Fix the printing of the installables on nix profile install conflict

- If the element comes from a flake, print the full flakeref (with the
  fragment part) and not just the reference to the flake itself
- If the element doesn't come from a flake, print its store path(s)

This is a bit too verbose, but has the advantages of being correct (and
not crashing), so it's strictly better than the previous situation

Fix https://github.com/NixOS/nix/issues/8284

src/nix/profile.cc

@@ -31,6 +31,11 @@ struct ProfileElementSource
             std::tuple(originalRef.to_string(), attrPath, outputs) <
             std::tuple(other.originalRef.to_string(), other.attrPath, other.outputs);
     }
+
+    std::string to_string() const
+    {
+        return fmt("%s#%s%s", originalRef, attrPath, outputs.to_string());
+    }
 };
 
 const int defaultPriority = 5;
@@ -45,13 +50,27 @@ struct ProfileElement
     std::string identifier() const
     {
         if (source)
-            return fmt("%s#%s%s", source->originalRef, source->attrPath, source->outputs.to_string());
+            return source->to_string();
         StringSet names;
         for (auto & path : storePaths)
             names.insert(DrvName(path.name()).name);
         return concatStringsSep(", ", names);
     }
 
+    /**
+     * Return a string representing an installable corresponding to the current
+     * element, either a flakeref or a plain store path
+     */
+    std::set<std::string> toInstallables(Store & store)
+    {
+        if (source)
+            return {source->to_string()};
+        StringSet rawPaths;
+        for (auto & path : storePaths)
+            rawPaths.insert(store.printStorePath(path));
+        return rawPaths;
+    }
+
     std::string versions() const
     {
         StringSet versions;
@@ -363,10 +382,10 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
                     auto profileElement = *it;
                     for (auto & storePath : profileElement.storePaths) {
                         if (conflictError.fileA.starts_with(store->printStorePath(storePath))) {
-                            return std::pair(conflictError.fileA, profileElement.source->originalRef);
+                            return std::pair(conflictError.fileA, profileElement.toInstallables(*store));
                         }
                         if (conflictError.fileB.starts_with(store->printStorePath(storePath))) {
-                            return std::pair(conflictError.fileB, profileElement.source->originalRef);
+                            return std::pair(conflictError.fileB, profileElement.toInstallables(*store));
                         }
                     }
                 }
@@ -375,9 +394,9 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
             // There are 2 conflicting files. We need to find out which one is from the already installed package and
             // which one is the package that is the new package that is being installed.
             // The first matching package is the one that was already installed (original).
-            auto [originalConflictingFilePath, originalConflictingRef] = findRefByFilePath(manifest.elements.begin(), manifest.elements.end());
+            auto [originalConflictingFilePath, originalConflictingRefs] = findRefByFilePath(manifest.elements.begin(), manifest.elements.end());
             // The last matching package is the one that was going to be installed (new).
-            auto [newConflictingFilePath, newConflictingRef] = findRefByFilePath(manifest.elements.rbegin(), manifest.elements.rend());
+            auto [newConflictingFilePath, newConflictingRefs] = findRefByFilePath(manifest.elements.rbegin(), manifest.elements.rend());
 
             throw Error(
                 "An existing package already provides the following file:\n"
@@ -403,8 +422,8 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
                 "  nix profile install %4% --priority %7%\n",
                 originalConflictingFilePath,
                 newConflictingFilePath,
-                originalConflictingRef.to_string(),
+                concatStringsSep(" ", originalConflictingRefs),
-                newConflictingRef.to_string(),
+                concatStringsSep(" ", newConflictingRefs),
                 conflictError.priority,
                 conflictError.priority - 1,
                 conflictError.priority + 1

tests/nix-profile.sh

@@ -157,17 +157,17 @@ error: An existing package already provides the following file:
 
        To remove the existing package:
 
-         nix profile remove path:${flake1Dir}
+         nix profile remove path:${flake1Dir}#packages.${system}.default
 
        The new package can also be installed next to the existing one by assigning a different priority.
        The conflicting packages have a priority of 5.
        To prioritise the new package:
 
-         nix profile install path:${flake2Dir} --priority 4
+         nix profile install path:${flake2Dir}#packages.${system}.default --priority 4
 
        To prioritise the existing package:
 
-         nix profile install path:${flake2Dir} --priority 6
+         nix profile install path:${flake2Dir}#packages.${system}.default --priority 6
 EOF
 )
 [[ $($TEST_HOME/.nix-profile/bin/hello) = "Hello World" ]]
@@ -177,3 +177,10 @@ nix profile install $flake2Dir --priority 0
 [[ $($TEST_HOME/.nix-profile/bin/hello) = "Hello World2" ]]
 # nix profile install $flake1Dir --priority 100
 # [[ $($TEST_HOME/.nix-profile/bin/hello) = "Hello World" ]]
+
+# Ensure that conflicts are handled properly even when the installables aren't
+# flake references.
+# Regression test for https://github.com/NixOS/nix/issues/8284
+clearProfiles
+nix profile install $(nix build $flake1Dir --no-link --print-out-paths)
+expect 1 nix profile install --impure --expr "(builtins.getFlake ''$flake2Dir'').packages.$system.default"