fixes #19013 [backport:1.6] (#19111)

* fixes #19013 [backport:1.6] * added test case

Author: Araq

compiler/ast.nim

@@ -2101,3 +2101,11 @@ proc skipAddr*(n: PNode): PNode {.inline.} =
 proc isNewStyleConcept*(n: PNode): bool {.inline.} =
  assert n.kind == nkTypeClassTy
  result = n[0].kind == nkEmpty
+
+const
+ nodesToIgnoreSet* = {nkNone..pred(nkSym), succ(nkSym)..nkNilLit,
+ nkTypeSection, nkProcDef, nkConverterDef,
+ nkMethodDef, nkIteratorDef, nkMacroDef, nkTemplateDef, nkLambda, nkDo,
+ nkFuncDef, nkConstSection, nkConstDef, nkIncludeStmt, nkImportStmt,
+ nkExportStmt, nkPragma, nkCommentStmt, nkBreakState,
+ nkTypeOfExpr, nkMixinStmt, nkBindStmt}

compiler/isolation_check.nim

@@ -77,6 +77,17 @@ proc canAlias*(arg, ret: PType): bool =
  var marker = initIntSet()
  result = canAlias(arg, ret, marker)
 
+proc containsVariable(n: PNode): bool =
+ case n.kind
+ of nodesToIgnoreSet:
+ result = false
+ of nkSym:
+ result = n.sym.kind in {skForVar, skParam, skVar, skLet, skConst, skResult, skTemp}
+ else:
+ for ch in n:
+ if containsVariable(ch): return true
+ result = false
+
 proc checkIsolate*(n: PNode): bool =
  if types.containsTyRef(n.typ):
  # XXX Maybe require that 'n.typ' is acyclic. This is not much
@@ -96,7 +107,11 @@ proc checkIsolate*(n: PNode): bool =
  else:
  let argType = n[i].typ
  if argType != nil and not isCompileTimeOnly(argType) and containsTyRef(argType):
- if argType.canAlias(n.typ):
+ if argType.canAlias(n.typ) or containsVariable(n[i]):
+ # bug #19013: Alias information is not enough, we need to check for potential
+ # "overlaps". I claim the problem can only happen by reading again from a location
+ # that materialized which is only possible if a variable that contains a `ref`
+ # is involved.
  return false
  result = true
  of nkIfStmt, nkIfExpr:

compiler/varpartitions.nim

@@ -647,13 +647,6 @@ proc deps(c: var Partitions; dest, src: PNode) =
  when explainCursors: echo "D not a cursor ", d.sym, " reassignedTo ", c.s[srcid].reassignedTo
  c.s[vid].flags.incl preventCursor
 
-const
- nodesToIgnoreSet = {nkNone..pred(nkSym), succ(nkSym)..nkNilLit,
- nkTypeSection, nkProcDef, nkConverterDef,
- nkMethodDef, nkIteratorDef, nkMacroDef, nkTemplateDef, nkLambda, nkDo,
- nkFuncDef, nkConstSection, nkConstDef, nkIncludeStmt, nkImportStmt,
- nkExportStmt, nkPragma, nkCommentStmt, nkBreakState,
- nkTypeOfExpr, nkMixinStmt, nkBindStmt}
 
 proc potentialMutationViaArg(c: var Partitions; n: PNode; callee: PType) =
  if constParameters in c.goals and tfNoSideEffect in callee.flags:

tests/isolate/tisolate2.nim

@@ -0,0 +1,22 @@
+discard """
+ errormsg: "expression cannot be isolated: a_to_b(a)"
+ line: 22
+"""
+
+# bug #19013
+import std/isolation
+
+type Z = ref object
+ i: int
+
+type A = object
+ z: Z
+
+type B = object
+ z: Z
+
+func a_to_b(a: A): B =
+ result = B(z: a.z)
+
+let a = A(z: Z(i: 3))
+let b = isolate(a_to_b(a))