From 9c9b6804a3d84190ac61a8e811608cee97175999 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan-Otto=20Kr=C3=B6pke?= <mail@jkroepke.de>
Date: Fri, 9 Oct 2026 11:14:57 +0200
Subject: [PATCH] collector: preserve fatal causes in joined build errors
 (#2599)
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Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>
---
 pkg/collector/collection.go      | 37 +++++++++++++++++++++++++-------
 pkg/collector/collection_test.go |  4 ++++
 2 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/pkg/collector/collection.go b/pkg/collector/collection.go
index d424cfa7..cb4e2579 100644
--- a/pkg/collector/collection.go
+++ b/pkg/collector/collection.go
@@ -280,14 +280,7 @@ func (c *Collection) Build(ctx context.Context, logger *slog.Logger) error {
 
 		// errors.ErrUnsupported marks a collector whose subsystem is not
 		// available on this host, e.g. a Windows feature that is not installed.
-		if errors.Is(err, errors.ErrUnsupported) ||
-			errors.Is(err, pdh.ErrNoData) ||
-			errors.Is(err, winregistry.ErrNotExist) ||
-			errors.Is(err, pdh.NewPdhError(pdh.CstatusNoObject)) ||
-			errors.Is(err, pdh.NewPdhError(pdh.CstatusNoCounter)) ||
-			errors.Is(err, mi.MI_RESULT_INVALID_OPERATION_TIMEOUT) ||
-			errors.Is(err, mi.MI_RESULT_INVALID_NAMESPACE) ||
-			errors.Is(err, mi.MI_RESULT_INVALID_CLASS) {
+		if expectedBuildError(err) {
 			logger.LogAttrs(ctx, slog.LevelWarn, "couldn't initialize collector",
 				slog.Any("err", err),
 			)
@@ -421,3 +414,31 @@ func (c *Collection) WithCollectors(collectors []string) (*Collection, error) {
 func (c *Collection) GetStartTime() gotime.Time {
 	return c.startTime
 }
+
+// expectedBuildError tolerates an error tree only if every independent cause is
+// an expected initialization failure for an optional Windows subsystem.
+func expectedBuildError(err error) bool {
+	if joined, ok := err.(interface{ Unwrap() []error }); ok {
+		causes := joined.Unwrap()
+		for _, cause := range causes {
+			if !expectedBuildError(cause) {
+				return false
+			}
+		}
+
+		return len(causes) != 0
+	}
+
+	if wrapped, ok := err.(interface{ Unwrap() error }); ok {
+		return expectedBuildError(wrapped.Unwrap())
+	}
+
+	return errors.Is(err, errors.ErrUnsupported) ||
+		errors.Is(err, pdh.ErrNoData) ||
+		errors.Is(err, winregistry.ErrNotExist) ||
+		errors.Is(err, pdh.NewPdhError(pdh.CstatusNoObject)) ||
+		errors.Is(err, pdh.NewPdhError(pdh.CstatusNoCounter)) ||
+		errors.Is(err, mi.MI_RESULT_INVALID_OPERATION_TIMEOUT) ||
+		errors.Is(err, mi.MI_RESULT_INVALID_NAMESPACE) ||
+		errors.Is(err, mi.MI_RESULT_INVALID_CLASS)
+}
diff --git a/pkg/collector/collection_test.go b/pkg/collector/collection_test.go
index f5cd24ea..ec1d5e58 100644
--- a/pkg/collector/collection_test.go
+++ b/pkg/collector/collection_test.go
@@ -72,6 +72,10 @@ func TestCollectionBuildAndClose(t *testing.T) {
 		{name: "optional counter missing", buildErr: pdh.ErrNoData},
 		{name: "unsupported on this host", buildErr: fmt.Errorf("feature missing: %w", errors.ErrUnsupported)},
 		{name: "close failure", closeErr: closeFailure},
+		{name: "all expected joined errors", buildErr: errors.Join(errors.ErrUnsupported, pdh.ErrNoData)},
+		{name: "joined fatal error", buildErr: errors.Join(errors.ErrUnsupported, buildFailure), wantBuildErr: buildFailure},
+		{name: "nested fatal error", buildErr: errors.Join(pdh.ErrNoData, fmt.Errorf("nested: %w", errors.Join(errors.ErrUnsupported, buildFailure))), wantBuildErr: buildFailure},
+		{name: "multiple wrapped fatal error", buildErr: fmt.Errorf("%w and %w", errors.ErrUnsupported, buildFailure), wantBuildErr: buildFailure},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()