haskellPackages.mkDerivation: show test outputs as they happen

Currently, the test output is only printed if the test suite fails. If a
test suite gets stuck, however, and is hit with a timeout by Hydra, it
can help to have the log available when diagnosing the issue.

1 files changed, 4 insertions, 1 deletions

diff --git a/pkgs/development/haskell-modules/generic-builder.nix b/pkgs/development/haskell-modules/generic-builder.nix
index bc43c39676c8..af4d31ab2a89 100644
--- a/pkgs/development/haskell-modules/generic-builder.nix
+++ b/pkgs/development/haskell-modules/generic-builder.nix
@@ -469,7 +469,10 @@ stdenv.mkDerivation ({
   # `--test-option`, so Cabal passes it to the underlying test suite binary.
   checkPhase = ''
     runHook preCheck
-    checkFlagsArray+=(${lib.escapeShellArgs (builtins.map (opt: "--test-option=${opt}") testFlags)})
+    checkFlagsArray+=(
+      "--show-details=streaming"
+      ${lib.escapeShellArgs (builtins.map (opt: "--test-option=${opt}") testFlags)}
+    )
     ${setupCommand} test ${testTarget} $checkFlags ''${checkFlagsArray:+"''${checkFlagsArray[@]}"}
     runHook postCheck
   '';