Actually enforce dashboard schema on devenv (#53797)

* Relocate dashboards test so it runs

* Cover newer schema versions in stripnulls

* Strip nulls and remove iteration fields

* Fix fiscalYearStartMonth bounds

* Fix up and format dashboard schema

* Update thema, tidy Go dependencies

pkg/coremodel/dashboard/dashboards_test.go

@@ -0,0 +1,90 @@
+package dashboard_test
+
+import (
+	"encoding/json"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"cuelang.org/go/cue/errors"
+	"github.com/stretchr/testify/require"
+
+	"github.com/grafana/grafana/pkg/coremodel/dashboard"
+	"github.com/grafana/grafana/pkg/cuectx"
+)
+
+func TestDevenvDashboardValidity(t *testing.T) {
+	path, err := filepath.Abs("../../../devenv/dev-dashboards")
+	require.NoError(t, err)
+
+	m, err := themaTestableDashboards(os.DirFS(path))
+	require.NoError(t, err)
+	cm, err := dashboard.New(cuectx.ProvideThemaLibrary())
+	require.NoError(t, err)
+
+	for path, b := range m {
+		t.Run(path, func(t *testing.T) {
+			// The path arg here only matters for error output
+			cv, err := cuectx.JSONtoCUE(path, b)
+			require.NoError(t, err, "error while decoding dashboard JSON into a CUE value")
+
+			_, err = cm.CurrentSchema().Validate(cv)
+			if err != nil {
+				// Testify trims errors to short length. We want the full text
+				errstr := errors.Details(err, nil)
+				t.Log(errstr)
+				if strings.Contains(errstr, "null") {
+					t.Log("validation failure appears to involve nulls - see if scripts/stripnulls.sh has any effect?")
+				}
+				t.FailNow()
+			}
+		})
+	}
+}
+
+func themaTestableDashboards(in fs.FS) (map[string][]byte, error) {
+	m := make(map[string][]byte)
+
+	err := fs.WalkDir(in, ".", func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if d.IsDir() || filepath.Ext(d.Name()) != ".json" {
+			return nil
+		}
+
+		// nolint:gosec
+		f, err := in.Open(path)
+		if err != nil {
+			return err
+		}
+		defer f.Close() // nolint: errcheck
+
+		b, err := io.ReadAll(f)
+		if err != nil {
+			return err
+		}
+
+		jtree := make(map[string]interface{})
+		err = json.Unmarshal(b, &jtree)
+		if err != nil {
+			return err
+		}
+		if oldschemav, has := jtree["schemaVersion"]; !has || !(oldschemav.(float64) > dashboard.HandoffSchemaVersion-1) {
+			return nil
+		}
+
+		m[path] = b
+		return nil
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	return m, nil
+}