fixes #2590; methods now require a .base annotation

compiler/ast.nim

@@ -297,6 +297,7 @@ const
   sfGoto* = sfOverriden               # var is used for 'goto' code generation
   sfWrittenTo* = sfBorrow             # param is assigned to
   sfEscapes* = sfProcvar              # param escapes
+  sfBase* = sfDiscriminant
 
 const
   # getting ready for the future expr/stmt merge

compiler/cgmeth.nim

@@ -47,8 +47,10 @@ proc methodCall*(n: PNode): PNode =
 var
   gMethods: seq[tuple[methods: TSymSeq, dispatcher: PSym]] = @[]
 
-proc sameMethodBucket(a, b: PSym): bool =
-  result = false
+type
+  MethodResult = enum No, Invalid, Yes
+
+proc sameMethodBucket(a, b: PSym): MethodResult =
   if a.name.id != b.name.id: return
   if sonsLen(a.typ) != sonsLen(b.typ):
     return                    # check for return type:
@@ -64,13 +66,15 @@ proc sameMethodBucket(a, b: PSym): bool =
         bb = bb.lastSon
       else:
         break
-    if sameType(aa, bb) or
-        (aa.kind == tyObject) and (bb.kind == tyObject) and
-        (inheritanceDiff(bb, aa) < 0):
-      discard
+    if sameType(aa, bb): discard
+    elif aa.kind == tyObject and bb.kind == tyObject:
+      let diff = inheritanceDiff(bb, aa)
+      if diff < 0: discard "Ok"
+      elif diff != high(int):
+        result = Invalid
     else:
-      return
-  result = true
+      return No
+  if result != Invalid: result = Yes
 
 proc attachDispatcher(s: PSym, dispatcher: PNode) =
   var L = s.ast.len-1
@@ -133,18 +137,31 @@ proc fixupDispatcher(meth, disp: PSym) =
 
 proc methodDef*(s: PSym, fromCache: bool) =
   var L = len(gMethods)
+  var witness: PSym
   for i in countup(0, L - 1):
     var disp = gMethods[i].dispatcher
-    if sameMethodBucket(disp, s):
+    case sameMethodBucket(disp, s)
+    of Yes:
       add(gMethods[i].methods, s)
       attachDispatcher(s, lastSon(disp.ast))
       fixupDispatcher(s, disp)
       when useEffectSystem: checkMethodEffects(disp, s)
+      if sfBase in s.flags and gMethods[i].methods[0] != s:
+        # already exists due to forwarding definition?
+        localError(s.info, "method is not a base")
       return
+    of No: discard
+    of Invalid:
+      if witness.isNil: witness = gMethods[i].methods[0]
   # create a new dispatcher:
   add(gMethods, (methods: @[s], dispatcher: createDispatcher(s)))
   if fromCache:
     internalError(s.info, "no method dispatcher found")
+  if witness != nil:
+    localError(s.info, "invalid declaration order; cannot attach '" & s.name.s &
+                       "' to method defined here: " & $witness.info)
+  elif sfBase notin s.flags:
+    message(s.info, warnUseBase)
 
 proc relevantCol(methods: TSymSeq, col: int): bool =
   # returns true iff the position is relevant

compiler/msgs.nim

@@ -118,7 +118,7 @@ type
     warnUnknownSubstitutionX, warnLanguageXNotSupported,
     warnFieldXNotSupported, warnCommentXIgnored,
     warnNilStatement, warnTypelessParam,
-    warnDifferentHeaps, warnWriteToForeignHeap, warnUnsafeCode,
+    warnUseBase, warnWriteToForeignHeap, warnUnsafeCode,
     warnEachIdentIsTuple, warnShadowIdent,
     warnProveInit, warnProveField, warnProveIndex, warnGcUnsafe, warnGcUnsafe2,
     warnUninit, warnGcMem, warnDestructor, warnLockLevel, warnResultShadowed,
@@ -391,7 +391,7 @@ const
     warnCommentXIgnored: "comment \'$1\' ignored",
     warnNilStatement: "'nil' statement is deprecated; use an empty 'discard' statement instead",
     warnTypelessParam: "'$1' has no type. Typeless parameters are deprecated; only allowed for 'template'",
-    warnDifferentHeaps: "possible inconsistency of thread local heaps",
+    warnUseBase: "use {.base.} for base methods; baseless methods are deprecated",
     warnWriteToForeignHeap: "write to foreign heap",
     warnUnsafeCode: "unsafe code: '$1'",
     warnEachIdentIsTuple: "each identifier is a tuple",

compiler/pragmas.nim

@@ -27,7 +27,7 @@ const
     wGensym, wInject, wRaises, wTags, wLocks, wDelegator, wGcSafe,
     wOverride, wConstructor}
   converterPragmas* = procPragmas
-  methodPragmas* = procPragmas
+  methodPragmas* = procPragmas+{wBase}
   templatePragmas* = {wImmediate, wDeprecated, wError, wGensym, wInject, wDirty,
     wDelegator}
   macroPragmas* = {FirstCallConv..LastCallConv, wImmediate, wImportc, wExportc,
@@ -867,6 +867,9 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: int,
           localError(it.info, "'experimental' pragma only valid as toplevel statement")
       of wNoRewrite:
         noVal(it)
+      of wBase:
+        noVal(it)
+        sym.flags.incl sfBase
       else: invalidPragma(it)
     else: invalidPragma(it)
 

compiler/wordrecg.nim

@@ -45,7 +45,7 @@ type
     wImportc, wExportc, wIncompleteStruct, wRequiresInit,
     wAlign, wNodecl, wPure, wSideeffect, wHeader,
     wNosideeffect, wGcSafe, wNoreturn, wMerge, wLib, wDynlib,
-    wCompilerproc, wProcVar,
+    wCompilerproc, wProcVar, wBase,
     wFatal, wError, wWarning, wHint, wLine, wPush, wPop, wDefine, wUndef,
     wLinedir, wStacktrace, wLinetrace, wLink, wCompile,
     wLinksys, wDeprecated, wVarargs, wCallconv, wBreakpoint, wDebugger,
@@ -128,7 +128,8 @@ const
     "importcompilerproc", "importc", "exportc", "incompletestruct",
     "requiresinit", "align", "nodecl", "pure", "sideeffect",
     "header", "nosideeffect", "gcsafe", "noreturn", "merge", "lib", "dynlib",
-    "compilerproc", "procvar", "fatal", "error", "warning", "hint", "line",
+    "compilerproc", "procvar", "base",
+    "fatal", "error", "warning", "hint", "line",
     "push", "pop", "define", "undef", "linedir", "stacktrace", "linetrace",
     "link", "compile", "linksys", "deprecated", "varargs",
     "callconv", "breakpoint", "debugger", "nimcall", "stdcall",