fix the config setting getting and add docs

Author: aignas

python/private/pypi/pep508_deps.bzl

@@ -111,7 +111,7 @@ def _platform_str(self):
 
     minor_version = self.abi[3:]
     if self.arch == None and self.os == None:
-        return "@//python/config_settings:is_python_3.{}".format(minor_version)
+        return str(Label("//python/config_settings:is_python_3.{}".format(minor_version)))
 
     return "cp3{}_{}_{}".format(
         minor_version,

python/private/pypi/pep508_env.bzl

@@ -15,7 +15,7 @@
 """This module is for implementing PEP508 environment definition.
 """
 
-# See https://stackoverflow.com/questions/45125516/possible-values-for-uname-m
+# See https://stackoverflow.com/a/45125525
 _platform_machine_aliases = {
     # These pairs mean the same hardware, but different values may be used
     # on different host platforms.
@@ -24,13 +24,41 @@ _platform_machine_aliases = {
     "i386": "x86_32",
     "i686": "x86_32",
 }
+
+# Platform system returns results from the `uname` call.
 _platform_system_values = {
     "linux": "Linux",
     "osx": "Darwin",
     "windows": "Windows",
 }
+
+# The copy of SO [answer](https://stackoverflow.com/a/13874620) containing
+# all of the platforms:
+# ┍━━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━━━━┑
+# │ System              │ Value               │
+# ┝━━━━━━━━━━━━━━━━━━━━━┿━━━━━━━━━━━━━━━━━━━━━┥
+# │ Linux               │ linux or linux2 (*) │
+# │ Windows             │ win32               │
+# │ Windows/Cygwin      │ cygwin              │
+# │ Windows/MSYS2       │ msys                │
+# │ Mac OS X            │ darwin              │
+# │ OS/2                │ os2                 │
+# │ OS/2 EMX            │ os2emx              │
+# │ RiscOS              │ riscos              │
+# │ AtheOS              │ atheos              │
+# │ FreeBSD 7           │ freebsd7            │
+# │ FreeBSD 8           │ freebsd8            │
+# │ FreeBSD N           │ freebsdN            │
+# │ OpenBSD 6           │ openbsd6            │
+# │ AIX                 │ aix (**)            │
+# ┕━━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━━━━━┙
+#
+# (*) Prior to Python 3.3, the value for any Linux version is always linux2; after, it is linux.
+# (**) Prior Python 3.8 could also be aix5 or aix7; use sys.platform.startswith()
+#
+# We are using only the subset that we actually support.
 _sys_platform_values = {
-    "linux": "posix",
+    "linux": "linux",
     "osx": "darwin",
     "windows": "win32",
 }

tests/pypi/pep508/deps_tests.bzl

@@ -264,9 +264,9 @@ def _test_can_get_version_select(env):
 
     env.expect.that_collection(got.deps).contains_exactly(["bar"])
     env.expect.that_dict(got.deps_select).contains_exactly({
-        "@//python/config_settings:is_python_3.7": ["baz"],
-        "@//python/config_settings:is_python_3.8": ["baz_new"],
-        "@//python/config_settings:is_python_3.9": ["baz_new"],
+        str(Label("//python/config_settings:is_python_3.7")): ["baz"],
+        str(Label("//python/config_settings:is_python_3.8")): ["baz_new"],
+        str(Label("//python/config_settings:is_python_3.9")): ["baz_new"],
         "@platforms//os:linux": ["baz", "posix_dep"],
         "cp37_linux_anyarch": ["baz", "posix_dep"],
         "cp37_linux_x86_64": ["arch_dep", "baz", "posix_dep"],
@@ -370,7 +370,7 @@ def _test_deps_are_not_duplicated_when_encountering_platform_dep_first(env):
     # I am not sure why. The starlark version behaviour looks more correct.
     env.expect.that_collection(got.deps).contains_exactly([])
     env.expect.that_dict(got.deps_select).contains_exactly({
-        "@//python/config_settings:is_python_3.10": ["bar"],
+        str(Label("//python/config_settings:is_python_3.10")): ["bar"],
         "cp310_linux_aarch64": ["bar"],
         "cp37_linux_aarch64": ["bar"],
         "linux_aarch64": ["bar"],