Rebase: Uninstall existing non-editable versions when installing editable requirements bug (#682)

Separate branch for rebasing #677 onto main because i don't trust the
rebase enough to force push.

Closes #677.

---

If you install `black` from PyPI, then `-e ../black`, we need to
uninstall the existing `black`. This sounds simple, but that in turn
requires that we _know_ `-e ../black` maps to the package `black`, so
that we can mark it for uninstallation in the install plan. This, in
turn, means that we need to build editable dependencies prior to the
install plan.

This is just a bunch of reorganization to fix that specific bug
(installing multiple versions of `black` if you run through the above
workflow): we now run through the list of editables upfront, mark those
that are already installed, build those that aren't, and then ensure
that `InstallPlan` correctly removes those that need to be removed, etc.

Closes #676.

Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>

crates/puffin-dispatch/src/lib.rs

@@ -16,7 +16,7 @@ use platform_tags::Tags;
 use puffin_build::{SourceBuild, SourceBuildContext};
 use puffin_cache::Cache;
 use puffin_client::RegistryClient;
-use puffin_installer::{Downloader, EditableMode, InstallPlan, Installer, Reinstall};
+use puffin_installer::{Downloader, InstallPlan, Installer, Reinstall, SitePackages};
 use puffin_interpreter::{Interpreter, Virtualenv};
 use puffin_resolver::{Manifest, ResolutionOptions, Resolver};
 use puffin_traits::{BuildContext, BuildKind, OnceMap};
@@ -131,23 +131,27 @@ impl BuildContext for BuildDispatch {
                 venv.root().display(),
             );
 
+            // Determine the current environment markers.
             let tags = Tags::from_interpreter(&self.interpreter)?;
 
+            // Determine the set of installed packages.
+            let site_packages =
+                SitePackages::from_executable(venv).context("Failed to list installed packages")?;
+
             let InstallPlan {
                 local,
                 remote,
                 reinstalls,
                 extraneous,
-                editables: _,
             } = InstallPlan::from_requirements(
                 &resolution.requirements(),
-                &[],
+                Vec::new(),
+                site_packages,
                 &Reinstall::None,
                 &self.index_urls,
                 self.cache(),
                 venv,
                 &tags,
-                EditableMode::default(),
             )?;
 
             // Resolve any registry-based requirements.