Fix Issue 18044: std.conv.to for implicitly convertible associative arrays

Author: John-Colvin

std/conv.d

@@ -1573,7 +1573,7 @@ Associative array to associative array conversion converts each key
 and each value in turn.
  */
 private T toImpl(T, S)(S value)
-if (isAssociativeArray!S &&
+if (!isImplicitlyConvertible!(S, T) && isAssociativeArray!S &&
     isAssociativeArray!T && !is(T == enum))
 {
     /* This code is potentially unsafe.
@@ -1619,6 +1619,16 @@ if (isAssociativeArray!S &&
     auto d = to!(immutable(short[immutable wstring])[immutable string[double[]]])(c);
 }
 
+@safe unittest
+{
+    import std.algorithm.comparison : equal;
+    import std.array : byPair;
+
+    int[int] a;
+    assert(a.to!(int[int]) == a);
+    assert(a.to!(const(int)[int]).byPair.equal(a.byPair));
+}
+
 private void testIntegralToFloating(Integral, Floating)()
 {
     Integral a = 42;