fixes #25123; fixes #11862; Case object from compileTime proc unable to be passed as static param (#25224)

fixes #25123; fixes #11862

follow up #24442
ref #24441

> To fix this, fields from inactive branches are now detected in
semmacrosanity.annotateType (called in fixupTypeAfterEval) and marked to
prevent the codegen of their assignments. In
#24441 these fields were excluded
from the resulting node, but this causes issues when the node is
directly supposed to go back into the VM, for example as const values. I
don't know if this is the only case where this happens, so I wasn't sure
about how to keep that implementation working.

Object variants fields coming from inactive branches from VM are now
flagged `nfPreventCg`. We can ignore them, as done by the C backends.

Author: ringabout

compiler/semobjconstr.nim

@@ -68,6 +68,10 @@ proc locateFieldInInitExpr(c: PContext, field: PSym, initExpr: PNode): PNode =
     let assignment = initExpr[i]
     if assignment.kind != nkExprColonExpr:
       invalidObjConstr(c, assignment)
+    elif nfPreventCg in assignment.flags:
+      # this is an object constructor node generated by the VM and
+      # this field is in an inactive case branch, just ignore it
+      discard
     elif fieldId == considerQuotedIdent(c, assignment[0]).id:
       return assignment
 
@@ -515,6 +519,10 @@ proc semObjConstr(c: PContext, n: PNode, flags: TExprFlags; expectedType: PType
         invalidObjConstr(c, field)
         hasError = true
         continue
+      elif nfPreventCg in field.flags:
+        # this is an object constructor node generated by the VM and
+        # this field is in an inactive case branch, just ignore it
+        continue
       let id = considerQuotedIdent(c, field[0])
       # This node was not processed. There are two possible reasons:
       # 1) It was shadowed by a field with the same name on the left

tests/objvariant/tconstvariants.nim

@@ -0,0 +1,40 @@
+import std/macros 
+
+# bug #11862
+type
+  Kind = enum kOne, kTwo
+
+  Thing = object
+    case kind: Kind
+      of kOne:
+        v1: int
+      of kTwo:
+        v2: int
+               
+macro magic(): untyped =
+  var b = Thing(kind: kOne, v1: 3)
+  quote do:                       
+    `b`    
+           
+const c = magic()
+
+# bug #25123
+type V = object
+  case a: bool
+  of false: discard
+  of true:  t: int
+
+proc s(): V {.compileTime.} = discard
+proc h(_: V) = discard
+
+proc e(m: static[V]) = h(m)
+template j(m: static[V]) = h(m)
+macro r(m: static[V]) = h(m)
+
+e(s())
+j(s())
+r(s())
+
+s().e()
+s().j()
+s().r()