https://issues.dlang.org/show_bug.cgi?id=18792

Per Nordlöw <per.nordlow@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |safe

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https://issues.dlang.org/show_bug.cgi?id=18792

Per Nordlöw <per.nordlow@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

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https://issues.dlang.org/show_bug.cgi?id=18792

Walter Bright <bugzilla@digitalmars.com> changed:

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

--- Comment #1 from Walter Bright <bugzilla@digitalmars.com> ---
Please reduce to a much smaller case of what the problem is.

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https://issues.dlang.org/show_bug.cgi?id=18792

--- Comment #2 from Per Nordlöw <per.nordlow@gmail.com> ---
I managed to reduce the code snippet to


struct SSOString
{
pure nothrow @nogc:

    inout(char)[] opSlice() inout return scope @trusted // TODO @safe for
-dip1000?
    {
        return small.data[0 .. small.length]; // scoped. TODO use .ptr when
proved stable
    }

    struct Small
    {
        ubyte length; // TODO only first 4 bits are needed to represent a
length between 0-15, use other 4 bits
        char[15] data;
    }

    struct Raw                  // same memory layout as `char[]`
    {
        size_t length;          // can be bit-fiddled without GC allocation
        char* ptr;
    }

    union
    {
        Raw raw; // PROBLEM this declaration prevents DIP-1000 scope analysis
from kicking in in `opSlice`
        Small small;
    }
}

@safe pure nothrow @nogc unittest
{
    char[] shouldFail1() @safe pure nothrow @nogc
    {
        SSOString x;
        return x[];             // TODO should fail with -dip1000
    }
}


When compiled with -dip100 the function `shouldFail1` should fail to compile but it does still compile. When I remove the line

    Raw raw;

scope analysis suddenly starts working which correctly triggers the error

foo.d(33,17): Error: returning `x.opSlice()` escapes a reference to local
variable `x`
        return x[];             // TODO should fail with -dip1000


Small enough, Walter?

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https://issues.dlang.org/show_bug.cgi?id=18792

--- Comment #3 from Per Nordlöw <per.nordlow@gmail.com> ---
(In reply to Per Nordlöw from comment #2)
> Small enough, Walter?

Forgot to remove obselete comments. Here's a new version with irrelevant comments removed.


struct SSOString
{
pure nothrow @nogc:

    inout(char)[] opSlice() inout return scope @trusted
    {
        return small.data[0 .. small.length];
    }

    struct Small
    {
        ubyte length;
        char[15] data;
    }

    struct Raw
    {
        size_t length;
        char* ptr;
    }

    union
    {
        Raw raw; // PROBLEM this declaration prevents DIP-1000 scope analysis
from kicking in in `opSlice`
        Small small;
    }
}

@safe pure nothrow @nogc unittest
{
    char[] shouldFail1() @safe pure nothrow @nogc
    {
        SSOString x;
        return x[];             // TODO should fail with -dip1000
    }
}

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https://issues.dlang.org/show_bug.cgi?id=18792

--- Comment #4 from Walter Bright <bugzilla@digitalmars.com> ---
much better, thank you

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https://issues.dlang.org/show_bug.cgi?id=18792

Dennis <dkorpel@live.nl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |dkorpel@live.nl
         Resolution|---                         |DUPLICATE
           Severity|enhancement                 |normal

--- Comment #5 from Dennis <dkorpel@live.nl> ---
I know this issue was first, but 21868 already got a pull.

It is the same problem: `return scope` without `ref return` applies return the values (e.g. SSOString.raw.ptr), not the address of SSOString itself (e.g. SSOString.small.data.ptr), but the compiler doesn't check for return-scope or return-ref, just return. The declaration of `Raw raw` is needed because otherwise SSOString has no pointers, so return scope is stripped away, so the compiler can't mistake the return attribute anymore and raises the correct error.

*** This issue has been marked as a duplicate of issue 21868 ***

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