feat: allow cross reference in the configuration (#131)

src/ahriman/application/application/application.py

@@ -120,8 +120,7 @@ class Application(ApplicationPackages, ApplicationRepository):
             process_dependencies(bool): if no set, dependencies will not be processed
 
         Returns:
-            list[Package]: updated packages list. Packager for dependencies will be copied from
-            original package
+            list[Package]: updated packages list. Packager for dependencies will be copied from the original package
 
         Examples:
             In the most cases, in order to avoid build failure, it is required to add missing packages, which can be

src/ahriman/core/build_tools/package_archive.py

@@ -236,7 +236,7 @@ class PackageArchive:
         extract list of the installed packages and their content
 
         Returns:
-            dict[str, FilesystemPackage]; map of package name to list of directories and files contained
+            dict[str, FilesystemPackage]: map of package name to list of directories and files contained
             by this package
         """
         result = {}

src/ahriman/core/configuration/shell_interpolator.py

@@ -19,21 +19,93 @@
 #
 import configparser
 import os
+import sys
 
-from collections.abc import Mapping, MutableMapping
+from collections.abc import Generator, Mapping, MutableMapping
 from string import Template
 
 
+class ExtendedTemplate(Template):
+    """
+    extension to the default :class:`Template` class, which also enabled braces regex to lookup in sections
+
+    Attributes:
+        braceidpattern(str): regular expression to match a colon inside braces
+    """
+
+    braceidpattern = r"(?a:[_a-z0-9][_a-z0-9:]*)"
+
+
 class ShellInterpolator(configparser.Interpolation):
     """
     custom string interpolator, because we cannot use defaults argument due to config validation
     """
 
+    DATA_LINK_ESCAPE = "\x10"
+
+    @staticmethod
+    def _extract_variables(parser: MutableMapping[str, Mapping[str, str]], value: str,
+                           defaults: Mapping[str, str]) -> Generator[tuple[str, str], None, None]:
+        """
+        extract keys and values (if available) from the configuration. In case if a key is not available, it will be
+        silently skipped from the result
+
+        Args:
+            parser(MutableMapping[str, Mapping[str, str]]): option parser
+            value(str): source (not-converted) value
+            defaults(Mapping[str, str]): default values
+
+        Yields:
+            tuple[str, str]: variable name used for substitution and its value
+        """
+        def identifiers() -> Generator[tuple[str | None, str], None, None]:
+            # extract all found identifiers and parse them
+            for identifier in ExtendedTemplate(value).get_identifiers():
+                match identifier.split(":"):
+                    case [lookup_option]:  # single option from the same section
+                        yield None, lookup_option
+                    case [lookup_section, lookup_option]:  # reference to another section
+                        yield lookup_section, lookup_option
+
+        for section, option in identifiers():
+            # key to be substituted
+            key = f"{section}:{option}" if section else option
+
+            if section is not None:  # foreign section case
+                if section not in parser:
+                    continue  # section was not found, silently skip it
+                values = parser[section]
+            else:  # same section
+                values = defaults
+
+            if (raw := values.get(option)) is not None:
+                yield key, raw
+
+    @staticmethod
+    def environment() -> dict[str, str]:
+        """
+        extract environment variables
+
+        Returns:
+            dict[str, str]: environment variables and some custom variables
+        """
+        return os.environ | {
+            "prefix": sys.prefix,
+        }
+
     def before_get(self, parser: MutableMapping[str, Mapping[str, str]], section: str, option: str, value: str,
                    defaults: Mapping[str, str]) -> str:
         """
         interpolate option value
 
+        Notes:
+            This method is using :class:`string.Template` class in order to render both cross-references and
+            environment variables, because it seems that it is the most legit way to handle it. In addition,
+            we are using shell-like variables in some cases (see :attr:`alpm.mirror` option),  thus we would like
+            to keep them alive.
+
+            First this method resolves substitution from the configuration and then renders environment variables
+
         Args:
             parser(MutableMapping[str, Mapping[str, str]]): option parser
             section(str): section name
@@ -44,8 +116,15 @@ class ShellInterpolator(configparser.Interpolation):
         Returns:
             str: substituted value
         """
-        # At the moment it seems that it is the most legit way to handle environment variables
-        # Template behaviour is literally the same as shell
-        # In addition, we are using shell-like variables in some cases (see :attr:`alpm.mirror` option),
-        # thus we would like to keep them alive
-        return Template(value).safe_substitute(os.environ)
+        # because any substitution effectively replace escaped $ ($$) in result, we have to escape it manually
+        escaped = value.replace("$$", self.DATA_LINK_ESCAPE)
+
+        # resolve internal references
+        variables = dict(self._extract_variables(parser, value, defaults))
+        internal = ExtendedTemplate(escaped).safe_substitute(variables)
+
+        # resolve enriched environment variables by using default Template class
+        environment = Template(internal).safe_substitute(self.environment())
+
+        # replace escaped values back
+        return environment.replace(self.DATA_LINK_ESCAPE, "$")

src/ahriman/models/package.py

@@ -161,10 +161,10 @@ class Package(LazyLogging):
             bool: ``True`` in case if package base looks like VCS package and ``False`` otherwise
         """
         return self.base.endswith("-bzr") \
-            or self.base.endswith("-csv")\
-            or self.base.endswith("-darcs")\
-            or self.base.endswith("-git")\
-            or self.base.endswith("-hg")\
+            or self.base.endswith("-csv") \
+            or self.base.endswith("-darcs") \
+            or self.base.endswith("-git") \
+            or self.base.endswith("-hg") \
             or self.base.endswith("-svn")
 
     @property
@@ -358,7 +358,7 @@ class Package(LazyLogging):
 
         Yields:
             Path: list of paths of files which belong to the package and distributed together with this tarball.
-                All paths are relative to the ``path``
+            All paths are relative to the ``path``
 
         Raises:
             PackageInfoError: if there are parsing errors
@@ -504,8 +504,8 @@ class Package(LazyLogging):
             timestamp(float | int): timestamp to check build date against
 
         Returns:
-            bool: ``True`` in case if package was built after the specified date and ``False`` otherwise. In case if build date
-            is not set by any of packages, it returns False
+            bool: ``True`` in case if package was built after the specified date and ``False`` otherwise.
+            In case if build date is not set by any of packages, it returns False
         """
         return any(
             package.build_date > timestamp
@@ -550,8 +550,8 @@ class Package(LazyLogging):
 
         Returns:
             str | None: new generated package release version if any. In case if the release contains dot (e.g. 1.2),
-                the minor part will be incremented by 1. If the release does not contain major.minor notation, the minor
-                version equals to 1 will be appended
+            the minor part will be incremented by 1. If the release does not contain major.minor notation, the minor
+            version equals to 1 will be appended
         """
         if local_version is None:
             return None  # local version not found, keep upstream pkgrel

src/ahriman/models/waiter.py

@@ -97,7 +97,7 @@ class Waiter:
     Attributes:
         interval(float): interval in seconds between checks
         wait_timeout(float): timeout in seconds to wait for. Negative value will result in immediate exit. Zero value
-    means infinite timeout
+            means infinite timeout
     """
 
     wait_timeout: float