fix: error out if multiple wheels with the same name are produced

We shouldn't silently overwrite wheels that are produced in the same run that have the same filename, as this implies a misconfiguration.

test/test_same_wheel.py

@@ -0,0 +1,42 @@
+import subprocess
+from test import test_projects
+
+import pytest
+
+from . import utils
+
+basic_project = test_projects.new_c_project()
+basic_project.files[
+    "repair.py"
+] = """
+import shutil
+import sys
+from pathlib import Path
+
+wheel = Path(sys.argv[1])
+dest_dir = Path(sys.argv[2])
+platform = wheel.stem.split("-")[-1]
+name = f"spam-0.1.0-py2-none-{platform}.whl"
+dest = dest_dir / name
+dest_dir.mkdir(parents=True, exist_ok=True)
+if dest.exists():
+    dest.unlink()
+shutil.copy(wheel, dest)
+"""
+
+
+def test(tmp_path, capfd):
+    # this test checks that a generated wheel name shall be unique in a given cibuildwheel run
+    project_dir = tmp_path / "project"
+    basic_project.generate(project_dir)
+
+    with pytest.raises(subprocess.CalledProcessError):
+        utils.cibuildwheel_run(
+            project_dir,
+            add_env={
+                "CIBW_REPAIR_WHEEL_COMMAND": "python repair.py {wheel} {dest_dir}",
+            },
+        )
+
+    captured = capfd.readouterr()
+    assert "Build failed because a wheel named" in captured.err