[Issue 21675] New: Unsafe aggregate field initializer causes undefined behavior in @safe code

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21675

          Issue ID: 21675
           Summary: Unsafe aggregate field initializer causes undefined
                    behavior in @safe code
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: snarwin+bugzilla at gmail.com

As of DMD 2.095.0, the following program compiles and exhibits undefined
behavior at runtime:

---
struct S
{
    int* p = cast(int*) 0xDEADBEEF;
}

@safe void main()
{
    S s;
    int n = *s.p;
}
---

To prevent this, the compiler must either forbid default initialization of
types with unsafe `.init` values, or enforce that all default initializers are
safe values. [1]

Related: issue 21664.

[1] https://dlang.org/spec/function.html#safe-values

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