build: add --clean option

Resolves: #1329

docs/cli.md

@@ -548,6 +548,7 @@ Note that, at the moment, only pure python wheels are supported.
 ### Options
 
 * `--format (-f)`: Limit the format to either `wheel` or `sdist`.
+* `--clean`: Clean output directory before building.
 * `--output (-o)`: Set output directory for build artifacts. Default is `dist`.
 
 ## publish

src/poetry/console/commands/build.py

@@ -6,6 +6,7 @@
 
 from poetry.console.commands.env_command import EnvCommand
 from poetry.utils.env import build_environment
+from poetry.utils.helpers import remove_directory
 
 
 class BuildCommand(EnvCommand):
@@ -14,6 +15,11 @@ class BuildCommand(EnvCommand):
 
     options = [
         option("format", "f", "Limit the format to either sdist or wheel.", flag=False),
+        option(
+            "clean",
+            "Clean output directory before building.",
+            flag=True,
+        ),
         option(
             "output",
             "o",
@@ -63,6 +69,10 @@ def handle(self) -> int:
 
             if not dist_dir.is_absolute():
                 dist_dir = self.poetry.pyproject_path.parent / dist_dir
+
+            if self.option("clean"):
+                remove_directory(path=dist_dir, force=True)
+
             self._build(fmt, executable=env.python, target_dir=dist_dir)
 
         return 0

tests/console/commands/test_build.py

@@ -62,6 +62,19 @@ def test_build_creates_packages_in_dist_directory_if_no_output_is_specified(
     assert all(archive.exists() for archive in build_artifacts)
 
 
+@pytest.mark.parametrize("clean", [True, False])
+def test_build_with_clean(
+    tmp_tester: CommandTester, tmp_project_path: Path, tmp_poetry: Poetry, clean: bool
+) -> None:
+    (tmp_project_path / "dist" / "hello").touch(exist_ok=True)
+
+    tmp_tester.execute("--clean" if clean else "")
+    build_artifacts = tuple((tmp_project_path / "dist").glob("*"))
+
+    assert len(build_artifacts) == 2 if clean else 3
+    assert all(archive.exists() for archive in build_artifacts)
+
+
 def test_build_not_possible_in_non_package_mode(
     fixture_dir: FixtureDirGetter,
     command_tester_factory: CommandTesterFactory,