From 261f674a2531eb4d4a5473a0179ec792dbd79ca2 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Tue, 4 Nov 2025 23:14:21 +0100
Subject: [PATCH] tests: Suppress environment-dependent warnings

... via _NIX_TEST_NO_ENVIRONMENT_WARNINGS

This environment variable suppresses warnings that depend on the test
environment (such as ulimit warnings in builds on systems with lower
limits, which may well succeed if it weren't for the warning).

This prevents non-deterministic test failures in golden/characterization
tests.

Alternative considered: filtering stderr in test scripts, but that approach
is fragile with binary test output, and potentially multiple call sites.
---
 src/libutil/current-process.cc  | 19 +++++++++++--------
 tests/functional/common/vars.sh |  3 +++
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/src/libutil/current-process.cc b/src/libutil/current-process.cc
index 10522d5ae..c07ed8371 100644
--- a/src/libutil/current-process.cc
+++ b/src/libutil/current-process.cc
@@ -7,6 +7,7 @@
 #include "nix/util/file-system.hh"
 #include "nix/util/processes.hh"
 #include "nix/util/signals.hh"
+#include "nix/util/environment-variables.hh"
 #include <math.h>
 
 #ifdef __APPLE__
@@ -66,14 +67,16 @@ void setStackSize(size_t stackSize)
     if (getrlimit(RLIMIT_STACK, &limit) == 0 && static_cast<size_t>(limit.rlim_cur) < stackSize) {
         savedStackSize = limit.rlim_cur;
         if (limit.rlim_max < static_cast<rlim_t>(stackSize)) {
-            logger->log(
-                lvlWarn,
-                HintFmt(
-                    "Stack size hard limit is %1%, which is less than the desired %2%. If possible, increase the hard limit, e.g. with 'ulimit -Hs %3%'.",
-                    limit.rlim_max,
-                    stackSize,
-                    stackSize / 1024)
-                    .str());
+            if (getEnv("_NIX_TEST_NO_ENVIRONMENT_WARNINGS") != "1") {
+                logger->log(
+                    lvlWarn,
+                    HintFmt(
+                        "Stack size hard limit is %1%, which is less than the desired %2%. If possible, increase the hard limit, e.g. with 'ulimit -Hs %3%'.",
+                        limit.rlim_max,
+                        stackSize,
+                        stackSize / 1024)
+                        .str());
+            }
         }
         auto requestedSize = std::min(static_cast<rlim_t>(stackSize), limit.rlim_max);
         limit.rlim_cur = requestedSize;
diff --git a/tests/functional/common/vars.sh b/tests/functional/common/vars.sh
index ed4b47727..d4d917dae 100644
--- a/tests/functional/common/vars.sh
+++ b/tests/functional/common/vars.sh
@@ -49,6 +49,9 @@ if ! isTestOnNixOS; then
   fi
   export _NIX_IN_TEST=$TEST_ROOT/shared
   export _NIX_TEST_NO_LSOF=1
+  # Suppress warnings that depend on the test environment (e.g., ulimit warnings)
+  # to avoid non-deterministic test failures in golden tests
+  export _NIX_TEST_NO_ENVIRONMENT_WARNINGS=1
   export NIX_REMOTE=${NIX_REMOTE_-}
 
 fi # ! isTestOnNixOS