use forward slashes in cue ctx (#49440)

because fstest.MapFS only recognizes forward slashes

go.mod

@@ -247,7 +247,7 @@ require (
 	github.com/blugelabs/bluge v0.1.9
 	github.com/golang-migrate/migrate/v4 v4.7.0
 	github.com/grafana/dskit v0.0.0-20211011144203-3a88ec0b675f
-	github.com/grafana/thema v0.0.0-20220427204245-a557e8970249
+	github.com/grafana/thema v0.0.0-20220523183731-72aebd14e751
 	go.etcd.io/etcd v3.3.25+incompatible
 	go.opentelemetry.io/contrib/propagators/jaeger v1.6.0
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.6.3

go.sum

@@ -1465,6 +1465,8 @@ github.com/grafana/thema v0.0.0-20220413232647-fc54c169b508 h1:6k0scTj6kRDjn/qLi
 github.com/grafana/thema v0.0.0-20220413232647-fc54c169b508/go.mod h1:KuqTKX9lfM87uu9vt9DS/q+REqSrAm2xYMnBBvlmevA=
 github.com/grafana/thema v0.0.0-20220427204245-a557e8970249 h1:PLB1iSjrosHU5MN3eJ2tSvjXX9zkek7gLeBF/L/3oFo=
 github.com/grafana/thema v0.0.0-20220427204245-a557e8970249/go.mod h1:KuqTKX9lfM87uu9vt9DS/q+REqSrAm2xYMnBBvlmevA=
+github.com/grafana/thema v0.0.0-20220523183731-72aebd14e751 h1:5PpsfN52XA0hxOjD/qQ0QNiEkp9Y9Tb+yz/Hj9fyL4M=
+github.com/grafana/thema v0.0.0-20220523183731-72aebd14e751/go.mod h1:KuqTKX9lfM87uu9vt9DS/q+REqSrAm2xYMnBBvlmevA=
 github.com/gregjones/httpcache v0.0.0-20180305231024-9cad4c3443a7/go.mod h1:FecbI9+v66THATjSRHfNgh1IVFe/9kFxbXtjV0ctIMA=
 github.com/grpc-ecosystem/go-grpc-middleware v1.0.0/go.mod h1:FiyG127CGDf3tlThmgyCl78X/SZQqEOJBCDaAfeWzPs=
 github.com/grpc-ecosystem/go-grpc-middleware v1.0.1-0.20190118093823-f849b5445de4/go.mod h1:FiyG127CGDf3tlThmgyCl78X/SZQqEOJBCDaAfeWzPs=

pkg/cuectx/ctx.go

@@ -84,7 +84,8 @@ func LoadGrafanaInstancesWithThema(
 
 func prefixWithGrafanaCUE(prefix string, inputfs fs.FS) (fs.FS, error) {
 	m := fstest.MapFS{
-		filepath.Join("cue.mod", "module.cue"): &fstest.MapFile{Data: []byte(`module: "github.com/grafana/grafana"`)},
+		// fstest can recognize only forward slashes.
+		filepath.ToSlash(filepath.Join("cue.mod", "module.cue")): &fstest.MapFile{Data: []byte(`module: "github.com/grafana/grafana"`)},
 	}
 
 	prefix = filepath.FromSlash(prefix)
@@ -107,8 +108,8 @@ func prefixWithGrafanaCUE(prefix string, inputfs fs.FS) (fs.FS, error) {
 		if err != nil {
 			return err
 		}
-
+		// fstest can recognize only forward slashes.
-		m[filepath.Join(prefix, path)] = &fstest.MapFile{Data: b}
+		m[filepath.ToSlash(filepath.Join(prefix, path))] = &fstest.MapFile{Data: b}
 		return nil
 	}))