textfile: use the explicit help text for families without one

collector/fixtures/textfile/metrics_merge_different_and_no_help.out

@@ -0,0 +1,14 @@
+# HELP events_total A nice help message.
+# TYPE events_total counter
+events_total{file="a",foo="bar"} 10
+events_total{file="a",foo="baz"} 20
+events_total{file="c",foo="bar"} 50
+events_total{file="c",foo="baz"} 60
+# HELP node_textfile_mtime_seconds Unixtime mtime of textfiles successfully read.
+# TYPE node_textfile_mtime_seconds gauge
+node_textfile_mtime_seconds{file="fixtures/textfile/metrics_merge_different_and_no_help/a.prom"} 1
+node_textfile_mtime_seconds{file="fixtures/textfile/metrics_merge_different_and_no_help/b.prom"} 1
+node_textfile_mtime_seconds{file="fixtures/textfile/metrics_merge_different_and_no_help/c.prom"} 1
+# HELP node_textfile_scrape_error 1 if there was an error opening or reading a file, 0 otherwise
+# TYPE node_textfile_scrape_error gauge
+node_textfile_scrape_error 1

collector/fixtures/textfile/metrics_merge_different_and_no_help/a.prom

@@ -0,0 +1,5 @@
+# HELP events_total A nice help message.
+# TYPE events_total counter
+events_total{foo="bar",file="a"} 10
+events_total{foo="baz",file="a"} 20
+

collector/fixtures/textfile/metrics_merge_different_and_no_help/b.prom

@@ -0,0 +1,5 @@
+# HELP events_total A different help message.
+# TYPE events_total counter
+events_total{foo="bar",file="b"} 30
+events_total{foo="baz",file="b"} 40
+

collector/fixtures/textfile/metrics_merge_different_and_no_help/c.prom

@@ -0,0 +1,3 @@
+# TYPE events_total counter
+events_total{foo="bar",file="c"} 50
+events_total{foo="baz",file="c"} 60

collector/fixtures/textfile/metrics_merge_partial_help.out

@@ -0,0 +1,16 @@
+# HELP events_total A nice help message.
+# TYPE events_total counter
+events_total{file="a",foo="bar"} 10
+events_total{file="a",foo="baz"} 20
+events_total{file="b",foo="bar"} 30
+events_total{file="b",foo="baz"} 40
+events_total{file="c",foo="bar"} 50
+events_total{file="c",foo="baz"} 60
+# HELP node_textfile_mtime_seconds Unixtime mtime of textfiles successfully read.
+# TYPE node_textfile_mtime_seconds gauge
+node_textfile_mtime_seconds{file="fixtures/textfile/metrics_merge_partial_help/a.prom"} 1
+node_textfile_mtime_seconds{file="fixtures/textfile/metrics_merge_partial_help/b.prom"} 1
+node_textfile_mtime_seconds{file="fixtures/textfile/metrics_merge_partial_help/c.prom"} 1
+# HELP node_textfile_scrape_error 1 if there was an error opening or reading a file, 0 otherwise
+# TYPE node_textfile_scrape_error gauge
+node_textfile_scrape_error 0

collector/fixtures/textfile/metrics_merge_partial_help/a.prom

@@ -0,0 +1,3 @@
+# TYPE events_total counter
+events_total{foo="bar",file="a"} 10
+events_total{foo="baz",file="a"} 20

collector/fixtures/textfile/metrics_merge_partial_help/b.prom

@@ -0,0 +1,4 @@
+# HELP events_total A nice help message.
+# TYPE events_total counter
+events_total{foo="bar",file="b"} 30
+events_total{foo="baz",file="b"} 40

collector/fixtures/textfile/metrics_merge_partial_help/c.prom

@@ -0,0 +1,3 @@
+# TYPE events_total counter
+events_total{foo="bar",file="c"} 50
+events_total{foo="baz",file="c"} 60

collector/textfile.go

@@ -217,8 +217,9 @@ func (c *textFileCollector) Update(ch chan<- prometheus.Metric) error {
 
 			for _, mf := range families {
 				// Check for metrics with inconsistent help texts and take the first help text occurrence.
-				if helpTexts, seen := metricsNamesToHelpTexts[*mf.Name]; seen {
-					if mf.Help != nil && helpTexts[0] != *mf.Help || helpTexts[1] != "" {
+				// Families without a help text can't conflict; they inherit one below.
+				if mf.Help != nil {
+					if helpTexts, seen := metricsNamesToHelpTexts[*mf.Name]; seen && (helpTexts[0] != *mf.Help || helpTexts[1] != "") {
 						metricsNamesToHelpTexts[*mf.Name] = [2]string{helpTexts[0], *mf.Help}
 						errored = true
 						c.logger.Error("inconsistent metric help text",
@@ -229,8 +230,6 @@ func (c *textFileCollector) Update(ch chan<- prometheus.Metric) error {
 							"file", metricsNamesToFiles[*mf.Name][0])
 						continue
 					}
-				}
-				if mf.Help != nil {
 					metricsNamesToHelpTexts[*mf.Name] = [2]string{*mf.Help}
 				}
 				metricsNamesToFiles[*mf.Name] = append(metricsNamesToFiles[*mf.Name], metricsFilePath)
@@ -247,7 +246,12 @@ func (c *textFileCollector) Update(ch chan<- prometheus.Metric) error {
 		}
 	}
 
-	mfHelp := make(map[string]*string)
+	// Families without a help text take the one another file gave for the same metric,
+	// so that all families of a metric share the same help text when they are merged.
+	mfHelp := make(map[string]*string, len(metricsNamesToHelpTexts))
+	for name, helpTexts := range metricsNamesToHelpTexts {
+		mfHelp[name] = &helpTexts[0]
+	}
 	for _, mf := range parsedFamilies {
 		if mf.Help == nil {
 			if help, ok := mfHelp[*mf.Name]; ok {

collector/textfile_test.go

@@ -121,6 +121,14 @@ func TestTextfileCollector(t *testing.T) {
 			paths: []string{"fixtures/textfile/metrics_merge_different_help"},
 			out:   "fixtures/textfile/metrics_merge_different_help.out",
 		},
+		{
+			paths: []string{"fixtures/textfile/metrics_merge_partial_help"},
+			out:   "fixtures/textfile/metrics_merge_partial_help.out",
+		},
+		{
+			paths: []string{"fixtures/textfile/metrics_merge_different_and_no_help"},
+			out:   "fixtures/textfile/metrics_merge_different_and_no_help.out",
+		},
 	}
 
 	for i, test := range tests {