...

example/program.nub

@@ -9,7 +9,7 @@ struct Human {
 export func main(args: []^string) {
     let i: i64
 
-    c::printf("%d\n", args.count)
+    c:printf("%d\n", args.count)
 
     while i < args.count {
         c::printf("%s\n", args[i])

src/lang/Nub.Lang/Frontend/Diagnostics/ConsoleColors.cs

@@ -139,8 +139,9 @@ public static class ConsoleColors
         }
     }
 
-    public static string ColorizeSource(SourceText sourceText)
+    public static string ColorizeSource(string source)
     {
+        var sourceText = new SourceText(string.Empty, source);
         var tokens = Lexer.Tokenize(sourceText).Value;
         var result = new StringBuilder();
         var lastCharIndex = 0;

src/lang/Nub.Lang/Frontend/Diagnostics/Diagnostic.cs

@@ -77,18 +77,18 @@ public class Diagnostic
         }
 
         sb.Append(": ");
-        sb.AppendLine(ConsoleColors.Colorize(Message, ConsoleColors.BrightWhite));
+        sb.Append(ConsoleColors.Colorize(Message, ConsoleColors.BrightWhite));
 
         if (Span.HasValue)
         {
+            sb.AppendLine();
             AppendSourceContext(sb, Span.Value);
         }
 
         if (!string.IsNullOrEmpty(Help))
         {
             sb.AppendLine();
-            var helpText = $"help: {Help}";
+            sb.Append(ConsoleColors.Colorize($"help: {Help}", ConsoleColors.Cyan));
-            sb.AppendLine(ConsoleColors.Colorize(helpText, ConsoleColors.Cyan));
         }
 
         return sb.ToString();
@@ -113,50 +113,61 @@ public class Diagnostic
 
         const int contextLines = 3;
 
-        if (startLine < 1 || startLine > lines.Length || endLine < 1 || endLine > lines.Length)
+        var lineNumWidth = Math.Min(endLine + contextLines, lines.Length).ToString().Length;
-        {
-            return;
-        }
-
-        var maxLineNum = Math.Min(endLine + contextLines, lines.Length);
-        var lineNumWidth = maxLineNum.ToString().Length;
 
         var contextStart = Math.Max(1, startLine - contextLines);
+        var contextEnd = Math.Min(lines.Length, endLine + contextLines);
+
+        var contextWidth = 0;
+        for (var i = contextStart; i < contextEnd; i++)
+        {
+            if (lines[i - 1].Length > contextWidth)
+            {
+                contextWidth = lines[i - 1].Length;
+            }
+        }
+
+        sb.AppendLine(ConsoleColors.Colorize('╭' + new string('─', lineNumWidth + 2) + '┬' + new string('─', contextWidth + 2) + '╮', ConsoleColors.Faint));
 
         for (var lineNum = contextStart; lineNum < startLine; lineNum++)
         {
-            var line = ConsoleColors.ColorizeSource(new SourceText(span.Text.Name, lines[lineNum - 1]));
+            AppendContextLine(sb, lineNum, lines[lineNum - 1], lineNumWidth, contextWidth);
-            AppendContextLine(sb, lineNum, line, lineNumWidth);
         }
 
         for (var lineNum = startLine; lineNum <= endLine; lineNum++)
         {
-            var line = ConsoleColors.ColorizeSource(new SourceText(span.Text.Name, lines[lineNum - 1]));
+            AppendContextLine(sb, lineNum, lines[lineNum - 1], lineNumWidth, contextWidth);
-            AppendContextLine(sb, lineNum, line, lineNumWidth);
+            AppendErrorIndicators(sb, span, lineNum, lines[lineNum - 1], lineNumWidth, contextWidth);
-            AppendErrorIndicators(sb, span, lineNum, line, lineNumWidth);
         }
 
-        var contextEnd = Math.Min(lines.Length, endLine + contextLines);
         for (var lineNum = endLine + 1; lineNum <= contextEnd; lineNum++)
         {
-            var line = ConsoleColors.ColorizeSource(new SourceText(span.Text.Name, lines[lineNum - 1]));
+            AppendContextLine(sb, lineNum, lines[lineNum - 1], lineNumWidth, contextWidth);
-            AppendContextLine(sb, lineNum, line, lineNumWidth);
         }
+        
+        sb.Append(ConsoleColors.Colorize('╰' + new string('─', lineNumWidth + 2) + '┴' + new string('─', contextWidth + 2) + '╯', ConsoleColors.Faint));
     }
 
-    private static void AppendContextLine(StringBuilder sb, int lineNum, string line, int lineNumWidth)
+    private static void AppendContextLine(StringBuilder sb, int lineNum, string line, int lineNumWidth, int contextWidth)
     {
+        sb.Append(ConsoleColors.Colorize('│' + " ", ConsoleColors.Faint));
         var lineNumStr = lineNum.ToString().PadLeft(lineNumWidth);
         sb.Append(ConsoleColors.Colorize(lineNumStr, ConsoleColors.Faint));
-        sb.Append(ConsoleColors.Colorize(" | ", ConsoleColors.Faint));
+        sb.Append(ConsoleColors.Colorize(" │ ", ConsoleColors.Faint));
-        sb.AppendLine(line);
+        sb.Append(ConsoleColors.ColorizeSource(line.PadRight(contextWidth)));
+        sb.Append(ConsoleColors.Colorize(" " + '│', ConsoleColors.Faint));
+        sb.AppendLine();
     }
 
-    private static void AppendErrorIndicators(StringBuilder sb, SourceSpan span, int lineNum, string line, int lineNumWidth)
+    private static void AppendErrorIndicators(StringBuilder sb, SourceSpan span, int lineNum, string line, int lineNumWidth, int contextWidth)
     {
-        sb.Append(new string(' ', lineNumWidth + 3));
+        sb.Append(ConsoleColors.Colorize('│' + " ", ConsoleColors.Faint));
+        sb.Append(new string(' ', lineNumWidth));
+        sb.Append(ConsoleColors.Colorize(" │ ", ConsoleColors.Faint));
         var indicators = GetIndicatorsForLine(span, lineNum, line);
-        sb.AppendLine(ConsoleColors.Colorize(indicators, ConsoleColors.Red));
+        sb.Append(ConsoleColors.Colorize(indicators.PadRight(contextWidth), ConsoleColors.Red));
+        sb.Append(ConsoleColors.Colorize(" " + '│', ConsoleColors.Faint));
+        sb.AppendLine();
     }
 
     private static string GetIndicatorsForLine(SourceSpan span, int lineNum, string line)

src/lang/Nub.Lang/Frontend/Diagnostics/DiagnosticsResult.cs

@@ -9,6 +9,7 @@ public class DiagnosticsResult(List<Diagnostic> diagnostics)
         foreach (var diagnostic in diagnostics)
         {
             Console.Error.WriteLine(diagnostic.Format());
+            Console.Error.WriteLine();
         }
     }
 }