Support shortening of revision with digest

The `\b` in the regular expression ensures we only match with a
hexadecimal notation as awhole, while still allowing to match with
e.g. `sha1:...` which would not have been possible by using `\W`
as this includes `_`.

Signed-off-by: Hidde Beydals <hello@hidde.co>

internal/utils/hex.go

@@ -0,0 +1,39 @@
+/*
+Copyright 2023 The Flux authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package utils
+
+import (
+	"regexp"
+	"strings"
+)
+
+// hexRegexp matches any hexadecimal notation between 40 and 128 characters.
+var hexRegexp = regexp.MustCompile(`\b[a-f0-9]{40,128}\b`)
+
+// TruncateHex will replace any hexadecimal notation between 40 and 128
+// characters (SHA-1 up to SHA-512) within the given string with a truncated
+// version of 8 characters.
+func TruncateHex(str string) string {
+	if str == "" {
+		return ""
+	}
+	hits := hexRegexp.FindAllString(str, -1)
+	for _, v := range hits {
+		str = strings.Replace(str, v, string([]rune(v)[:8]), -1)
+	}
+	return str
+}