remove the arbitrary 2 letter truncation for implementation_name and use the standard

Author: aignas

python/private/pypi/parse_requirements.bzl

@@ -411,16 +411,14 @@ def _add_dists(*, requirement, index_urls, target_platform, logger = None):
         ]))
 
     if not target_platform:
-        # The pipstar platforms are undefined here
-        # TODO @aignas 2025-07-05: should we fail hard? It should only be the case in unit
-        # tests or maybe WORKSPACE.
+        # The pipstar platforms are undefined here, so we cannot do any matching
         return sdist
 
     # Select a single wheel that can work on the target_platform
     return select_whl(
         whls = whls,
         python_version = target_platform.env["python_full_version"],
-        implementation = target_platform.env["implementation_name"][:2],
+        implementation_name = target_platform.env["implementation_name"],
         want_abis = target_platform.want_abis,
         platforms = target_platform.platform_tags,
         logger = logger,

python/private/pypi/select_whl.bzl

@@ -3,6 +3,17 @@
 load("//python/private:version.bzl", "version")
 load(":parse_whl_name.bzl", "parse_whl_name")
 
+# Taken from
+# https://packaging.python.org/en/latest/specifications/platform-compatibility-tags/#python-tag
+_PY_TAGS = {
+    # "py": Generic Python (does not require implementation-specific features)
+    "cpython": "cp",
+    "ironpython": "ip",
+    "jython": "jy",
+    "pypy": "pp",
+}
+_PY = "py"
+
 def _get_priority(*, tag, values, allow_wildcard = True):
     for priority, wp in enumerate(values):
         head, sep, tail = wp.partition("*")
@@ -19,7 +30,7 @@ def _get_priority(*, tag, values, allow_wildcard = True):
 
     return None
 
-def select_whl(*, whls, python_version, platforms, want_abis, implementation = "cp", limit = 1, logger = None):
+def select_whl(*, whls, python_version, platforms, want_abis, implementation_name = "cpython", limit = 1, logger = None):
     """Select a whl that is the most suitable for the given platform.
 
     Args:
@@ -28,7 +39,7 @@ def select_whl(*, whls, python_version, platforms, want_abis, implementation = "
         python_version: {type}`str` the target python version.
         platforms: {type}`list[str]` the target platform identifiers that may contain
             a single `*` character.
-        implementation: {type}`str` a 2 letter implementation name. Defaults to "cp"
+        implementation_name: {type}`str` the `implementation_name` from the target_platform env.
         want_abis: {type}`str` the ABIs that the target_platform is compatible with.
         limit: {type}`int` number of wheels to return. Defaults to 1.
         logger: {type}`struct` the logger instance.
@@ -40,11 +51,12 @@ def select_whl(*, whls, python_version, platforms, want_abis, implementation = "
     """
     py_version = version.parse(python_version, strict = True)
     candidates = {}
+    implementation = _PY_TAGS.get(implementation_name, implementation_name)
 
     for whl in whls:
         parsed = parse_whl_name(whl.filename)
 
-        if parsed.python_tag.startswith("py"):
+        if parsed.python_tag.startswith(_PY):
             pass
         elif not parsed.python_tag.startswith(implementation):
             if logger:
@@ -57,7 +69,7 @@ def select_whl(*, whls, python_version, platforms, want_abis, implementation = "
         if parsed.python_tag == "py2.py3":
             min_version = "2"
         else:
-            min_version = parsed.python_tag[2:]
+            min_version = parsed.python_tag[len(implementation):]
 
         if len(min_version) > 1:
             min_version = "{}.{}".format(min_version[0], min_version[1:])