[Issue 23657] New: [REG2.101] Incorrect error escape reference to stack allocated value

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23657

          Issue ID: 23657
           Summary: [REG2.101] Incorrect error escape reference to stack
                    allocated value
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: johanengelen at weka.io

Testcase succeeds with dmd <= 2.100, but fails since dmd 2.101

> ~/dcompilers/dmd-2.101.2/osx/bin/dmd -c -o- testcase.d
testcase.d(46): Error: escaping reference to stack allocated value returned by
`theLA().agent.members()`

I believe this diagnostic is incorrect, there is no escaping of a stack
allocated value. (but I am not 100.000% sure)


Testcase:
```
import std.algorithm: map;
import std.array: array;

struct SmallTable(K, V, ushort capacity) {
    ushort _length = 5;
    K[capacity] keys;
    V[capacity] values;

    auto byKey()  {
        return keys[0 .. _length];
    }
}

struct SmallSet(K, ushort capacity) {
    private alias V = ubyte[1];
    private SmallTable!(K, V, capacity) table;

    auto items()  {
        return table.byKey;
    }
}

struct NodeId {
    ushort value;
}

struct RaftId {
    NodeId nodeId;
}

public struct RA {
    SmallSet!(RaftId, 13) members() { return SmallSet!(RaftId, 13)(); }
}

class LA {
    RA agent;
}

private __gshared LA leadAI = new LA();

ref auto theLA() {
    return leadAI;
}

auto foo() {
    return theLA.agent.members.items.map!(rid => rid.nodeId).array;
}

void main() {
    int i = 0;
    auto a = foo();

    import std.stdio;
    writeln("&i = ", &i);
    writeln("&leadAI = ", &leadAI);
    writeln("leadAI = ", cast(void*)leadAI);
    writeln("a.ptr = ", a.ptr);
    writeln("a.length = ", a.length);
    writeln("a = ", a);
    import core.memory : GC;
    writeln("is_gc_allocated = ", GC.addrOf(a.ptr) != null);
}
```

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