special typing rules for owned pointers

compiler/commands.nim

@@ -738,7 +738,8 @@ proc processSwitch*(switch, arg: string, pass: TCmdLinePass, info: TLineInfo;
     expectNoArg(conf, switch, arg, pass, info)
     doAssert(conf != nil)
     incl(conf.features, destructor)
-    defineSymbol(conf.symbols, "nimNewRuntime")
+    incl(conf.globalOptions, optNimV2)
+    defineSymbol(conf.symbols, "nimV2")
   of "stylecheck":
     case arg.normalize
     of "off": conf.globalOptions = conf.globalOptions - {optStyleHint, optStyleError}

compiler/options.nim

@@ -19,7 +19,7 @@ const
   useEffectSystem* = true
   useWriteTracking* = false
   hasFFI* = defined(nimHasLibFFI)
-  copyrightYear* = "2018"
+  copyrightYear* = "2019"
 
 type                          # please make sure we have under 32 options
                               # (improves code efficiency a lot!)
@@ -82,6 +82,7 @@ type                          # please make sure we have under 32 options
     optNoNimblePath
     optHotCodeReloading
     optDynlibOverrideAll
+    optNimV2
 
   TGlobalOptions* = set[TGlobalOption]
 

compiler/semexprs.nim

@@ -1516,6 +1516,10 @@ proc asgnToResultVar(c: PContext, n, le, ri: PNode) {.inline.} =
       n.sons[1] = takeImplicitAddr(c, ri, x.typ.kind == tyLent)
       x.typ.flags.incl tfVarIsPtr
       #echo x.info, " setting it for this type ", typeToString(x.typ), " ", n.info
+  # Special typing rule: do not allow to pass 'owned T' to 'T' in 'result = x':
+  if ri.typ != nil and ri.typ.skipTypes(abstractInst).kind == tyOwned and
+      le.typ != nil and le.typ.skipTypes(abstractInst).kind != tyOwned:
+    localError(c.config, n.info, "cannot return an owned pointer as an unowned pointer")
 
 template resultTypeIsInferrable(typ: PType): untyped =
   typ.isMetaType and typ.kind != tyTypeDesc

compiler/semobjconstr.nim

@@ -263,8 +263,11 @@ proc semObjConstr(c: PContext, n: PNode, flags: TExprFlags): PNode =
     localError(c.config, n.info, errGenerated, "object constructor needs an object type")
     return
 
-  t = skipTypes(t, {tyGenericInst, tyAlias, tySink})
+  t = skipTypes(t, {tyGenericInst, tyAlias, tySink, tyOwned})
-  if t.kind == tyRef: t = skipTypes(t.sons[0], {tyGenericInst, tyAlias, tySink})
+  if t.kind == tyRef:
+    t = skipTypes(t.sons[0], {tyGenericInst, tyAlias, tySink, tyOwned})
+    if optNimV2 in c.config.globalOptions:
+      result.typ = makeVarType(c, result.typ, tyOwned)
   if t.kind != tyObject:
     localError(c.config, n.info, errGenerated, "object constructor needs an object type")
     return

compiler/semstmts.nim

@@ -474,6 +474,10 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
                      ($typ.kind).substr(2).toLowerAscii)
         elif typ.kind == tyProc and tfUnresolved in typ.flags:
           localError(c.config, def.info, errProcHasNoConcreteType % def.renderTree)
+        elif symkind == skVar and typ.kind == tyOwned and def.kind notin nkCallKinds:
+          # special type inference rule: 'var it = ownedPointer' is turned
+          # into an unowned pointer.
+          typ = typ.lastSon
     else:
       if symkind == skLet: localError(c.config, a.info, errLetNeedsInit)
 

lib/system.nim

@@ -1341,6 +1341,26 @@ proc `is`*[T, S](x: T, y: S): bool {.magic: "Is", noSideEffect.}
 template `isnot`*(x, y: untyped): untyped = not (x is y)
   ## Negated version of `is`. Equivalent to ``not(x is y)``.
 
+when defined(nimV2):
+  type owned*[T]{.magic: "BuiltinType".}
+
+  proc new*[T](a: var owned(ref T)) {.magic: "New", noSideEffect.}
+    ## creates a new object of type ``T`` and returns a safe (traced)
+    ## reference to it in ``a``.
+
+  proc new*(t: typedesc): auto =
+    ## creates a new object of type ``T`` and returns a safe (traced)
+    ## reference to it as result value.
+    ##
+    ## When ``T`` is a ref type then the resulting type will be ``T``,
+    ## otherwise it will be ``ref T``.
+    when (t is ref):
+      var r: owned t
+    else:
+      var r: owned(ref t)
+    new(r)
+    return r
+else:
   proc new*[T](a: var ref T) {.magic: "New", noSideEffect.}
     ## creates a new object of type ``T`` and returns a safe (traced)
     ## reference to it in ``a``.