Remove unnecessary Future usage (#3020)

The tox.config.api.Loader.load() method was manually creating a Future
and passing it to the .build() context manager method, but no executor
was involved and nothing was asynchronous.  This commit moves the call
to self.to() from the .load() method to the .build() method.  This
allows dropping the Future and changing .build() from a context manager
to a regular method.

docs/changelog/3020.misc.rst

@@ -0,0 +1 @@
+Remove unnecessary usage of ``Future`` from ``tox.config.api.Loader.load()``.

src/tox/config/loader/api.py

@@ -2,9 +2,7 @@
 
 from abc import abstractmethod
 from argparse import ArgumentTypeError
-from concurrent.futures import Future
-from contextlib import contextmanager
-from typing import TYPE_CHECKING, Any, Generator, List, Mapping, TypeVar
+from typing import TYPE_CHECKING, Any, List, Mapping, TypeVar
 
 from tox.plugin import impl
 
@@ -122,22 +120,17 @@ def load(
         if key in self.overrides:
             return _STR_CONVERT.to(self.overrides[key].value, of_type, factory)
         raw = self.load_raw(key, conf, args.env_name)
-        future: Future[V] = Future()
-        with self.build(future, key, of_type, conf, raw, args) as prepared:
-            converted = self.to(prepared, of_type, factory)
-            future.set_result(converted)
-        return converted
+        return self.build(key, of_type, factory, conf, raw, args)
 
-    @contextmanager
     def build(
         self,
-        future: Future[V],  # noqa: U100
         key: str,  # noqa: U100
-        of_type: type[V],  # noqa: U100
+        of_type: type[V],
+        factory: Factory[V],
         conf: Config | None,  # noqa: U100
         raw: T,
         args: ConfigLoadArgs,  # noqa: U100
-    ) -> Generator[T, None, None]:
+    ) -> V:
         """
         Materialize the raw configuration value from the loader.
 
@@ -148,7 +141,7 @@ def build(
         :param raw: the raw value
         :param args: env args
         """
-        yield raw
+        return self.to(raw, of_type, factory)
 
 
 @impl

src/tox/config/loader/ini/__init__.py

@@ -2,12 +2,11 @@
 
 import inspect
 import re
-from concurrent.futures import Future
 from configparser import ConfigParser, SectionProxy
-from contextlib import contextmanager
-from typing import TYPE_CHECKING, Generator, TypeVar
+from typing import TYPE_CHECKING, TypeVar
 
 from tox.config.loader.api import ConfigLoadArgs, Loader, Override
+from tox.config.loader.convert import Factory
 from tox.config.loader.ini.factor import filter_for_env
 from tox.config.loader.ini.replace import replace
 from tox.config.loader.section import Section
@@ -57,16 +56,15 @@ def process_raw(conf: Config | None, env_name: str | None, value: str) -> str:
         collapsed = factor_filtered.replace("\r", "").replace("\\\n", "")  # collapse explicit new-line escape
         return collapsed
 
-    @contextmanager
     def build(
         self,
-        future: Future[V],
         key: str,
         of_type: type[V],
+        factory: Factory[V],
         conf: Config | None,
         raw: str,
         args: ConfigLoadArgs,
-    ) -> Generator[str, None, None]:
+    ) -> V:
         delay_replace = inspect.isclass(of_type) and issubclass(of_type, SetEnv)
 
         def replacer(raw_: str, args_: ConfigLoadArgs) -> str:
@@ -83,12 +81,11 @@ def replacer(raw_: str, args_: ConfigLoadArgs) -> str:
                     raise HandledError(msg) from exception
             return replaced
 
-        if not delay_replace:
-            raw = replacer(raw, args)
-        yield raw
+        prepared = replacer(raw, args) if not delay_replace else raw
+        converted = self.to(prepared, of_type, factory)
         if delay_replace:
-            converted = future.result()
             converted.use_replacer(replacer, args)  # type: ignore[attr-defined] # this can be only set_env that has it
+        return converted
 
     def found_keys(self) -> set[str]:
         return set(self._section_proxy.keys())