Fully automatic indentation

Overview

Since 0.9.29 the lazarus source editor has a new algorithm for automatic indentation on pressing Enter or on pasting code from clipboard. This new algorithm works only for pascal and does not use static rules, but parses the sources to imitate the indentation. Most other editors use either a fixed set of rules or a set of options to configure the rules. This is semi automatic indentation. These options are either too simple or too complex. And the other editors only allow one set of rules, so editing sources with different policies is difficult.

Fully automatic indentation tries to guess the rules from the surrounding code. It does that by searching for similar code and copying the indent.

Because it works fully automatic there are only a few options. You can disable it, you can setup the search scope and you can provide an example code: Codetools Options: Indentation. You do not need to learn rules, just write pascal.

How it works

Indent on paste from clipboard

For example you have the code:

procedure TMainForm.Button1Click(Sender: TObject);
begin
|
end;

You place the cursor at column 1 and paste the code

    if Visible then
    begin
    end;

Note that the code on the clipboard is already indented by 4.

The indenter first scans the code, finds out, that the insertion position is in a begin..end block of a procedure. With the standard options it searches the code in front for other procedure begin..end blocks. If it does not find the code it searches behind the code, then in all units of the project (or package) and finally in the example code of the options. For instance it finds:

procedure TMainForm.FormPaint(Sender: TObject);
begin
  with Canvas do FillRect(0,0,Width,Height);
end;

The indentation of the first token with is 2. The indentation of the first token of clipboard code is 4, so the indenter unindents the code by 2, resulting in:

procedure TMainForm.Button1Click(Sender: TObject);
begin
  if Visible then
  begin
  end;|
end;

The indenter always indents the whole block, not every line. For example pasting

DoSomething(Param1,
            Param2);

will keep the indent both lines by the same amount, keeping the two Params aligned.

The indenter scans what is inserted. For instance pasting

end;

will end the the begin block, resulting in:

procedure TMainForm.Button1Click(Sender: TObject);
begin
end;|
end;

Examples

Sometimes record and classes are aligned to the keywords instead of start of last line.

type TMyRecord = record
                 i: integer;
                 end;

At the moment the indenter supports only amount of spaces, not aligning to keywords or symbols.

begin end

procedure Do;
var
  i: integer; // indent after var
begin         // no indent after procedure, no indent before procedure-begin, unindent after var section
  if expr then
  begin       // no indent after then, no indent before then-begin
    Code;     // indent after begin
  end;        // unindent before end
end;

procedure Do;
begin
  if expr then begin  
    Code;             // indent after begin
  end;                // unindent before end
end;

procedure Do;
begin
  if expr then
    begin   // indent after then and unindent after then-statement
    Code;   // no indent after begin
    end;    // no unindent before end
end;

procedure Do;
begin
  if expr then
    begin     // indent after then and unindent after then-statement
      Code;   // indent after begin
    end;      // unindent before end
end;

repeat until

I never saw code other than this:

repeat
  Code; // indent after repeat
until ; // unindent before until

try finally

I never saw code other than this:

try
  Code;     // indent after try
finally     // unindent before finally
  on e do ; // indent after finally
end;        // unindent before finally-end

case of end

case expr of
1: ;   // no indent after case-of
2: 
  Code;    // indent after case-colon
3: 
  begin    // indent after case-colon
    Code;  // indent after case-colon-begin
  end;     // unindent before case-colon-end, unindent after case-colon-end
else       // no indent case-else 
  Code;    // indent after case-else
end;       // unindent after case-else statements

case expr of
           
  1: ; // indent after case-of

  2: 
  begin    // no indent after case-colon
  end;
else       // no indent before case-else
end;       // no indent before case-end

if then else

if expr then
  Code
else
  Code;

if expr or
  expr or
  expr then
  Code
else
  Code;

if expr 
  or expr
then
  Code
else
  Code;

if SrcEdit.SelectionAvailable
and SrcEdit.CaretInSelection(CaretPos)
then Expression := SrcEdit.GetText(True)
else Expression := Identifier;
if not DebugBoss.Evaluate(Expression, DebugEval)
or (DebugEval = '')
then DebugEval := '???';