Fix #1561

compiler/procfind.nim

@@ -11,7 +11,7 @@
 # This is needed for proper handling of forward declarations.
 
 import
-  ast, astalgo, msgs, semdata, types, trees
+  ast, astalgo, msgs, semdata, types, trees, strutils
 
 proc equalGenericParams(procA, procB: PNode): bool =
   if sonsLen(procA) != sonsLen(procB): return
@@ -68,11 +68,17 @@ proc searchForProcNew(c: PContext, scope: PScope, fn: PSym): PSym =
                  ExactConstraints, IgnoreCC}
 
   var it: TIdentIter
+
   result = initIdentIter(it, scope.symbols, fn.name)
   while result != nil:
     if result.kind in skProcKinds and sameType(result.typ, fn.typ, flags):
       case equalParams(result.typ.n, fn.typ.n)
       of paramsEqual:
+        if (sfExported notin result.flags) and (sfExported in fn.flags):
+          let message = ("public implementation '$1' has non-public " &
+                         "forward declaration in $2") %
+                        [getProcHeader(result), $result.info]
+          localError(fn.info, errGenerated, message)
         return
       of paramsIncompatible:
         localError(fn.info, errNotOverloadable, fn.name.s)

config/nim.cfg

@@ -40,6 +40,7 @@ path="$lib/pure/unidecode"
 
 @if nimbabel:
   babelpath="$home/.babel/pkgs/"
+  nimblepath="$home/.nimble/pkgs/"
 @end
 
 @if release or quick:

tests/modules/tmismatchedvisibility.nim

@@ -0,0 +1,9 @@
+discard """
+  line: 8
+  errormsg: "public implementation 'tmismatchedvisibility.foo(a: int): int' has non-public forward declaration in tmismatchedvisibility.nim(6,5)"
+"""
+
+proc foo(a: int): int
+
+proc foo*(a: int): int =
+  result = a + a