flakes: Differentiate self.outPath and self.sourceInfo.outPath

It would be incorrect to say that the `sourceInfo` has an `outPath`
that isn't the root. `sourceInfo` is about the root, whereas only
the flake may not be about the root. Thanks Eelco for pointing that
out.

src/libexpr/flake/call-flake.nix

@@ -9,16 +9,14 @@ let
       (key: node:
         let
 
-          rawSourceInfo =
+          sourceInfo =
             if key == lockFile.root
             then rootSrc
             else fetchTree (node.info or {} // removeAttrs node.locked ["dir"]);
 
           subdir = if key == lockFile.root then rootSubdir else node.locked.dir or "";
 
-          outPath = rawSourceInfo + ((if subdir == "" then "" else "/") + subdir);
+          outPath = sourceInfo + ((if subdir == "" then "" else "/") + subdir);
-
-          sourceInfo = rawSourceInfo // { inherit outPath; };
 
           flake = import (outPath + "/flake.nix");
 
@@ -47,7 +45,21 @@ let
 
           outputs = flake.outputs (inputs // { self = result; });
 
-          result = outputs // sourceInfo // { inherit inputs; inherit outputs; inherit sourceInfo; _type = "flake"; };
+          result =
+            outputs
+            # We add the sourceInfo attribute for its metadata, as they are
+            # relevant metadata for the flake. However, the outPath of the
+            # sourceInfo does not necessarily match the outPath of the flake,
+            # as the flake may be in a subdirectory of a source.
+            # This is shadowed in the next //
+            // sourceInfo
+            // {
+              # This shadows the sourceInfo.outPath
+              inherit outPath;
+
+              inherit inputs; inherit outputs; inherit sourceInfo; _type = "flake";
+            };
+
         in
           if node.flake or true then
             assert builtins.isFunction flake.outputs;

tests/flakes/inputs.sh

@@ -46,6 +46,7 @@ test_git_subdir_self_path() {
       default =
         assert builtins.readFile ./message == "all good\n";
         assert builtins.readFile (inputs.self + "/message") == "all good\n";
+        assert inputs.self.outPath == inputs.self.sourceInfo.outPath + "/b-low";
         import ./simple.nix;
     };
   };