caddyfile: Correctly close the heredoc when the closing marker appear…

…s immediately (#6062)

caddyconfig/caddyfile/lexer.go

@@ -186,7 +186,7 @@ func (l *lexer) next() (bool, error) {
 			}
 
 			// check if we're done, i.e. that the last few characters are the marker
-			if len(val) > len(heredocMarker) && heredocMarker == string(val[len(val)-len(heredocMarker):]) {
+			if len(val) >= len(heredocMarker) && heredocMarker == string(val[len(val)-len(heredocMarker):]) {
 				// set the final value
 				val, err = l.finalizeHeredoc(val, heredocMarker)
 				if err != nil {

caddyconfig/caddyfile/lexer_test.go

@@ -285,6 +285,18 @@ EOF same-line-arg
 		},
 		{
 			input: []byte(`heredoc <<EOF
+EOF
+	HERE same-line-arg
+	`),
+			expected: []Token{
+				{Line: 1, Text: `heredoc`},
+				{Line: 1, Text: ``},
+				{Line: 3, Text: `HERE`},
+				{Line: 3, Text: `same-line-arg`},
+			},
+		},
+		{
+			input: []byte(`heredoc <<EOF
 		EOF same-line-arg
 	`),
 			expected: []Token{