ensure rules_python never overrides settings from the root module

Author: aignas

python/uv/private/uv.bzl

@@ -132,31 +132,40 @@ for a particular version.
     },
 )
 
-def _configure(config, *, platform, compatible_with, target_settings, urls = [], sha256 = "", **values):
+def _configure(config, *, platform, compatible_with, target_settings, urls = [], sha256 = "", override = False, **values):
     """Set the value in the config if the value is provided"""
     for key, value in values.items():
         if not value:
             continue
 
+        if not override and config.get(key):
+            continue
+
         config[key] = value
 
     config.setdefault("platforms", {})
-    if platform and not (compatible_with or target_settings or urls):
-        config["platforms"].pop(platform)
-    elif platform:
-        if compatible_with or target_settings:
-            config["platforms"][platform] = struct(
-                name = platform.replace("-", "_").lower(),
-                compatible_with = compatible_with,
-                target_settings = target_settings,
-            )
-        if urls:
-            config.setdefault("urls", {})[platform] = struct(
-                sha256 = sha256,
-                urls = urls,
-            )
+    if not platform:
+        if compatible_with or target_settings or urls:
+            fail("`platform` name must be specified when specifying `compatible_with`, `target_settings` or `urls`")
     elif compatible_with or target_settings:
-        fail("`platform` name must be specified when specifying `compatible_with` or `target_settings`")
+        if not override and config.get("platforms", {}).get(platform):
+            return
+
+        config["platforms"][platform] = struct(
+            name = platform.replace("-", "_").lower(),
+            compatible_with = compatible_with,
+            target_settings = target_settings,
+        )
+    elif urls:
+        if not override and config.get("urls", {}).get(platform):
+            return
+
+        config.setdefault("urls", {})[platform] = struct(
+            sha256 = sha256,
+            urls = urls,
+        )
+    else:
+        config["platforms"].pop(platform)
 
 def process_modules(
         module_ctx,
@@ -205,6 +214,7 @@ def process_modules(
                 platform = tag.platform,
                 compatible_with = tag.compatible_with,
                 target_settings = tag.target_settings,
+                override = mod.is_root,
             )
 
     for key in [
@@ -259,6 +269,7 @@ def process_modules(
                 target_settings = tag.target_settings,
                 sha256 = tag.sha256,
                 urls = tag.urls,
+                override = mod.is_root,
             )
 
     if not versions:

tests/uv/uv/uv_tests.bzl

@@ -487,6 +487,62 @@ def _test_non_rules_python_non_root_is_ignored(env):
 
 _tests.append(_test_non_rules_python_non_root_is_ignored)
 
+def _test_rules_python_does_not_take_precedence(env):
+    calls = []
+    uv = _process_modules(
+        env,
+        module_ctx = _mock_mctx(
+            _mod(
+                default = [
+                    _default(
+                        base_url = "https://example.org",
+                        manifest_filename = "manifest.json",
+                        version = "1.0.0",
+                        platform = "osx",
+                        compatible_with = ["@platforms//os:os"],
+                    ),
+                ],
+                configure = [
+                    _configure(),  # use defaults
+                ],
+            ),
+            _mod(
+                name = "rules_python",
+                configure = [
+                    _configure(
+                        version = "1.0.0",
+                        base_url = "https://foobar.org",
+                        platform = "osx",
+                        compatible_with = ["@platforms//os:osx"],
+                    ),
+                ],
+            ),
+        ),
+        uv_repository = lambda **kwargs: calls.append(kwargs),
+    )
+
+    uv.names().contains_exactly([
+        "1_0_0_osx",
+    ])
+    uv.implementations().contains_exactly({
+        "1_0_0_osx": "@uv_1_0_0_osx//:uv_toolchain",
+    })
+    uv.compatible_with().contains_exactly({
+        "1_0_0_osx": ["@platforms//os:os"],
+    })
+    uv.target_settings().contains_exactly({})
+    env.expect.that_collection(calls).contains_exactly([
+        {
+            "name": "uv_1_0_0_osx",
+            "platform": "osx",
+            "sha256": "deadb00f",
+            "urls": ["https://example.org/1.0.0/osx"],
+            "version": "1.0.0",
+        },
+    ])
+
+_tests.append(_test_rules_python_does_not_take_precedence)
+
 _analysis_tests = []
 
 def _test_toolchain_precedence(name):