Allow relative paths and environment variables in all editable representations (#1000)

## Summary

I don't know if this is actually a good change, but it tries to make the
editable install experience more consistent. Specifically, we now
support...

```
# Use a relative path with a `file://` prefix.
# Prior to this PR, we supported `file:../foo`, but not `file://../foo`, which felt inconsistent.
-e file://../foo

# Use environment variables with paths, not just URLs.
# Prior to this PR, we supported `file://${PROJECT_ROOT}/../foo`, but not the below.
-e ${PROJECT_ROOT}/../foo
```

Importantly, `-e file://../foo` is actually not supported by pip... `-e
file:../foo` _is_ supported though. We support both, as of this PR. Open
to feedback.

crates/distribution-types/src/editable.rs

@@ -1,45 +1,40 @@
 use std::borrow::Cow;
-use std::path::{Path, PathBuf};
+use std::path::PathBuf;
 
 use url::Url;
 
 use pep508_rs::VerbatimUrl;
-use requirements_txt::EditableRequirement;
 
 use crate::Verbatim;
 
 #[derive(Debug, Clone)]
 pub struct LocalEditable {
-    pub requirement: EditableRequirement,
+    /// The underlying [`EditableRequirement`] from the `requirements.txt` file.
+    pub url: VerbatimUrl,
     /// Either the path to the editable or its checkout.
     pub path: PathBuf,
 }
 
 impl LocalEditable {
-    /// Return the [`VerbatimUrl`] of the editable.
+    /// Return the editable as a [`Url`].
     pub fn url(&self) -> &VerbatimUrl {
-        self.requirement.url()
-    }
-
-    /// Return the underlying [`Url`] of the editable.
-    pub fn raw(&self) -> &Url {
-        self.requirement.raw()
+        &self.url
     }
 
     /// Return the resolved path to the editable.
-    pub fn path(&self) -> &Path {
-        &self.path
+    pub fn raw(&self) -> &Url {
+        self.url.raw()
     }
 }
 
 impl Verbatim for LocalEditable {
     fn verbatim(&self) -> Cow<'_, str> {
-        self.url().verbatim()
+        self.url.verbatim()
     }
 }
 
 impl std::fmt::Display for LocalEditable {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        self.requirement.fmt(f)
+        std::fmt::Display::fmt(&self.url, f)
     }
 }

crates/distribution-types/src/lib.rs

@@ -43,7 +43,6 @@ use distribution_filename::{DistFilename, SourceDistFilename, WheelFilename};
 use pep440_rs::Version;
 use pep508_rs::VerbatimUrl;
 use puffin_normalize::PackageName;
-use requirements_txt::EditableRequirement;
 
 pub use crate::any::*;
 pub use crate::cached::*;
@@ -272,24 +271,13 @@ impl Dist {
 
     /// Create a [`Dist`] for a local editable distribution.
     pub fn from_editable(name: PackageName, editable: LocalEditable) -> Result<Self, Error> {
-        match editable.requirement {
-            EditableRequirement::Path { url, path } => {
-                Ok(Self::Source(SourceDist::Path(PathSourceDist {
-                    name,
-                    url,
-                    path,
-                    editable: true,
-                })))
-            }
-            EditableRequirement::Url { url, path } => {
-                Ok(Self::Source(SourceDist::Path(PathSourceDist {
-                    name,
-                    path,
-                    url,
-                    editable: true,
-                })))
-            }
-        }
+        let LocalEditable { url, path } = editable;
+        Ok(Self::Source(SourceDist::Path(PathSourceDist {
+            name,
+            url,
+            path,
+            editable: true,
+        })))
     }
 
     /// Returns the [`File`] instance, if this dist is from a registry with simple json api support
@@ -353,11 +341,7 @@ impl SourceDist {
                 url: VerbatimUrl::unknown(url),
                 ..dist
             }),
-            SourceDist::Path(dist) => SourceDist::Path(PathSourceDist {
-                url: VerbatimUrl::unknown(url),
-                ..dist
-            }),
-            dist @ SourceDist::Registry(_) => dist,
+            dist => dist,
         }
     }
 }