https://issues.dlang.org/show_bug.cgi?id=20581

Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
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                 CC|                            |bugzilla@digitalmars.com

--- Comment #1 from Walter Bright <bugzilla@digitalmars.com> ---
The cause of this is that assert() may throw an exception and so the stack
reference (used by -checkaction=context) will outlive main() as the stack is
unwound.

The error is correctly generated, suppressing it will lead to stack corruption. I don't think much can be done about it. For context to work, the assert() expression needs to not rely on pointers into the stack frame.

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https://issues.dlang.org/show_bug.cgi?id=20581

--- Comment #2 from moonlightsentinel@disroot.org ---
(In reply to Walter Bright from comment #1)
> The cause of this is that assert() may throw an exception and so the stack
> reference (used by -checkaction=context) will outlive main() as the stack is
> unwound.
> 
> The error is correctly generated, suppressing it will lead to stack corruption. I don't think much can be done about it. For context to work, the assert() expression needs to not rely on pointers into the stack frame.

No, the stack reference is not part of the exception because __assertOp4 is turned into a string before throwing an exception.

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https://issues.dlang.org/show_bug.cgi?id=20581

kinke <kinke@gmx.net> changed:

           What    |Removed                     |Added
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                 CC|                            |kinke@gmx.net

--- Comment #3 from kinke <kinke@gmx.net> ---
This seems to be a 2.091 regression. Using an explicit non-temporary still works, with an equivalent lifetime of the temporary:

void main() @safe
{
    int[5] a = [ 1, 2, 3, 4, 5 ];
    {
        auto blub = retro(a[]).source;
        assert(blub is a[]);
    }
}

The original expression with temporary is lowered to:

assert(((int[] __assertOp4 = retro(a[]).source;) , __assertOp4) is a[],
_d_assert_fail(__assertOp4, a[]));

// Generates the message for -checkaction=context and takes both
// operands by `auto ref const`.
string _d_assert_fail(ref const(int[]) a, const(int[]) b) { ... }

_d_assert_msg might throw later, using the generated msg, as Florian mentioned.

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https://issues.dlang.org/show_bug.cgi?id=20581

--- Comment #4 from moonlightsentinel@disroot.org ---
(In reply to kinke from comment #3)
> This seems to be a 2.091 regression.

That a side effect of https://github.com/dlang/dmd/pull/10550 which made dmd use ref whenever possible. This avoids behaviour changes due to additional constructor/destructor calls when -checkaction=context is used.

> Using an explicit non-temporary still works, with an equivalent lifetime of the temporary:

DIP1000 handles variables from different statements just fine but struggles if multiple temporaries are used within a single statement. Note that this problem is not tied to -checkaction=context, see e.g. https://github.com/dlang/dmd/pull/10550#issuecomment-559996626

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https://issues.dlang.org/show_bug.cgi?id=20581

Dlang Bot <dlang-bot@dlang.rocks> changed:

           What    |Removed                     |Added
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           Keywords|                            |pull

--- Comment #5 from Dlang Bot <dlang-bot@dlang.rocks> ---
@MoonlightSentinel created dlang/dmd pull request #12258 "Fix Issue 20581 - DIP1000 wrongly flags hidden ref temporary" fixing this issue:

- Fix Issue 20581 - DIP1000 wrongly flags hidden ref temporary

  Restrict errors for escaping by ref to `VarDeclaration`'s that actually
  outlive the referenced `VarDeclaration`.

  The only exceptions to this rule are references to other `ref` parameters

https://github.com/dlang/dmd/pull/12258

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https://issues.dlang.org/show_bug.cgi?id=20581

Dlang Bot <dlang-bot@dlang.rocks> changed:

           What    |Removed                     |Added
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             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #6 from Dlang Bot <dlang-bot@dlang.rocks> ---
dlang/dmd pull request #12258 "Fix Issue 20581 - DIP1000 wrongly flags hidden ref temporary" was merged into master:

- 7fa99471be7ecaba5c9472a1a5d7f2f78c3c1fde by MoonlightSentinel:
  Fix Issue 20581 - DIP1000 wrongly flags hidden ref temporary

  Restrict errors for escaping by ref to `VarDeclaration`'s that actually
  outlive the referenced `VarDeclaration`.

  The only exceptions to this rule are references to other `ref` parameters

https://github.com/dlang/dmd/pull/12258

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