Add python (et al.) to used variants even if only referenced via special selectors

conda_build/metadata.py

@@ -107,6 +107,59 @@ def remove_constructor(cls, tag):
 used_vars_cache = {}
 
 
+def _get_package_dependent_selectors(config: Config) -> dict[str, bool]:
+    """Get package-dependent selectors got get_selectors below.
+
+    Derives selectors from the config and variants to be injected
+    into the Jinja environment prior to templating.
+
+    Args:
+        config (Config): The config object
+
+    Returns:
+        dict[str, bool]: Dictionary of selectors for Jinja
+    """
+    defaults = variants.get_default_variant(config)
+    py = config.variant.get("python", defaults["python"])
+    # there are times when python comes in as a tuple
+    if not hasattr(py, "split"):
+        py = py[0]
+    # go from "3.6 *_cython" -> "36"
+    # or from "3.6.9" -> "36"
+    py_major, py_minor, *_ = py.split(" ")[0].split(".")
+    py = int(f"{py_major}{py_minor}")
+    d = dict(
+        py=py,
+        py3k=bool(py_major == "3"),
+        py2k=bool(py_major == "2"),
+        py26=bool(py == 26),
+        py27=bool(py == 27),
+        py33=bool(py == 33),
+        py34=bool(py == 34),
+        py35=bool(py == 35),
+        py36=bool(py == 36),
+    )
+
+    np = config.variant.get("numpy")
+    if not np:
+        np = defaults["numpy"]
+        if config.verbose:
+            utils.get_logger(__name__).warn(
+                "No numpy version specified in conda_build_config.yaml.  "
+                "Falling back to default numpy value of {}".format(defaults["numpy"])
+            )
+    d["np"] = int("".join(np.split(".")[:2]))
+
+    pl = config.variant.get("perl", defaults["perl"])
+    d["pl"] = pl
+
+    lua = config.variant.get("lua", defaults["lua"])
+    d["lua"] = lua
+    d["luajit"] = bool(lua[0] == "2")
+
+    return d
+
+
 def get_selectors(config: Config) -> dict[str, bool]:
     """Aggregates selectors for use in recipe templating.
 
@@ -152,48 +205,9 @@ def get_selectors(config: Config) -> dict[str, bool]:
         if arch == "32":
             d["x86"] = plat.endswith(("-32", "-64"))
 
-    defaults = variants.get_default_variant(config)
-    py = config.variant.get("python", defaults["python"])
-    # there are times when python comes in as a tuple
-    if not hasattr(py, "split"):
-        py = py[0]
-    # go from "3.6 *_cython" -> "36"
-    # or from "3.6.9" -> "36"
-    py_major, py_minor, *_ = py.split(" ")[0].split(".")
-    py = int(f"{py_major}{py_minor}")
-
     d["build_platform"] = config.build_subdir
 
-    d.update(
-        dict(
-            py=py,
-            py3k=bool(py_major == "3"),
-            py2k=bool(py_major == "2"),
-            py26=bool(py == 26),
-            py27=bool(py == 27),
-            py33=bool(py == 33),
-            py34=bool(py == 34),
-            py35=bool(py == 35),
-            py36=bool(py == 36),
-        )
-    )
-
-    np = config.variant.get("numpy")
-    if not np:
-        np = defaults["numpy"]
-        if config.verbose:
-            utils.get_logger(__name__).warn(
-                "No numpy version specified in conda_build_config.yaml.  "
-                "Falling back to default numpy value of {}".format(defaults["numpy"])
-            )
-    d["np"] = int("".join(np.split(".")[:2]))
-
-    pl = config.variant.get("perl", defaults["perl"])
-    d["pl"] = pl
-
-    lua = config.variant.get("lua", defaults["lua"])
-    d["lua"] = lua
-    d["luajit"] = bool(lua[0] == "2")
+    d.update(_get_package_dependent_selectors(config))
 
     for feature, value in feature_list:
         d[feature] = value

conda_build/variants.py

@@ -94,6 +94,13 @@
     "R": "r_base",
 }
 
+PACKAGE_SELECTOR_MAP = {
+    "python": ("py", "py3k", "py2k", "py26", "py27", "py33", "py34", "py35", "py36"),
+    "numpy": ("np",),
+    "perl": ("pl",),
+    "lua": ("lua", "luajit"),
+}
+
 
 @lru_cache(maxsize=None)
 def _get_default_compilers(platform, py_ver):
@@ -739,14 +746,28 @@ def find_used_variables_in_text(variant, recipe_text, selectors_only=False):
             ]
         else:
             variant_lines = [
-                line for line in recipe_lines if v in line.replace("-", "_")
+                line
+                for line in recipe_lines
+                if v in line.replace("-", "_")
+                or any(v_sel in line for v_sel in PACKAGE_SELECTOR_MAP.get(v, ()))
             ]
         if not variant_lines:
             continue
+
         v_regex = re.escape(v)
+        # Recognize package-dependent selectors: e.g., "py>2" marks "python" as used.
+        v_sel_regex = "|".join(
+            (
+                v_regex,
+                *(re.escape(sel) for sel in PACKAGE_SELECTOR_MAP.get(v, ())),
+            )
+        )
         v_req_regex = "[-_]".join(map(re.escape, v.split("_")))
+
         variant_regex = r"\{\s*(?:pin_[a-z]+\(\s*?['\"])?%s[^'\"]*?\}\}" % v_regex
-        selector_regex = r"^[^#\[]*?\#?\s\[[^\]]*?(?<![_\w\d])%s[=\s<>!\]]" % v_regex
+        selector_regex = (
+            r"^[^#\[]*?\#?\s\[[^\]]*?(?<![_\w\d])(%s)[=\s<>!\]]" % v_sel_regex
+        )
         conditional_regex = (
             r"(?:^|[^\{])\{%\s*(?:el)?if\s*.*" + v_regex + r"\s*(?:[^%]*?)?%\}"
         )

news/5139-special-selector-variants

@@ -0,0 +1,19 @@
+### Enhancements
+
+* Add python (et al.) to used variants even if only referenced via special selectors. (#5139)
+
+### Bug fixes
+
+* <news item>
+
+### Deprecations
+
+* <news item>
+
+### Docs
+
+* <news item>
+
+### Other
+
+* <news item>

tests/test-recipes/variants/32_variant_implicit_via_special_selector/meta.yaml

@@ -0,0 +1,13 @@
+package:
+  name: test_variant_implicit_via_special_selector
+  version: 1.0
+
+build:
+  # "python" variant implicitly injected via "py" selector, but not explicit.
+  skip: true  # [py<33]
+
+outputs:                                                         # [with_outputs]
+  - name: test_variant_implicit_via_special_selector_subpackage  # [with_outputs]
+    requirements:                                                # [with_outputs]
+      host:                                                      # [with_outputs]
+        - python                                                 # [with_outputs]

tests/test_metadata.py

@@ -5,6 +5,7 @@
 import os
 import subprocess
 import sys
+from itertools import chain
 
 import pytest
 from conda import __version__ as conda_version
@@ -24,7 +25,7 @@
     yamlize,
 )
 from conda_build.utils import DEFAULT_SUBDIRS
-from conda_build.variants import DEFAULT_VARIANTS
+from conda_build.variants import DEFAULT_VARIANTS, PACKAGE_SELECTOR_MAP
 
 from .utils import metadata_dir, metadata_path, thisdir
 
@@ -437,7 +438,10 @@ def test_get_selectors(
     monkeypatch.setenv("FEATURE_NOMKL", str(nomkl))
 
     config = Config(host_subdir=subdir)
-    assert get_selectors(config) == {
+    selectors = get_selectors(config)
+    for selector in chain(*PACKAGE_SELECTOR_MAP.values()):
+        assert selector in selectors
+    assert selectors == {
         # defaults
         "build_platform": context.subdir,
         "lua": DEFAULT_VARIANTS["lua"],

tests/test_variants.py

@@ -14,6 +14,7 @@
 from conda_build import api, exceptions
 from conda_build.utils import ensure_list, package_has_file
 from conda_build.variants import (
+    PACKAGE_SELECTOR_MAP,
     combine_specs,
     dict_of_lists_to_list_of_dicts,
     filter_combined_spec_to_used_keys,
@@ -660,6 +661,19 @@ def test_variant_subkeys_retained():
     get_all_replacements(outputs[0][1].config.variant)
 
 
+@pytest.mark.parametrize("with_outputs", [False, True])
+def test_variant_implicit_via_special_selector(with_outputs):
+    ms = api.render(
+        os.path.join(variants_dir, "32_variant_implicit_via_special_selector"),
+        variants={"python": ["2.7", "3.3", "3.4"], "with_outputs": [with_outputs]},
+        finalize=False,
+        bypass_env_check=True,
+    )
+    assert sorted(m.config.variant["python"] for m, _, _ in ms) == ["3.3", "3.4"]
+    for m, _, _ in ms:
+        assert m.get_used_vars().intersection(PACKAGE_SELECTOR_MAP) == {"python"}
+
+
 @pytest.mark.parametrize(
     "internal_defaults, low_prio_config, high_prio_config, expected",
     [