Merge pull request dlang#2927 from Geod24/what-the-heck-seriously

Fix issue 20559: AA.clear segfault when used with alias this
merged-on-behalf-of: Nicholas Wilson <thewilsonator@users.noreply.github.com>

src/object.d

@@ -2163,13 +2163,13 @@ alias AssociativeArray(Key, Value) = Value[Key];
  * Params:
  *      aa =     The associative array.
  */
-void clear(T : Value[Key], Value, Key)(T aa)
+void clear(Value, Key)(Value[Key] aa)
 {
     _aaClear(*cast(AA *) &aa);
 }
 
 /* ditto */
-void clear(T : Value[Key], Value, Key)(T* aa)
+void clear(Value, Key)(Value[Key]* aa)
 {
     _aaClear(*cast(AA *) aa);
 }
@@ -2182,6 +2182,25 @@ void clear(T : Value[Key], Value, Key)(T* aa)
     assert("k1" !in aa);
 }
 
+// Issue 20559
+@system unittest
+{
+    static class Foo
+    {
+        int[string] aa;
+        alias aa this;
+    }
+
+    auto v = new Foo();
+    v["Hello World"] = 42;
+    v.clear;
+    assert("Hello World" !in v);
+
+    // Test for T*
+    static assert(!__traits(compiles, (&v).clear));
+    static assert( __traits(compiles, (*(&v)).clear));
+}
+
 /***********************************
  * Reorganizes the associative array in place so that lookups are more
  * efficient.