[Issue 23314] New: Language spec falsely states that struct field invariants are checked

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23314

          Issue ID: 23314
           Summary: Language spec falsely states that struct field
                    invariants are checked
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dlang.org
          Assignee: nobody at puremagic.com
          Reporter: snarwin+bugzilla at gmail.com

The language spec's section on struct invariants [1] states the following:

> Any invariants for fields are applied before the struct invariant.

However, this has apparently never been true. According to run.dlang.io, all
compiler versions since DMD 2.066.1 compile the following program such that it
runs to completion successfully, which is only possible if S's invariant is
never checked:

---
struct S
{
    invariant {
        assert(0);
    }
}

struct T
{
    S s;
    invariant {
        assert(1);
    }
    void fun() {}
}

void main()
{
    T t;
    t.fun();
}
---

Earlier versions of DMD are unable to parse the invariant contract, which
suggests this behavior has never worked as described in the spec.

See also issue 19537 for a similar error in the spec for class invariants.

[1] https://dlang.org/spec/struct.html#Invariant

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