Deprecate format strings

Add deprecation notice to format strings to allow transition to new
functionality.

Signed-off-by: SuperQ <superq@gmail.com>

expfmt/expfmt.go

@@ -35,19 +35,27 @@ const (
 	TextVersion              = "0.0.4"
 	ProtoType                = `application/vnd.google.protobuf`
 	ProtoProtocol            = `io.prometheus.client.MetricFamily`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeProtoCompact) instead.
 	ProtoFmt                 = ProtoType + "; proto=" + ProtoProtocol + ";"
 	OpenMetricsType          = `application/openmetrics-text`
 	OpenMetricsVersion_0_0_1 = "0.0.1"
 	OpenMetricsVersion_1_0_0 = "1.0.0"
 
 	// The Content-Type values for the different wire protocols. Do not do direct
 	// comparisons to these constants, instead use the comparison functions.
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeUnknown) instead.
 	FmtUnknown           Format = `<unknown>`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeTextPlain) instead.
 	FmtText              Format = `text/plain; version=` + TextVersion + `; charset=utf-8`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeProtoDelim) instead.
 	FmtProtoDelim        Format = ProtoFmt + ` encoding=delimited`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeProtoText) instead.
 	FmtProtoText         Format = ProtoFmt + ` encoding=text`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeProtoCompact) instead.
 	FmtProtoCompact      Format = ProtoFmt + ` encoding=compact-text`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeOpenMetrics) instead.
 	FmtOpenMetrics_1_0_0 Format = OpenMetricsType + `; version=` + OpenMetricsVersion_1_0_0 + `; charset=utf-8`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeOpenMetrics) instead.
 	FmtOpenMetrics_0_0_1 Format = OpenMetricsType + `; version=` + OpenMetricsVersion_0_0_1 + `; charset=utf-8`
 )