Support --python-platform in uv tree (#5764)

## Summary

This allows you to set (e.g.) `--python-platform windows` to view the
resolved dependencies on Windows.

Closes https://github.com/astral-sh/uv/issues/5760.

crates/uv-cli/src/lib.rs

@@ -2370,6 +2370,21 @@ pub struct TreeArgs {
     #[command(flatten)]
     pub resolver: ResolverArgs,
 
+    /// The Python version to use when filtering the tree (via `--filter`). For example, pass
+    /// `--python-version 3.10` to display the dependencies that would be included when installing
+    /// on Python 3.10.
+    #[arg(long, conflicts_with = "universal")]
+    pub python_version: Option<PythonVersion>,
+
+    /// The platform to use when filtering the tree (via `--filter`). For example, pass `--platform
+    /// windows` to display the dependencies that would be included when installing on Windows.
+    ///
+    /// Represented as a "target triple", a string that describes the target platform in terms of
+    /// its CPU, vendor, and operating system name, like `x86_64-unknown-linux-gnu` or
+    /// `aaarch64-apple-darwin`.
+    #[arg(long, conflicts_with = "universal")]
+    pub python_platform: Option<TargetTriple>,
+
     /// The Python interpreter for which packages should be listed.
     ///
     /// By default, uv installs into the virtual environment in the current working directory or

crates/uv/src/commands/pip/mod.rs

@@ -16,7 +16,7 @@ pub(crate) mod sync;
 pub(crate) mod tree;
 pub(crate) mod uninstall;
 
-// Determine the tags, markers, and interpreter to use for resolution.
+/// Determine the tags, markers, and interpreter to use for resolution.
 pub(crate) fn resolution_environment(
     python_version: Option<PythonVersion>,
     python_platform: Option<TargetTriple>,

crates/uv/src/commands/project/tree.rs

@@ -1,3 +1,4 @@
+use std::borrow::Cow;
 use std::fmt::Write;
 
 use anyhow::Result;
@@ -5,9 +6,9 @@ use anyhow::Result;
 use pep508_rs::PackageName;
 use uv_cache::Cache;
 use uv_client::Connectivity;
-use uv_configuration::{Concurrency, PreviewMode};
+use uv_configuration::{Concurrency, PreviewMode, TargetTriple};
 use uv_fs::CWD;
-use uv_python::{PythonFetch, PythonPreference, PythonRequest};
+use uv_python::{PythonFetch, PythonPreference, PythonRequest, PythonVersion};
 use uv_resolver::TreeDisplay;
 use uv_warnings::warn_user_once;
 use uv_workspace::{DiscoveryOptions, Workspace};
@@ -30,6 +31,8 @@ pub(crate) async fn tree(
     package: Vec<PackageName>,
     no_dedupe: bool,
     invert: bool,
+    python_version: Option<PythonVersion>,
+    python_platform: Option<TargetTriple>,
     python: Option<String>,
     settings: ResolverSettings,
     python_preference: PythonPreference,
@@ -79,10 +82,20 @@ pub(crate) async fn tree(
     )
     .await?;
 
+    // Apply the platform tags to the markers.
+    let markers = match (python_platform, python_version) {
+        (Some(python_platform), Some(python_version)) => {
+            Cow::Owned(python_version.markers(&python_platform.markers(interpreter.markers())))
+        }
+        (Some(python_platform), None) => Cow::Owned(python_platform.markers(interpreter.markers())),
+        (None, Some(python_version)) => Cow::Owned(python_version.markers(interpreter.markers())),
+        (None, None) => Cow::Borrowed(interpreter.markers()),
+    };
+
     // Render the tree.
     let tree = TreeDisplay::new(
         &lock.lock,
-        (!universal).then(|| interpreter.markers()),
+        (!universal).then(|| markers.as_ref()),
         depth.into(),
         prune,
         package,

crates/uv/src/lib.rs

@@ -1127,6 +1127,8 @@ async fn run_project(
                 args.package,
                 args.no_dedupe,
                 args.invert,
+                args.python_version,
+                args.python_platform,
                 args.python,
                 args.resolver,
                 globals.python_preference,

crates/uv/src/settings.rs

@@ -775,6 +775,8 @@ pub(crate) struct TreeSettings {
     pub(crate) package: Vec<PackageName>,
     pub(crate) no_dedupe: bool,
     pub(crate) invert: bool,
+    pub(crate) python_version: Option<PythonVersion>,
+    pub(crate) python_platform: Option<TargetTriple>,
     pub(crate) python: Option<String>,
     pub(crate) resolver: ResolverSettings,
 }
@@ -789,6 +791,8 @@ impl TreeSettings {
             frozen,
             build,
             resolver,
+            python_version,
+            python_platform,
             python,
         } = args;
 
@@ -801,6 +805,8 @@ impl TreeSettings {
             package: tree.package,
             no_dedupe: tree.no_dedupe,
             invert: tree.invert,
+            python_version,
+            python_platform,
             python,
             resolver: ResolverSettings::combine(resolver_options(resolver, build), filesystem),
         }

crates/uv/tests/tree.rs

@@ -219,7 +219,27 @@ fn platform_dependencies() -> Result<()> {
     Resolved 8 packages in [TIME]
     "###);
 
-    // Should include `colorama`, even though it's only included on Windows.
+    // Unless `--python-platform` is set to `windows`, in which case it should be included.
+    uv_snapshot!(context.filters(), context.tree().arg("--python-platform").arg("windows"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    project v0.1.0
+    └── black v24.3.0
+        ├── click v8.1.7
+        │   └── colorama v0.4.6
+        ├── mypy-extensions v1.0.0
+        ├── packaging v24.0
+        ├── pathspec v0.12.1
+        └── platformdirs v4.2.0
+
+    ----- stderr -----
+    warning: `uv tree` is experimental and may change without warning
+    Resolved 8 packages in [TIME]
+    "###);
+
+    // When `--universal` is _not_ provided, should include `colorama`, even though it's only
+    // included on Windows.
     uv_snapshot!(context.filters(), context.tree().arg("--universal"), @r###"
     success: true
     exit_code: 0

docs/reference/cli.md

@@ -3392,6 +3392,47 @@ uv tree [OPTIONS]
 
 <li><code>symlink</code>:  Symbolically link packages from the wheel into the <code>site-packages</code> directory</li>
 </ul>
+</dd><dt><code>--python-version</code> <i>python-version</i></dt><dd><p>The Python version to use when filtering the tree (via <code>--filter</code>). For example, pass <code>--python-version 3.10</code> to display the dependencies that would be included when installing on Python 3.10</p>
+
+</dd><dt><code>--python-platform</code> <i>python-platform</i></dt><dd><p>The platform to use when filtering the tree (via <code>--filter</code>). For example, pass <code>--platform windows</code> to display the dependencies that would be included when installing on Windows.</p>
+
+<p>Represented as a &quot;target triple&quot;, a string that describes the target platform in terms of its CPU, vendor, and operating system name, like <code>x86_64-unknown-linux-gnu</code> or <code>aaarch64-apple-darwin</code>.</p>
+
+<p>Possible values:</p>
+
+<ul>
+<li><code>windows</code>:  An alias for <code>x86_64-pc-windows-msvc</code>, the default target for Windows</li>
+
+<li><code>linux</code>:  An alias for <code>x86_64-unknown-linux-gnu</code>, the default target for Linux</li>
+
+<li><code>macos</code>:  An alias for <code>aarch64-apple-darwin</code>, the default target for macOS</li>
+
+<li><code>x86_64-pc-windows-msvc</code>:  An x86 Windows target</li>
+
+<li><code>x86_64-unknown-linux-gnu</code>:  An x86 Linux target. Equivalent to <code>x86_64-manylinux_2_17</code></li>
+
+<li><code>aarch64-apple-darwin</code>:  An ARM-based macOS target, as seen on Apple Silicon devices</li>
+
+<li><code>x86_64-apple-darwin</code>:  An x86 macOS target</li>
+
+<li><code>aarch64-unknown-linux-gnu</code>:  An ARM64 Linux target. Equivalent to <code>aarch64-manylinux_2_17</code></li>
+
+<li><code>aarch64-unknown-linux-musl</code>:  An ARM64 Linux target</li>
+
+<li><code>x86_64-unknown-linux-musl</code>:  An <code>x86_64</code> Linux target</li>
+
+<li><code>x86_64-manylinux_2_17</code>:  An <code>x86_64</code> target for the <code>manylinux_2_17</code> platform</li>
+
+<li><code>x86_64-manylinux_2_28</code>:  An <code>x86_64</code> target for the <code>manylinux_2_28</code> platform</li>
+
+<li><code>x86_64-manylinux_2_31</code>:  An <code>x86_64</code> target for the <code>manylinux_2_31</code> platform</li>
+
+<li><code>aarch64-manylinux_2_17</code>:  An ARM64 target for the <code>manylinux_2_17</code> platform</li>
+
+<li><code>aarch64-manylinux_2_28</code>:  An ARM64 target for the <code>manylinux_2_28</code> platform</li>
+
+<li><code>aarch64-manylinux_2_31</code>:  An ARM64 target for the <code>manylinux_2_31</code> platform</li>
+</ul>
 </dd><dt><code>--python</code>, <code>-p</code> <i>python</i></dt><dd><p>The Python interpreter for which packages should be listed.</p>
 
 <p>By default, uv installs into the virtual environment in the current working directory or any parent directory. The <code>--python</code> option allows you to specify a different interpreter, which is intended for use in continuous integration (CI) environments or other automated workflows.</p>