Variant segfault (#10697)

* Reference correct issue for test

* Variant: Fix Segfault on adding in wrapped AA

Author: Inkrementator

std/variant.d

@@ -850,7 +850,14 @@ public:
      */
     @property inout(T) get(T)() inout
     {
-        inout(T) result = void;
+        static union SupressDestructor {
+            T val;
+        }
+
+        /* If this function fails and it throws, copy elision will not run and the destructor might be called.
+         * But since this value is void initialized, this is undesireable.
+         */
+        inout(SupressDestructor) result = void;
         static if (is(T == shared))
             alias R = shared Unqual!T;
         else
@@ -861,7 +868,7 @@ public:
         {
             throw new VariantException(type, typeid(T));
         }
-        return result;
+        return result.val;
     }
 
     /// Ditto
@@ -3256,7 +3263,7 @@ if (isAlgebraic!VariantType && Handler.length > 0)
     auto v = Variant(aa); // compile error
 }
 
-// https://issues.dlang.org/show_bug.cgi?id=8195
+// https://github.com/dlang/phobos/issues/9585
 // Verify that alignment is respected
 @safe unittest
 {
@@ -3268,3 +3275,31 @@ if (isAlgebraic!VariantType && Handler.length > 0)
     enum FP_SIZE = (int function()).sizeof;
     static assert(AFoo1.sizeof >= double.sizeof + FP_SIZE);
 }
+
+// https://github.com/dlang/phobos/issues/10518
+@system unittest
+{
+    import std.exception : assertThrown;
+
+    struct Huge {
+        real a, b, c, d, e, f, g;
+    }
+    Huge h = {1,1,1,1,1,1,1};
+    Variant variant = Variant([
+            "one": Variant(1),
+    ]);
+    // Testing that this doesn't segfault. Future work might make enable this
+    assertThrown!VariantException(variant["three"] = 3);
+    assertThrown!VariantException(variant["four"] = Variant(4));
+    /* Storing huge works too, value will moved to the heap
+    * Testing this as a regression test here as the AA handling code is still somewhat brittle and might add changes
+    * that depend payload size in the future
+    */
+    assertThrown!VariantException(variant["huge"] = Variant(h));
+    /+
+    assert(variant["one"] == Variant(1));
+    assert(variant["three"] == Variant(3));
+    assert(variant["three"] == 3);
+    assert(variant["huge"] == Variant(h));
+    +/
+}