Guide to debugging WvdS FPC RAD Studio extensions and applications.

Debug logging requires two conditions:

1. Compile-time: Compile with -dDEBUG
2. Runtime: Start extension with –debug parameter

{$IFDEF DEBUG}
procedure LogDebugTrace(const AMessage: string; const AArgs: array of const);
begin
  if not DebugEnabled then Exit;
  WriteToDebugLog(Format('[%s] %s', [
    FormatDateTime('hh:nn:ss.zzz', Now),
    Format(AMessage, AArgs)
  ]));
end;
{$ENDIF}

• Format: debug-yymmddhhnnss.log
• Location: ~/binaries/logs/
• Never commit to ~/sources/

For detailed debugging with call stack:

procedure LogDebugTrace(const AMessage: string; const AArgs: array of const);
var
  CallStack: string;
begin
  {$IFDEF DEBUG}
  if not DebugEnabled then Exit;
 
  (* Call Stack with get_caller_frame / get_frame *)
  CallStack := GetCallStackTrace;
 
  WriteToDebugLog(Format(
    '[%s] %s'#13#10 +
    '   at %s'#13#10 +
    '   Parameters: %s',
    [
      FormatDateTime('yyyy-MM-dd hh:nn:ss.zzz', Now),
      Format(AMessage, AArgs),
      CallStack,
      FormatParams(AArgs)
    ]
  ));
  {$ENDIF}
end;

function GetCallStackTrace: string;
var
  Frame: Pointer;
  Addr: Pointer;
  Info: string;
begin
  Result := '';
  {$IFDEF DEBUG}
  Frame := get_frame;
  while Frame <> nil do
  begin
    Addr := get_caller_addr(Frame);
    Info := BackTraceStrFunc(Addr);  (* Unit:Line Format *)
    if Info <> '' then
      Result := Result + '   at ' + Info + #13#10;
    Frame := get_caller_frame(Frame);
  end;
  {$ENDIF}
end;

================================================================================
DEBUG LOG: debug-260112143022.log
Started: 2026-01-12 14:30:22.001
================================================================================

[2026-01-12 14:30:22.001] Application started with --debug
   at TWvdSApplication.Initialize(Application.Main.pas:42)
   at program.main(extension_main.pas:398)
   Parameters: (CommandLine='--debug')

[2026-01-12 14:30:22.015] Loading configuration
   at TWvdSToolchainConfigService.LoadFromSettings(Toolchain.ConfigService.pas:156)
   at TWvdSToolchainConfigService.AutoDetectAll(Toolchain.ConfigService.pas:89)
   at DoActivate(extension_main.pas:368)
   Parameters: (ConfigPath='~/.vscode/settings.json')

[2026-01-12 14:30:22.042] Service initialized
   at TWvdSBuildService.Initialize(Build.Service.pas:45)
   at DoActivate(extension_main.pas:370)
   Parameters: (ServiceName='BuildService', Mode=debug)

================================================================================
ERROR TRACE (if any):
================================================================================

[2026-01-12 14:30:24.500] ERROR: File not found
   at ValidateBuildPath(Build.Service.pas:144)
   at GenerateCleanCommand(Build.Service.pas:174)
   at OnBuildClean(extension_main.pas:112)
   Parameters: (Path='~/invalid/path', ValidationResult=False)
   Exception: EFileNotFound
   Message: The specified path does not exist
   Stack Trace:
      Build.Service.ValidateBuildPath(144)
      Build.Service.GenerateCleanCommand(179)
      extension_main.OnBuildClean(112)
      VSCode.Commands.ExecuteCommand(89)

1. Open the extension project in VS Code
2. Press F5 or Run > Start Debugging
3. A new VS Code window opens
4. The extension is loaded there

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Run Extension",
      "type": "extensionHost",
      "request": "launch",
      "args": [
        "--extensionDevelopmentPath=${workspaceFolder}"
      ],
      "outFiles": [
        "${workspaceFolder}/dist/**/*.js"
      ]
    }
  ]
}

Since the code is transpiled (Pascal → JavaScript), breakpoints only work with source maps:

1. Compile with -Jm (generate source map)
2. Set breakpoints in the .pas file
3. VS Code maps to the JavaScript position

The WvdS Output Channel shows runtime messages:

1. View → Output
2. Select „WvdS“ in the dropdown

// In code
LogInfo('Information message');
LogWarn('Warning message');
LogError('Error: %s', [E.Message]);

For low-level debugging:

1. Help → Toggle Developer Tools
2. Open Console tab
3. JavaScript errors and console.log visible

Diagnosis:

# Check extension logs
code --verbose --log trace

Common causes:

• Syntax error in generated JavaScript
• Missing dependencies in package.json
• Wrong path in „main“

Diagnosis:

1. Open Developer Console
2. Execute command
3. Check for errors

Common causes:

• Command not in contributes.commands
• Handler not registered
• Exception in handler

Diagnosis:

1. Right-click in WebView → „Inspect“
2. Browser DevTools open

Common causes:

• Wrong HTML
• CSP blocks resources
• JavaScript error

{$IFDEF DEBUG}
var
  StartTime: TDateTime;
 
procedure StartTiming(const AOperation: string);
begin
  StartTime := Now;
  LogDebug('Starting: %s', [AOperation]);
end;
 
procedure EndTiming(const AOperation: string);
begin
  LogDebug('Completed: %s in %d ms', [
    AOperation,
    MilliSecondsBetween(Now, StartTime)
  ]);
end;
{$ENDIF}

pas2js/JavaScript has garbage collection, but watch out for:

• Circular references with closures
• Event handlers not removed
• Large arrays/objects in memory

// Test with debug output
procedure TMyTest.TestFeature;
begin
  {$IFDEF DEBUG}
  LogDebug('Testing with input: %s', [TestInput]);
  {$ENDIF}
 
  Result := ProcessInput(TestInput);
 
  {$IFDEF DEBUG}
  LogDebug('Result: %s', [Result]);
  {$ENDIF}
 
  CheckEquals(Expected, Result);
end;

• Security Guidelines
• Testing
• Extension Development