Support custom variant labels (#108)

* Initial support for custom variant labels

Add initial support for using wheels with non-variant hash labels.
This mostly means replacing "variant hash" with "variant label"
in a bunch of places, updating the regex and removing validation where
we permit a different label.

* Permit `_` in labels

* Add custom label support to `make-variant` command

* Detect duplicate variants in `generate-index-json`

* Sort variant collision output for consistency and readability

* Update `get_variants_by_priority()` for labels

Rename the `get_variant_hashes_by_priority()` function
to `get_variants_by_priority()`, and update them to return variant
labels rather than hashes.  For the time being, we just use a reverse
map from hashes to labels -- but it may be cleaner to start storing
labels in `VariantDescription`.

* Test null variant with custom label as well

* Remove tests for custom label of null variants

* make-vairant: block --variant-label + --null-variant, add more tests

* Add a `NULL_VARIANT_HASH` constant

* Validate null variant label in `variants.json`

* Avoid labeling null variant in tests

Author: mgorny

tests/artifacts/test-package/Makefile

@@ -39,4 +39,12 @@ build: clean ## builds source and wheel package
 		-p "installable_plugin :: feat1 :: val1c" \
 		-p "installable_plugin :: feat2 :: val2b"
 
+	flit build --format wheel \
+		-p "installable_plugin :: feat1 :: val1c" \
+		--variant-label=foo
+
+	flit build --format wheel \
+		-p "installable_plugin :: feat2 :: val2b" \
+		--variant-label=bar
+
 	variantlib generate-index-json -d dist/

tests/artifacts/test-package/dist/test_package-0-py3-none-any-00000000.whl

@@ -38,12 +38,26 @@
                 ]
             }
         },
+        "bar": {
+            "installable_plugin": {
+                "feat2": [
+                    "val2b"
+                ]
+            }
+        },
         "fbe82642": {
             "installable_plugin": {
                 "feat2": [
                     "val2b"
                 ]
             }
+        },
+        "foo": {
+            "installable_plugin": {
+                "feat1": [
+                    "val1c"
+                ]
+            }
         }
     }
-}
+}

tests/artifacts/test-package/dist/test_package-0-py3-none-any-5d8be4b9.whl

@@ -3,6 +3,7 @@
 from typing import TYPE_CHECKING
 
 from variantlib.commands.main import main
+from variantlib.constants import NULL_VARIANT_HASH
 
 if TYPE_CHECKING:
     import pytest
@@ -32,13 +33,15 @@ def test_analyze_wheel_null_variant(
         [
             "analyze-wheel",
             "-i",
-            "tests/artifacts/test-package/dist/test_package-0-py3-none-any-00000000.whl",
+            "tests/artifacts/test-package/dist/test_package-0-py3-none-any-"
+            f"{NULL_VARIANT_HASH}.whl",
         ]
     )
     assert (
         capsys.readouterr().out
-        == """\
-############################## Variant: `00000000` #############################
+        == f"""\
+############################## Variant: `{NULL_VARIANT_HASH}` \
+#############################
 ################################################################################
 """
     )
@@ -64,3 +67,24 @@ def test_analyze_wheel_variant(
 ################################################################################
 """
     )
+
+
+def test_analyze_wheel_variant_custom_label(
+    capsys: pytest.CaptureFixture[str],
+    mocked_entry_points: None,
+) -> None:
+    main(
+        [
+            "analyze-wheel",
+            "-i",
+            "tests/artifacts/test-package/dist/test_package-0-py3-none-any-foo.whl",
+        ]
+    )
+    assert (
+        capsys.readouterr().out
+        == """\
+############################## Variant: `60567bd9` #############################
+installable_plugin :: feat1 :: val1c
+################################################################################
+"""
+    )