Fix Issue 22054 - Referencing a fwd-declared field results in many er…

…ror messages

src/dmd/typesem.d

@@ -2209,7 +2209,17 @@ Expression getProperty(Type t, Scope* scope_, const ref Loc loc, Identifier iden
             if (mt.ty == Tstruct || mt.ty == Tclass || mt.ty == Tenum)
                 s = mt.toDsymbol(null);
             if (s)
+            {
+                // https://issues.dlang.org/show_bug.cgi?id=22054
+                // At this point, a forward referenced struct or class
+                // has already issued an error.
+                auto aggDecl = s.isAggregateDeclaration();
+                if (aggDecl && !aggDecl.members)
+                {
+                    return ErrorExp.get;
+                }
                 s = s.search_correct(ident);
+            }
             if (s && !symbolIsVisible(scope_, s))
                 s = null;
             if (mt != Type.terror)
@@ -3569,7 +3579,11 @@ Expression dotExp(Type mt, Scope* sc, Expression e, Identifier ident, int flag)
         assert(mt.ty == Tstruct || mt.ty == Tclass);
         auto sym = mt.toDsymbol(sc).isAggregateDeclaration();
         assert(sym);
-        if (ident != Id.__sizeof &&
+        if (// https://issues.dlang.org/show_bug.cgi?id=22054
+            // if a class or struct is forward referenced
+            // there is no point in searching for its members
+            sym.members &&
+            ident != Id.__sizeof &&
             ident != Id.__xalignof &&
             ident != Id._init &&
             ident != Id._mangleof &&

test/fail_compilation/test22054.d

@@ -0,0 +1,15 @@
+// https://issues.dlang.org/show_bug.cgi?id=22054
+
+/*
+TEST_OUTPUT:
+---
+fail_compilation/test22054.d(10): Error: class `test22054.exception` is forward referenced when looking for `what`
+---
+*/
+
+class exception;
+
+void main ()
+{
+    assert(exception.what() == "Hello");
+}