uv/tests: add regression test from #5086

The snapshot saved here is wrong, but we'll update it in a subsequent
commit.

crates/uv/tests/pip_compile.rs

@@ -7877,6 +7877,91 @@ fn universal_unnecessary_python() -> Result<()> {
     Ok(())
 }
 
+/// Tests the markers are propagated correctly.
+///
+/// The main issue here is that we depend on `torch` and `torchvision`
+/// directly, but our dependency on the specific `torch` version is conditional
+/// on the marker environment. This is usually fine, except in this case,
+/// `torchvision` has an unconditional dependency on `torch`, and this resulted
+/// in the markers being dropped. As a result, we'd previously write a
+/// `requirements.txt` file that unconditionally dependended on two different
+/// versions of `torch`.
+///
+/// See: <https://github.com/astral-sh/uv/issues/5086>
+#[test]
+fn universal_marker_propagation() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str(indoc::indoc! {r"
+        --find-links https://download.pytorch.org/whl/torch_stable.html
+
+        torch==2.0.0 ; platform_machine == 'x86_64'
+        torch==2.2.0 ; platform_machine != 'x86_64'
+        torchvision
+    "})?;
+
+    uv_snapshot!(context.filters(), windows_filters=false, context.pip_compile()
+            .arg("requirements.in")
+            .arg("-p")
+            .arg("3.8")
+            .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 -p 3.8 --universal
+    certifi==2024.2.2
+        # via requests
+    charset-normalizer==3.3.2
+        # via requests
+    filelock==3.13.1
+        # via torch
+    fsspec==2024.3.1
+        # via torch
+    idna==3.6
+        # via requests
+    jinja2==3.1.3
+        # via torch
+    markupsafe==2.1.5
+        # via jinja2
+    mpmath==1.3.0
+        # via sympy
+    networkx==3.2.1
+        # via torch
+    numpy==1.26.3
+        # via torchvision
+    pillow==10.2.0
+        # via torchvision
+    requests==2.31.0
+        # via torchvision
+    sympy==1.12
+        # via torch
+    torch==2.0.0
+        # via
+        #   -r requirements.in
+        #   torchvision
+    torch==2.2.0
+        # via
+        #   -r requirements.in
+        #   torchvision
+    torchvision==0.15.1+rocm5.4.2
+        # via -r requirements.in
+    torchvision==0.17.0+rocm5.7
+        # via -r requirements.in
+    typing-extensions==4.10.0
+        # via torch
+    urllib3==2.2.1
+        # via requests
+
+    ----- stderr -----
+    warning: The requested Python version 3.8 is not available; 3.12.[X] will be used to build dependencies instead.
+    Resolved 19 packages in [TIME]
+    "###
+    );
+
+    Ok(())
+}
+
 /// Resolve a package from a `requirements.in` file, with a `constraints.txt` file pinning one of
 /// its transitive dependencies to a specific version.
 #[test]