2 files changed, 27 insertions, 0 deletions
diff --git a/nix/utils/default.nix b/nix/utils/default.nix
index 0c6c88fafd5a..a29f346519b8 100644
--- a/nix/utils/default.nix
+++ b/nix/utils/default.nix
@@ -43,6 +43,21 @@ let
     else builtins.throw "Don't know how to get (base)name of "
       + lib.generators.toPretty { } p;
 
+  /* Retrieves the drvPath attribute from a given derivation, but ensures that
+     the resulting string only depends on the `.drv` file in the nix store and
+     not on its realised outputs as well.
+
+     Type: drv -> string
+  */
+  onlyDrvPath = drv:
+    let
+      inherit (drv) drvPath;
+      unsafeDrvPath = builtins.unsafeDiscardStringContext drvPath;
+    in
+    builtins.appendContext unsafeDrvPath {
+      ${unsafeDrvPath} = { path = true; };
+    };
+
   /* Query the type of a path exposing the same information as would be by
      `builtins.readDir`, but for a single, specific target path.
 
@@ -152,6 +167,7 @@ in
 {
   inherit
     storePathName
+    onlyDrvPath
     pathType
     isDirectory
     isRegularFile
diff --git a/nix/utils/tests/default.nix b/nix/utils/tests/default.nix
index 344a1771d7d9..d5159a8433b4 100644
--- a/nix/utils/tests/default.nix
+++ b/nix/utils/tests/default.nix
@@ -15,6 +15,7 @@ let
     isSymlink
     pathType
     storePathName
+    onlyDrvPath
     ;
 
   assertUtilsPred = msg: act: exp: [
@@ -91,9 +92,19 @@ let
       (storePathName cleanedSource)
       cleanedSource.name)
   ];
+
+  onlyDrvPathTests = it "correctly updates the string context of drvPath" [
+    (assertEq "onlyDrvPath only produces path dependencies"
+      (builtins.all
+        (dep: dep.path or false)
+        (builtins.attrValues
+          (builtins.getContext (onlyDrvPath depot.tools.cheddar))))
+      true)
+  ];
 in
 
 runTestsuite "nix.utils" [
   pathPredicates
   storePathNameTests
+  onlyDrvPathTests
 ]