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overlays.nix

@@ -150,6 +150,35 @@ let
     );
   };
 
+  # usage: nix-build . -A <package>.tests.mainProgram
+  overlays.withTestMainProgram = mkDerivationOverlay (
+    final: prev: prevStdenv: finalAttrs: prevAttrs: {
+      passthru = prevAttrs.passthru or { } // {
+        tests =
+          lib.optionalAttrs ((prevAttrs.meta or { }) ? mainProgram) {
+            mainProgram = final.runCommandLocal "${finalAttrs.finalPackage.name}-check-mainProgram" { } ''
+              fname=${lib.getBin finalAttrs.finalPackage}/bin/${lib.escapeShellArg finalAttrs.finalPackage.meta.mainProgram}
+              if [[ -x "$fname" ]]; then
+                echo "Found $fname"
+                touch $out
+              elif [[ -f "$fname" ]]; then
+                echo >&2 "ERROR: '$fname' is not executable!"
+                false
+              elif [[ -d "$fname" ]]; then
+                echo >&2 "ERROR: '$fname' is a directory!"
+                false
+              else
+                echo >&2 "ERROR: '$fname' not found!"
+                (set -x; find ${lib.getBin finalAttrs.finalPackage}/bin -type f)
+                false
+              fi
+            '';
+          }
+          // (prevAttrs.passthru.tests or { });
+      };
+    }
+  );
+
   # usage: nix-build . -A <package>.shellcheck
   overlays.withShellCheck = mkDerivationOverlay (
     final: prev: prevStdenv: finalAttrs: prevAttrs:
@@ -509,6 +538,7 @@ in
   overlays.srcOnly
   overlays.withInvalidateFetcherByDrvHash
   overlays.withUnpacked
+  overlays.withTestMainProgram
   overlays.withShellCheck
   # overlays.withCudaOrRocm # WIP
   overlays.withCcache # WIP