textfile: use stable fallback HELP strings (#2591)

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

internal/collector/textfile/help_collect_test.go

@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: Apache-2.0
+//
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build windows
+
+package textfile
+
+import (
+	"fmt"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSplitFamilyWithoutHelp(t *testing.T) {
+	t.Parallel()
+
+	directory := t.TempDir()
+
+	for _, source := range []string{"a", "b"} {
+		content := fmt.Sprintf("probe{source=%q} 1\n", source)
+		require.NoError(t, os.WriteFile(filepath.Join(directory, source+".prom"), []byte(content), 0o600))
+	}
+
+	c := New(&Config{TextFileDirectories: []string{directory}})
+	require.NoError(t, c.Build(slog.New(slog.DiscardHandler), nil))
+	wrapper := &helpTestCollector{collector: c}
+	registry := prometheus.NewRegistry()
+	registry.MustRegister(wrapper)
+	families, err := registry.Gather()
+	require.NoError(t, err)
+	require.NoError(t, wrapper.err)
+
+	found := false
+
+	for _, family := range families {
+		if family.GetName() == "probe" {
+			found = true
+
+			require.Len(t, family.GetMetric(), 2)
+			require.NotContains(t, family.GetHelp(), directory)
+		}
+	}
+
+	require.True(t, found)
+}
+
+type helpTestCollector struct {
+	collector *Collector
+	err       error
+}
+
+func (c *helpTestCollector) Describe(_ chan<- *prometheus.Desc) {}
+
+func (c *helpTestCollector) Collect(ch chan<- prometheus.Metric) {
+	c.err = c.collector.Collect(ch, 0)
+}

internal/collector/textfile/textfile.go

@@ -426,7 +426,7 @@ func scrapeFile(path string, logger *slog.Logger) ([]*dto.MetricFamily, error) {
 		}
 
 		if mf.Help == nil {
-			help := "Metric read from " + path
+			help := "Metric read from textfile collector"
 			mf.Help = &help
 		}
 	}