[Solved] Need warning about missing bool result

[AlexTP]

Code: Pascal  [Select][+][-]

1. {$mode objfpc}
2. program test_bool_res;
3.  
4. function AskTest: boolean;
5. begin
6.   if Random(2)=0 then exit;
7.  
8.   writeln('body');
9.  
10.   Result:= true;
11. end;
12.  
13. begin
14.   if AskTest then writeln('ok') else writeln('no');
15. end.
16.  

Can FPC show the warning about missing bool result when I do "exit" and not "exit(false)" at line 6?

[Jonas Maebe]

If you compile with -Oodfa (enabled data flow analysis), the compiler will print a warning that the function result is not initialised at that point.

[AlexTP]

Great!
This test shows the DFA fails here, false warning.

Code: Pascal  [Select][+][-]

1. {$mode objfpc}
2. program test_bool_res;
3.  
4. function GetItem(out S: UnicodeString): boolean;
5. const
6.   cnt: integer = 0;
7. begin
8.   inc(cnt);
9.   Result:= cnt<2;
10.   S:= 'aa';
11. end;
12.  
13. var
14.   S: UnicodeString;
15. begin
16.   while GetItem(S) do
17.     writeln('item: ', S);
18. end.
19.  

[Jonas Maebe]

That bug has been fixed in trunk already.

[AlexTP]

Great.
I am fighting with these 2 false positives of DFA (variable result not inited).
Did not yet make simple example.

1. function api_ed_attr
2. function api_msg_box_ex

Here:
https://github.com/Alexey-T/CudaText/blob/master/app/formmain_py_api.inc

[Thaddy]

https://www.freepascal.org/docs-html/rtl/system/exit.html
Why should you want a warning? Exit is not a good idea anyway.

[AlexTP]

@Thaddy
I don't want a warning, bug DFA analysis gives the warning that 'variable result not initialized'. It is false positive as  I see.

For these cases
1. function api_ed_attr
2. function api_msg_box_ex

[AlexTP]

@Jonas,
can you tell why DFA gives warning here?

test_bool_res.pas(11,3) Hint: Local variable "res" of a managed type does not seem to be initialized

[Jonas Maebe]

That's also fixed on trunk.

Unrelated: using fillchar on managed types (as you do in proc_appvariant) is always very dangerous, and wrong in your program. The reason is that with the result variable this can result in memory leaks in case the compiler passes a temp that was already used before and still contains valid data as result (because the Items field won't be finalized in that case). If you want to intiialize it in a safe way, use "result := default(TAppVariant);".

[AlexTP]

Fixed, avoided FillChar here, thanks.