PEP 665: make filename required

pep-0665.rst

@@ -401,18 +401,13 @@ alternative means (e.g. on the file system in a cache directory).
 ``package._name_._version_.filename``
 -------------------------------------
 
-A string representing the file name to be used on behalf of the URL
-specified in ``url``.
-
-This field is provided in case the URL specified in ``url`` has an
-opaque file name compared to what the actual file name would be for
-installation purposes. If this key is unset then the file name is to
-be taken from ``url``.
-
-Lockers SHOULD provide an accurate value for this field if ``url``
-does not. This helps facilitate connecting which file the hashes
-(discussed below) are for.
+This field is **required**.
 
+A string representing the name of the file as represented by an entry
+in the array. This field is required to simplify installers as the
+file name is required to resolve wheel tags derived from the file
+name. It also guarantees that the association of the array entry to
+the file it is meant for is always clear.
 
 ``package._name_._version_.direct``
 -----------------------------------
@@ -476,21 +471,25 @@ Example
 
         [[package.attrs."21.2.0"]]
         url = "https://files.pythonhosted.org/packages/20/a9/ba6f1cd1a1517ff022b35acd6a7e4246371dfab08b8e42b829b6d07913cc/attrs-21.2.0-py2.py3-none-any.whl"
+        filename = "attrs-21.2.0-py2.py3-none-any.whl"
         hashes.sha256 = "149e90d6d8ac20db7a955ad60cf0e6881a3f20d37096140088356da6c716b0b1"
 
         [[package.mousebender."2.0.0"]]
         url = "https://files.pythonhosted.org/packages/f4/b3/f6fdbff6395e9b77b5619160180489410fb2f42f41272994353e7ecf5bdf/mousebender-2.0.0-py3-none-any.whl"
+        filename = "mousebender-2.0.0-py3-none-any.whl"
         hashes.sha256 = "a6f9adfbd17bfb0e6bb5de9a27083e01dfb86ed9c3861e04143d9fd6db373f7c"
         requires = ["attrs", "packaging"]
 
         [[package.packaging."20.9"]]
         url = "https://files.pythonhosted.org/packages/3e/89/7ea760b4daa42653ece2380531c90f64788d979110a2ab51049d92f408af/packaging-20.9-py2.py3-none-any.whl"
+        filename = "packaging-20.9-py2.py3-none-any.whl"
         hashes.blake-256 = "3e897ea760b4daa42653ece2380531c90f64788d979110a2ab51049d92f408af"
         hashes.sha256 = "67714da7f7bc052e064859c05c595155bd1ee9f69f76557e21f051443c20947a"
         requires = ["pyparsing"]
 
         [[package.pyparsing."2.4.7"]]
         url = "https://files.pythonhosted.org/packages/8a/bb/488841f56197b13700afd5658fc279a2025a39e22449b7cf29864669b15d/pyparsing-2.4.7-py2.py3-none-any.whl"
+        filename = "pyparsing-2.4.7-py2.py3-none-any.whl"
         hashes.sha256="ef9d7589ef3c200abe66653d3f1ab1033c3c419ae9b9bdb1240a85b024efc88b"