Added support for extended interpolations for .ini files.

CHANGELOG.rst

@@ -1,6 +1,11 @@
 Changelog
 =========
 
+Snapshot
+--------
+
+* Added support for extended interpolation for .ini files.
+
 1.2.7 (2022-04-04)
 ------------------
 

docs/usage.rst

@@ -52,6 +52,29 @@ Or, with multiple root packages:
 
 .. _the Grimp build_graph documentation: https://grimp.readthedocs.io/en/latest/usage.html#grimp.build_graph
 
+**Interpolations**
+
+When using `.ini` file, extended interpolation may be used, which may be helpful when
+groups of modules need to be referenced in multiple places.
+
+.. code-block:: ini
+
+    [importlinter:contract:1]
+    name = Ports should not depend on adapters.
+    type = forbidden
+    source_modules = ${ports:all}
+    forbidden_modules = ${adapters:all}
+
+    [ports]
+    all =
+        mypackage.inbound
+        yourpackage.outbound
+
+    [adapters]
+    all =
+        mypackage.adapters
+        yourpackage.adapters
+
 Contracts
 ---------
 

src/importlinter/adapters/user_options.py

@@ -51,7 +51,9 @@ class IniFileUserOptionReader(AbstractUserOptionReader):
     section_name = "importlinter"
 
     def _read_config_filename(self, config_filename: str) -> Optional[UserOptions]:
-        config = configparser.ConfigParser()
+        config = configparser.ConfigParser(
+            interpolation=configparser.ExtendedInterpolation(),
+        )
         file_contents = settings.FILE_SYSTEM.read(config_filename)
         config.read_string(file_contents)
         if self.section_name in config.sections():

tests/assets/testpackage/.interpolationcontract.ini

@@ -0,0 +1,15 @@
+[importlinter]
+root_package = testpackage
+include_external_packages = True
+
+[importlinter:contract:one]
+name=Expected kept contract
+type=forbidden
+source_modules=
+    ${section_to_interpolate:source}
+forbidden_modules=
+    sqlalchemy
+
+[section_to_interpolate]
+source=
+    testpackage.high.green

tests/functional/test_lint_imports.py

@@ -18,6 +18,7 @@
     (
         (testpackage_directory, None, cli.EXIT_STATUS_SUCCESS),
         (testpackage_directory, ".brokencontract.ini", cli.EXIT_STATUS_ERROR),
+        (testpackage_directory, ".interpolationcontract.ini", cli.EXIT_STATUS_SUCCESS),
         (testpackage_directory, ".malformedcontract.ini", cli.EXIT_STATUS_ERROR),
         (testpackage_directory, ".customkeptcontract.ini", cli.EXIT_STATUS_SUCCESS),
         (testpackage_directory, ".externalbrokencontract.ini", cli.EXIT_STATUS_ERROR),