Deprecate kind, lang, and path from front matter

These were added to the page meta object when we implemented "pages from data", but were not meant to be used in front matter.

That is not supported, so we might as well add validation.

Fixes #12484

common/hugo/hugo.go

@@ -414,6 +414,15 @@ func Deprecate(item, alternative string, version string) {
 	DeprecateLevel(item, alternative, version, level)
 }
 
+// DeprecateLevelMin informs about a deprecation starting at the given version, but with a minimum log level.
+func DeprecateLevelMin(item, alternative string, version string, minLevel logg.Level) {
+	level := deprecationLogLevelFromVersion(version)
+	if level < minLevel {
+		level = minLevel
+	}
+	DeprecateLevel(item, alternative, version, level)
+}
+
 // DeprecateLevel informs about a deprecation logging at the given level.
 func DeprecateLevel(item, alternative, version string, level logg.Level) {
 	var msg string

common/loggers/loggerglobal.go

@@ -21,7 +21,15 @@ import (
 	"github.com/bep/logg"
 )
 
-func InitGlobalLogger(level logg.Level, panicOnWarnings bool) {
+// SetGlobalLogger sets the global logger.
+// This is used in a few places in Hugo, e.g. deprecated functions.
+func SetGlobalLogger(logger Logger) {
+	logMu.Lock()
+	defer logMu.Unlock()
+	log = logger
+}
+
+func initGlobalLogger(level logg.Level, panicOnWarnings bool) {
 	logMu.Lock()
 	defer logMu.Unlock()
 	var logHookLast func(e *logg.Entry) error
@@ -50,5 +58,5 @@ func Log() Logger {
 var log Logger
 
 func init() {
-	InitGlobalLogger(logg.LevelWarn, false)
+	initGlobalLogger(logg.LevelWarn, false)
 }