features: return ErrNotSupportedOnOS on windows

This reverts commit 8d7c47f.

Return a sentinel error instead of removing the API outright. This
avoids compilation failures on non-Linux platforms.

Signed-off-by: Lorenz Bauer <[email protected]>

Author: lmb

.github/workflows/ci.yml

@@ -352,6 +352,7 @@ jobs:
           ./
           ./asm
           ./btf
+          ./features
           ./internal
           ./internal/efw
           ./internal/kallsyms

features/map.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package features
 
 import (

features/map_test.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package features
 
 import (

features/misc.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package features
 
 import (

features/misc_test.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package features
 
 import (

features/prog.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package features
 
 import (

features/prog_test.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package features
 
 import (
@@ -74,6 +72,7 @@ func TestHaveProgramHelper(t *testing.T) {
 			testutils.SkipOnOldKernel(t, tc.version, feature)
 
 			err := HaveProgramHelper(tc.prog, tc.helper)
+			testutils.SkipIfNotSupportedOnOS(t, err)
 			if !errors.Is(err, tc.expected) {
 				t.Fatalf("%s/%s: %v", tc.prog.String(), tc.helper.String(), err)
 			}

features/version.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package features
 
 import "github.com/cilium/ebpf/internal/linux"

internal/feature.go

@@ -161,12 +161,18 @@ type FeatureMatrix[K comparable] map[K]*FeatureTest
 // Result returns the outcome of the feature test for the given key.
 //
 // It's safe to call this function concurrently.
+//
+// Always returns [ErrNotSupportedOnOS] on Windows.
 func (fm FeatureMatrix[K]) Result(key K) error {
 	ft, ok := fm[key]
 	if !ok {
 		return fmt.Errorf("no feature probe for %v", key)
 	}
 
+	if platform.IsWindows {
+		return fmt.Errorf("%s: %w", ft.Name, ErrNotSupportedOnOS)
+	}
+
 	return ft.execute()
 }
 
@@ -187,6 +193,10 @@ func NewFeatureCache[K comparable](newTest func(K) *FeatureTest) *FeatureCache[K
 }
 
 func (fc *FeatureCache[K]) Result(key K) error {
+	if platform.IsWindows {
+		return fmt.Errorf("feature probe for %v: %w", key, ErrNotSupportedOnOS)
+	}
+
 	// NB: Executing the feature test happens without fc.mu taken.
 	return fc.retrieve(key).execute()
 }