Fix #22713: Make size unknown for tyForward (#22714)

Close #22713

---------

Co-authored-by: SirOlaf <>
(cherry picked from commit fcf4c1ae17)

compiler/sizealignoffsetimpl.nim

@@ -433,10 +433,9 @@ proc computeSizeAlign(conf: ConfigRef; typ: PType) =
     typ.paddingAtEnd = typ.base.paddingAtEnd
 
   of tyForward:
-    # is this really illegal recursion, or maybe just unknown?
-    typ.size = szIllegalRecursion
-    typ.align = szIllegalRecursion
-    typ.paddingAtEnd = szIllegalRecursion
+    typ.size = szUnknownSize
+    typ.align = szUnknownSize
+    typ.paddingAtEnd = szUnknownSize
 
   of tyStatic:
     if typ.n != nil:

tests/pragmas/t22713.nim

@@ -0,0 +1,12 @@
+import std/macros
+
+
+template myPragma(x: int) {.pragma.}
+
+type
+  A = object
+    x: int64
+
+  B {.myPragma(sizeof(A)).} = object
+
+doAssert B.getCustomPragmaVal(myPragma) == 8