BUG False positive warning 214 on mutable output buffer parameter

[by-not]

Bug Report: False positive warning 214 on mutable output buffer parameter

Description

The compiler emits warning 214: possibly a "const" array argument was intended on a function parameter that is intentionally mutable — it is used as an output buffer written to by format(). The warning is a false positive because the parameter is never intended to be read-only.

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Compiler version

pawncc — compiler (version 3.10.10)

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Minimal reproducible example

stock GetPlayerOrgRankName(playerid, dest[], len = sizeof(dest))
{
    if(!IsPlayerInOrg(playerid))
    {
        format(dest, len, "Sin organizacion");
        return false;
    }
    new rank = GetPlayerOrgRank(playerid) - 1;
    format(dest, len, "%s", g_PlayerOrgRanks[playerid][rank]);
    return true;
}

Compiler output:

warning 214: possibly a "const" array argument was intended: "dest"

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Expected behavior

No warning should be emitted. dest[] is a write-only output buffer explicitly passed to format() which modifies it. The compiler should recognize that passing an array as a non-const argument to format() (a native function) marks it as modified/mutable, and therefore const is not appropriate.

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Actual behavior

The compiler emits warning 214 suggesting dest should be const, which is incorrect — declaring it const would prevent format() from writing into it and break the intended functionality.

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Root cause analysis

This appears to be related to the issue described in PR #302 (pawn-lang/compiler): the compiler's flow analysis fails to mark an array symbol as modified when it is passed as a non-const argument to a native function such as format().

In this case:

1. dest[] is passed directly to format() as the output destination.
2. format() is a native whose signature accepts a non-const array — meaning it mutates the buffer.
3. The compiler does not propagate the "modified" flag from the native call back to the dest symbol in the caller's scope.
4. As a result, the compiler incorrectly concludes that dest is never modified and suggests it be marked const.

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Workaround

Adding a dummy write before the format() call suppresses the warning:

dest[0] = EOS; // forces compiler to recognize dest as mutable
format(dest, len, "...");

This should not be necessary and is purely a workaround for this false positive.