restrict keyword highlighting to Cordial lines, fix nested block comments and HR text visibility

src/EditorView.swift

@@ -1191,7 +1191,9 @@ func applySyntaxHighlighting(to textStorage: NSTextStorage) {
             continue
         }
 
-        highlightCodeLine(line, lineRange: lineRange, textStorage: textStorage, syn: syn)
+        if isCordialLine(trimmed) {
+            highlightCodeLine(line, lineRange: lineRange, textStorage: textStorage, syn: syn)
+        }
         highlightInlineCode(textStorage: textStorage, lineRange: lineRange, palette: palette, baseFont: baseFont)
         highlightStrikethrough(textStorage: textStorage, lineRange: lineRange, palette: palette)
         highlightFootnoteRefs(textStorage: textStorage, lineRange: lineRange, palette: palette)
@@ -1266,6 +1268,7 @@ private func highlightMarkdownLine(_ trimmed: String, line: String, lineRange: N
 
     if isHorizontalRule(trimmed) {
         textStorage.addAttribute(.foregroundColor, value: palette.base, range: lineRange)
+        textStorage.addAttribute(.font, value: NSFont.systemFont(ofSize: 0.01), range: lineRange)
         return true
     }
 
@@ -1446,15 +1449,37 @@ private func highlightBlockComments(textStorage: NSTextStorage, syn: Theme.Synta
     let text = textStorage.string
     let nsText = text as NSString
     let italicFont = NSFontManager.shared.convert(baseFont, toHaveTrait: .italicFontMask)
+    let len = nsText.length
+    guard len >= 4 else { return }
 
-    guard let regex = try? NSRegularExpression(pattern: "/\\*.*?\\*/", options: .dotMatchesLineSeparators) else { return }
-    let fullRange = NSRange(location: 0, length: nsText.length)
-    let matches = regex.matches(in: text, range: fullRange)
-    for match in matches {
-        textStorage.addAttributes([
-            .foregroundColor: syn.comment,
-            .font: italicFont
-        ], range: match.range)
+    var i = 0
+    while i < len - 1 {
+        if nsText.character(at: i) == 0x2F && nsText.character(at: i + 1) == 0x2A { // /*
+            let start = i
+            var depth = 1
+            i += 2
+            while i < len - 1 && depth > 0 {
+                let c = nsText.character(at: i)
+                let n = nsText.character(at: i + 1)
+                if c == 0x2F && n == 0x2A { // /*
+                    depth += 1
+                    i += 2
+                } else if c == 0x2A && n == 0x2F { // */
+                    depth -= 1
+                    i += 2
+                } else {
+                    i += 1
+                }
+            }
+            if i > len { i = len }
+            let range = NSRange(location: start, length: i - start)
+            textStorage.addAttributes([
+                .foregroundColor: syn.comment,
+                .font: italicFont
+            ], range: range)
+        } else {
+            i += 1
+        }
     }
 }
 
@@ -1686,6 +1711,23 @@ private func applyListIndent(line: String, lineRange: NSRange, textStorage: NSTe
     }
 }
 
+private func isCordialLine(_ trimmed: String) -> Bool {
+    if trimmed.isEmpty { return false }
+    if trimmed.hasPrefix("/=") { return true }
+    if trimmed.hasPrefix("//") { return true }
+    if trimmed.hasPrefix("/*") { return true }
+    if trimmed.hasPrefix("let ") {
+        return trimmed.contains("=")
+    }
+    guard let eqIdx = trimmed.firstIndex(of: "=") else { return false }
+    if eqIdx == trimmed.startIndex { return false }
+    let after = trimmed.index(after: eqIdx)
+    if after < trimmed.endIndex && trimmed[after] == "=" { return false }
+    let before = trimmed[trimmed.index(before: eqIdx)]
+    if before == "!" || before == "<" || before == ">" { return false }
+    return true
+}
+
 private func isHorizontalRule(_ trimmed: String) -> Bool {
     if trimmed.isEmpty { return false }
     let stripped = trimmed.replacingOccurrences(of: " ", with: "")