dml: Infer not-available relation scalar fields as empty

...instead of crashing. This is bad relation logic in dml that can't
really be fixed. The long term solution is to switch to rendering to the
AST.

closes prisma/prisma#11013

libs/datamodel/connectors/datamodel-connector/src/walker_ext_traits.rs

@@ -94,17 +94,16 @@ impl<'ast> InlineRelationWalkerExt<'ast> for InlineRelationWalker<'ast, '_> {
     fn constraint_name(self, connector: &dyn Connector) -> Cow<'ast, str> {
         self.foreign_key_name().map(Cow::Borrowed).unwrap_or_else(|| {
             let model_database_name = self.referencing_model().final_database_name();
-            match self.referencing_fields() {
-                ReferencingFields::Concrete(fields) => {
-                    let field_names: Vec<&str> = fields.map(|f| f.database_name()).collect();
-                    ConstraintNames::foreign_key_constraint_name(model_database_name, &field_names, connector).into()
-                }
+            let field_names: Vec<&str> = match self.referencing_fields() {
+                ReferencingFields::Concrete(fields) => fields.map(|f| f.database_name()).collect(),
                 ReferencingFields::Inferred(fields) => {
-                    let field_names: Vec<&str> = fields.iter().map(|f| f.name.as_str()).collect();
-                    ConstraintNames::foreign_key_constraint_name(model_database_name, &field_names, connector).into()
+                    let field_names: Vec<_> = fields.iter().map(|f| f.name.as_str()).collect();
+                    return ConstraintNames::foreign_key_constraint_name(model_database_name, &field_names, connector)
+                        .into();
                 }
-                ReferencingFields::NA => unreachable!(),
-            }
+                ReferencingFields::NA => Vec::new(),
+            };
+            ConstraintNames::foreign_key_constraint_name(model_database_name, &field_names, connector).into()
         })
     }
 }