Require 2024 edition for error

Author: ntrel

compiler/src/dmd/expression.d

@@ -2363,7 +2363,7 @@ extern (C++) final class CallExp : UnaExp
     bool inDebugStatement;  /// true if this was in a debug statement
     bool ignoreAttributes;  /// don't enforce attributes (e.g. call @gc function in @nogc code)
     bool isUfcsRewrite;     /// the first argument was pushed in here by a UFCS rewrite
-    bool fromOpAssignment;  // set when operator overload method call from assignment
+    bool fromOpAssignment;  // set when operator overload method call from assignment (2024 edition)
     VarDeclaration vthis2;  // container for multi-context
     Expression loweredFrom; // set if this is the result of a lowering
 

compiler/src/dmd/expressionsem.d

@@ -5305,7 +5305,8 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
     {
         result = e;
         auto ce = e.isCallExp();
-        if (!ce)
+        // rvalue error in discardValue from 2024 edition
+        if (!ce || !sc.hasEdition(Edition.v2024))
             return;
         ce.fromOpAssignment = true;
     }