Avoid duplicates in the list of built packages

pyodide_build/buildall.py

@@ -106,7 +106,8 @@ def make_parser(parser):
         help='The path to the target Python installation')
     parser.add_argument(
         '--only', type=str, nargs='?', default=None,
-        help='Only build the specified packages')
+        help=('Only build the specified packages, provided as a comma '
+              'separated list'))
     return parser
 
 

pyodide_build/common.py

@@ -1,5 +1,5 @@
 from pathlib import Path
-from typing import Optional, List
+from typing import Optional, Set
 
 
 ROOTDIR = Path(__file__).parents[1].resolve() / 'tools'
@@ -27,17 +27,17 @@ def parse_package(package):
         return yaml.load(fd)
 
 
-def _parse_package_subset(query: Optional[str]) -> Optional[List[str]]:
+def _parse_package_subset(query: Optional[str]) -> Optional[Set[str]]:
     """Parse the list of packages specified with PYODIDE_PACKAGES env var.
 
     Also add the list of mandatory packages: ['micropip', 'distlib']
 
     Returns:
-      a list of package names to build or None. The list may contain duplicate
-      values.
+      a set of package names to build or None.
     """
     if query is None:
         return None
     packages = query.split(',')
     packages = [el.strip() for el in packages]
-    return ['micropip', 'distlib'] + packages
+    packages = ['micropip', 'distlib'] + packages
+    return set(packages)

test/pyodide_build/test_common.py

@@ -9,6 +9,11 @@ from pyodide_build.common import _parse_package_subset  # noqa
 def test_parse_package_subset():
     assert _parse_package_subset(None) is None
     # micropip is always included
-    assert _parse_package_subset("numpy,pandas") == [
+    assert _parse_package_subset("numpy,pandas") == {
         'micropip', 'distlib', 'numpy', 'pandas'
-    ]
+    }
+
+    # duplicates are removed
+    assert _parse_package_subset("numpy,numpy") == {
+        'micropip', 'distlib', 'numpy'
+    }