PRTEMP

compiler/options.nim

@@ -191,6 +191,8 @@ type
     strictFuncs,
     views,
     strictNotNil
+    oldImplicitCstringConv,
+      # deprecated features start with `old` # PRTEMP: legacy
 
   LegacyFeature* = enum
     allowSemcheckedAstModification,
@@ -369,6 +371,14 @@ template setErrorMaxHighMaybe*(conf: ConfigRef) =
   ## do not stop after first error (but honor --errorMax if provided)
   assignIfDefault(conf.errorMax, high(int))
 
+template toSet(a: typedesc[enum]): untyped = {a.low..a.high}
+
+const
+  FeatureDepr* = {oldImplicitCstringConv}
+    # can't use `LegacyFeature` because we want to be able to localize
+    # to a context, eg {.push experimental: "oldImplicitCstringConv".} .. {.pop.}
+  FeatureExp* = Feature.toSet - FeatureDepr
+
 proc setNoteDefaults*(conf: ConfigRef, note: TNoteKind, enabled = true) =
   template fun(op) =
     conf.notes.op note

compiler/sigmatch.nim

@@ -1405,11 +1405,10 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
     of tyNil: result = f.allowsNil
     of tyString: result = isConvertible
     of tyPtr:
-      # https://github.com/nim-lang/Nim/issues/13790
-      when true:
-        result = isNone # PRTEMP
-      else:
+      if oldImplicitCstringConv in c.c.features:
+        # issue #13790
         # ptr[Tag, char] is not convertible to 'cstring' for now:
+        # xxx: aren't memory regions not used anymore?
         if a.len == 1:
           let pointsTo = a[0].skipTypes(abstractInst)
           if pointsTo.kind == tyChar: result = isConvertible
@@ -1419,6 +1418,11 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
               skipTypes(pointsTo[0], {tyRange}).kind in {tyInt..tyInt64} and
               pointsTo[1].kind == tyChar:
             result = isConvertible
+          # if result == isConvertible:
+            # message(c.config, a.info, warnOldImplicitCstringConv)
+            # warnProveInit
+      else:
+        result = isNone
     else: discard
 
   of tyEmpty, tyVoid: