"bob@example.com","count":13,"user":{"id":2,"sub":{"num":2,"custom_obj":"obj-world"},"some_numbers":[10.32,1.618]}},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"__stream_name__","record":{"email":"charlie@example.com","count":19,"user":{"id":3,"sub":{"num":3,"custom_obj":"obj-hello"},"some_numbers":[1.414,1.732]}},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"STATE","value":{"bookmarks":{"mystream":{}}}}

tests/snapshots/mapped_stream/builtin_variable_stream_name_alias.jsonl

@@ -0,0 +1,6 @@
+{"type":"STATE","value":{}}
+{"type":"SCHEMA","stream":"aliased_mystream","schema":{"properties":{"email":{"type":["string"]},"count":{"type":["integer","null"]},"user":{"properties":{"id":{"type":["integer","null"]},"sub":{"properties":{"num":{"type":["integer","null"]},"custom_obj":{"type":["string","null"]}},"type":["object","null"]},"some_numbers":{"items":{"type":["number"]},"type":["array","null"]}},"type":["object","null"]}},"type":"object","required":["email"]},"key_properties":[]}
+{"type":"RECORD","stream":"aliased_mystream","record":{"email":"alice@example.com","count":21,"user":{"id":1,"sub":{"num":1,"custom_obj":"obj-hello"},"some_numbers":[3.14,2.718]}},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"aliased_mystream","record":{"email":"bob@example.com","count":13,"user":{"id":2,"sub":{"num":2,"custom_obj":"obj-world"},"some_numbers":[10.32,1.618]}},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"aliased_mystream","record":{"email":"charlie@example.com","count":19,"user":{"id":3,"sub":{"num":3,"custom_obj":"obj-hello"},"some_numbers":[1.414,1.732]}},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"STATE","value":{"bookmarks":{"mystream":{}}}}

tests/snapshots/mapped_stream/builtin_variable_stream_name_alias_expr.jsonl

@@ -0,0 +1,6 @@
+{"type":"STATE","value":{}}
+{"type":"SCHEMA","stream":"MYSTREAM","schema":{"properties":{"email":{"type":["string"]},"count":{"type":["integer","null"]},"user":{"properties":{"id":{"type":["integer","null"]},"sub":{"properties":{"num":{"type":["integer","null"]},"custom_obj":{"type":["string","null"]}},"type":["object","null"]},"some_numbers":{"items":{"type":["number"]},"type":["array","null"]}},"type":["object","null"]}},"type":"object","required":["email"]},"key_properties":[]}
+{"type":"RECORD","stream":"MYSTREAM","record":{"email":"alice@example.com","count":21,"user":{"id":1,"sub":{"num":1,"custom_obj":"obj-hello"},"some_numbers":[3.14,2.718]}},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"MYSTREAM","record":{"email":"bob@example.com","count":13,"user":{"id":2,"sub":{"num":2,"custom_obj":"obj-world"},"some_numbers":[10.32,1.618]}},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"MYSTREAM","record":{"email":"charlie@example.com","count":19,"user":{"id":3,"sub":{"num":3,"custom_obj":"obj-hello"},"some_numbers":[1.414,1.732]}},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"STATE","value":{"bookmarks":{"mystream":{}}}}