Do not walk into type sub-nodes for cast/conv expr (#10616)

compiler/destroyer.nim

@@ -601,6 +601,12 @@ proc p(n: PNode; c: var Con): PNode =
   of nkNone..nkNilLit, nkTypeSection, nkProcDef, nkConverterDef, nkMethodDef,
       nkIteratorDef, nkMacroDef, nkTemplateDef, nkLambda, nkDo, nkFuncDef:
     result = n
+  of nkCast, nkHiddenStdConv, nkHiddenSubConv, nkConv:
+    result = copyNode(n)
+    # Destination type
+    result.add n[0]
+    # Analyse the inner expression
+    result.add p(n[1], c)
   else:
     result = copyNode(n)
     recurse(n, result)

tests/destructor/tcast.nim

@@ -0,0 +1,18 @@
+discard """
+  cmd: '''nim c --newruntime $file'''
+"""
+
+# Make sure we don't walk cast[T] type section while injecting sinks/destructors
+block:
+  type
+    XY[T] = object
+      discard
+
+  proc `=`[T](x: var XY[T]; v: XY[T]) {.error.}
+  proc `=sink`[T](x: var XY[T]; v: XY[T]) {.error.}
+
+  proc main[T]() =
+    var m = cast[ptr XY[T]](alloc0(sizeof(XY[T])))
+    doAssert(m != nil)
+
+  main[int]()