Collapse redundant dependency clauses enumerating available versions (#…

…6160)

In #5046, we show the tautological
proof:

```
  ╰─▶ Because colabfold[alphafold]==1.5.5 depends on jax>=0.4.20 and only the following versions of jax are available:
          jax<=0.4.20
          jax==0.4.21
          jax==0.4.22
          jax==0.4.23
          jax==0.4.24
          jax==0.4.25
          jax==0.4.26
          jax==0.4.27
          jax==0.4.28
          jax==0.4.29
          jax==0.4.30
          jax==0.4.31
      we can conclude that colabfold[alphafold]==1.5.5 depends on jax>=0.4.20.
      And because jax>=0.4.20 depends on numpy>=1.26.0, we can conclude that colabfold[alphafold]==1.5.5 depends on numpy>=1.26.0.
      (1)
```

This is a part of the error tree because the statement
`colabfold[alphafold]==1.5.5 depends on jax>=0.4.20` is actually a
simplification of `colabfold[alphafold]==1.5.5 depends on
jax>=0.4.20,<0.5.0` and the no versions clause is a proof of that
simplification.

Without simplification, the clause looks like:

```
  ╰─▶ Because colabfold[alphafold]==1.5.5 depends on jax>=0.4.20,<0.5.0 and only the following versions of jax are available:
          jax<=0.4.20
          jax==0.4.21
          jax==0.4.22
          jax==0.4.23
          jax==0.4.24
          jax==0.4.25
          jax==0.4.26
          jax==0.4.27
          jax==0.4.28
          jax==0.4.29
          jax==0.4.30
          jax==0.4.31
      we can conclude that colabfold[alphafold]==1.5.5 depends on one of:
          jax==0.4.20
          jax==0.4.21
          jax==0.4.22
          jax==0.4.23
          jax==0.4.24
          jax==0.4.25
          jax==0.4.26
          jax==0.4.27
          jax==0.4.28
          jax==0.4.29
          jax==0.4.30
          jax==0.4.31
      And because jax>=0.4.20 depends on numpy>=1.26.0, we can conclude that colabfold[alphafold]==1.5.5 depends on numpy>=1.26.0.
```

I don't think we have a great way to avoid performing the simplification
of the range conditionally and it makes the error simpler to just jump
straight to `colabfold[alphafold]==1.5.5 depends on jax>=0.4.20`.

The derivation for this clause looks like:

```
          jax==0.4.20 | ==0.4.21 | ==0.4.22 | ==0.4.23 | ==0.4.24 | ==0.4.25 | ==0.4.26 | ==0.4.27 | ==0.4.28 | ==0.4.29 | ==0.4.30 | ==0.4.31 depends on numpy>=1.26.0
            no versions of jax>0.4.20, <0.4.21 | >0.4.21, <0.4.22 | >0.4.22, <0.4.23 | >0.4.23, <0.4.24 | >0.4.24, <0.4.25 | >0.4.25, <0.4.26 | >0.4.26, <0.4.27 | >0.4.27, <0.4.28 | >0.4.28, <0.4.29 | >0.4.29, <0.4.30 | >0.4.30, <0.4.31 | >0.4.31, <0.5.0
            colabfold[alphafold]==1.5.5 depends on jax>=0.4.20, <0.5.0
```

So it looks like we can take trees of this form and drop the "no
versions" clause _if_ the ranges are compatible[*]. See [this
comment](#6160 (comment))
for a simpler explanation.

With this pull request, the clause simplifies to

```
╰─▶ Because colabfold[alphafold]==1.5.5 depends on jax>=0.4.20 and jax>=0.4.20 depends on numpy>=1.26.0,
     we can conclude that colabfold[alphafold]==1.5.5 depends on numpy>=1.26.0. (1)
```

Unfortunately, this doesn't change any snapshots in our test suite so
I'm uncertain if the strategy generalizes. In some incorrect iterations
of this logic, the snapshots did reveal my mistakes.

[*] "if the ranges are compatible" includes a bit of hand-waving. I'm
not 100% sure if I've chosen the correct range heuristic here.

crates/uv-resolver/src/error.rs

@@ -237,6 +237,7 @@ impl std::fmt::Display for NoSolutionError {
         }
 
         collapse_unavailable_versions(&mut tree);
+        collapse_redundant_depends_on_no_versions(&mut tree);
 
         if should_display_tree {
             display_tree(&tree, "Resolver derivation tree after reduction");
@@ -364,6 +365,107 @@ fn collapse_no_versions_of_workspace_members(
     }
 }
 
+/// Given a [`DerivationTree`], collapse `NoVersions` incompatibilities that are redundant children
+/// of a dependency. For example, if we have a tree like:
+///     
+///     A>=1,<2 depends on B
+///         A has no versions >1,<2
+///         C depends on A>=1,<2
+///
+/// We can simplify this to `C depends A>=1 and A>=1 depends on B so C depends on B` without
+/// explaining that there are no other versions of A. This is dependent on range of A in "A depends
+/// on" being a subset of range of A in "depends on A". For example, in a tree like:
+///
+///     A>=1,<3 depends on B
+///         A has no versions >2,<3
+///         C depends on A>=2,<3
+///
+/// We cannot say `C depends on A>=2 and A>=1 depends on B so C depends on B` because there is a
+/// hole in the range — `A>=1,<3` is not a subset of `A>=2,<3`.
+fn collapse_redundant_depends_on_no_versions(
+    tree: &mut DerivationTree<PubGrubPackage, Range<Version>, UnavailableReason>,
+) {
+    match tree {
+        DerivationTree::External(_) => {}
+        DerivationTree::Derived(derived) => {
+            // If one node is a dependency incompatibility...
+            match (
+                Arc::make_mut(&mut derived.cause1),
+                Arc::make_mut(&mut derived.cause2),
+            ) {
+                (
+                    DerivationTree::External(External::FromDependencyOf(package, versions, _, _)),
+                    ref mut other,
+                )
+                | (
+                    ref mut other,
+                    DerivationTree::External(External::FromDependencyOf(package, versions, _, _)),
+                ) => {
+                    // Check if the other node is the relevant form of subtree...
+                    collapse_redundant_depends_on_no_versions_inner(other, package, versions);
+                }
+                // If not, just recurse
+                _ => {
+                    collapse_redundant_depends_on_no_versions(Arc::make_mut(&mut derived.cause1));
+                    collapse_redundant_depends_on_no_versions(Arc::make_mut(&mut derived.cause2));
+                }
+            }
+        }
+    }
+}
+
+/// Helper for [`collapse_redundant_depends_on_no_versions`].
+fn collapse_redundant_depends_on_no_versions_inner(
+    tree: &mut DerivationTree<PubGrubPackage, Range<Version>, UnavailableReason>,
+    package: &PubGrubPackage,
+    versions: &Range<Version>,
+) {
+    match tree {
+        DerivationTree::External(_) => {}
+        DerivationTree::Derived(derived) => {
+            // If we're a subtree with dependency and no versions incompatibilities...
+            match (&*derived.cause1, &*derived.cause2) {
+                (
+                    DerivationTree::External(External::NoVersions(no_versions_package, _)),
+                    dependency_clause @ DerivationTree::External(External::FromDependencyOf(
+                        _,
+                        _,
+                        dependency_package,
+                        dependency_versions,
+                    )),
+                )
+                | (
+                    dependency_clause @ DerivationTree::External(External::FromDependencyOf(
+                        _,
+                        _,
+                        dependency_package,
+                        dependency_versions,
+                    )),
+                    DerivationTree::External(External::NoVersions(no_versions_package, _)),
+                )
+                // And these incompatibilities (and the parent incompatibility) all are referring to
+                // the same package... 
+                if no_versions_package == dependency_package
+                    && package == no_versions_package
+                // And parent dependency versions are a subset of the versions in this tree...
+                    && versions.subset_of(dependency_versions) =>
+                {
+                    // Enumerating the available versions will be redundant and we can drop the no
+                    // versions clause entirely in favor of the dependency clause.
+                    *tree = dependency_clause.clone();
+
+                    // Note we are at a leaf of the tree so there's no further recursion to do
+                }
+                // If not, just recurse
+                _ => {
+                    collapse_redundant_depends_on_no_versions(Arc::make_mut(&mut derived.cause1));
+                    collapse_redundant_depends_on_no_versions(Arc::make_mut(&mut derived.cause2));
+                }
+            }
+        }
+    }
+}
+
 /// Given a [`DerivationTree`], collapse incompatibilities for versions of a package that are
 /// unavailable for the same reason to avoid repeating the same message for every unavailable
 /// version.