Implement "Requires" field in pip show (#2347)

## Summary
Follow-up for
395be442fc

adds `Requires` field to pip show output.

I've aimed to make it behave exactly the same as `pip` does for now, but
there seem to be subtle issues that may require some discussion going
forward:
- Should `uv pip show` support extras? `pip` has an open issue for it,
but currently does not support https://github.com/pypa/pip/issues/4824.
- Relatedly, `Requred-by` field (not implemented in this PR) in `pip
show` currently doesn't take the extras into account transparently, i.e.
when `PySocks` has been installed as an extra for `requests[socks]`,
`pip show PySocks` doesn't have `requests` or `requests[socks]` under
`Requred-by` field. Should `uv pip show` for now just replicate `pip`'s
behavior for now for simplicity and parity or try to cover the extras
for completeness?

## Test Plan
Added a couple of tests:
1. `requests==2.31.0` has four dependencies that would be ordered
differently unless sorted. Additionally, it has two dependencies that
are optionally included for extras.
2. `pandas==2.1.3` depends on different versions of `numpy` depending on
the python version used.

crates/uv/src/commands/pip_show.rs

@@ -1,6 +1,8 @@
+use std::collections::BTreeSet;
 use std::fmt::Write;
 
 use anyhow::Result;
+use itertools::Itertools;
 use owo_colors::OwoColorize;
 use tracing::debug;
 
@@ -62,6 +64,9 @@ pub(crate) fn pip_show(
     // Build the installed index.
     let site_packages = SitePackages::from_executable(&venv)?;
 
+    // Determine the markers to use for resolution.
+    let markers = venv.interpreter().markers();
+
     // Sort and deduplicate the packages, which are keyed by name.
     packages.sort_unstable();
     packages.dedup();
@@ -116,6 +121,25 @@ pub(crate) fn pip_show(
                 .expect("package path is not root")
                 .simplified_display()
         )?;
+
+        // If available, print the requirements.
+        if let Ok(metadata) = distribution.metadata() {
+            let requires_dist = metadata
+                .requires_dist
+                .into_iter()
+                .filter(|req| req.evaluate_markers(markers, &[]))
+                .map(|req| req.name)
+                .collect::<BTreeSet<_>>();
+            if requires_dist.is_empty() {
+                writeln!(printer.stdout(), "Requires:")?;
+            } else {
+                writeln!(
+                    printer.stdout(),
+                    "Requires: {}",
+                    requires_dist.into_iter().join(", ")
+                )?;
+            }
+        }
     }
 
     // Validate that the environment is consistent.

crates/uv/tests/pip_show.rs

@@ -56,6 +56,124 @@ fn show_empty() {
     );
 }
 
+#[test]
+fn show_requires_multiple() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let requirements_txt = context.temp_dir.child("requirements.txt");
+    requirements_txt.touch()?;
+    requirements_txt.write_str("requests==2.31.0")?;
+
+    uv_snapshot!(install_command(&context)
+        .arg("-r")
+        .arg("requirements.txt")
+        .arg("--strict"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 5 packages in [TIME]
+    Downloaded 5 packages in [TIME]
+    Installed 5 packages in [TIME]
+     + certifi==2023.11.17
+     + charset-normalizer==3.3.2
+     + idna==3.4
+     + requests==2.31.0
+     + urllib3==2.1.0
+    "###
+    );
+
+    context.assert_command("import requests").success();
+    let filters = [(
+        r"Location:.*site-packages",
+        "Location: [WORKSPACE_DIR]/site-packages",
+    )]
+    .to_vec();
+
+    // Guards against the package names being sorted.
+    uv_snapshot!(filters, Command::new(get_bin())
+        .arg("pip")
+        .arg("show")
+        .arg("requests")
+        .arg("--cache-dir")
+        .arg(context.cache_dir.path())
+        .env("VIRTUAL_ENV", context.venv.as_os_str())
+        .current_dir(&context.temp_dir), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Name: requests
+    Version: 2.31.0
+    Location: [WORKSPACE_DIR]/site-packages
+    Requires: certifi, charset-normalizer, idna, urllib3
+
+    ----- stderr -----
+    "###
+    );
+
+    Ok(())
+}
+
+/// Asserts that the Python version marker in the metadata is correctly evaluated.
+/// `click` v8.1.7 requires `importlib-metadata`, but only when `python_version < "3.8"`.
+#[test]
+fn show_python_version_marker() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let requirements_txt = context.temp_dir.child("requirements.txt");
+    requirements_txt.touch()?;
+    requirements_txt.write_str("click==8.1.7")?;
+
+    uv_snapshot!(install_command(&context)
+        .arg("-r")
+        .arg("requirements.txt")
+        .arg("--strict"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 1 package in [TIME]
+    Downloaded 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + click==8.1.7
+    "###
+    );
+
+    context.assert_command("import click").success();
+
+    let mut filters = vec![(
+        r"Location:.*site-packages",
+        "Location: [WORKSPACE_DIR]/site-packages",
+    )];
+    if cfg!(windows) {
+        filters.push(("Requires: colorama", "Requires:"));
+    }
+
+    uv_snapshot!(filters, Command::new(get_bin())
+        .arg("pip")
+        .arg("show")
+        .arg("click")
+        .arg("--cache-dir")
+        .arg(context.cache_dir.path())
+        .env("VIRTUAL_ENV", context.venv.as_os_str())
+        .current_dir(&context.temp_dir), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Name: click
+    Version: 8.1.7
+    Location: [WORKSPACE_DIR]/site-packages
+    Requires:
+
+    ----- stderr -----
+    "###
+    );
+
+    Ok(())
+}
+
 #[test]
 fn show_found_single_package() -> Result<()> {
     let context = TestContext::new("3.12");
@@ -81,11 +199,11 @@ fn show_found_single_package() -> Result<()> {
     );
 
     context.assert_command("import markupsafe").success();
-    let filters = [(
+
+    let filters = vec![(
         r"Location:.*site-packages",
         "Location: [WORKSPACE_DIR]/site-packages",
-    )]
-    .to_vec();
+    )];
 
     uv_snapshot!(filters, Command::new(get_bin())
         .arg("pip")
@@ -101,6 +219,7 @@ fn show_found_single_package() -> Result<()> {
     Name: markupsafe
     Version: 2.1.3
     Location: [WORKSPACE_DIR]/site-packages
+    Requires:
 
     ----- stderr -----
     "###
@@ -162,10 +281,12 @@ fn show_found_multiple_packages() -> Result<()> {
     Name: markupsafe
     Version: 2.1.3
     Location: [WORKSPACE_DIR]/site-packages
+    Requires:
     ---
     Name: pip
     Version: 21.3.1
     Location: [WORKSPACE_DIR]/site-packages
+    Requires:
 
     ----- stderr -----
     "###
@@ -227,6 +348,7 @@ fn show_found_one_out_of_two() -> Result<()> {
     Name: markupsafe
     Version: 2.1.3
     Location: [WORKSPACE_DIR]/site-packages
+    Requires:
 
     ----- stderr -----
     warning: Package(s) not found for: flask
@@ -378,6 +500,7 @@ fn show_editable() -> Result<()> {
     Name: poetry-editable
     Version: 0.1.0
     Location: [WORKSPACE_DIR]/site-packages
+    Requires: numpy
 
     ----- stderr -----
     "###