Reuse build (virtual) environments across resolution and installation (#14338)

## Summary

The basic idea here is that we can (should) reuse a build environment
across resolution (`prepare_metadata_for_build_wheel`) and installation.
This also happens to solve the build-PyTorch-from-source problem, since
we use a consistent build environment between the invocations.

Since `SourceDistributionBuilder` is stateless, we instead store the
builds on `BuildContext`, and we key them by various properties: the
underlying interpreter, the configuration settings, etc. This just
ensures that if we build the same package twice within a process, we
don't accidentally reuse an incompatible build (virtual) environment.
(Note that still drop build environments at the end of the command, and
don't attempt to reuse them across processes.)

Closes #14269.

crates/uv-types/Cargo.toml

@@ -31,9 +31,8 @@ uv-redacted = { workspace = true }
 uv-workspace = { workspace = true }
 
 anyhow = { workspace = true }
-boxcar = { workspace = true }
+dashmap = { workspace = true }
 rustc-hash = { workspace = true }
-tempfile = { workspace = true }
 thiserror = { workspace = true }
 
 [features]

crates/uv-types/src/builds.rs

@@ -1,5 +1,9 @@
+use std::path::Path;
 use std::sync::Arc;
-use tempfile::TempDir;
+
+use dashmap::DashMap;
+
+use uv_configuration::{BuildKind, SourceStrategy};
 use uv_pep508::PackageName;
 use uv_python::PythonEnvironment;
 
@@ -40,13 +44,41 @@ impl BuildIsolation<'_> {
     }
 }
 
-/// An arena of temporary directories used for builds.
-#[derive(Default, Debug, Clone)]
-pub struct BuildArena(Arc<boxcar::Vec<TempDir>>);
+/// A key for the build cache, which includes the interpreter, source root, subdirectory, source
+/// strategy, and build kind.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct BuildKey {
+    pub base_python: Box<Path>,
+    pub source_root: Box<Path>,
+    pub subdirectory: Option<Box<Path>>,
+    pub source_strategy: SourceStrategy,
+    pub build_kind: BuildKind,
+}
 
-impl BuildArena {
-    /// Push a new temporary directory into the arena.
-    pub fn push(&self, temp_dir: TempDir) {
-        self.0.push(temp_dir);
+/// An arena of in-process builds.
+#[derive(Debug)]
+pub struct BuildArena<T>(Arc<DashMap<BuildKey, T>>);
+
+impl<T> Default for BuildArena<T> {
+    fn default() -> Self {
+        Self(Arc::new(DashMap::new()))
+    }
+}
+
+impl<T> Clone for BuildArena<T> {
+    fn clone(&self) -> Self {
+        Self(self.0.clone())
+    }
+}
+
+impl<T> BuildArena<T> {
+    /// Insert a build entry into the arena.
+    pub fn insert(&self, key: BuildKey, value: T) {
+        self.0.insert(key, value);
+    }
+
+    /// Remove a build entry from the arena.
+    pub fn remove(&self, key: &BuildKey) -> Option<T> {
+        self.0.remove(key).map(|entry| entry.1)
     }
 }

crates/uv-types/src/traits.rs

@@ -5,9 +5,7 @@ use std::path::{Path, PathBuf};
 
 use anyhow::Result;
 use rustc_hash::FxHashSet;
-use tempfile::TempDir;
 
-use crate::BuildArena;
 use uv_cache::Cache;
 use uv_configuration::{BuildKind, BuildOptions, BuildOutput, ConfigSettings, SourceStrategy};
 use uv_distribution_filename::DistFilename;
@@ -20,6 +18,8 @@ use uv_pep508::PackageName;
 use uv_python::{Interpreter, PythonEnvironment};
 use uv_workspace::WorkspaceCache;
 
+use crate::BuildArena;
+
 ///  Avoids cyclic crate dependencies between resolver, installer and builder.
 ///
 /// To resolve the dependencies of a packages, we may need to build one or more source
@@ -70,7 +70,7 @@ pub trait BuildContext {
     fn git(&self) -> &GitResolver;
 
     /// Return a reference to the build arena.
-    fn build_arena(&self) -> &BuildArena;
+    fn build_arena(&self) -> &BuildArena<Self::SourceDistBuilder>;
 
     /// Return a reference to the discovered registry capabilities.
     fn capabilities(&self) -> &IndexCapabilities;
@@ -153,9 +153,6 @@ pub trait BuildContext {
 /// You can either call only `wheel()` to build the wheel directly, call only `metadata()` to get
 /// the metadata without performing the actual or first call `metadata()` and then `wheel()`.
 pub trait SourceBuildTrait {
-    /// Return the temporary build directory.
-    fn into_build_dir(self) -> TempDir;
-
     /// A wrapper for `uv_build::SourceBuild::get_metadata_without_build`.
     ///
     /// For PEP 517 builds, this calls `prepare_metadata_for_build_wheel`
@@ -188,13 +185,13 @@ pub trait InstalledPackagesProvider: Clone + Send + Sync + 'static {
 pub struct EmptyInstalledPackages;
 
 impl InstalledPackagesProvider for EmptyInstalledPackages {
-    fn get_packages(&self, _name: &PackageName) -> Vec<&InstalledDist> {
-        Vec::new()
-    }
-
     fn iter(&self) -> impl Iterator<Item = &InstalledDist> {
         std::iter::empty()
     }
+
+    fn get_packages(&self, _name: &PackageName) -> Vec<&InstalledDist> {
+        Vec::new()
+    }
 }
 
 /// [`anyhow::Error`]-like wrapper type for [`BuildDispatch`] method return values, that also makes