Dynamic array as a typed constant can easily be modifed

Summary

With writable constants off typed constant dynamic array can easily be modified.

System Information

• Operating system: Linux (Arch Linux)
• Processor architecture: x86-64
• Compiler version: 3.3.1-12060-g3db1415a
• Device: Computer

Steps to reproduce

Compile and run the following program:

program testarr;
{$mode objfpc}
{$WriteableConst off}
const
  i_arr: array of integer = (1, 2, 3);
var
  i: integer;
begin
  for i := 0 to high(i_arr) do begin
    inc(i_arr[i]);
    writeln(i_arr[i]);
  end;
end.

Example Project

See "Steps to reproduce"

What is the current bug behavior?

$ fpc testarr.pas && ./testarr 
Free Pascal Compiler version 3.3.1 [2022/11/05] for x86_64
Copyright (c) 1993-2022 by Florian Klaempfl and others
Target OS: Linux for x86-64
Compiling testarr.pas
Linking testarr
13 lines compiled, 0.1 sec, 143856 bytes code, 55040 bytes data
2
3
4

What is the expected (correct) behavior?

Because this regarding a complete typed constant I expected the compiler to say I could not do the following: inc(i_arr[i]);

To be explicit, this is what I expected:

Free Pascal Compiler version 3.3.1 [2022/11/05] for x86_64
Copyright (c) 1993-2022 by Florian Klaempfl and others
Target OS: Linux for x86-64
Compiling testarr.pas
testarr.pas(10,9) Error: Can't assign values to const variable
testarr.pas(14) Fatal: There were 1 errors compiling module, stopping
Fatal: Compilation aborted
Error: /home/dev/fpc_usr/lib/fpc/3.3.1/ppcx64 returned an error exitcode

I expect this because when I try to modify a complete typed constant record the compiler says it can't assign values to a const variable.

Example:

program testrec;
{$mode objfpc}
{$WriteableConst off}

type
  SomeRec = record
    a: integer;
  end;

const
  rec: SomeRec = (a: 5);

begin
  inc(rec.a);
  writeln(rec.a);
end.

When trying to compile that I get:

Free Pascal Compiler version 3.3.1 [2022/11/05] for x86_64
Copyright (c) 1993-2022 by Florian Klaempfl and others
Target OS: Linux for x86-64
Compiling testrec.pas
testrec.pas(14,7) Error: Can't assign values to const variable
testrec.pas(17) Fatal: There were 1 errors compiling module, stopping
Fatal: Compilation aborted
Error: /home/dev/fpc_usr/lib/fpc/3.3.1/ppcx64 returned an error exitcode

Which I consider to be correct behavior, because of "writable constants off" and this an attempt at direct modification of a typed constant.

Relevant logs and/or screenshots

See "What is the current bug behavior?"