Revert "Allow environment markers as keys (#5)"

This reverts commit 375aea5.
python · brettcannon · Sep 14, 2020 · Sep 2, 2020 · Sep 2, 2020 · Sep 2, 2020
commit 16e65a6397248e5a94a813c66e1481f6dbf3cd9c
diff --git a/pep-9999.rst b/pep-9999.rst
@@ -52,10 +52,11 @@ between this format and :pep:`508`-style specifiers.
 One example is the need to allow for specifying distributions in multiple
 dependencies (environment markers will choose the appropriate dependency).
 
-The environment markers are modelled from `Poetry`_ and `Pipfile`_, and the
-ability to specify environment markers in keys was allowed due to the
-improved ease-of-use. The decision to convert underscores ``_`` to hyphens
-``-`` was made to keep keys consistent with the rest of :pep:`621`.
+Some dependency specifications, as in `Poetry`_, separate the :pep:`508`
+environment markers into separate keys in the requirement. This loses the
+general Python-like syntax for environment markers, and also removes the
+ability to logically combines the markers with grouped `and` and `or`
+operations.
 
 The direct-reference keys closely align with and utilise pep:`610` and
 :pep:`440` as to reduce differences in the packaging ecosystem and rely on
@@ -139,26 +140,6 @@ logically conflict with each other in the requirement: ``version``, ``url``,
 
 An empty requirement table ``{}`` places no restriction on the requirement.
 
-Environment markers
-*******************
-
-All of the :pep:`508` environment marker variables are allowed as keys in the
-requirement table, with underscores ``_`` replace with hyphens ``-``. The
-values are strings which consitute the remainder of the environment marker.
-
-As an example, for the environment marker ``python_version < "2.7"``, the
-following is included in the requirement table:
-
-.. code-block:: toml
-
-    python-version = "< '2.7'"
-
-All of these environment markers must be satisfied, in addition to the value of
-the ``markers`` key, for a requirement to be included.
-
-The ``extra`` marker must not be confused with the ``extras`` key defined
-above.
-
 optional-dependencies
 ---------------------
 
@@ -194,33 +175,8 @@ performed):
                 pep508 += " @ " + vcs + "+" requirement[vcs]
                 if "revision" in requirement:
                     pep508 += "@" + revision
-        markers = ""
-        for variable in (
-            "os_name",
-            "sys_platform",
-            "platform_machine",
-            "platform_python_implementation",
-            "platform_release",
-            "platform_system",
-            "platform_version",
-            "python_version",
-            "python_full_version",
-            "implementation_name",
-            "implementation_version",
-            "extra",
-        ):
-            key = variable.replace("_", "-")
-            if key in requirement:
-                if markers:
-                    markers += " and "
-                markers += variable + " " + requirement[key]
         if "markers" in requirement:
-            markers_explicit = requirement["markers"]
-            if markers:
-                markers_explicit = " and (" + markers_explicit + ")"
-            markers += markers_explicit
-        if markers:
-            pep508 += " ; " + markers
+            pep508 += "; " + requirement["markers"]
         return pep508
 
 
@@ -253,13 +209,13 @@ Full example:
     [project.dependencies]
     flask = { }
     django = { }
-    requests = { version = ">= 2.8.1, == 2.8.*", extras = ["security", "tests"], python-version = "< '2.7'" }
+    requests = { version = ">= 2.8.1, == 2.8.*", extras = ["security", "tests"], markers = "python_version < '2.7'" }
     pip = { url = "https://github.com/pypa/pip/archive/1.3.1.zip" }
     sphinx = { git = "ssh://git@github.com/sphinx-doc/sphinx.git" }
     numpy = "~=1.18"
     pytest = [
-        { version = "<6", python-version = "< '3.5'" },
-        { version = ">=6", python-version = ">= '3.5'" },
+        { version = "<6", markers = "python_version < '3.5'" },
+        { version = ">=6", markers = "python_version >= '3.5'" },
     ]
 
 In homage to :pep:`631`, the following is an equivalent dependencies
@@ -280,12 +236,12 @@ specification for `docker-compose`_:
     websocket-client = ">= 0.32.0, < 1"
 
     # Conditional
-    "backports.shutil_get_terminal_size" = { version = "== 1.0.0", python-version = "< '3.3'" }
-    "backports.ssl_match_hostname" = { version = ">= 3.5, < 4", python-version = "< '3.5'" }
-    colorama = { version = ">= 0.4, < 1", sys-platform = "== 'win32'" }
-    enum34 = { version = ">= 1.0.4, < 2", python-version = "< '3.4'" }
-    ipaddress = { version = ">= 1.0.16, < 2", python-version = "< '3.3'" }
-    subprocess32 = { version = ">= 3.5.4, < 4", python-version = "< '3.2'" }
+    "backports.shutil_get_terminal_size" = { version = "== 1.0.0", markers = "python_version < '3.3'" }
+    "backports.ssl_match_hostname" = { version = ">= 3.5, < 4", markers = "python_version < '3.5'" }
+    colorama = { version = ">= 0.4, < 1", markers = "sys_platform == 'win32'" }
+    enum34 = { version = ">= 1.0.4, < 2", markers = "python_version < '3.4'" }
+    ipaddress = { version = ">= 1.0.16, < 2", markers = "python_version < '3.3'" }
+    subprocess32 = { version = ">= 3.5.4, < 4", markers = "python_version < '3.2'" }
 
     [project.optional-dependencies.socks]
     PySocks = { version = ">= 1.5.6, != 1.5.7, < 2" }
@@ -325,17 +281,17 @@ Rejected Ideas
 - Include hash in direct-reference requirements. This was only for package
   lock-files, and didn't really have a place in the project's metadata.
 
-- Only allowing environment markers in ``markers`` key. The environment marker
-  keys allows for increases in readability and ease of parsing for common
-  cases, with no major drawbacks.
-
 
 Open Issues
 ===========
 
-- Prefixing all environment-marker keys with ``if-``. This increases verbosity,
-  but makes environment-markers less likely to conflict with future keys and
-  better states the intention of these keys.
+- Making each :pep:`508` environment marker as a key (or child-table key) in
+  the requirement. This arguably increases readability and ease of parsing,
+  however the ability to have nested groups of ``and`` and ``or`` operations
+  on the markers is lost.
+
+  A solution to this is to still allow the ``markers`` key, with which the
+  key-specified environment markers and ``and``'d with the result of.
 
 - Including a required ``for-extra`` key in extra requirements, which specifies
   the extra for which the requirement is required for. This allows the