Accept setup.py and setup.cfg files in compile (#2634)

## Summary

This costs us ~nothing now that we support using PEP 517 hooks for
`pyproject.toml`.

## Test Plan

`cargo test`

crates/uv/tests/pip_compile.rs

@@ -510,6 +510,108 @@ setup(
     Ok(())
 }
 
+/// Compile a `setup.cfg` file.
+#[test]
+fn compile_setup_cfg() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let setup_cfg = context.temp_dir.child("setup.cfg");
+    setup_cfg.write_str(
+        r#"[options]
+packages = find:
+install_requires=
+    anyio
+
+[options.extras_require]
+dev =
+    iniconfig; python_version >= "3.7"
+    mypy; python_version <= "3.8"
+"#,
+    )?;
+
+    let setup_py = context.temp_dir.child("setup.py");
+    setup_py.write_str(
+        r#"# setup.py
+from setuptools import setup
+
+
+setup(
+    name="dummypkg",
+    description="A dummy package",
+)
+"#,
+    )?;
+
+    uv_snapshot!(context.compile()
+            .arg("setup.cfg")
+            .arg("--extra")
+            .arg("dev"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv pip compile --cache-dir [CACHE_DIR] --exclude-newer 2024-03-25T00:00:00Z setup.cfg --extra dev
+    anyio==4.3.0
+    idna==3.6
+        # via anyio
+    iniconfig==2.0.0
+    sniffio==1.3.1
+        # via anyio
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    "###
+    );
+
+    Ok(())
+}
+
+/// Compile a `setup.py` file.
+#[test]
+fn compile_setup_py() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let setup_py = context.temp_dir.child("setup.py");
+    setup_py.write_str(
+        r#"# setup.py
+from setuptools import setup
+
+
+setup(
+    name="dummypkg",
+    description="A dummy package",
+    install_requires=["anyio"],
+    extras_require={
+        "dev": ["iniconfig; python_version >= '3.7'", "mypy; python_version <= '3.8'"],
+    },
+)
+"#,
+    )?;
+
+    uv_snapshot!(context.compile()
+            .arg("setup.py")
+            .arg("--extra")
+            .arg("dev"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv pip compile --cache-dir [CACHE_DIR] --exclude-newer 2024-03-25T00:00:00Z setup.py --extra dev
+    anyio==4.3.0
+    idna==3.6
+        # via anyio
+    iniconfig==2.0.0
+    sniffio==1.3.1
+        # via anyio
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    "###
+    );
+
+    Ok(())
+}
+
 /// Request multiple extras that do not exist as a dependency group in a `pyproject.toml` file.
 #[test]
 fn compile_pyproject_toml_extras_missing() -> Result<()> {
@@ -564,7 +666,7 @@ fn compile_requirements_file_extra() -> Result<()> {
     ----- stdout -----
 
     ----- stderr -----
-    error: Requesting extras requires a pyproject.toml input file.
+    error: Requesting extras requires a `pyproject.toml`, `setup.cfg`, or `setup.py` file.
     "###
     );