[Issue 20073] New: Wrong implicit conversion for return type

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20073

          Issue ID: 20073
           Summary: Wrong implicit conversion for return type
           Product: D
           Version: D2
          Hardware: All
               URL: http://dlang.org/
                OS: All
            Status: NEW
          Severity: major
          Priority: P3
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: eyal at weka.io

It seems that some weird interaction between "alias this", "inout" and implicit
return conversions is incorrectly allowing a conversion from an S instance,
which isn't immutable, to an immutable(char)[].

Note the assignment is (correctly) rejected but the return is (incorrectly)
allowed:


struct S {
    char[10] x;
    auto slice() inout { return x[0 .. 10]; }
    alias slice this;
}

string test() {
    S s;
    string str = s; // cannot implicitly convert expression `s` of type `S` to
`string`
    return s;       // and suddenly we can!
}


I'd expect both the assignment and return to fail.

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