metadecoders: Add support for native org dates in frontmatter

PR #7433 added support for Org timestamps for the DATE header. This PR widens the support with additional front matter headers LASTMOD, PUBLISHDATE and EXPIRYDATE.

Fixes #8536

parser/metadecoders/decoder.go

@@ -244,7 +244,7 @@ func (d Decoder) unmarshalORG(data []byte, v any) error {
 		} else if k == "tags" || k == "categories" || k == "aliases" {
 			jww.WARN.Printf("Please use '#+%s[]:' notation, automatic conversion is deprecated.", k)
 			frontMatter[k] = strings.Fields(v)
-		} else if k == "date" {
+		} else if k == "date" || k == "lastmod" || k == "publishdate" || k == "expirydate" {
 			frontMatter[k] = parseORGDate(v)
 		} else {
 			frontMatter[k] = v

parser/metadecoders/decoder_test.go

@@ -126,6 +126,9 @@ func TestUnmarshalToInterface(t *testing.T) {
 		{[]byte(nil), JSON, map[string]any{}},
 		{[]byte(`#+a: b`), ORG, expect},
 		{[]byte(`#+DATE: <2020-06-26 Fri>`), ORG, map[string]any{"date": "2020-06-26"}},
+		{[]byte(`#+LASTMOD: <2020-06-26 Fri>`), ORG, map[string]any{"lastmod": "2020-06-26"}},
+		{[]byte(`#+PUBLISHDATE: <2020-06-26 Fri>`), ORG, map[string]any{"publishdate": "2020-06-26"}},
+		{[]byte(`#+EXPIRYDATE: <2020-06-26 Fri>`), ORG, map[string]any{"expirydate": "2020-06-26"}},
 		{[]byte(`a = "b"`), TOML, expect},
 		{[]byte(`a: "b"`), YAML, expect},
 		{[]byte(`<root><a>b</a></root>`), XML, expect},