diagnostic

compiler/Compiler/Diagnostic.cs

@@ -74,4 +74,81 @@ public enum DiagnosticSeverity
 public sealed class CompileException(Diagnostic diagnostic) : Exception
 {
     public readonly Diagnostic Diagnostic = diagnostic;
+}
+
+public static class DiagnosticFormatter
+{
+    public static void Print(Diagnostic diagnostic, TextWriter writer)
+    {
+        var (label, color) = diagnostic.Severity switch
+        {
+            DiagnosticSeverity.Info => ("info", Ansi.Cyan),
+            DiagnosticSeverity.Warning => ("warning", Ansi.Yellow),
+            DiagnosticSeverity.Error => ("error", Ansi.Red),
+            _ => ("unknown", Ansi.Reset),
+        };
+
+        writer.Write(color);
+        writer.Write(label);
+        writer.Write(Ansi.Reset);
+        writer.Write(": ");
+        writer.WriteLine(diagnostic.Message);
+
+        if (diagnostic.File is null)
+            return;
+
+        var file = diagnostic.File;
+        var lineNumberWidth = diagnostic.File.Line.ToString().Length;
+
+        writer.WriteLine($" {new string(' ', lineNumberWidth)}{file.File}:{file.Line}:{file.Column}");
+        writer.WriteLine($"{new string(' ', lineNumberWidth)} | ");
+
+        var sourceLine = TryReadLine(file.File, file.Line);
+        if (sourceLine != null)
+        {
+            writer.Write($"{file.Line.ToString().PadLeft(lineNumberWidth)} | ");
+            writer.WriteLine(sourceLine);
+
+            writer.Write(new string(' ', lineNumberWidth));
+            writer.Write(" | ");
+            writer.Write(new string(' ', file.Column - 1));
+            writer.Write(color);
+            writer.Write(new string('^', Math.Max(1, file.Length)));
+            writer.WriteLine(Ansi.Reset);
+        }
+
+        writer.WriteLine($"{new string(' ', lineNumberWidth)} |");
+
+        if (!string.IsNullOrWhiteSpace(diagnostic.Help))
+        {
+            writer.WriteLine($"   = help: {diagnostic.Help}");
+        }
+    }
+
+    private static string? TryReadLine(string file, int line)
+    {
+        try
+        {
+            using var reader = new StreamReader(file);
+            for (var i = 1; i < line; i++)
+            {
+                if (reader.ReadLine() == null)
+                    return null;
+            }
+
+            return reader.ReadLine();
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    private static class Ansi
+    {
+        public const string Reset = "\e[0m";
+        public const string Red = "\e[31m";
+        public const string Yellow = "\e[33m";
+        public const string Cyan = "\e[36m";
+    }
 }