Don't do literal regex matching optimisation when case insensitive. (#8013)

Fixes #7994

Signed-off-by: Brian Brazil <brian.brazil@robustperception.io>

pkg/labels/regexp.go

@@ -86,10 +86,10 @@ func optimizeConcatRegex(r *syntax.Regexp) (prefix, suffix, contains string) {
 	// Given Prometheus regex matchers are always anchored to the begin/end
 	// of the text, if the first/last operations are literals, we can safely
 	// treat them as prefix/suffix.
-	if sub[0].Op == syntax.OpLiteral {
+	if sub[0].Op == syntax.OpLiteral && (sub[0].Flags&syntax.FoldCase) == 0 {
 		prefix = string(sub[0].Rune)
 	}
-	if last := len(sub) - 1; sub[last].Op == syntax.OpLiteral {
+	if last := len(sub) - 1; sub[last].Op == syntax.OpLiteral && (sub[last].Flags&syntax.FoldCase) == 0 {
 		suffix = string(sub[last].Rune)
 	}
 
@@ -97,7 +97,7 @@ func optimizeConcatRegex(r *syntax.Regexp) (prefix, suffix, contains string) {
 	// 1st one. We do not keep the whole list of literals to simplify the
 	// fast path.
 	for i := 1; i < len(sub)-1; i++ {
-		if sub[i].Op == syntax.OpLiteral {
+		if sub[i].Op == syntax.OpLiteral && (sub[i].Flags&syntax.FoldCase) == 0 {
 			contains = string(sub[i].Rune)
 			break
 		}

pkg/labels/regexp_test.go

@@ -76,6 +76,13 @@ func TestOptimizeConcatRegex(t *testing.T) {
 		{regex: ".*foo.*bar.*", prefix: "", suffix: "", contains: "foo"},
 		{regex: ".*(foo|bar).*", prefix: "", suffix: "", contains: ""},
 		{regex: ".*[abc].*", prefix: "", suffix: "", contains: ""},
+		{regex: ".*((?i)abc).*", prefix: "", suffix: "", contains: ""},
+		{regex: ".*(?i:abc).*", prefix: "", suffix: "", contains: ""},
+		{regex: "(?i:abc).*", prefix: "", suffix: "", contains: ""},
+		{regex: ".*(?i:abc)", prefix: "", suffix: "", contains: ""},
+		{regex: ".*(?i:abc)def.*", prefix: "", suffix: "", contains: "def"},
+		{regex: "(?i).*(?-i:abc)def", prefix: "", suffix: "", contains: "abc"},
+		{regex: ".*(?msU:abc).*", prefix: "", suffix: "", contains: "abc"},
 	}
 
 	for _, c := range cases {

promql/testdata/selectors.test

@@ -58,6 +58,51 @@ eval instant at 0s http_requests{foo!~"bar", job="api-server", instance="1", x!=
 	http_requests{job="api-server", instance="1", group="production"} 0
 	http_requests{job="api-server", instance="1", group="canary"} 0
 
+# https://github.com/prometheus/prometheus/issues/7994
+eval instant at 8000s rate(http_requests{group=~"(?i:PRO).*"}[1m])
+	{job="api-server", instance="0", group="production"} 1
+	{job="api-server", instance="1", group="production"} 2
+
+eval instant at 8000s rate(http_requests{group=~".*?(?i:PRO).*"}[1m])
+	{job="api-server", instance="0", group="production"} 1
+	{job="api-server", instance="1", group="production"} 2
+
+eval instant at 8000s rate(http_requests{group=~".*(?i:DUC).*"}[1m])
+	{job="api-server", instance="0", group="production"} 1
+	{job="api-server", instance="1", group="production"} 2
+
+eval instant at 8000s rate(http_requests{group=~".*(?i:TION)"}[1m])
+	{job="api-server", instance="0", group="production"} 1
+	{job="api-server", instance="1", group="production"} 2
+
+eval instant at 8000s rate(http_requests{group=~".*(?i:TION).*?"}[1m])
+	{job="api-server", instance="0", group="production"} 1
+	{job="api-server", instance="1", group="production"} 2
+
+
+eval instant at 8000s rate(http_requests{group=~"((?i)PRO).*"}[1m])
+	{job="api-server", instance="0", group="production"} 1
+	{job="api-server", instance="1", group="production"} 2
+
+eval instant at 8000s rate(http_requests{group=~".*((?i)DUC).*"}[1m])
+	{job="api-server", instance="0", group="production"} 1
+	{job="api-server", instance="1", group="production"} 2
+
+eval instant at 8000s rate(http_requests{group=~".*((?i)TION)"}[1m])
+	{job="api-server", instance="0", group="production"} 1
+	{job="api-server", instance="1", group="production"} 2
+
+
+eval instant at 8000s rate(http_requests{group=~"(?i:PRODUCTION)"}[1m])
+	{job="api-server", instance="0", group="production"} 1
+	{job="api-server", instance="1", group="production"} 2
+
+eval instant at 8000s rate(http_requests{group=~".*(?i:C).*"}[1m])
+	{job="api-server", instance="0", group="production"} 1
+	{job="api-server", instance="1", group="production"} 2
+	{job="api-server", instance="0", group="canary"} 3
+	{job="api-server", instance="1", group="canary"} 4
+
 clear
 load 1m
     metric1{a="a"} 0+1x100