Add support for extras tox configuration option

Install only non-optional project dependencies by default
Install dependencies for extras when specified

Fixes #4

tox_poetry_installer.py

@@ -52,6 +52,9 @@ _REPORTER_PREFIX = f"[{__title__}]:"
 _MAGIC_SUFFIX_MARKER = "@poetry"
 
 
+PackageMap = Dict[str, PoetryPackage]
+
+
 class _SortedEnvDeps(NamedTuple):
     unlocked_deps: List[ToxDepConfig]
     locked_deps: List[ToxDepConfig]
@@ -140,7 +143,7 @@ def _install_to_venv(
         installer.install(dependency)
 
 
-def _find_transients(poetry: Poetry, dependency_name: str) -> Set[PoetryPackage]:
+def _find_transients(packages: PackageMap, dependency_name: str) -> Set[PoetryPackage]:
     """Using a poetry object identify all dependencies of a specific dependency
 
     :param poetry: Populated poetry object which can be used to build a populated locked
@@ -152,10 +155,6 @@ def _find_transients(poetry: Poetry, dependency_name: str) -> Set[PoetryPackage]
     .. note:: The package corresponding to the dependency named by ``dependency_name`` is included
               in the list of returned packages.
     """
-    packages: Dict[str, PoetryPackage] = {
-        package.name: package
-        for package in poetry.locker.locked_repository(True).packages
-    }
 
     try:
         top_level = packages[dependency_name]
@@ -185,13 +184,15 @@ def _find_transients(poetry: Poetry, dependency_name: str) -> Set[PoetryPackage]
         ) from None
 
 
-def _install_env_dependencies(venv: ToxVirtualEnv, poetry: Poetry):
+def _install_env_dependencies(
+    venv: ToxVirtualEnv, poetry: Poetry, packages: PackageMap
+):
     env_deps = _sort_env_deps(venv)
 
     dependencies: List[PoetryPackage] = []
     for dep in env_deps.locked_deps:
         try:
-            dependencies += _find_transients(poetry, dep.name.lower())
+            dependencies += _find_transients(packages, dep.name.lower())
         except ToxPoetryInstallerException as err:
             venv.status = "lockfile installation failed"
             reporter.error(f"{_REPORTER_PREFIX} {err}")
@@ -212,21 +213,39 @@ def _install_env_dependencies(venv: ToxVirtualEnv, poetry: Poetry):
     _install_to_venv(poetry, venv, dependencies)
 
 
-def _install_package_dependencies(venv: ToxVirtualEnv, poetry: Poetry):
+def _install_package_dependencies(
+    venv: ToxVirtualEnv, poetry: Poetry, packages: PackageMap
+):
     reporter.verbosity1(
         f"{_REPORTER_PREFIX} performing installation of project dependencies"
     )
 
-    primary_dependencies = poetry.locker.locked_repository(False).packages
+    base_dependencies = [
+        packages[item.name] for item in poetry.packages.requires if not item.is_optional
+    ]
+
+    for extra in venv.envconfig.extras:
+        extra_dependencies = [
+            packages[item.name] for item in poetry.package.extras[extra]
+        ]
+
+    dependencies: List[PoetryPackage] = []
+    for dep in base_dependencies + extra_dependencies:
+        try:
+            dependencies += _find_transients(packages, dep.name.lower())
+        except ToxPoetryInstallerException as err:
+            venv.status = "lockfile installation failed"
+            reporter.error(f"{_REPORTER_PREFIX} {err}")
+            raise err
 
     reporter.verbosity1(
-        f"{_REPORTER_PREFIX} identified {len(primary_dependencies)} dependencies of project '{poetry.package.name}'"
+        f"{_REPORTER_PREFIX} identified {len(dependencies)} dependencies of project '{poetry.package.name}'"
     )
 
     reporter.verbosity0(
-        f"{_REPORTER_PREFIX} ({venv.name}) installing {len(primary_dependencies)} project dependencies from lockfile"
+        f"{_REPORTER_PREFIX} ({venv.name}) installing {len(dependencies)} project dependencies from lockfile"
     )
-    _install_to_venv(poetry, venv, primary_dependencies)
+    _install_to_venv(poetry, venv, dependencies)
 
 
 @hookimpl
@@ -283,19 +302,26 @@ def tox_testenv_install_deps(venv: ToxVirtualEnv, action: ToxAction):
         f"{_REPORTER_PREFIX} loaded project pyproject.toml from {poetry.file}"
     )
 
+    package_map: PackageMap = {
+        package.name: package
+        for package in poetry.locker.locked_repository(True).packages
+    }
+
     # Handle the installation of any locked env dependencies from the lockfile
-    _install_env_dependencies(venv, poetry)
+    _install_env_dependencies(venv, poetry, package_map)
 
     # Handle the installation of the package dependencies from the lockfile if the package is
     # being installed to this venv; otherwise skip installing the package dependencies
-    if not venv.envconfig.skip_install and not venv.envconfig.config.skipsdist:
-        _install_package_dependencies(venv, poetry)
-    else:
     if venv.envconfig.skip_install:
         reporter.verbosity1(
             f"{_REPORTER_PREFIX} env specifies 'skip_install = true', skipping installation of project package"
         )
-        elif venv.envconfig.config.skipsdist:
+        return
+
+    if venv.envconfig.config.skipsdist:
         reporter.verbosity1(
             f"{_REPORTER_PREFIX} config specifies 'skipsdist = true', skipping installation of project package"
         )
+        return
+
+    _install_package_dependencies(venv, poetry, package_map)