Bug: Local variables with duplicate names shows wrong value in debugger

[Lars Fosdal 1792]

https://quality.embarcadero.com/browse/RSP-23056

 

Debugger watch / evaluate shows wrong values for inline declared local variables with duplicate names within same routine.

Put a breakpoint on each of the lines with breakpoint in the comment.
Run
at A, hover over variable s, or evaluate s shows value A
at C, hover over variable s, or evaluate s shows value A - should have been C
The actual value is C - so it is a debugger bug

program ReusedLocalVariables;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;

type
  TTest = class
  public
    procedure Check(const aValue: String);
    procedure Test;
  end;

procedure TTest.Check(const aValue: String);
begin
  Writeln(aValue);
end;

procedure TTest.Test;
begin
  begin
    var s := 'A';
    Check(s);   // Breakpoint: S shows 'A' - Output in check = 'A'
  end;
  begin
    var s := 'C';
    Check(s);   // Breakpoint: S shows 'A' - should have been 'C' - Output in check = 'C'
  end;
end;

begin
  try
    var Test := TTest.Create;
    try
      Test.Test;
      Test.Free;
    except
      on E: Exception do
        Writeln(E.ClassName, ': ', E.Message);
    end;
  finally
    Write('Press Enter: ');
    Readln;
  end;
end.

 

[Sherlock 663]

1) Don't use it.

Secondly: Don't use it like that.

 

😉

[David Heffernan 2345]

You reap what you sow. Don't create multiple variables with the same name. 

 

 

[Clément 148]

This really should be fixed! Debugging this code structure will be more common as soon as 10.4 will fix inline declaration or when LSP will be released.
 

procedure TTest.Test;
begin
  if SomeCondition then
  begin
    var Qry := 'select * from sometable';
    Check(Qry);   // Breakpoint: S shows 'A' - Output in check = 'A'
  end;
  {..}
  if SomeOtherCondition then
  begin
    var Qry := 'select * from sometable where condition';
    Check(Qry);   // Breakpoint: S shows 'A' - should have been 'C' - Output in check = 'C'
  end;
  {..}
  while SomeCondition do begin
     var Qry := SomeFunction( SomeParameter );
     Check(Qry);
  end;
  
end;

I'm not saying this construction is good or not, but if the new feature allows it, should work as advertised!

 

Don't have much hair left to pull out.