Avoid shallow clone of notmuch

Shallow clones are the default in Nix 2.23, but the Git server for
notmuch does not seem to allow shallow clones of specific revisions.

Disable them, which should make no difference for Nix < 2.23.

This is mostly to (hopefully) unblock CI. If this fixes it, I should
investigate if it is possible for Nix to fall back to a full clone in
this scenario.

default.nix

@@ -59,7 +59,7 @@
 }:
 let
   inherit (lib) optionalAttrs optionalString;
-  inherit (import ./fetch-overrides.nix) extraPins extraUrls;
+  inherit (import ./fetch-overrides.nix) extraPins extraUrls forceDeepClone;
 
   # Step 1: determine which Emacs packages to pull in.
   #
@@ -260,7 +260,8 @@ let
 
             }
             // optionalAttrs (p ? recipe.branch) { ref = p.recipe.branch; }
-            // optionalAttrs (p ? recipe.depth) { shallow = p.recipe.depth == 1; };
+            // optionalAttrs (p ? recipe.depth) { shallow = p.recipe.depth == 1; }
+            // optionalAttrs (forceDeepClone.${url} or false) { shallow = false; };
             src =
               if experimentalFetchTree
               then builtins.fetchTree (

fetch-overrides.nix

@@ -54,4 +54,9 @@
     # CI should fail again the next time Doom updates magit, so this won't go stale.
     git-commit = "ea0f07e54967197ac0b072a69ba314314a4080c1";
   };
+
+  # Repositories for which to force `shallow = false`.
+  forceDeepClone = {
+      "https://git.notmuchmail.org/git/notmuch" = true;
+  };
 }