agdaPackages: Build reverse dependencies on test

pkgs/build-support/agda/default.nix

@@ -77,7 +77,12 @@ let
           find -not \( -path ${everythingFile} -or -path ${lib.interfaceFile everythingFile} \) -and \( ${concatMapStringsSep " -or " (p: "-name '*.${p}'") (extensions ++ extraExtensions)} \) -exec cp -p --parents -t "$out" {} +
           runHook postInstall
         '';
+
         meta = if meta.broken or false then meta // { hydraPlatforms = lib.platforms.none; } else meta;
+
+        # Retrieve all packages from the finished package set that have the current package as a dependency and build them
+        passthru.tests = with builtins;
+          lib.filterAttrs (name: pkg: self.lib.isUnbrokenAgdaPackage pkg && elem pname (map (pkg: pkg.pname) pkg.buildInputs)) self;
       };
 in
 {

pkgs/build-support/agda/lib.nix

@@ -7,4 +7,9 @@
   * interfaceFile "src/Everything.lagda.tex" == "src/Everything.agdai"
   */
   interfaceFile = agdaFile: lib.head (builtins.match ''(.*\.)l?agda(\.(md|org|rst|tex))?'' agdaFile) + "agdai";
+
+  /* Takes an arbitrary derivation and says whether it is an agda library package
+  *  that is not marked as broken.
+  */
+  isUnbrokenAgdaPackage = pkg: pkg.isAgdaDerivation or false && !pkg.meta.broken;
 }