Add support for inputs.self fetching attrs

default.nix

@@ -133,7 +133,18 @@ let
         src:
         if isGit then
           let
-            res = builtins.fetchGit src;
+            # Peek at flake.nix to check for submodule settings, mirroring
+            # what Nix does (lazy fetch of flake.nix before full fetch).
+            flake = import (src + "/flake.nix");
+            submodules = flake.inputs.self.submodules or false;
+            lfs = flake.inputs.self.lfs or false;
+            res = builtins.fetchGit (
+              {
+                url = src;
+              }
+              // (if submodules then { inherit submodules; } else { })
+              // (if lfs then { inherit lfs; } else { })
+            );
           in
           if res.rev == "0000000000000000000000000000000000000000" then
             removeAttrs res [

dev/config.nix

@@ -73,6 +73,96 @@
 
               echo "All tests passed!"
             '';
+
+        # Integration test: submodule content is accessible through flake-compat
+        submodules =
+          pkgs.runCommand "submodule-test"
+            {
+              nativeBuildInputs = [
+                pkgs.git
+                pkgs.nix
+              ];
+            }
+            ''
+              export HOME=$TMPDIR
+              git config --global user.email "test@test"
+              git config --global user.name "test"
+              git config --global protocol.file.allow always
+
+              # Create a repo to use as a submodule
+              mkdir -p $TMPDIR/sub
+              cd $TMPDIR/sub
+              git init
+              echo "hello from submodule" > sub-file.txt
+              git add . && git commit -m "init sub"
+
+              # Invoke flake-compat using an alternative store so this
+              # works in sandboxed builds on both Linux and darwin.
+              export NIX_STORE_DIR=$TMPDIR/store
+              export NIX_STATE_DIR=$TMPDIR/state
+
+              # Without inputs.self.submodules, submodule content should
+              # not be accessible.
+              mkdir -p $TMPDIR/main-no-sub
+              cd $TMPDIR/main-no-sub
+              git init
+              git submodule add $TMPDIR/sub sub
+              cat > flake.nix << 'EOF'
+              {
+                outputs = { self, ... }: {
+                  subFileExists = builtins.pathExists (self + "/sub/sub-file.txt");
+                };
+              }
+              EOF
+              git add . && git commit -m "init main-no-sub"
+
+              result=$(nix-instantiate --eval --strict --expr '
+                let
+                  r = import ${../.} { src = '"$TMPDIR/main-no-sub"'; };
+                in
+                r.defaultNix.subFileExists
+              ')
+
+              if [ "$result" = "false" ]; then
+                echo "PASS: submodule content not accessible without flag"
+              else
+                echo "FAIL: expected false, got: $result"
+                exit 1
+              fi
+
+              # With inputs.self.submodules = true, submodule content
+              # should be accessible.
+              mkdir -p $TMPDIR/main
+              cd $TMPDIR/main
+              git init
+              git submodule add $TMPDIR/sub sub
+              cat > flake.nix << 'EOF'
+              {
+                inputs.self.submodules = true;
+                outputs = { self, ... }: {
+                  subFileExists = builtins.pathExists (self + "/sub/sub-file.txt");
+                  subFileContent = builtins.readFile (self + "/sub/sub-file.txt");
+                };
+              }
+              EOF
+              git add . && git commit -m "init main"
+
+              result=$(nix-instantiate --eval --strict --expr '
+                let
+                  r = import ${../.} { src = '"$TMPDIR/main"'; };
+                in
+                r.defaultNix.subFileContent
+              ')
+
+              if [ "$result" = '"hello from submodule\n"' ]; then
+                echo "PASS: submodule content accessible"
+              else
+                echo "FAIL: expected submodule content, got: $result"
+                exit 1
+              fi
+
+              touch $out
+            '';
       };
 
       # Development shell