Nonref object inheritance hints and converts to base in varargs a…

compiler/ccgexprs.nim

@@ -262,7 +262,9 @@ proc genGenericAsgn(p: BProc, dest, src: TLoc, flags: TAssignmentFlags) =
   # tfShallow flag for the built-in string type too! So we check only
   # here for this flag, where it is reasonably safe to do so
   # (for objects, etc.):
-  if optSeqDestructors in p.config.globalOptions:
+  if optSeqDestructors in p.config.globalOptions or src.lode.kind in {nkObjUpConv, nkObjDownConv}:
+    # If it's an up/down conv it's an non-ref -> non-ref inheritance which is a copy or assignment.
+    # As such the assignment is direct, semantic analysis should handle any errors statically.
     linefmt(p, cpsStmts,
         "$1 = $2;$n",
         [rdLoc(dest), rdLoc(src)])
@@ -2604,11 +2606,12 @@ proc upConv(p: BProc, n: PNode, d: var TLoc) =
                    else:
                      genTypeInfoV1(p.module, dest, n.info)
     if nilCheck != nil:
+      # We only need to do a conversion check if it's a ref object.
+      # Since with non refs either a copy is done or a ptr to the element is passed,
+      # there is nothing dynamic with them and the compiler knows the error happens at semantic analysis.
       linefmt(p, cpsStmts, "if ($1 && !#isObj($2, $3)){ #raiseObjectConversionError(); $4}$n",
               [nilCheck, r, checkFor, raiseInstr(p)])
-    else:
-      linefmt(p, cpsStmts, "if (!#isObj($1, $2)){ #raiseObjectConversionError(); $3}$n",
-              [r, checkFor, raiseInstr(p)])
+
   if n[0].typ.kind != tyObject:
     if n.isLValue:
       putIntoDest(p, d, n,

compiler/lineinfos.nim

@@ -93,6 +93,7 @@ type
     hintUser = "User", hintUserRaw = "UserRaw", hintExtendedContext = "ExtendedContext",
     hintMsgOrigin = "MsgOrigin", # since 1.3.5
     hintDeclaredLoc = "DeclaredLoc", # since 1.5.1
+    hintImplicitObjConv = "ImplicitObjConv"
 
 const
   MsgKindToStr*: array[TMsgKind, string] = [
@@ -202,6 +203,7 @@ const
     hintExtendedContext: "$1",
     hintMsgOrigin: "$1",
     hintDeclaredLoc: "$1",
+    hintImplicitObjConv: "Implicit conversion: Receiver '$2' will not receive fields of sub-type '$1' [$3]"
   ]
 
 const

compiler/semexprs.nim

@@ -633,7 +633,12 @@ proc semArrayConstr(c: PContext, n: PNode, flags: TExprFlags): PNode =
 
       let xx = semExprWithType(c, x, {})
       result.add xx
-      typ = commonType(c, typ, xx.typ)
+      if {xx.typ.kind, typ.kind} == {tyObject} and typ != xx.typ:
+        # Check if both are objects before getting common type,
+        # this prevents `[Derived(), Parent(), Derived()]` from working for non ref objects.
+        result[i] = typeMismatch(c.config, x.info, typ, xx.typ, x)
+      else:
+        typ = commonType(c, typ, xx.typ)
       #n[i] = semExprWithType(c, x, {})
       #result.add fitNode(c, typ, n[i])
       inc(lastIndex)

compiler/transf.nim

@@ -569,10 +569,17 @@ proc transformConv(c: PTransf, n: PNode): PNode =
       result = transformSons(c, n)
   of tyObject:
     var diff = inheritanceDiff(dest, source)
+    template convHint =
+      if n.kind == nkHiddenSubConv and n.typ.kind notin abstractVarRange:
+        # Creates hint on converstion to parent type where information is lost,
+        # presently hints on `proc(thing)` where thing converts to non var base.
+        rawMessage(c.graph.config, hintImplicitObjConv, [typeToString(source), typeToString(dest), toFileLineCol(c.graph.config, n[1].info)])
     if diff < 0:
+      convHint()
       result = newTransNode(nkObjUpConv, n, 1)
       result[0] = transform(c, n[1])
     elif diff > 0 and diff != high(int):
+      convHint()
       result = newTransNode(nkObjDownConv, n, 1)
       result[0] = transform(c, n[1])
     else:

tests/types/tinheritance_arrays.nim

@@ -0,0 +1,53 @@
+discard """
+  cmd: "nim check --hints:off $file"
+  action: reject
+  nimout: '''
+tinheritance_arrays.nim(20, 18) Error: type mismatch: got <B> but expected 'A = object'
+tinheritance_arrays.nim(20, 23) Error: type mismatch: got <C> but expected 'A = object'
+tinheritance_arrays.nim(21, 18) Error: type mismatch: got <B> but expected 'C = object'
+tinheritance_arrays.nim(21, 23) Error: type mismatch: got <A> but expected 'C = object'
+tinheritance_arrays.nim(22, 23) Error: type mismatch: got <A> but expected 'B = object'
+'''
+"""
+
+
+block: # Value test
+  type
+    A = object of RootObj
+    B = object of A
+    C = object of A
+
+  discard [A(), B(), C()]
+  discard [C(), B(), A()]
+  discard [B(), B(), A()]
+  discard [B(), B(), B()]
+  discard [A(), A(), A()]
+
+block: # ref test
+  type
+    A = ref object of RootObj
+    B = ref object of A
+    C = ref object of A
+
+  discard [A(), B(), C()]
+  discard [C(), B(), A()]
+  discard [B(), B(), A()]
+  discard [B(), B(), B()]
+  discard [A(), A(), A()]
+
+block: # ptr test
+  type
+    A = object of RootObj
+    B = object of A
+    C = object of A
+
+  template make(t: typedesc): ptr t =
+    let res = createU(t)
+    res[] = t()
+    res
+
+  discard [make A, make B, make C]
+  discard [make C, make B, make A]
+  discard [make B, make B, make A]
+  discard [make B, make B, make B]
+  discard [make A, make A, make A]

tests/types/tinheritance_conversion.nim

@@ -0,0 +1,71 @@
+discard """
+  cmd: "nim c --hint[Conf]:off --verbosity:0 $file"
+  nimout: '''
+Hint: Implicit conversion: Receiver 'Base' will not receive fields of sub-type 'Derived' [tinheritance_conversion.nim(30, 15)] [ImplicitObjConv]
+Hint: Implicit conversion: Receiver 'Base' will not receive fields of sub-type 'Derived' [tinheritance_conversion.nim(30, 34)] [ImplicitObjConv]
+Hint: Implicit conversion: Receiver 'Base' will not receive fields of sub-type 'Derived2' [tinheritance_conversion.nim(38, 3)] [ImplicitObjConv]
+
+'''
+"""
+
+
+type
+  Base {.inheritable.} = object
+    field: int
+
+  Derived = object of Base
+    field2: int
+    field3: int
+  Derived2 = object of Base
+
+block: # Value tests
+  proc test(args: varargs[Base]) =
+    for x in args:
+      assert x.field == 0
+
+  proc test2(base: var Base) = base.field = 400
+  proc test3(base: Base) = discard
+  var a: Derived = Derived(Base())
+  a = Derived(Base(Derived2()))
+  test(Derived(), Base(), Derived())
+  a.field2 = 300
+  test2(a)
+  assert a.field == 400
+  assert a.field2 == 300
+  var b = Derived2(field: 800)
+  b.test2()
+  assert b.field == 400
+  b.test3()
+
+
+
+block: # Ref tests
+  type
+    Base = ref object of RootObj
+      field: int
+    Derived = ref object of Base
+      field2: int
+    Derived2 = ref object of Base
+
+  var a: Base = Derived()
+  assert Derived(a) is Derived
+  doAssertRaises(ObjectConversionDefect): discard Derived2(a)[]
+  doAssertRaises(ObjectConversionDefect): discard Base(Derived2()).Derived
+  assert Base(Derived()) is Base
+  assert Derived2(Base(Derived2())) is Derived2
+  assert Derived(Base(Derived())) is Derived
+
+block: # Pointer tests
+  template make(t: typedesc): ptr t =
+    let res = createU(t)
+    res[] = t()
+    res
+  var a: ptr Base = make(Derived)
+  assert (ptr Derived)(a) is (ptr Derived)
+  doAssertRaises(ObjectConversionDefect): discard (ptr Derived2)(a)[]
+  doAssertRaises(ObjectConversionDefect):
+    var a = make(Derived2)
+    discard (ptr Derived)((ptr Base)(a))
+  assert (ptr Base)(make(Derived)) is (ptr Base)
+  assert (ptr Derived2)((ptr Base)(make(Derived2))) is (ptr Derived2)
+  assert (ptr Derived)((ptr Base)(make(Derived))) is (ptr Derived)