[r266-tech]

Closes part of #577.

parse_wheel_filename / parse_tag silently build nonsense Tag('', 'none', 'any') instances from filenames with an empty interpreter/ABI/platform component, e.g.:

• foo-1.0--none-any.whl (empty interpreter)
• foo-1.0-py3-none-.whl (empty platform)
• foo-1.0-py3.-none-any.whl (empty member of a compressed tag set)

An empty component can never match a real sys_tags() entry, so accepting it silently masks upstream filename corruption/truncation instead of surfacing it.

This raises a new InvalidTag(ValueError) from parse_tag and wraps it as InvalidWheelFilename, mirroring the UnsortedTagsError handling added in #1150.

Deliberately narrow: it only rejects empty components — the slice that is illegal under every spec reading. It does not add the broader interpreter-format grammar check discussed in #577 (the \w+\d+ / shortname-grammar variants), which was left unresolved feature-vs-bug in the original thread.

[henryiii]

I've got a potential (hand-written) follow-up to reduce the number of times this is parsed. I also asked Claude for a review after I reviewed it, it was happy with it too.

Dumping followup here so I don't lose the stash

diff --git a/src/packaging/tags.py b/src/packaging/tags.py
index 086d42a..8bd4ec1 100644
--- a/src/packaging/tags.py
+++ b/src/packaging/tags.py
@@ -234,23 +234,24 @@ def parse_tag(tag: str, *, validate_order: bool = False) -> frozenset[Tag]:
     .. versionadded:: 26.3
        Raises :class:`InvalidTag` on empty tag components.
     """
-    tags = set()
-    interpreters, abis, platforms = tag.split("-")
-    for component in (interpreters, abis, platforms):
-        if "" in component.split("."):
+    component_parts = [component.split(".") for component in tag.split("-")]
+    for parts in component_parts:
+        if "" in parts:
+            component = ".".join(parts)
             raise InvalidTag(f"Tag {tag!r} has an empty component: {component!r}")
-    if validate_order:
-        for component in (interpreters, abis, platforms):
-            parts = component.split(".")
-            if parts != sorted(parts):
-                raise UnsortedTagsError(
-                    f"Tag component {component!r} is not in sorted order per PEP 425"
-                )
-    for interpreter in interpreters.split("."):
-        for abi in abis.split("."):
-            for platform_ in platforms.split("."):
-                tags.add(Tag(interpreter, abi, platform_))
-    return frozenset(tags)
+        if validate_order and parts != sorted(parts):
+            component = ".".join(parts)
+            raise UnsortedTagsError(
+                f"Tag component {component!r} is not in sorted order per PEP 425"
+            )
+
+    interpreters, abis, platforms = component_parts
+    return frozenset(
+        Tag(interpreter, abi, platform_)
+        for interpreter in interpreters
+        for abi in abis
+        for platform_ in platforms
+    )


 def _get_config_var(name: str, warn: bool = False) -> int | str | None: