[Issue 17261] Implicit cast from static array to immutable should not be allowed

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17261

ZombineDev <petar.p.kirov at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |safe
             Status|NEW                         |RESOLVED
                 CC|                            |petar.p.kirov at gmail.com
           Hardware|x86_64                      |All
         Resolution|---                         |DUPLICATE
                 OS|Linux                       |All

--- Comment #6 from ZombineDev <petar.p.kirov at gmail.com> ---
(In reply to hsteoh from comment #0)
> Code:
> --------
> import std.stdio;
> 
> char[32] func() {
>     char[32] staticArr = "A123456789abcdefB123456789abcdef"; // canary
>     return staticArr; // OK, by-value return
> }
> 
> string gunk() {
>     string x = func(); // implicit conversion char[16] -> string
>     writeln(x.ptr);
>     writeln(x);
>     return x;
> }
> 
> void main() {
>     auto s = gunk();
>     writeln(s.ptr);
>     writeln(s);
> }
> --------
> 
> 
> Output:
> --------
> 7FFCD89895C0
> A123456789abcdefB123456789abcdef
> 7FFCD89895C0
> 9abcdef ����
> --------
> 
> 
> Basically, func() returns a static array by value, so it resides on the
> stack. The implicit conversion in gunk() produces a slice of this stack data
> (red flag), which gets corrupted (overwritten) when it returns to main().
> 
> Implicitly casting static arrays to immutable should not be allowed.

After commenting-out the writeln calls I get:
scope_test2.d(12): Error: scope variable x may not be returned
when compiling with -dip1000 & DMD 2.073.2.

(Without commenting-out the writeln calls I still get a compiler error, but
it's because not all of Phobos is compatible with -dip1000.)

After replacing gunk with the one posted above:
string gunk() {
    string x = func()[]; // still allowed, but shouldn't be
    writeln(x.ptr);
    writeln(x);
    return x;
}

I get the same message:
scope_test3.d(12): Error: scope variable x may not be returned

*** This issue has been marked as a duplicate of issue 12625 ***

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