[Issue 19030] New: CTorFlow checking is too aggressive and only checks whether a this call is present

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19030

          Issue ID: 19030
           Summary: CTorFlow checking is too aggressive and only checks
                    whether a this call is present
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: greensunny12 at gmail.com

https://issues.dlang.org/show_bug.cgi?id=18719 introduced a regression as it
only checks whether a this() call is present, but not what the this call
actually does.
For example, this slightly modified example from 18719 no produces an error
even though it sets x only once:

---
struct S
{
    int x = -1;
    this(int y) immutable
    {
        x = y;
        import std.stdio;
        writeln("Ctor called with ", y);
    }
    void opAssign(int) immutable;
}

class C
{
    S x;
    this() immutable
    {
        this(42); /* Initializes x. */
        x = 13; /* Breaking immutable, or ok? */
    }
    this(int x) immutable
    {
    }
}
---

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