Merge markers when applying constraints (#4648)

## Summary

When a constraint is applied to a requirement with a marker, the marker
needs to be propagated to the constraint.

If both the constraint and the requirement have a marker, they need to
be merged together (via `and`).

Closes https://github.com/astral-sh/uv/issues/4575.

crates/uv-resolver/src/resolver/mod.rs

@@ -1218,7 +1218,7 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
         dev: Option<&'a GroupName>,
         name: Option<&PackageName>,
         markers: &'a MarkerTree,
-    ) -> Vec<&'a Requirement> {
+    ) -> Vec<Cow<'a, Requirement>> {
         // Start with the requirements for the current extra of the package (for an extra
         // requirement) or the non-extra (regular) dependencies (if extra is None), plus
         // the constraints for the current package.
@@ -1227,9 +1227,9 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
         } else {
             Either::Right(dependencies.iter())
         };
-        let mut requirements: Vec<&Requirement> = self
+        let mut requirements = self
             .requirements_for_extra(regular_and_dev_dependencies, extra, markers)
-            .collect();
+            .collect::<Vec<_>>();
 
         // Check if there are recursive self inclusions and we need to go into the expensive branch.
         if !requirements
@@ -1245,21 +1245,23 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
         let mut queue: VecDeque<_> = requirements
             .iter()
             .filter(|req| name == Some(&req.name))
-            .flat_map(|req| &req.extras)
+            .flat_map(|req| req.extras.iter().cloned())
             .collect();
         while let Some(extra) = queue.pop_front() {
-            if !seen.insert(extra) {
+            if !seen.insert(extra.clone()) {
                 continue;
             }
-            // Add each transitively included extra.
+            for requirement in self.requirements_for_extra(dependencies, Some(&extra), markers) {
-            queue.extend(
+                if name == Some(&requirement.name) {
-                self.requirements_for_extra(dependencies, Some(extra), markers)
+                    // Add each transitively included extra.
-                    .filter(|req| name == Some(&req.name))
+                    queue.extend(requirement.extras.iter().cloned());
-                    .flat_map(|req| &req.extras),
+                } else {
-            );
+                    // Add the requirements for that extra.
-            // Add the requirements for that extra
+                    requirements.push(requirement);
-            requirements.extend(self.requirements_for_extra(dependencies, Some(extra), markers));
+                }
+            }
         }
+
         // Drop all the self-requirements now that we flattened them out.
         requirements.retain(|req| name != Some(&req.name));
 
@@ -1268,12 +1270,15 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
 
     /// The set of the regular and dev dependencies, filtered by Python version,
     /// the markers of this fork and the requested extra.
-    fn requirements_for_extra<'a>(
+    fn requirements_for_extra<'data, 'parameters>(
-        &'a self,
+        &'data self,
-        dependencies: impl IntoIterator<Item = &'a Requirement>,
+        dependencies: impl IntoIterator<Item = &'data Requirement> + 'parameters,
-        extra: Option<&'a ExtraName>,
+        extra: Option<&'parameters ExtraName>,
-        markers: &'a MarkerTree,
+        markers: &'parameters MarkerTree,
-    ) -> impl Iterator<Item = &'a Requirement> {
+    ) -> impl Iterator<Item = Cow<'data, Requirement>> + 'parameters
+    where
+        'data: 'parameters,
+    {
         self.overrides
             .apply(dependencies)
             .filter(move |requirement| {
@@ -1322,7 +1327,7 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                 true
             })
             .flat_map(move |requirement| {
-                iter::once(requirement).chain(
+                iter::once(Cow::Borrowed(requirement)).chain(
                     self.constraints
                         .get(&requirement.name)
                         .into_iter()
@@ -1359,7 +1364,27 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                             }
 
                             true
-                        }),
+                        })
+                        .map(move |constraint| {
+                            // If the requirement is `requests ; sys_platform == 'darwin'` and the
+                            // constraint is `requests ; python_version == '3.6'`, the constraint
+                            // should only apply when _both_ markers are true.
+                            if let Some(marker) = requirement.marker.as_ref() {
+                                let marker = constraint.marker.as_ref().map(|m| {
+                                    MarkerTree::And(vec![marker.clone(), m.clone()])
+                                }).or_else(|| Some(marker.clone()));
+
+                                Cow::Owned(Requirement {
+                                    name: constraint.name.clone(),
+                                    extras: constraint.extras.clone(),
+                                    source: constraint.source.clone(),
+                                    origin: constraint.origin.clone(),
+                                    marker
+                                })
+                            } else {
+                                Cow::Borrowed(constraint)
+                            }
+                        })
                 )
             })
     }

crates/uv/tests/pip_compile.rs

@@ -6390,7 +6390,8 @@ fn universal_cycles() -> Result<()> {
     let context = TestContext::new("3.12");
     let requirements_in = context.temp_dir.child("requirements.in");
     requirements_in.write_str(indoc::indoc! {r"
-        poetry
+        testtools==2.3.0
+        fixtures==3.0.0
     "})?;
 
     uv_snapshot!(context.filters(), windows_filters=false, context.pip_compile()
@@ -6401,114 +6402,162 @@ fn universal_cycles() -> Result<()> {
     ----- stdout -----
     # This file was autogenerated by uv via the following command:
     #    uv pip compile --cache-dir [CACHE_DIR] requirements.in --universal
-    build==1.1.1
+    argparse==1.4.0
-        # via poetry
+        # via unittest2
-    cachecontrol==0.14.0
+    extras==1.0.0
-        # via poetry
+        # via testtools
-    certifi==2024.2.2
+    fixtures==3.0.0
-        # via requests
-    cffi==1.16.0 ; sys_platform == 'darwin' or (platform_python_implementation != 'PyPy' and sys_platform == 'linux')
-        # via
-        #   cryptography
-        #   xattr
-    charset-normalizer==3.3.2
-        # via requests
-    cleo==2.1.0
-        # via poetry
-    colorama==0.4.6 ; os_name == 'nt'
-        # via build
-    crashtest==0.4.1
-        # via
-        #   cleo
-        #   poetry
-    cryptography==42.0.5 ; sys_platform == 'linux'
-        # via secretstorage
-    distlib==0.3.8
-        # via virtualenv
-    dulwich==0.21.7
-        # via poetry
-    fastjsonschema==2.19.1
-        # via poetry
-    filelock==3.13.1
-        # via
-        #   cachecontrol
-        #   virtualenv
-    idna==3.6
-        # via requests
-    installer==0.7.0
-        # via poetry
-    jaraco-classes==3.3.1
-        # via keyring
-    jeepney==0.8.0 ; sys_platform == 'linux'
-        # via
-        #   keyring
-        #   secretstorage
-    keyring==24.3.1
-        # via poetry
-    more-itertools==10.2.0
-        # via jaraco-classes
-    msgpack==1.0.8
-        # via cachecontrol
-    packaging==24.0
-        # via
-        #   build
-        #   poetry
-    pexpect==4.9.0
-        # via poetry
-    pkginfo==1.10.0
-        # via poetry
-    platformdirs==4.2.0
-        # via
-        #   poetry
-        #   virtualenv
-    poetry==1.8.2
         # via
         #   -r requirements.in
-        #   poetry-plugin-export
+        #   testtools
-    poetry-core==1.9.0
+    linecache2==1.0.0
+        # via traceback2
+    pbr==6.0.0
         # via
-        #   poetry
+        #   fixtures
-        #   poetry-plugin-export
+        #   testtools
-    poetry-plugin-export==1.7.1
+    python-mimeparse==1.6.0
-        # via poetry
+        # via testtools
-    ptyprocess==0.7.0
+    six==1.16.0
-        # via pexpect
-    pycparser==2.21 ; sys_platform == 'darwin' or (platform_python_implementation != 'PyPy' and sys_platform == 'linux')
-        # via cffi
-    pyproject-hooks==1.0.0
         # via
-        #   build
+        #   fixtures
-        #   poetry
+        #   testtools
-    pywin32-ctypes==0.2.2 ; sys_platform == 'win32'
+        #   unittest2
-        # via keyring
+    testtools==2.3.0
-    rapidfuzz==3.7.0
-        # via cleo
-    requests==2.31.0
         # via
-        #   cachecontrol
+        #   -r requirements.in
-        #   poetry
+        #   fixtures
-        #   requests-toolbelt
+    traceback2==1.4.0
-    requests-toolbelt==1.0.0
-        # via poetry
-    secretstorage==3.3.3 ; sys_platform == 'linux'
-        # via keyring
-    shellingham==1.5.4
-        # via poetry
-    tomlkit==0.12.4
-        # via poetry
-    trove-classifiers==2024.3.3
-        # via poetry
-    urllib3==2.2.1
         # via
-        #   dulwich
+        #   testtools
-        #   requests
+        #   unittest2
-    virtualenv==20.25.1
+    unittest2==1.1.0
-        # via poetry
+        # via testtools
-    xattr==1.1.0 ; sys_platform == 'darwin'
-        # via poetry
 
     ----- stderr -----
-    Resolved 41 packages in [TIME]
+    Resolved 10 packages in [TIME]
+    "###
+    );
+
+    Ok(())
+}
+
+/// Perform a universal resolution with a constraint.
+#[test]
+fn universal_constraint() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str(indoc::indoc! {r"
+        anyio ; sys_platform == 'win32'
+    "})?;
+
+    let constraints_txt = context.temp_dir.child("constraints.txt");
+    constraints_txt.write_str(indoc::indoc! {r"
+        anyio==3.0.0
+    "})?;
+
+    uv_snapshot!(context.filters(), windows_filters=false, context.pip_compile()
+            .arg("requirements.in")
+            .arg("-c")
+            .arg("constraints.txt")
+            .arg("--universal"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv pip compile --cache-dir [CACHE_DIR] requirements.in -c constraints.txt --universal
+    anyio==3.0.0 ; sys_platform == 'win32'
+        # via
+        #   -c constraints.txt
+        #   -r requirements.in
+    idna==3.6 ; sys_platform == 'win32'
+        # via anyio
+    sniffio==1.3.1 ; sys_platform == 'win32'
+        # via anyio
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    "###
+    );
+
+    Ok(())
+}
+
+/// Perform a universal resolution with a constraint, where the constraint itself has a marker.
+#[test]
+fn universal_constraint_marker() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str(indoc::indoc! {r"
+        anyio ; sys_platform == 'win32'
+    "})?;
+
+    let constraints_txt = context.temp_dir.child("constraints.txt");
+    constraints_txt.write_str(indoc::indoc! {r"
+        anyio==3.0.0 ; os_name == 'nt'
+    "})?;
+
+    uv_snapshot!(context.filters(), windows_filters=false, context.pip_compile()
+            .arg("requirements.in")
+            .arg("-c")
+            .arg("constraints.txt")
+            .arg("--universal"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv pip compile --cache-dir [CACHE_DIR] requirements.in -c constraints.txt --universal
+    anyio==3.0.0 ; sys_platform == 'win32' or (os_name == 'nt' and sys_platform == 'win32')
+        # via
+        #   -c constraints.txt
+        #   -r requirements.in
+    idna==3.6 ; sys_platform == 'win32' or (os_name == 'nt' and sys_platform == 'win32')
+        # via anyio
+    sniffio==1.3.1 ; sys_platform == 'win32' or (os_name == 'nt' and sys_platform == 'win32')
+        # via anyio
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    "###
+    );
+
+    Ok(())
+}
+
+/// Perform a universal resolution with a divergent requirement, and a third requirement that's
+/// compatible with both forks.
+///
+/// This currently fails, but should succeed.
+///
+/// See: <https://github.com/astral-sh/uv/issues/4640>
+#[test]
+fn universal_multi_version() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str(indoc::indoc! {r"
+        iniconfig
+        iniconfig==2.0.0 ; python_version > '3.12'
+        iniconfig==1.0.0 ; python_version == '3.12'
+    "})?;
+
+    let constraints_txt = context.temp_dir.child("constraints.txt");
+    constraints_txt.write_str(indoc::indoc! {r"
+        anyio==3.0.0 ; os_name == 'nt'
+    "})?;
+
+    uv_snapshot!(context.filters(), windows_filters=false, context.pip_compile()
+            .arg("requirements.in")
+            .arg("-c")
+            .arg("constraints.txt")
+            .arg("--universal"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+      × No solution found when resolving dependencies:
+      ╰─▶ Because iniconfig{python_version > '3.12'}==2.0.0 depends on iniconfig==2.0.0 and you require iniconfig{python_version > '3.12'}==2.0.0, we can conclude that your requirements and iniconfig{python_version == '3.12'}==1.0.0 are incompatible.
+          And because you require iniconfig{python_version == '3.12'}==1.0.0, we can conclude that the requirements are unsatisfiable.
     "###
     );