fixes #2420; negative indexing for slicing is obsolete (breaking change!)

compiler/semcall.nim

@@ -201,7 +201,8 @@ proc resolveOverloads(c: PContext, n, orig: PNode,
 
     elif nfDotSetter in n.flags:
       internalAssert f.kind == nkIdent and n.sonsLen == 3
-      let calleeName = newStrNode(nkStrLit, f.ident.s[0.. -2]).withInfo(n.info)
+      let calleeName = newStrNode(nkStrLit,
+        f.ident.s[0..f.ident.s.len-2]).withInfo(n.info)
       let callOp = newIdentNode(getIdent".=", n.info)
       n.sons[0..1] = [callOp, n[1], calleeName]
       orig.sons[0..1] = [callOp, orig[1], calleeName]

compiler/semdestruct.nim

@@ -71,11 +71,12 @@ proc destroyCase(c: PContext, n: PNode, holder: PNode): PNode =
   result.addSon(newNode(nkDotExpr, n.info, @[holder, n.sons[0]]))
   for i in countup(1, n.len - 1):
     # of A, B:
-    var caseBranch = newNode(n[i].kind, n[i].info, n[i].sons[0 .. -2])
+    let ni = n[i]
+    var caseBranch = newNode(ni.kind, ni.info, ni.sons[0..ni.len-2])
 
-    let stmt = destroyFieldOrFields(c, n[i].lastSon, holder)
+    let stmt = destroyFieldOrFields(c, ni.lastSon, holder)
     if stmt == nil:
-      caseBranch.addSon(newNode(nkStmtList, n[i].info, @[]))
+      caseBranch.addSon(newNode(nkStmtList, ni.info, @[]))
     else:
       caseBranch.addSon(stmt)
       nonTrivialFields += stmt.len
@@ -209,7 +210,7 @@ proc insertDestructors(c: PContext,
 
       if j < totalVars - 1:
         var remainingVars = newNodeI(varSection.kind, info)
-        remainingVars.sons = varSection.sons[(j+1)..(-1)]
+        remainingVars.sons = varSection.sons[(j+1)..varSection.len-1]
         let (outer, inner) = insertDestructors(c, remainingVars)
         if outer != nil:
           tryStmt.addSon(outer)

compiler/semmagic.nim

@@ -167,10 +167,10 @@ proc magicsAfterOverloadResolution(c: PContext, n: PNode,
     result.typ = n[1].typ
   of mDotDot:
     result = n
-    # we only need to warnings here about negative indexing:
+    # disallow negative indexing for now:
+    if not c.p.bracketExpr.isNil:
       if isNegative(n.sons[1]) or (n.len > 2 and isNegative(n.sons[2])):
-      message(n.info, warnDeprecated,
+        localError(n.info, "use '^' instead of '-'; negative indexing is obsolete")
-        "use '^' instead of '-'; negative indexing")
   of mRoof:
     # error correction:
     result = n.sons[1]

compiler/semstmts.nim

@@ -1281,7 +1281,7 @@ proc semStmtList(c: PContext, n: PNode, flags: TExprFlags): PNode =
       var tryStmt = newNodeI(nkTryStmt, n.sons[i].info)
       var body = newNodeI(nkStmtList, n.sons[i].info)
       if i < n.sonsLen - 1:
-        body.sons = n.sons[(i+1)..(-1)]
+        body.sons = n.sons[(i+1)..n.len-1]
       tryStmt.addSon(body)
       tryStmt.addSon(deferPart)
       n.sons[i] = semTry(c, tryStmt)

lib/pure/asyncio.nim

@@ -256,7 +256,7 @@ proc asyncSockHandleWrite(h: RootRef) =
           # do nothing instead.
           discard
         elif bytesSent != sock.sendBuffer.len:
-          sock.sendBuffer = sock.sendBuffer[bytesSent .. -1]
+          sock.sendBuffer = sock.sendBuffer[bytesSent .. ^1]
         elif bytesSent == sock.sendBuffer.len:
           sock.sendBuffer = ""
 
@@ -550,7 +550,7 @@ proc send*(sock: AsyncSocket, data: string) =
     sock.sendBuffer.add(data)
     sock.deleg.mode = fmReadWrite
   elif bytesSent != data.len:
-    sock.sendBuffer.add(data[bytesSent .. -1])
+    sock.sendBuffer.add(data[bytesSent .. ^1])
     sock.deleg.mode = fmReadWrite
 
 proc timeValFromMilliseconds(timeout = 500): Timeval =

lib/system.nim

@@ -2865,7 +2865,7 @@ template spliceImpl(s, a, L, b: expr): stmt {.immediate.} =
 when hostOS != "standalone":
   proc `[]`*(s: string, x: Slice[int]): string {.inline.} =
     ## slice operation for strings.
-    result = s.substr(x.a-|s, x.b-|s)
+    result = s.substr(x.a, x.b)
 
   proc `[]=`*(s: var string, x: Slice[int], b: string) =
     ## slice assignment for strings. If
@@ -2876,8 +2876,8 @@ when hostOS != "standalone":
     ##   var s = "abcdef"
     ##   s[1 .. -2] = "xyz"
     ##   assert s == "axyzf"
-    var a = x.a-|s
+    var a = x.a
-    var L = x.b-|s - a + 1
+    var L = x.b - a + 1
     if L == b.len:
       for i in 0 .. <L: s[i+a] = b[i]
     else:
@@ -2919,8 +2919,8 @@ proc `[]=`*[Idx, T](a: var array[Idx, T], x: Slice[Idx], b: openArray[T]) =
 
 proc `[]`*[T](s: seq[T], x: Slice[int]): seq[T] =
   ## slice operation for sequences.
-  var a = x.a-|s
+  var a = x.a
-  var L = x.b-|s - a + 1
+  var L = x.b - a + 1
   newSeq(result, L)
   for i in 0.. <L: result[i] = s[i + a]
 
@@ -2928,8 +2928,8 @@ proc `[]=`*[T](s: var seq[T], x: Slice[int], b: openArray[T]) =
   ## slice assignment for sequences. If
   ## ``b.len`` is not exactly the number of elements that are referred to
   ## by `x`, a `splice`:idx: is performed.
-  var a = x.a-|s
+  var a = x.a
-  var L = x.b-|s - a + 1
+  var L = x.b - a + 1
   if L == b.len:
     for i in 0 .. <L: s[i+a] = b[i]
   else:

web/news.txt

@@ -59,11 +59,12 @@ News
       echo x.T
       inc x
 
-  - **Negative indexing for slicing is deprecated and will be removed in the
+  - **Negative indexing for slicing does not work anymore!** Instead
-    next version of the language.** Instead of ``a[0.. -1]`` you can
+    of ``a[0.. -1]`` you can
     use ``a[0.. ^1]``. This also works with accessing a single
     element ``a[^1]``. Note that we cannot detect this reliably as it is
     determined at **runtime** whether negative indexing is used!
+    ``a[0.. -1]`` now produces the empty string/sequence.
   - The compiler now warns about code like ``foo +=1`` which uses inconsistent
     spacing around binary operators. Later versions of the language will parse
     these as unary operators instead so that ``echo $foo`` finally can do what