fetchClosure: Allow input addressed paths in pure mode

When explicitly requested by the caller, as suggested in the meeting
(https://github.com/NixOS/nix/pull/8090#issuecomment-1531139324)

> @edolstra: { toPath } vs { fromPath } is too implicit

I've opted for the `inputAddressed = true` requirement, because it
we did not agree on renaming the path attributes.

> @roberth: more explicit
> @edolstra: except for the direction; not immediately clear in which direction the rewriting happens

This is in fact the most explicit syntax and a bit redundant, which is
good, because that redundancy lets us deliver an error message that
reminds expression authors that CA provides a better experience to
their users.

1 files changed, 14 insertions, 2 deletions

diff --git a/tests/fetchClosure.sh b/tests/fetchClosure.sh
index 21650eb06..4b8198e94 100644
--- a/tests/fetchClosure.sh
+++ b/tests/fetchClosure.sh
@@ -35,16 +35,28 @@ clearStore
 
 if [[ "$NIX_REMOTE" != "daemon" ]]; then
 
-    # In impure mode, we can use non-CA paths.
-    [[ $(nix eval --raw --no-require-sigs --impure --expr "
+    # We can use non-CA paths when we ask explicitly.
+    [[ $(nix eval --raw --no-require-sigs --expr "
       builtins.fetchClosure {
         fromStore = \"file://$cacheDir\";
         fromPath = $nonCaPath;
+        inputAddressed = true;
       }
     ") = $nonCaPath ]]
 
     [ -e $nonCaPath ]
 
+    # .. but only if we ask explicitly.
+    expectStderr 1 nix eval --raw --no-require-sigs --expr "
+      builtins.fetchClosure {
+        fromStore = \"file://$cacheDir\";
+        fromPath = $nonCaPath;
+      }
+    " | grepQuiet -E "The .fromPath. value .* is input addressed, but input addressing was not requested. If you do intend to return an input addressed store path, add .inputAddressed = true;. to the .fetchClosure. arguments."
+
+    [ -e $nonCaPath ]
+
+
 fi
 
 # 'toPath' set to empty string should fail but print the expected path.