fix: Properly handle macro when extracting Metadata

When a macro is set in the header, only the first line will be read and then
discarded. This makes sure we keep the macro in and stop processing metadata
when we hit a macro.

Co-authored-by: Manuel Rüger <[email protected]>

README.md

@@ -120,6 +120,9 @@ be replaced with specified template:
      <yaml-data> -->
 ```
 
+**NOTE**: Make sure to define your macros after your metadata (Title/Space), 
+mark will stop processing metadata if it hits a Macro.
+
 Capture groups can be defined in the macro's <regexp> which can be later
 referenced in the `<yaml-data>` using `${<number>}` syntax, where `<number>` is
 number of a capture group in regexp (`${0}` is used for entire regexp match),

pkg/mark/meta.go

@@ -34,8 +34,9 @@ type Meta struct {
 }
 
 var (
-	reHeaderPatternV1 = regexp.MustCompile(`\[\]:\s*#\s*\(([^:]+):\s*(.*)\)`)
-	reHeaderPatternV2 = regexp.MustCompile(`<!--\s*([^:]+):\s*(.*)\s*-->`)
+	reHeaderPatternV1    = regexp.MustCompile(`\[\]:\s*#\s*\(([^:]+):\s*(.*)\)`)
+	reHeaderPatternV2    = regexp.MustCompile(`<!--\s*([^:]+):\s*(.*)\s*-->`)
+	reHeaderPatternMacro = regexp.MustCompile(`<!-- Macro: .*`)
 )
 
 func ExtractMeta(data []byte) (*Meta, []byte, error) {
@@ -58,6 +59,12 @@ func ExtractMeta(data []byte) (*Meta, []byte, error) {
 		if matches == nil {
 			matches = reHeaderPatternV1.FindStringSubmatch(line)
 			if matches == nil {
+				matches = reHeaderPatternMacro.FindStringSubmatch(line)
+				// If we have a match, then we started reading a macro.
+				// We want to keep it in the document for it to be read by ExtractMacros
+				if matches != nil {
+					offset -= len(line) + 1
+				}
 				break
 			}