Make optional

examples/unsat_root_message_no_version.rs

@@ -66,7 +66,7 @@ impl ReportFormatter<Package, Range<SemanticVersion>> for CustomReportFormatter
             External::NotRoot(package, version) => {
                 format!("we are solving dependencies of {package} {version}")
             }
-            External::NoVersions(package, set) => {
+            External::NoVersions(package, set, _) => {
                 if set == &Range::full() {
                     format!("there is no available version for {package}")
                 } else {

src/internal/incompatibility.rs

@@ -43,8 +43,8 @@ pub type IncompId<P, VS> = Id<Incompatibility<P, VS>>;
 pub enum Kind<P: Package, VS: VersionSet> {
     /// Initial incompatibility aiming at picking the root package for the first decision.
     NotRoot(P, VS::V),
-    /// There are no versions in the given range for this package. A string reason is included.
-    NoVersions(P, VS, String),
+    /// There are no versions in the given range for this package. A string reason may be included.
+    NoVersions(P, VS, Option<String>),
     /// The package is unavailable for versions in the range. A string reason is included.
     Unavailable(P, VS, String),
     /// Incompatibility coming from the dependencies of a given package.
@@ -84,7 +84,7 @@ impl<P: Package, VS: VersionSet> Incompatibility<P, VS> {
 
     /// Create an incompatibility to remember
     /// that a given set does not contain any version.
-    pub fn no_versions(package: P, term: Term<VS>, reason: String) -> Self {
+    pub fn no_versions(package: P, term: Term<VS>, reason: Option<String>) -> Self {
         let set = match &term {
             Term::Positive(r) => r.clone(),
             Term::Negative(_) => panic!("No version should have a positive term"),

src/report.rs

@@ -47,7 +47,7 @@ pub enum External<P: Package, VS: VersionSet> {
     /// Initial incompatibility aiming at picking the root package for the first decision.
     NotRoot(P, VS::V),
     /// There are no versions in the given set for this package. A string reason is included.
-    NoVersions(P, VS, String),
+    NoVersions(P, VS, Option<String>),
     /// The package is unusable in the given set. A string reason is included.
     Unavailable(P, VS, String),
     /// Incompatibility coming from the dependencies of a given package.

src/solver.rs

@@ -128,11 +128,8 @@ pub fn resolve<P: Package, VS: VersionSet, DP: DependencyProvider<P, VS>>(
         // Pick the next compatible version.
         let v = match decision {
             None => {
-                let inc = Incompatibility::no_versions(
-                    next.clone(),
-                    term_intersection.clone(),
-                    "no compatible versions".to_string(),
-                );
+                let inc =
+                    Incompatibility::no_versions(next.clone(), term_intersection.clone(), None);
                 state.add_incompatibility(inc);
                 continue;
             }