fix Issue 17145 - [REG2.066.0] Tuple expansion error in local enum de…

…claration

src/dmd/sideeffect.d

@@ -390,7 +390,16 @@ VarDeclaration copyToTemp(StorageClass stc, const char[] name, Expression e)
 Expression extractSideEffect(Scope* sc, const char[] name,
     ref Expression e0, Expression e, bool alwaysCopy = false)
 {
-    if (!alwaysCopy && isTrivialExp(e))
+    //printf("extractSideEffect(e: %s)\n", e.toChars());
+
+    /* The trouble here is that if CTFE is running, extracting the side effect
+     * results in an assignment, and then the interpreter says it cannot evaluate the
+     * side effect assignment variable. But we don't have to worry about side
+     * effects in function calls anyway, because then they won't CTFE.
+     * https://issues.dlang.org/show_bug.cgi?id=17145
+     */
+    if (!alwaysCopy &&
+        (sc.flags & SCOPE.ctfe) ? !hasSideEffect(e) : isTrivialExp(e))
         return e;
 
     auto vd = copyToTemp(0, name, e);

test/compilable/fix17145.d

@@ -0,0 +1,13 @@
+// https://issues.dlang.org/show_bug.cgi?id=17145
+
+auto tuple(T...)(T t) {
+    struct Result {
+        T expand;
+    }
+    return Result(t);
+}
+
+void baz()
+{
+    enum zoo = tuple(1, 2).expand; // Error: value of __tup1847 is not known at compile time
+}