uv-resolver: partially revert Requires-Python version narrowing

_typos.toml

@@ -13,6 +13,7 @@ extend-ignore-re = [
     "eb1ba5f5",
     "github_pat_[0-9a-zA-Z_]+",
     "LICENSEs",
+    "astroid",
 ]
 
 [default.extend-identifiers]

crates/uv-resolver/src/python_requirement.rs

@@ -50,7 +50,19 @@ impl PythonRequirement {
 
     /// Narrow the [`PythonRequirement`] to the given version, if it's stricter (i.e., greater)
     /// than the current `Requires-Python` minimum.
-    pub fn narrow(&self, target: &RequiresPythonBound) -> Option<Self> {
+    pub fn narrow(&self, _target: &RequiresPythonBound) -> Option<Self> {
+        // This represents a "small revert" of the PR that added
+        // Requires-Python version narrowing[1]. But narrowing has
+        // led to at least one bug[2] whose fix is not clear. We
+        // decided to revert narrowing under the idea that it is better
+        // to be strict (i.e., fail to resolve in some cases, like
+        // universal_requires_python in uv/tests/pip_compile) than it
+        // is to output an incorrect lock, as in [2].
+        //
+        // [1]: https://github.com/astral-sh/uv/pull/4707
+        // [2]: https://github.com/astral-sh/uv/issues/4885
+        None
+        /*
         let Some(PythonTarget::RequiresPython(requires_python)) = self.target.as_ref() else {
             return None;
         };
@@ -59,6 +71,7 @@ impl PythonRequirement {
             installed: self.installed.clone(),
             target: Some(PythonTarget::RequiresPython(requires_python)),
         })
+        */
     }
 
     /// Return the installed version of Python.

crates/uv/tests/pip_compile.rs

@@ -6624,6 +6624,14 @@ fn universal_multi_version() -> Result<()> {
 
 /// Perform a universal resolution that requires narrowing the supported Python range in one of the
 /// fork branches.
+///
+/// Note that this test is currently asserted to be a failed resolution, which is part of
+/// a small revert of the PR[1] that added Requires-Python version narrowing. This test
+/// should ideally pass, but we aren't sure how to make it pass without producing
+/// incorrect answers in other cases[2].
+///
+/// [1]: https://github.com/astral-sh/uv/pull/4707
+/// [2]: https://github.com/astral-sh/uv/issues/4885
 #[test]
 fn universal_requires_python() -> Result<()> {
     let context = TestContext::new("3.12");
@@ -6633,6 +6641,53 @@ fn universal_requires_python() -> Result<()> {
         numpy <1.26 ; python_version < '3.9'
     "})?;
 
+    uv_snapshot!(context.filters(), windows_filters=false, context.pip_compile()
+            .arg("requirements.in")
+            .arg("-p")
+            .arg("3.8")
+            .arg("--universal"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: The requested Python version 3.8 is not available; 3.12.[X] will be used to build dependencies instead.
+      × No solution found when resolving dependencies:
+      ╰─▶ Because only the following versions of numpy{python_version >= '3.9'} are available:
+              numpy{python_version >= '3.9'}<=1.26.0
+              numpy{python_version >= '3.9'}==1.26.1
+              numpy{python_version >= '3.9'}==1.26.2
+              numpy{python_version >= '3.9'}==1.26.3
+              numpy{python_version >= '3.9'}==1.26.4
+          and the requested Python version (>=3.8) does not satisfy Python>=3.9, we can conclude that any of:
+              numpy{python_version >= '3.9'}>=1.26.0,<1.26.2
+              numpy{python_version >= '3.9'}>1.26.2,<1.26.3
+              numpy{python_version >= '3.9'}>1.26.3,<1.26.4
+              numpy{python_version >= '3.9'}>1.26.4
+           are incompatible.
+          And because the requested Python version (>=3.8) does not satisfy Python>=3.9 and you require numpy{python_version >= '3.9'}>=1.26, we can conclude that the requirements are unsatisfiable.
+    "###
+    );
+
+    Ok(())
+}
+
+// This test captures a case[1] that was broken by Requires-Python version
+// narrowing[2] in the universal resolver. When version narrowing is enabled
+// (at time of writing), the `requirements.txt` generated includes several
+// duplicate and unconditional dependencies without marker expressions.
+//
+// [1]: https://github.com/astral-sh/uv/issues/4885
+// [2]: https://github.com/astral-sh/uv/pull/4707
+#[test]
+fn universal_no_repeated_unconditional_distributions() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str(indoc::indoc! {r"
+        pylint
+        sphinx
+    "})?;
+
     uv_snapshot!(context.filters(), windows_filters=false, context.pip_compile()
             .arg("requirements.in")
             .arg("-p")
@@ -6643,14 +6698,82 @@ fn universal_requires_python() -> Result<()> {
     ----- stdout -----
     # This file was autogenerated by uv via the following command:
     #    uv pip compile --cache-dir [CACHE_DIR] requirements.in -p 3.8 --universal
-    numpy==1.24.4 ; python_version < '3.9'
+    alabaster==0.7.13
+        # via sphinx
+    astroid==3.1.0
+        # via pylint
+    babel==2.14.0
+        # via sphinx
+    certifi==2024.2.2
+        # via requests
+    charset-normalizer==3.3.2
+        # via requests
+    colorama==0.4.6 ; sys_platform == 'win32'
+        # via
+        #   pylint
+        #   sphinx
+    dill==0.3.8
+        # via pylint
+    docutils==0.20.1
+        # via sphinx
+    idna==3.6
+        # via requests
+    imagesize==1.4.1
+        # via sphinx
+    importlib-metadata==7.1.0 ; python_version < '3.10'
+        # via sphinx
+    isort==5.13.2
+        # via pylint
+    jinja2==3.1.3
+        # via sphinx
+    markupsafe==2.1.5
+        # via jinja2
+    mccabe==0.7.0
+        # via pylint
+    packaging==24.0
+        # via sphinx
+    platformdirs==4.2.0
+        # via pylint
+    pygments==2.17.2
+        # via sphinx
+    pylint==3.1.0
         # via -r requirements.in
-    numpy==1.26.4 ; python_version >= '3.9'
+    pytz==2024.1 ; python_version < '3.9'
+        # via babel
+    requests==2.31.0
+        # via sphinx
+    snowballstemmer==2.2.0
+        # via sphinx
+    sphinx==7.1.2
         # via -r requirements.in
+    sphinxcontrib-applehelp==1.0.4
+        # via sphinx
+    sphinxcontrib-devhelp==1.0.2
+        # via sphinx
+    sphinxcontrib-htmlhelp==2.0.1
+        # via sphinx
+    sphinxcontrib-jsmath==1.0.1
+        # via sphinx
+    sphinxcontrib-qthelp==1.0.3
+        # via sphinx
+    sphinxcontrib-serializinghtml==1.1.5
+        # via sphinx
+    tomli==2.0.1 ; python_version < '3.11'
+        # via pylint
+    tomlkit==0.12.4
+        # via pylint
+    typing-extensions==4.10.0 ; python_version < '3.11'
+        # via
+        #   astroid
+        #   pylint
+    urllib3==2.2.1
+        # via requests
+    zipp==3.18.1 ; python_version < '3.10'
+        # via importlib-metadata
 
     ----- stderr -----
     warning: The requested Python version 3.8 is not available; 3.12.[X] will be used to build dependencies instead.
-    Resolved 2 packages in [TIME]
+    Resolved 34 packages in [TIME]
     "###
     );