More strict checks in alerts/template

docs/changelog.md

@@ -1,5 +1,25 @@
 # Changelog
 
+## v0.47.0
+
+### Added
+
+- `alerts/template` check can now report problems with alerting rules
+  when trying to use templates on a query that doesn't produce any labels
+  at all.
+  For example when using [`vector(...)`](https://prometheus.io/docs/prometheus/latest/querying/functions/#vector) function:
+
+  {% raw %}
+
+  ```yaml
+  - alert: DeadMansSwitch
+    expr: vector(1)
+    annotations:
+      summary: Deadman's switch on {{ $labels.instance }} is firing
+  ```
+
+  {% endraw %}
+
 ## v0.46.0
 
 ### Added
@@ -115,7 +135,7 @@
   ```yaml
   - record: my:sum
     expr: sum(http_requests_total)
-  
+
   - alert: my alert
     expr: rate(my:sum[5m])
   ```
@@ -195,7 +215,7 @@
   snooze them instead of disabling forever.
 
   The difference between `# pint disable ...` and `# pint snooze ...` comments is that
-  the snooze comment must include a timestamp. Selected check will be disabled *until*
+  the snooze comment must include a timestamp. Selected check will be disabled _until_
   that timestamp.
   Timestamp must either use [RFC3339](https://www.rfc-editor.org/rfc/rfc3339) syntax
   or `YYYY-MM-DD` (if you don't care about time and want to snooze until given date).
@@ -640,7 +660,7 @@
 ### Changed
 
 - The way `pint` sends API requests to Prometheus was changed to improve performance.
-  
+
   First change is that each `prometheus` server definition in `pint` config file can
   now accept optional `concurrency` field (defaults to 16) that sets a limit on how
   many concurrent requests can that server receive. There is a new metric that
@@ -800,10 +820,10 @@
 
   ```yaml
   groups:
-  - name: example
-    rules:
-    - record: ...
-      expr: ...
+    - name: example
+      rules:
+        - record: ...
+          expr: ...
   ```
 
   Previous releases were only looking for individual rules so `groups` object
@@ -815,7 +835,7 @@
 
   ```yaml
   parser {
-    relaxed = ["(.*)"]
+  relaxed = ["(.*)"]
   }
   ```
 
@@ -974,7 +994,7 @@
 
 ### Added
 
-- Added  `pint_last_run_time_seconds` and `pint_rules_parsed_total` metrics when running `pint watch`.
+- Added `pint_last_run_time_seconds` and `pint_rules_parsed_total` metrics when running `pint watch`.
 
 ### Changed
 
@@ -997,7 +1017,7 @@
 ### Added
 
 - Added `promql/regexp` check that will warn about unnecessary regexp matchers.
-- Added  `pint_prometheus_queries_total` and `pint_prometheus_query_errors_total`
+- Added `pint_prometheus_queries_total` and `pint_prometheus_query_errors_total`
   metric when running `pint watch`.
 
 ## v0.10.1
@@ -1090,7 +1110,7 @@
 ### Fixed
 
 - `promql/rate`, `query/series` and `promql/vector_matching` checks were not enabled
-  for all defined `prometheus {}` blocks  unless there was at least one `rule {}` block.
+  for all defined `prometheus {}` blocks unless there was at least one `rule {}` block.
 - `annotation` based `match` blocks didn't work correctly.
 
 ## v0.6.6
@@ -1224,7 +1244,7 @@
   - alert: Foo
     expr: absent(foo{env="prod"})
     annotations:
-      summary: 'foo metric is missing for job {{ $labels.job }}'
+      summary: "foo metric is missing for job {{ $labels.job }}"
   ```
 
   {% endraw %}
@@ -1291,7 +1311,7 @@
   - alert: Foo
     expr: count(up) without(instance) == 0
     annotations:
-      summary: 'foo is down on {{ $labels.instance }}'
+      summary: "foo is down on {{ $labels.instance }}"
   ```
 
   {% endraw %}
@@ -1302,7 +1322,7 @@
 
 ### Fixed
 
-- Fixed file descriptor leak due to missing file `Close()`  #69.
+- Fixed file descriptor leak due to missing file `Close()` #69.
 
 ## v0.1.4
 

internal/checks/alerts_template.go

@@ -101,6 +101,7 @@ func (c TemplateCheck) Check(ctx context.Context, _ string, rule parser.Rule, _
 
 	aggrs := utils.HasOuterAggregation(rule.AlertingRule.Expr.Query)
 	absentCalls := utils.HasOuterAbsent(rule.AlertingRule.Expr.Query)
+	vectors := utils.HasVectorSelector(rule.AlertingRule.Expr.Query)
 
 	var safeLabels []string
 	for _, be := range binaryExprs(rule.AlertingRule.Expr.Query) {
@@ -179,6 +180,19 @@ func (c TemplateCheck) Check(ctx context.Context, _ string, rule parser.Rule, _
 					})
 				}
 			}
+
+			labelNames := getTemplateLabels(label.Key.Value, label.Value.Value)
+			if len(labelNames) > 0 && len(vectors) == 0 {
+				for _, name := range labelNames {
+					problems = append(problems, Problem{
+						Fragment: fmt.Sprintf("%s: %s", label.Key.Value, label.Value.Value),
+						Lines:    mergeLines(label.Lines(), rule.AlertingRule.Expr.Lines()),
+						Reporter: c.Reporter(),
+						Text:     fmt.Sprintf("template is using %q label but the query doesn't produce any labels", name),
+						Severity: Bug,
+					})
+				}
+			}
 		}
 	}
 
@@ -228,6 +242,19 @@ func (c TemplateCheck) Check(ctx context.Context, _ string, rule parser.Rule, _
 				}
 			}
 
+			labelNames := getTemplateLabels(annotation.Key.Value, annotation.Value.Value)
+			if len(labelNames) > 0 && len(vectors) == 0 {
+				for _, name := range labelNames {
+					problems = append(problems, Problem{
+						Fragment: fmt.Sprintf("%s: %s", annotation.Key.Value, annotation.Value.Value),
+						Lines:    mergeLines(annotation.Lines(), rule.AlertingRule.Expr.Lines()),
+						Reporter: c.Reporter(),
+						Text:     fmt.Sprintf("template is using %q label but the query doesn't produce any labels", name),
+						Severity: Bug,
+					})
+				}
+			}
+
 			if hasValue(annotation.Key.Value, annotation.Value.Value) && !hasHumanize(annotation.Key.Value, annotation.Value.Value) {
 				for _, problem := range c.checkHumanizeIsNeeded(rule.AlertingRule.Expr.Query) {
 					problems = append(problems, Problem{
@@ -458,24 +485,50 @@ func getVariables(node parse.Node) (vars [][]string) {
 	return vars
 }
 
-func checkMetricLabels(msg, name, text string, metricLabels []string, excludeLabels bool, safeLabels []string) (msgs []string) {
+func findTemplateVariables(name, text string) (vars [][]string, aliases aliasMap, ok bool) {
 	t, err := textTemplate.
 		New(name).
 		Funcs(templateFuncMap).
 		Option("missingkey=zero").
 		Parse(strings.Join(append(templateDefs, text), ""))
 	if err != nil {
 		// no need to double report errors
-		return nil
+		return vars, aliases, false
 	}
 
-	aliases := aliasMap{aliases: map[string]map[string]struct{}{}}
-	vars := [][]string{}
+	aliases.aliases = map[string]map[string]struct{}{}
 	for _, node := range t.Root.Nodes {
 		getAliases(node, &aliases)
 		vars = append(vars, getVariables(node)...)
 	}
 
+	return vars, aliases, true
+}
+
+func getTemplateLabels(name, text string) (names []string) {
+	vars, aliases, ok := findTemplateVariables(name, text)
+	if !ok {
+		return nil
+	}
+
+	labelsAliases := aliases.varAliases(".Labels")
+	for _, v := range vars {
+		for _, a := range labelsAliases {
+			if len(v) > 1 && v[0] == a {
+				names = append(names, v[1])
+			}
+		}
+	}
+
+	return names
+}
+
+func checkMetricLabels(msg, name, text string, metricLabels []string, excludeLabels bool, safeLabels []string) (msgs []string) {
+	vars, aliases, ok := findTemplateVariables(name, text)
+	if !ok {
+		return nil
+	}
+
 	done := map[string]struct{}{}
 	labelsAliases := aliases.varAliases(".Labels")
 	for _, v := range vars {

internal/checks/alerts_template_test.go

@@ -1017,6 +1017,64 @@ func TestTemplateCheck(t *testing.T) {
 			prometheus: noProm,
 			problems:   noProblems,
 		},
+		{
+			description: "annotation label from vector(0)",
+			content:     "- alert: DeadMansSwitch\n  expr: vector(1)\n  annotations:\n    summary: 'Deadmans switch on {{ $labels.instance }} is firing'\n",
+			checker:     newTemplateCheck,
+			prometheus:  noProm,
+			problems: func(uri string) []checks.Problem {
+				return []checks.Problem{
+					{
+						Fragment: `summary: Deadmans switch on {{ $labels.instance }} is firing`,
+						Lines:    []int{2, 4},
+						Reporter: checks.TemplateCheckName,
+						Text:     `template is using "instance" label but the query doesn't produce any labels`,
+						Severity: checks.Bug,
+					},
+				}
+			},
+		},
+		{
+			description: "labels label from vector(0)",
+			content:     "- alert: DeadMansSwitch\n  expr: vector(1)\n  labels:\n    summary: 'Deadmans switch on {{ $labels.instance }} is firing'\n",
+			checker:     newTemplateCheck,
+			prometheus:  noProm,
+			problems: func(uri string) []checks.Problem {
+				return []checks.Problem{
+					{
+						Fragment: `summary: Deadmans switch on {{ $labels.instance }} is firing`,
+						Lines:    []int{2, 4},
+						Reporter: checks.TemplateCheckName,
+						Text:     `template is using "instance" label but the query doesn't produce any labels`,
+						Severity: checks.Bug,
+					},
+				}
+			},
+		},
+		{
+			description: "annotation label from number",
+			content:     "- alert: DeadMansSwitch\n  expr: 1 > bool 0\n  annotations:\n    summary: 'Deadmans switch on {{ $labels.instance }} / {{ $labels.job }} is firing'\n",
+			checker:     newTemplateCheck,
+			prometheus:  noProm,
+			problems: func(uri string) []checks.Problem {
+				return []checks.Problem{
+					{
+						Fragment: `summary: Deadmans switch on {{ $labels.instance }} / {{ $labels.job }} is firing`,
+						Lines:    []int{2, 4},
+						Reporter: checks.TemplateCheckName,
+						Text:     `template is using "instance" label but the query doesn't produce any labels`,
+						Severity: checks.Bug,
+					},
+					{
+						Fragment: `summary: Deadmans switch on {{ $labels.instance }} / {{ $labels.job }} is firing`,
+						Lines:    []int{2, 4},
+						Reporter: checks.TemplateCheckName,
+						Text:     `template is using "job" label but the query doesn't produce any labels`,
+						Severity: checks.Bug,
+					},
+				}
+			},
+		},
 	}
 	runTests(t, testCases)
 }