diff --git a/changelog.md b/changelog.md
index ddfeb4d362..2c24467b22 100644
--- a/changelog.md
+++ b/changelog.md
@@ -11,7 +11,7 @@
   to deal with!
 - Indexing into a ``cstring`` for the JS target is now mapped
   to ``charCodeAt``.
-- Assignments that would "slice" an object into its supertype are not prevented
+- Assignments that would "slice" an object into its supertype are now prevented
   at runtime. Use ``ref object`` with inheritance rather than ``object`` with
   inheritance to prevent this issue.
 
@@ -81,7 +81,10 @@
   Imported exceptions can be raised and caught just like Nim exceptions.
   More details in language manual.
 
-- Range float typed, example `range[0.0 .. Inf]`. More details in language manual.
+- ``nil`` for strings/seqs is finally gone. Instead the default value for
+  these is ``"" / @[]``.
+
+- Range float types, example `range[0.0 .. Inf]`. More details in language manual.
 
 ### Tool changes
 
diff --git a/compiler/ccgcalls.nim b/compiler/ccgcalls.nim
index 5f14b68046..2ddc88509b 100644
--- a/compiler/ccgcalls.nim
+++ b/compiler/ccgcalls.nim
@@ -125,15 +125,15 @@ proc openArrayLoc(p: BProc, n: PNode): Rope =
     of tyString, tySequence:
       if skipTypes(n.typ, abstractInst).kind == tyVar and
             not compileToCpp(p.module):
-        result = "(*$1)->data, (*$1)->$2" % [a.rdLoc, lenField(p)]
+        result = "(*$1)->data, (*$1 ? (*$1)->$2 : 0)" % [a.rdLoc, lenField(p)]
       else:
-        result = "$1->data, $1->$2" % [a.rdLoc, lenField(p)]
+        result = "$1->data, ($1 ? $1->$2 : 0)" % [a.rdLoc, lenField(p)]
     of tyArray:
       result = "$1, $2" % [rdLoc(a), rope(lengthOrd(a.t))]
     of tyPtr, tyRef:
       case lastSon(a.t).kind
       of tyString, tySequence:
-        result = "(*$1)->data, (*$1)->$2" % [a.rdLoc, lenField(p)]
+        result = "(*$1)->data, (*$1 ? (*$1)->$2 : 0)" % [a.rdLoc, lenField(p)]
       of tyArray:
         result = "$1, $2" % [rdLoc(a), rope(lengthOrd(lastSon(a.t)))]
       else:
@@ -143,7 +143,7 @@ proc openArrayLoc(p: BProc, n: PNode): Rope =
 proc genArgStringToCString(p: BProc, n: PNode): Rope {.inline.} =
   var a: TLoc
   initLocExpr(p, n.sons[0], a)
-  result = "$1->data" % [a.rdLoc]
+  result = "($1 ? $1->data : (NCSTRING)\"\")" % [a.rdLoc]
 
 proc genArg(p: BProc, n: PNode, param: PSym; call: PNode): Rope =
   var a: TLoc
diff --git a/compiler/ccgexprs.nim b/compiler/ccgexprs.nim
index ea373f5a6a..562d6d1657 100644
--- a/compiler/ccgexprs.nim
+++ b/compiler/ccgexprs.nim
@@ -882,7 +882,7 @@ proc genIndexCheck(p: BProc; arr, idx: TLoc) =
               rdCharLoc(idx), first, intLiteral(lastOrd(ty)))
   of tySequence, tyString:
     linefmt(p, cpsStmts,
-          "if ((NU)($1) >= (NU)($2->$3)) #raiseIndexError();$n",
+          "if (!$2 || (NU)($1) >= (NU)($2->$3)) #raiseIndexError();$n",
           rdLoc(idx), rdLoc(arr), lenField(p))
   else: discard
 
@@ -907,11 +907,11 @@ proc genSeqElem(p: BProc, n, x, y: PNode, d: var TLoc) =
   if optBoundsCheck in p.options:
     if ty.kind == tyString:
       linefmt(p, cpsStmts,
-           "if ((NU)($1) > (NU)($2->$3)) #raiseIndexError();$n",
+           "if (!$2 || (NU)($1) > (NU)($2->$3)) #raiseIndexError();$n",
            rdLoc(b), rdLoc(a), lenField(p))
     else:
       linefmt(p, cpsStmts,
-           "if ((NU)($1) >= (NU)($2->$3)) #raiseIndexError();$n",
+           "if (!$2 || (NU)($1) >= (NU)($2->$3)) #raiseIndexError();$n",
            rdLoc(b), rdLoc(a), lenField(p))
   if d.k == locNone: d.storage = OnHeap
   if skipTypes(a.t, abstractVar).kind in {tyRef, tyPtr}:
@@ -980,10 +980,10 @@ proc genEcho(p: BProc, n: PNode) =
     var a: TLoc
     for it in n.sons:
       if it.skipConv.kind == nkNilLit:
-        add(args, ", \"nil\"")
+        add(args, ", \"\"")
       else:
         initLocExpr(p, it, a)
-        addf(args, ", $1? ($1)->data:\"nil\"", [rdLoc(a)])
+        addf(args, ", $1? ($1)->data:\"\"", [rdLoc(a)])
     p.module.includeHeader("<base/log.h>")
     linefmt(p, cpsStmts, """Genode::log(""$1);$n""", args)
   else:
@@ -1034,7 +1034,7 @@ proc genStrConcat(p: BProc, e: PNode, d: var TLoc) =
       if e.sons[i + 1].kind in {nkStrLit..nkTripleStrLit}:
         inc(L, len(e.sons[i + 1].strVal))
       else:
-        addf(lens, "$1->$2 + ", [rdLoc(a), lenField(p)])
+        addf(lens, "($1 ? $1->$2 : 0) + ", [rdLoc(a), lenField(p)])
       add(appends, rfmt(p.module, "#appendString($1, $2);$n", tmp.r, rdLoc(a)))
   linefmt(p, cpsStmts, "$1 = #rawNewString($2$3);$n", tmp.r, lens, rope(L))
   add(p.s(cpsStmts), appends)
@@ -1073,7 +1073,7 @@ proc genStrAppend(p: BProc, e: PNode, d: var TLoc) =
       if e.sons[i + 2].kind in {nkStrLit..nkTripleStrLit}:
         inc(L, len(e.sons[i + 2].strVal))
       else:
-        addf(lens, "$1->$2 + ", [rdLoc(a), lenField(p)])
+        addf(lens, "($1 ? $1->$2 : 0) + ", [rdLoc(a), lenField(p)])
       add(appends, rfmt(p.module, "#appendString($1, $2);$n",
                         rdLoc(dest), rdLoc(a)))
   linefmt(p, cpsStmts, "$1 = #resizeString($1, $2$3);$n",
@@ -1086,17 +1086,17 @@ proc genSeqElemAppend(p: BProc, e: PNode, d: var TLoc) =
   #    seq = (typeof seq) incrSeq(&seq->Sup, sizeof(x));
   #    seq->data[seq->len-1] = x;
   let seqAppendPattern = if not p.module.compileToCpp:
-                           "$1 = ($2) #incrSeqV2(&($1)->Sup, sizeof($3));$n"
+                           "$1 = ($2) #incrSeqV3(&($1)->Sup, $3);$n"
                          else:
-                           "$1 = ($2) #incrSeqV2($1, sizeof($3));$n"
+                           "$1 = ($2) #incrSeqV3($1, $3);$n"
   var a, b, dest, tmpL: TLoc
   initLocExpr(p, e.sons[1], a)
   initLocExpr(p, e.sons[2], b)
-  let bt = skipTypes(e.sons[2].typ, {tyVar})
+  let seqType = skipTypes(e.sons[1].typ, {tyVar})
   lineCg(p, cpsStmts, seqAppendPattern, [
       rdLoc(a),
       getTypeDesc(p.module, e.sons[1].typ),
-      getTypeDesc(p.module, bt)])
+      genTypeInfo(p.module, seqType, e.info)])
   #if bt != b.t:
   #  echo "YES ", e.info, " new: ", typeToString(bt), " old: ", typeToString(b.t)
   initLoc(dest, locExpr, e.sons[2], OnHeap)
@@ -1417,7 +1417,7 @@ proc genRepr(p: BProc, e: PNode, d: var TLoc) =
       putIntoDest(p, b, e, "$1, $1Len_0" % [rdLoc(a)], a.storage)
     of tyString, tySequence:
       putIntoDest(p, b, e,
-                  "$1->data, $1->$2" % [rdLoc(a), lenField(p)], a.storage)
+                  "$1->data, ($1 ? $1->$2 : 0)" % [rdLoc(a), lenField(p)], a.storage)
     of tyArray:
       putIntoDest(p, b, e,
                   "$1, $2" % [rdLoc(a), rope(lengthOrd(a.t))], a.storage)
@@ -1500,13 +1500,13 @@ proc genSetLengthSeq(p: BProc, e: PNode, d: var TLoc) =
   initLocExpr(p, e.sons[2], b)
   let t = skipTypes(e.sons[1].typ, {tyVar})
   let setLenPattern = if not p.module.compileToCpp:
-      "$1 = ($3) #setLengthSeq(&($1)->Sup, sizeof($4), $2);$n"
+      "$1 = ($3) #setLengthSeqV2(&($1)->Sup, $4, $2);$n"
     else:
-      "$1 = ($3) #setLengthSeq($1, sizeof($4), $2);$n"
+      "$1 = ($3) #setLengthSeqV2($1, $4, $2);$n"
 
   lineCg(p, cpsStmts, setLenPattern, [
       rdLoc(a), rdLoc(b), getTypeDesc(p.module, t),
-      getTypeDesc(p.module, t.skipTypes(abstractInst).sons[0])])
+      genTypeInfo(p.module, t.skipTypes(abstractInst), e.info)])
   gcUsage(e)
 
 proc genSetLengthStr(p: BProc, e: PNode, d: var TLoc) =
@@ -1740,7 +1740,7 @@ proc genConv(p: BProc, e: PNode, d: var TLoc) =
 proc convStrToCStr(p: BProc, n: PNode, d: var TLoc) =
   var a: TLoc
   initLocExpr(p, n.sons[0], a)
-  putIntoDest(p, d, n, "$1->data" % [rdLoc(a)],
+  putIntoDest(p, d, n, "($1 ? $1->data : (NCSTRING)\"\")" % [rdLoc(a)],
               a.storage)
 
 proc convCStrToStr(p: BProc, n: PNode, d: var TLoc) =
@@ -1755,16 +1755,14 @@ proc genStrEquals(p: BProc, e: PNode, d: var TLoc) =
   var x: TLoc
   var a = e.sons[1]
   var b = e.sons[2]
-  if (a.kind == nkNilLit) or (b.kind == nkNilLit):
-    binaryExpr(p, e, d, "($1 == $2)")
-  elif (a.kind in {nkStrLit..nkTripleStrLit}) and (a.strVal == ""):
+  if a.kind in {nkStrLit..nkTripleStrLit} and a.strVal == "":
     initLocExpr(p, e.sons[2], x)
     putIntoDest(p, d, e,
-      rfmt(nil, "(($1) && ($1)->$2 == 0)", rdLoc(x), lenField(p)))
-  elif (b.kind in {nkStrLit..nkTripleStrLit}) and (b.strVal == ""):
+      rfmt(nil, "(!($1) || ($1)->$2 == 0)", rdLoc(x), lenField(p)))
+  elif b.kind in {nkStrLit..nkTripleStrLit} and b.strVal == "":
     initLocExpr(p, e.sons[1], x)
     putIntoDest(p, d, e,
-      rfmt(nil, "(($1) && ($1)->$2 == 0)", rdLoc(x), lenField(p)))
+      rfmt(nil, "(!($1) || ($1)->$2 == 0)", rdLoc(x), lenField(p)))
   else:
     binaryExpr(p, e, d, "#eqStrings($1, $2)")
 
diff --git a/compiler/condsyms.nim b/compiler/condsyms.nim
index 028aedb5b5..08dda9b6a8 100644
--- a/compiler/condsyms.nim
+++ b/compiler/condsyms.nim
@@ -82,7 +82,6 @@ proc countDefinedSymbols*(): int =
 
 proc initDefines*() =
   gSymbols = newStringTable(modeStyleInsensitive)
-  defineSymbol("nimrod") # 'nimrod' is always defined
   # for bootstrapping purposes and old code:
   defineSymbol("nimhygiene")
   defineSymbol("niminheritable")
@@ -115,3 +114,4 @@ proc initDefines*() =
   defineSymbol("nimHasNilChecks")
   defineSymbol("nimSymKind")
   defineSymbol("nimVmEqIdent")
+  defineSymbol("nimNoNil")
diff --git a/compiler/nimfix/nimfix.nim b/compiler/nimfix/nimfix.nim
index a97d88078e..2ef375b002 100644
--- a/compiler/nimfix/nimfix.nim
+++ b/compiler/nimfix/nimfix.nim
@@ -47,7 +47,7 @@ proc mainCommand =
   compileProject(newModuleGraph(), newIdentCache())
   pretty.overwriteFiles()
 
-proc processCmdLine*(pass: TCmdLinePass, cmd: string) =
+proc processCmdLine*(pass: TCmdLinePass, cmd: string, config: ConfigRef) =
   var p = parseopt.initOptParser(cmd)
   var argsCount = 0
   gOnlyMainfile = true
@@ -76,16 +76,16 @@ proc processCmdLine*(pass: TCmdLinePass, cmd: string) =
       of "wholeproject": gOnlyMainfile = false
       of "besteffort": msgs.gErrorMax = high(int) # don't stop after first error
       else:
-        processSwitch(pass, p)
+        processSwitch(pass, p, config)
     of cmdArgument:
       options.gProjectName = unixToNativePath(p.key)
       # if processArgument(pass, p, argsCount): break
 
-proc handleCmdLine() =
+proc handleCmdLine(config: ConfigRef) =
   if paramCount() == 0:
     stdout.writeLine(Usage)
   else:
-    processCmdLine(passCmd1, "")
+    processCmdLine(passCmd1, "", config)
     if gProjectName != "":
       try:
         gProjectFull = canonicalizePath(gProjectName)
@@ -96,11 +96,11 @@ proc handleCmdLine() =
       gProjectName = p.name
     else:
       gProjectPath = getCurrentDir()
-    loadConfigs(DefaultConfig) # load all config files
+    loadConfigs(DefaultConfig, config) # load all config files
     # now process command line arguments again, because some options in the
     # command line can overwite the config file's settings
     extccomp.initVars()
-    processCmdLine(passCmd2, "")
+    processCmdLine(passCmd2, "", config)
     mainCommand()
 
 when compileOption("gc", "v2") or compileOption("gc", "refc"):
@@ -108,4 +108,4 @@ when compileOption("gc", "v2") or compileOption("gc", "refc"):
 
 condsyms.initDefines()
 defineSymbol "nimfix"
-handleCmdline()
+handleCmdline newConfigRef()
diff --git a/compiler/sem.nim b/compiler/sem.nim
index 041f2e1274..52282d0e49 100644
--- a/compiler/sem.nim
+++ b/compiler/sem.nim
@@ -153,8 +153,9 @@ proc commonType*(x, y: PType): PType =
     if a.kind in {tyRef, tyPtr}:
       k = a.kind
       if b.kind != a.kind: return x
-      a = a.lastSon
-      b = b.lastSon
+      # bug #7601, array construction of ptr generic
+      a = a.lastSon.skipTypes({tyGenericInst})
+      b = b.lastSon.skipTypes({tyGenericInst})
     if a.kind == tyObject and b.kind == tyObject:
       result = commonSuperclass(a, b)
       # this will trigger an error later:
diff --git a/compiler/semcall.nim b/compiler/semcall.nim
index f443339f59..aa53fda3b4 100644
--- a/compiler/semcall.nim
+++ b/compiler/semcall.nim
@@ -59,7 +59,8 @@ proc pickBestCandidate(c: PContext, headSymbol: PNode,
                        filter: TSymKinds,
                        best, alt: var TCandidate,
                        errors: var CandidateErrors,
-                       diagnosticsFlag = false) =
+                       diagnosticsFlag: bool,
+                       errorsEnabled: bool) =
   var o: TOverloadIter
   var sym = initOverloadIter(o, c, headSymbol)
   var scope = o.lastOverloadScope
@@ -68,6 +69,7 @@ proc pickBestCandidate(c: PContext, headSymbol: PNode,
   # This can occur in cases like 'init(a, 1, (var b = new(Type2); b))'
   let counterInitial = c.currentScope.symbols.counter
   var syms: seq[tuple[s: PSym, scope: int]]
+  var noSyms = true
   var nextSymIndex = 0
   while sym != nil:
     if sym.kind in filter:
@@ -102,7 +104,7 @@ proc pickBestCandidate(c: PContext, headSymbol: PNode,
           var cmp = cmpCandidates(best, z)
           if cmp < 0: best = z   # x is better than the best so far
           elif cmp == 0: alt = z # x is as good as the best so far
-      elif errors != nil or z.diagnostics != nil:
+      elif errorsEnabled or z.diagnosticsEnabled:
         errors.safeAdd(CandidateError(
           sym: sym,
           unmatchedVarParam: int z.mutabilityProblem,
@@ -113,7 +115,8 @@ proc pickBestCandidate(c: PContext, headSymbol: PNode,
       # before any further candidate init and compare. SLOW, but rare case.
       syms = initCandidateSymbols(c, headSymbol, initialBinding, filter,
                                   best, alt, o, diagnosticsFlag)
-    if syms == nil:
+      noSyms = false
+    if noSyms:
       sym = nextOverloadIter(o, c, headSymbol)
       scope = o.lastOverloadScope
     elif nextSymIndex < syms.len:
@@ -206,7 +209,7 @@ proc notFoundError*(c: PContext, n: PNode, errors: CandidateErrors) =
   if errorOutputs == {}:
     # fail fast:
     globalError(n.info, errTypeMismatch, "")
-  if errors.isNil or errors.len == 0:
+  if errors.len == 0:
     localError(n.info, errExprXCannotBeCalled, n[0].renderTree)
     return
 
@@ -227,7 +230,8 @@ proc bracketNotFoundError(c: PContext; n: PNode) =
     if symx.kind in routineKinds:
       errors.add(CandidateError(sym: symx,
                                 unmatchedVarParam: 0, firstMismatch: 0,
-                                diagnostics: nil))
+                                diagnostics: nil,
+                                enabled: false))
     symx = nextOverloadIter(o, c, headSymbol)
   if errors.len == 0:
     localError(n.info, "could not resolve: " & $n)
@@ -236,7 +240,8 @@ proc bracketNotFoundError(c: PContext; n: PNode) =
 
 proc resolveOverloads(c: PContext, n, orig: PNode,
                       filter: TSymKinds, flags: TExprFlags,
-                      errors: var CandidateErrors): TCandidate =
+                      errors: var CandidateErrors,
+                      errorsEnabled: bool): TCandidate =
   var initialBinding: PNode
   var alt: TCandidate
   var f = n.sons[0]
@@ -249,7 +254,8 @@ proc resolveOverloads(c: PContext, n, orig: PNode,
 
   template pickBest(headSymbol) =
     pickBestCandidate(c, headSymbol, n, orig, initialBinding,
-                      filter, result, alt, errors, efExplain in flags)
+                      filter, result, alt, errors, efExplain in flags,
+                      errorsEnabled)
   pickBest(f)
 
   let overloadsState = result.state
@@ -423,9 +429,8 @@ proc tryDeref(n: PNode): PNode =
 
 proc semOverloadedCall(c: PContext, n, nOrig: PNode,
                        filter: TSymKinds, flags: TExprFlags): PNode =
-  var errors: CandidateErrors = if efExplain in flags: @[]
-                                else: nil
-  var r = resolveOverloads(c, n, nOrig, filter, flags, errors)
+  var errors: CandidateErrors = if efExplain in flags: @[] else: nil
+  var r = resolveOverloads(c, n, nOrig, filter, flags, errors, efExplain in flags)
   if r.state == csMatch:
     # this may be triggered, when the explain pragma is used
     if errors.len > 0:
@@ -443,7 +448,7 @@ proc semOverloadedCall(c: PContext, n, nOrig: PNode,
     # into sigmatch with hidden conversion produced there
     #
     n.sons[1] = n.sons[1].tryDeref
-    var r = resolveOverloads(c, n, nOrig, filter, flags, errors)
+    var r = resolveOverloads(c, n, nOrig, filter, flags, errors, efExplain in flags)
     if r.state == csMatch: result = semResolvedCall(c, n, r)
     else:
       # get rid of the deref again for a better error message:
diff --git a/compiler/semdata.nim b/compiler/semdata.nim
index 8159abf8f9..fc0488814c 100644
--- a/compiler/semdata.nim
+++ b/compiler/semdata.nim
@@ -63,7 +63,7 @@ type
       # to the user.
     efWantStmt, efAllowStmt, efDetermineType, efExplain,
     efAllowDestructor, efWantValue, efOperand, efNoSemCheck,
-    efNoProcvarCheck, efNoEvaluateGeneric, efInCall, efFromHlo,
+    efNoEvaluateGeneric, efInCall, efFromHlo
 
   TExprFlags* = set[TExprFlag]
 
diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index 6ad5d931d4..feca087fce 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -51,7 +51,6 @@ proc semExprWithType(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
                 renderTree(result, {renderNoComments}))
     result.typ = errorType(c)
   else:
-    if efNoProcvarCheck notin flags: semProcvarCheck(c, result)
     if result.typ.kind in {tyVar, tyLent}: result = newDeref(result)
 
 proc semExprNoDeref(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
@@ -63,8 +62,6 @@ proc semExprNoDeref(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
     localError(n.info, errExprXHasNoType,
                renderTree(result, {renderNoComments}))
     result.typ = errorType(c)
-  else:
-    semProcvarCheck(c, result)
 
 proc semSymGenericInstantiation(c: PContext, n: PNode, s: PSym): PNode =
   result = symChoice(c, n, s, scClosed)
@@ -308,7 +305,9 @@ proc isOpImpl(c: PContext, n: PNode, flags: TExprFlags): PNode =
     maybeLiftType(t2, c, n.info)
     var m: TCandidate
     initCandidate(c, m, t2)
-    if efExplain in flags: m.diagnostics = @[]
+    if efExplain in flags:
+      m.diagnostics = @[]
+      m.diagnosticsEnabled = true
     let match = typeRel(m, t2, t1) >= isSubtype # isNone
     result = newIntNode(nkIntLit, ord(match))
 
@@ -540,7 +539,6 @@ proc analyseIfAddressTakenInCall(c: PContext, n: PNode) =
       # we need to recurse explicitly here as converters can create nested
       # calls and then they wouldn't be analysed otherwise
       analyseIfAddressTakenInCall(c, n.sons[i])
-    semProcvarCheck(c, n.sons[i])
     if i < sonsLen(t) and
         skipTypes(t.sons[i], abstractInst-{tyTypeDesc}).kind == tyVar:
       if n.sons[i].kind != nkHiddenAddr:
@@ -1245,7 +1243,7 @@ proc semSubscript(c: PContext, n: PNode, flags: TExprFlags): PNode =
   checkMinSonsLen(n, 2)
   # make sure we don't evaluate generic macros/templates
   n.sons[0] = semExprWithType(c, n.sons[0],
-                              {efNoProcvarCheck, efNoEvaluateGeneric})
+                              {efNoEvaluateGeneric})
   let arr = skipTypes(n.sons[0].typ, {tyGenericInst,
                                       tyVar, tyLent, tyPtr, tyRef, tyAlias, tySink})
   case arr.kind
diff --git a/compiler/semstmts.nim b/compiler/semstmts.nim
index 94090852f8..eafc9ee667 100644
--- a/compiler/semstmts.nim
+++ b/compiler/semstmts.nim
@@ -71,37 +71,12 @@ proc toCover(t: PType): BiggestInt =
   else:
     result = lengthOrd(skipTypes(t, abstractVar-{tyTypeDesc}))
 
-when false:
-  proc performProcvarCheck(c: PContext, info: TLineInfo, s: PSym) =
-    ## Checks that the given symbol is a proper procedure variable, meaning
-    ## that it
-    var smoduleId = getModule(s).id
-    if sfProcvar notin s.flags and s.typ.callConv == ccDefault and
-        smoduleId != c.module.id:
-      block outer:
-        for module in c.friendModules:
-          if smoduleId == module.id:
-            break outer
-        localError(info, errXCannotBePassedToProcVar, s.name.s)
-
-template semProcvarCheck(c: PContext, n: PNode) =
-  when false:
-    var n = n.skipConv
-    if n.kind in nkSymChoices:
-      for x in n:
-        if x.sym.kind in {skProc, skMethod, skConverter, skIterator}:
-          performProcvarCheck(c, n.info, x.sym)
-    elif n.kind == nkSym and n.sym.kind in {skProc, skMethod, skConverter,
-                                          skIterator}:
-      performProcvarCheck(c, n.info, n.sym)
-
 proc semProc(c: PContext, n: PNode): PNode
 
 proc semExprBranch(c: PContext, n: PNode): PNode =
   result = semExpr(c, n)
   if result.typ != nil:
     # XXX tyGenericInst here?
-    semProcvarCheck(c, result)
     if result.typ.kind in {tyVar, tyLent}: result = newDeref(result)
 
 proc semExprBranchScope(c: PContext, n: PNode): PNode =
@@ -384,7 +359,7 @@ proc checkNilable(v: PSym) =
 
 include semasgn
 
-proc addToVarSection(c: PContext; result: var PNode; orig, identDefs: PNode) =
+proc addToVarSection(c: PContext; result: PNode; orig, identDefs: PNode) =
   let L = identDefs.len
   let value = identDefs[L-1]
   if result.kind == nkStmtList:
@@ -525,12 +500,11 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
         localError(a.info, errXExpected, "tuple")
       elif length-2 != sonsLen(tup):
         localError(a.info, errWrongNumberOfVariables)
-      else:
-        b = newNodeI(nkVarTuple, a.info)
-        newSons(b, length)
-        b.sons[length-2] = a.sons[length-2] # keep type desc for doc generator
-        b.sons[length-1] = def
-        addToVarSection(c, result, n, b)
+      b = newNodeI(nkVarTuple, a.info)
+      newSons(b, length)
+      b.sons[length-2] = a.sons[length-2] # keep type desc for doc generator
+      b.sons[length-1] = def
+      addToVarSection(c, result, n, b)
     elif tup.kind == tyTuple and def.kind in {nkPar, nkTupleConstr} and
         a.kind == nkIdentDefs and a.len > 3:
       message(a.info, warnEachIdentIsTuple)
@@ -572,7 +546,9 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
         addToVarSection(c, result, n, b)
       else:
         if def.kind in {nkPar, nkTupleConstr}: v.ast = def[j]
-        setVarType(v, tup.sons[j])
+        # bug #7663, for 'nim check' this can be a non-tuple:
+        if tup.kind == tyTuple: setVarType(v, tup.sons[j])
+        else: v.typ = tup
         b.sons[j] = newSymNode(v)
       checkNilable(v)
       if sfCompileTime in v.flags: hasCompileTime = true
@@ -1588,9 +1564,11 @@ proc semProcAux(c: PContext, n: PNode, kind: TSymKind,
   if sfOverriden in s.flags or s.name.s[0] == '=': semOverride(c, s, n)
   if s.name.s[0] in {'.', '('}:
     if s.name.s in [".", ".()", ".="] and {destructor, dotOperators} * c.features == {}:
-      message(n.info, warnDeprecated, "overloaded '.' and '()' operators are now .experimental; " & s.name.s)
+      localError(n.info, "the overloaded " & s.name.s &
+        " operator has to be enabled with {.experimental: \"dotOperators\".}")
     elif s.name.s == "()" and callOperator notin c.features:
-      message(n.info, warnDeprecated, "overloaded '()' operators are now .experimental; " & s.name.s)
+      localError(n.info, "the overloaded " & s.name.s &
+        " operator has to be enabled with {.experimental: \"callOperator\".}")
 
   if n.sons[bodyPos].kind != nkEmpty:
     # for DLL generation it is annoying to check for sfImportc!
@@ -1682,11 +1660,6 @@ proc semIterator(c: PContext, n: PNode): PNode =
     incl(s.typ.flags, tfCapturesEnv)
   else:
     s.typ.callConv = ccInline
-  when false:
-    if s.typ.callConv != ccInline:
-      s.typ.callConv = ccClosure
-      # and they always at least use the 'env' for the state field:
-      incl(s.typ.flags, tfCapturesEnv)
   if n.sons[bodyPos].kind == nkEmpty and s.magic == mNone:
     localError(n.info, errImplOfXexpected, s.name.s)
 
@@ -1792,14 +1765,6 @@ proc semStaticStmt(c: PContext, n: PNode): PNode =
   evalStaticStmt(c.module, c.cache, a, c.p.owner)
   result = newNodeI(nkDiscardStmt, n.info, 1)
   result.sons[0] = emptyNode
-  when false:
-    result = evalStaticStmt(c.module, a, c.p.owner)
-    if result.isNil:
-      LocalError(n.info, errCannotInterpretNodeX, renderTree(n))
-      result = emptyNode
-    elif result.kind == nkEmpty:
-      result = newNodeI(nkDiscardStmt, n.info, 1)
-      result.sons[0] = emptyNode
 
 proc usesResult(n: PNode): bool =
   # nkStmtList(expr) properly propagates the void context,
@@ -1841,80 +1806,47 @@ proc semStmtList(c: PContext, n: PNode, flags: TExprFlags): PNode =
   #                                         nkNilLit, nkEmpty}:
   #  dec last
   for i in countup(0, length - 1):
-    let k = n.sons[i].kind
-    case k
-    of nkFinally, nkExceptBranch:
-      # stand-alone finally and except blocks are
-      # transformed into regular try blocks:
-      #
-      # var f = fopen("somefile") | var f = fopen("somefile")
-      # finally: fclose(f)        | try:
-      # ...                       |   ...
-      #                           | finally:
-      #                           |   fclose(f)
-      var deferPart: PNode
-      if k == nkDefer:
-        deferPart = newNodeI(nkFinally, n.sons[i].info)
-        deferPart.add n.sons[i].sons[0]
-      elif k == nkFinally:
-        message(n.info, warnDeprecated,
-                "use 'defer'; standalone 'finally'")
-        deferPart = n.sons[i]
-      else:
-        message(n.info, warnDeprecated,
-                "use an explicit 'try'; standalone 'except'")
-        deferPart = n.sons[i]
-      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)..n.len-1]
-      tryStmt.addSon(body)
-      tryStmt.addSon(deferPart)
-      n.sons[i] = semTry(c, tryStmt)
-      n.sons.setLen(i+1)
-      n.typ = n.sons[i].typ
-      return
-    else:
-      var expr = semExpr(c, n.sons[i], flags)
-      n.sons[i] = expr
-      if c.matchedConcept != nil and expr.typ != nil and
-         (nfFromTemplate notin n.flags or i != last):
-        case expr.typ.kind
-        of tyBool:
-          if expr.kind == nkInfix and
-             expr[0].kind == nkSym and
-             expr[0].sym.name.s == "==":
-            if expr[1].typ.isUnresolvedStatic:
-              inferConceptStaticParam(c, expr[1], expr[2])
-              continue
-            elif expr[2].typ.isUnresolvedStatic:
-              inferConceptStaticParam(c, expr[2], expr[1])
-              continue
+    var expr = semExpr(c, n.sons[i], flags)
+    n.sons[i] = expr
+    if c.matchedConcept != nil and expr.typ != nil and
+        (nfFromTemplate notin n.flags or i != last):
+      case expr.typ.kind
+      of tyBool:
+        if expr.kind == nkInfix and
+            expr[0].kind == nkSym and
+            expr[0].sym.name.s == "==":
+          if expr[1].typ.isUnresolvedStatic:
+            inferConceptStaticParam(c, expr[1], expr[2])
+            continue
+          elif expr[2].typ.isUnresolvedStatic:
+            inferConceptStaticParam(c, expr[2], expr[1])
+            continue
 
-          let verdict = semConstExpr(c, n[i])
-          if verdict.intVal == 0:
-            localError(result.info, "concept predicate failed")
-        of tyUnknown: continue
-        else: discard
-      if n.sons[i].typ == enforceVoidContext: #or usesResult(n.sons[i]):
-        voidContext = true
-        n.typ = enforceVoidContext
-      if i == last and (length == 1 or efWantValue in flags):
-        n.typ = n.sons[i].typ
-        if not isEmptyType(n.typ): n.kind = nkStmtListExpr
-      elif i != last or voidContext:
-        discardCheck(c, n.sons[i])
-      else:
-        n.typ = n.sons[i].typ
-        if not isEmptyType(n.typ): n.kind = nkStmtListExpr
-      if n.sons[i].kind in LastBlockStmts or
-         n.sons[i].kind in nkCallKinds and n.sons[i][0].kind == nkSym and sfNoReturn in n.sons[i][0].sym.flags:
-        for j in countup(i + 1, length - 1):
-          case n.sons[j].kind
-          of nkPragma, nkCommentStmt, nkNilLit, nkEmpty, nkBlockExpr,
-             nkBlockStmt, nkState: discard
-          else: localError(n.sons[j].info, errStmtInvalidAfterReturn)
+        let verdict = semConstExpr(c, n[i])
+        if verdict.intVal == 0:
+          localError(result.info, "concept predicate failed")
+      of tyUnknown: continue
       else: discard
+    if n.sons[i].typ == enforceVoidContext: #or usesResult(n.sons[i]):
+      voidContext = true
+      n.typ = enforceVoidContext
+    if i == last and (length == 1 or efWantValue in flags):
+      n.typ = n.sons[i].typ
+      if not isEmptyType(n.typ): n.kind = nkStmtListExpr
+    elif i != last or voidContext:
+      discardCheck(c, n.sons[i])
+    else:
+      n.typ = n.sons[i].typ
+      if not isEmptyType(n.typ): n.kind = nkStmtListExpr
+    if n.sons[i].kind in LastBlockStmts or
+        n.sons[i].kind in nkCallKinds and n.sons[i][0].kind == nkSym and
+        sfNoReturn in n.sons[i][0].sym.flags:
+      for j in countup(i + 1, length - 1):
+        case n.sons[j].kind
+        of nkPragma, nkCommentStmt, nkNilLit, nkEmpty, nkBlockExpr,
+            nkBlockStmt, nkState: discard
+        else: localError(n.sons[j].info, errStmtInvalidAfterReturn)
+    else: discard
 
   if result.len == 1 and
      # concept bodies should be preserved as a stmt list:
@@ -1930,15 +1862,6 @@ proc semStmtList(c: PContext, n: PNode, flags: TExprFlags): PNode =
         not (result.comment[0] == '#' and result.comment[1] == '#'):
       # it is an old-style comment statement: we replace it with 'discard ""':
       prettybase.replaceComment(result.info)
-  when false:
-    # a statement list (s; e) has the type 'e':
-    if result.kind == nkStmtList and result.len > 0:
-      var lastStmt = lastSon(result)
-      if lastStmt.kind != nkNilLit and not implicitlyDiscardable(lastStmt):
-        result.typ = lastStmt.typ
-        #localError(lastStmt.info, errGenerated,
-        #  "Last expression must be explicitly returned if it " &
-        #  "is discardable or discarded")
 
 proc semStmt(c: PContext, n: PNode): PNode =
   # now: simply an alias:
diff --git a/compiler/sigmatch.nim b/compiler/sigmatch.nim
index cb821c02f2..9f4a995f45 100644
--- a/compiler/sigmatch.nim
+++ b/compiler/sigmatch.nim
@@ -26,6 +26,7 @@ type
     sym*: PSym
     unmatchedVarParam*, firstMismatch*: int
     diagnostics*: seq[string]
+    enabled*: bool
 
   CandidateErrors* = seq[CandidateError]
 
@@ -60,7 +61,8 @@ type
                               # matching. they will be reset if the matching
                               # is not successful. may replace the bindings
                               # table in the future.
-    diagnostics*: seq[string] # when this is not nil, the matching process
+    diagnostics*: seq[string] # \
+                              # when diagnosticsEnabled, the matching process
                               # will collect extra diagnostics that will be
                               # displayed to the user.
                               # triggered when overload resolution fails
@@ -70,6 +72,7 @@ type
     inheritancePenalty: int   # to prefer closest father object type
     firstMismatch*: int       # position of the first type mismatch for
                               # better error messages
+    diagnosticsEnabled*: bool
 
   TTypeRelFlag* = enum
     trDontBind
@@ -124,7 +127,8 @@ proc put(c: var TCandidate, key, val: PType) {.inline.} =
   idTablePut(c.bindings, key, val.skipIntLit)
 
 proc initCandidate*(ctx: PContext, c: var TCandidate, callee: PSym,
-                    binding: PNode, calleeScope = -1, diagnostics = false) =
+                    binding: PNode, calleeScope = -1,
+                    diagnosticsEnabled = false) =
   initCandidateAux(ctx, c, callee.typ)
   c.calleeSym = callee
   if callee.kind in skProcKinds and calleeScope == -1:
@@ -139,7 +143,8 @@ proc initCandidate*(ctx: PContext, c: var TCandidate, callee: PSym,
       c.calleeScope = 1
   else:
     c.calleeScope = calleeScope
-  c.diagnostics = if diagnostics: @[] else: nil
+  c.diagnostics = if diagnosticsEnabled: @[] else: nil
+  c.diagnosticsEnabled = diagnosticsEnabled
   c.magic = c.calleeSym.magic
   initIdTable(c.bindings)
   if binding != nil and callee.kind in routineKinds:
@@ -724,7 +729,7 @@ proc matchUserTypeClass*(m: var TCandidate; ff, a: PType): PType =
     diagnostics: seq[string]
     errorPrefix: string
     flags: TExprFlags = {}
-    collectDiagnostics = m.diagnostics != nil or
+    collectDiagnostics = m.diagnosticsEnabled or
                          sfExplain in typeClass.sym.flags
 
   if collectDiagnostics:
@@ -743,7 +748,9 @@ proc matchUserTypeClass*(m: var TCandidate; ff, a: PType): PType =
 
   if collectDiagnostics:
     writelnHook = oldWriteHook
-    for msg in diagnostics: m.diagnostics.safeAdd msg
+    for msg in diagnostics:
+      m.diagnostics.safeAdd msg
+      m.diagnosticsEnabled = true
 
   if checkedBody == nil: return nil
 
@@ -1395,8 +1402,13 @@ proc typeRelImpl(c: var TCandidate, f, aOrig: PType,
 
         var aAsObject = roota.lastSon
 
-        if fKind in {tyRef, tyPtr} and aAsObject.kind == fKind:
-          aAsObject = aAsObject.base
+        if fKind in {tyRef, tyPtr}:
+          if aAsObject.kind == tyObject:
+            # bug #7600, tyObject cannot be passed
+            # as argument to tyRef/tyPtr
+            return isNone
+          elif aAsObject.kind == fKind:
+            aAsObject = aAsObject.base
 
         if aAsObject.kind == tyObject:
           let baseType = aAsObject.base
diff --git a/compiler/vmdeps.nim b/compiler/vmdeps.nim
index 071cc7706e..ba37237e82 100644
--- a/compiler/vmdeps.nim
+++ b/compiler/vmdeps.nim
@@ -208,7 +208,12 @@ proc mapTypeToAstX(t: PType; info: TLineInfo;
       result.add mapTypeToAst(t.sons[0], info)
     else:
       result = mapTypeToBracket("ref", mRef, t, info)
-  of tyVar: result = mapTypeToBracket("var", mVar, t, info)
+  of tyVar:
+    if inst:
+      result = newNodeX(nkVarTy)
+      result.add mapTypeToAst(t.sons[0], info)
+    else:
+      result = mapTypeToBracket("var", mVar, t, info)
   of tyLent: result = mapTypeToBracket("lent", mBuiltinType, t, info)
   of tySink: result = mapTypeToBracket("sink", mBuiltinType, t, info)
   of tySequence: result = mapTypeToBracket("seq", mSeq, t, info)
diff --git a/compiler/vmgen.nim b/compiler/vmgen.nim
index c3eaf89461..0544dc311f 100644
--- a/compiler/vmgen.nim
+++ b/compiler/vmgen.nim
@@ -1553,6 +1553,7 @@ proc getNullValue(typ: PType, info: TLineInfo): PNode =
     result = newNodeIT(nkFloatLit, info, t)
   of tyCString, tyString:
     result = newNodeIT(nkStrLit, info, t)
+    result.strVal = ""
   of tyVar, tyLent, tyPointer, tyPtr, tySequence, tyExpr,
      tyStmt, tyTypeDesc, tyStatic, tyRef, tyNil:
     result = newNodeIT(nkNilLit, info, t)
diff --git a/lib/impure/nre.nim b/lib/impure/nre.nim
index 3d4afc0ae1..582f5ab3bc 100644
--- a/lib/impure/nre.nim
+++ b/lib/impure/nre.nim
@@ -645,7 +645,6 @@ template replaceImpl(str: string, pattern: Regex,
     let bounds = match.matchBounds
     result.add(str.substr(lastIdx, bounds.a - 1))
     let nextVal = replacement
-    assert(nextVal != nil)
     result.add(nextVal)
 
     lastIdx = bounds.b + 1
diff --git a/lib/system.nim b/lib/system.nim
index 98c1334281..5c0970f853 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -1280,15 +1280,13 @@ proc setLen*[T](s: var seq[T], newlen: Natural) {.
   ## sets the length of `s` to `newlen`.
   ## ``T`` may be any sequence type.
   ## If the current length is greater than the new length,
-  ## ``s`` will be truncated. `s` cannot be nil! To initialize a sequence with
-  ## a size, use ``newSeq`` instead.
+  ## ``s`` will be truncated.
 
 proc setLen*(s: var string, newlen: Natural) {.
   magic: "SetLengthStr", noSideEffect.}
   ## sets the length of `s` to `newlen`.
   ## If the current length is greater than the new length,
-  ## ``s`` will be truncated. `s` cannot be nil! To initialize a string with
-  ## a size, use ``newString`` instead.
+  ## ``s`` will be truncated.
   ##
   ## .. code-block:: Nim
   ##  var myS = "Nim is great!!"
@@ -2414,8 +2412,9 @@ proc `==` *[T](x, y: seq[T]): bool {.noSideEffect.} =
     if seqToPtr(x) == seqToPtr(y):
       return true
 
-  if x.isNil or y.isNil:
-    return false
+  when not defined(nimNoNil):
+    if x.isNil or y.isNil:
+      return false
 
   if x.len != y.len:
     return false
@@ -4012,18 +4011,18 @@ proc addQuoted*[T](s: var string, x: T) =
 
 when hasAlloc:
   # XXX: make these the default (or implement the NilObject optimization)
-  proc safeAdd*[T](x: var seq[T], y: T) {.noSideEffect.} =
+  proc safeAdd*[T](x: var seq[T], y: T) {.noSideEffect, deprecated.} =
     ## Adds ``y`` to ``x`` unless ``x`` is not yet initialized; in that case,
     ## ``x`` becomes ``@[y]``
     if x == nil: x = @[y]
     else: x.add(y)
 
-  proc safeAdd*(x: var string, y: char) =
+  proc safeAdd*(x: var string, y: char) {.noSideEffect, deprecated.} =
     ## Adds ``y`` to ``x``. If ``x`` is ``nil`` it is initialized to ``""``
     if x == nil: x = ""
     x.add(y)
 
-  proc safeAdd*(x: var string, y: string) =
+  proc safeAdd*(x: var string, y: string) {.noSideEffect, deprecated.} =
     ## Adds ``y`` to ``x`` unless ``x`` is not yet initalized; in that
     ## case, ``x`` becomes ``y``
     if x == nil: x = y
diff --git a/lib/system/sysstr.nim b/lib/system/sysstr.nim
index ea0273340d..bba59e9309 100644
--- a/lib/system/sysstr.nim
+++ b/lib/system/sysstr.nim
@@ -22,21 +22,34 @@ proc resize(old: int): int {.inline.} =
 
 proc cmpStrings(a, b: NimString): int {.inline, compilerProc.} =
   if a == b: return 0
-  if a == nil: return -1
-  if b == nil: return 1
-  let minlen = min(a.len, b.len)
+  when defined(nimNoNil):
+    let alen = if a == nil: 0 else: a.len
+    let blen = if b == nil: 0 else: b.len
+  else:
+    if a == nil: return -1
+    if b == nil: return 1
+    let alen = a.len
+    let blen = b.len
+  let minlen = min(alen, blen)
   if minlen > 0:
     result = c_memcmp(addr a.data, addr b.data, minlen.csize)
     if result == 0:
-      result = a.len - b.len
+      result = alen - blen
   else:
-    result = a.len - b.len
+    result = alen - blen
 
 proc eqStrings(a, b: NimString): bool {.inline, compilerProc.} =
   if a == b: return true
-  if a == nil or b == nil: return false
-  return a.len == b.len and
-    equalMem(addr(a.data), addr(b.data), a.len)
+  when defined(nimNoNil):
+    let alen = if a == nil: 0 else: a.len
+    let blen = if b == nil: 0 else: b.len
+  else:
+    if a == nil or b == nil: return false
+    let alen = a.len
+    let blen = b.len
+  if alen == blen:
+    if alen == 0: return true
+    return equalMem(addr(a.data), addr(b.data), alen)
 
 when declared(allocAtomic):
   template allocStr(size: untyped): untyped =
@@ -101,9 +114,6 @@ proc cstrToNimstr(str: cstring): NimString {.compilerRtl.} =
   if str == nil: NimString(nil)
   else: toNimStr(str, str.len)
 
-template wasMoved(x: NimString): bool = false
-# (x.reserved and seqShallowFlag) != 0
-
 proc copyString(src: NimString): NimString {.compilerRtl.} =
   if src != nil:
     if (src.reserved and seqShallowFlag) != 0:
@@ -161,14 +171,16 @@ proc hashString(s: string): int {.compilerproc.} =
 
 proc addChar(s: NimString, c: char): NimString =
   # is compilerproc!
-  result = s
-  if result.len >= result.space:
-    let r = resize(result.space)
-    result = cast[NimString](growObj(result,
-      sizeof(TGenericSeq) + r + 1))
-    result.reserved = r
-  elif wasMoved(s):
-    result = newOwnedString(s, s.len)
+  if s == nil:
+    result = rawNewStringNoInit(1)
+    result.len = 0
+  else:
+    result = s
+    if result.len >= result.space:
+      let r = resize(result.space)
+      result = cast[NimString](growObj(result,
+        sizeof(TGenericSeq) + r + 1))
+      result.reserved = r
   result.data[result.len] = c
   result.data[result.len+1] = '\0'
   inc(result.len)
@@ -205,7 +217,9 @@ proc addChar(s: NimString, c: char): NimString =
 #   s = rawNewString(0);
 
 proc resizeString(dest: NimString, addlen: int): NimString {.compilerRtl.} =
-  if dest.len + addlen <= dest.space and not wasMoved(dest):
+  if dest == nil:
+    result = rawNewStringNoInit(addlen)
+  elif dest.len + addlen <= dest.space:
     result = dest
   else: # slow path:
     var sp = max(resize(dest.space), dest.len + addlen)
@@ -216,8 +230,9 @@ proc resizeString(dest: NimString, addlen: int): NimString {.compilerRtl.} =
     # DO NOT UPDATE LEN YET: dest.len = newLen
 
 proc appendString(dest, src: NimString) {.compilerproc, inline.} =
-  copyMem(addr(dest.data[dest.len]), addr(src.data), src.len + 1)
-  inc(dest.len, src.len)
+  if src != nil:
+    copyMem(addr(dest.data[dest.len]), addr(src.data), src.len + 1)
+    inc(dest.len, src.len)
 
 proc appendChar(dest: NimString, c: char) {.compilerproc, inline.} =
   dest.data[dest.len] = c
@@ -226,8 +241,8 @@ proc appendChar(dest: NimString, c: char) {.compilerproc, inline.} =
 
 proc setLengthStr(s: NimString, newLen: int): NimString {.compilerRtl.} =
   var n = max(newLen, 0)
-  if wasMoved(s):
-    result = newOwnedString(s, n)
+  if s == nil:
+    result = mnewString(newLen)
   elif n <= s.space:
     result = s
   else:
@@ -261,6 +276,18 @@ proc incrSeqV2(seq: PGenericSeq, elemSize: int): PGenericSeq {.compilerProc.} =
                                GenericSeqSize))
     result.reserved = r
 
+proc incrSeqV3(s: PGenericSeq, typ: PNimType): PGenericSeq {.compilerProc.} =
+  if s == nil:
+    result = cast[PGenericSeq](newSeq(typ, 1))
+    result.len = 0
+  else:
+    result = s
+    if result.len >= result.space:
+      let r = resize(result.space)
+      result = cast[PGenericSeq](growObj(result, typ.base.size * r +
+                                GenericSeqSize))
+      result.reserved = r
+
 proc setLengthSeq(seq: PGenericSeq, elemSize, newLen: int): PGenericSeq {.
     compilerRtl, inl.} =
   result = seq
@@ -301,6 +328,13 @@ proc setLengthSeq(seq: PGenericSeq, elemSize, newLen: int): PGenericSeq {.
            (newLen*%elemSize)), (result.len-%newLen) *% elemSize)
   result.len = newLen
 
+proc setLengthSeqV2(s: PGenericSeq, typ: PNimType, newLen: int): PGenericSeq {.
+    compilerRtl.} =
+  if s == nil:
+    result = cast[PGenericSeq](newSeq(typ, newLen))
+  else:
+    result = setLengthSeq(s, typ.base.size, newLen)
+
 # --------------- other string routines ----------------------------------
 proc add*(result: var string; x: int64) =
   let base = result.len
diff --git a/tests/array/tarraycons_ptr_generic.nim b/tests/array/tarraycons_ptr_generic.nim
new file mode 100644
index 0000000000..eb89a196fc
--- /dev/null
+++ b/tests/array/tarraycons_ptr_generic.nim
@@ -0,0 +1,51 @@
+discard """
+  output: '''apple
+banana
+Fruit
+2
+4
+3
+none
+skin
+paper
+'''
+"""
+type
+  Fruit = object of RootObj
+    name: string
+  Apple = object of Fruit
+  Banana = object of Fruit
+
+var
+  ir = Fruit(name: "Fruit")
+  ia = Apple(name: "apple")
+  ib = Banana(name: "banana")
+
+let x = [ia.addr, ib.addr, ir.addr]
+for c in x: echo c.name
+
+type
+  Vehicle[T] = object of RootObj
+    tire: T
+  Car[T] = object of Vehicle[T]
+  Bike[T] = object of Vehicle[T]
+
+var v = Vehicle[int](tire: 3)
+var c = Car[int](tire: 4)
+var b = Bike[int](tire: 2)
+
+let y = [b.addr, c.addr, v.addr]
+for c in y: echo c.tire
+
+type
+  Book[T] = ref object of RootObj
+    cover: T
+  Hard[T] = ref object of Book[T]
+  Soft[T] = ref object of Book[T]
+
+var bn = Book[string](cover: "none")
+var hs = Hard[string](cover: "skin")
+var bp = Soft[string](cover: "paper")
+
+let z = [bn, hs, bp]
+for c in z: echo c.cover
diff --git a/tests/array/tarraycons_ptr_generic2.nim b/tests/array/tarraycons_ptr_generic2.nim
new file mode 100644
index 0000000000..fce7af6691
--- /dev/null
+++ b/tests/array/tarraycons_ptr_generic2.nim
@@ -0,0 +1,17 @@
+discard """
+  file: "tarraycons_ptr_generic2.nim"
+  line: 17
+  errormsg: "type mismatch: got <ptr Hard[system.string]> but expected 'Book[system.string]'"
+"""
+
+type
+  Book[T] = ref object of RootObj
+    cover: T
+  Hard[T] = ref object of Book[T]
+  Soft[T] = ref object of Book[T]
+
+var bn = Book[string](cover: "none")
+var hs = Hard[string](cover: "skin")
+var bp = Soft[string](cover: "paper")
+
+let z = [bn, hs.addr, bp]
diff --git a/tests/errmsgs/tproper_stacktrace2.nim b/tests/errmsgs/tproper_stacktrace2.nim
index 5f312b8703..44b208c87d 100644
--- a/tests/errmsgs/tproper_stacktrace2.nim
+++ b/tests/errmsgs/tproper_stacktrace2.nim
@@ -3,7 +3,7 @@ discard """
   exitcode: 1
 """
 
-proc returnsNil(): string = return nil
+proc returnsNil(): ref int = return nil
 
 iterator fields*(a, b: int): int =
   if a == b:
@@ -17,6 +17,6 @@ proc main(): string =
   result = ""
   for i in fields(0, 1):
     let x = returnsNil()
-    result &= "string literal " & $x
+    result &= "string literal " & $x[]
 
 echo main()
diff --git a/tests/manyloc/argument_parser/argument_parser.nim b/tests/manyloc/argument_parser/argument_parser.nim
index 14352066d4..1095a893e0 100644
--- a/tests/manyloc/argument_parser/argument_parser.nim
+++ b/tests/manyloc/argument_parser/argument_parser.nim
@@ -209,7 +209,7 @@ proc `$`*(data: Tcommandline_results): string =
 
 # - Parse code
 
-template raise_or_quit(exception, message: expr): stmt {.immediate.} =
+template raise_or_quit(exception, message: untyped) =
   ## Avoids repeating if check based on the default quit_on_failure variable.
   ##
   ## As a special case, if message has a zero length the call to quit won't
@@ -230,15 +230,15 @@ template run_custom_proc(parsed_parameter: Tparsed_parameter,
   ##
   ## Pass in the string of the parameter triggering the call. If the
   if not custom_validator.isNil:
+    try:
+      let message = custom_validator(parameter, parsed_parameter)
+      if not message.isNil and message.len > 0:
+        raise_or_quit(ValueError, ("Failed to validate value for " &
+          "parameter $1:\n$2" % [escape(parameter), message]))
     except:
       raise_or_quit(ValueError, ("Couldn't run custom proc for " &
         "parameter $1:\n$2" % [escape(parameter),
         getCurrentExceptionMsg()]))
-    let message = custom_validator(parameter, parsed_parameter)
-    if not message.isNil and message.len > 0:
-      raise_or_quit(ValueError, ("Failed to validate value for " &
-        "parameter $1:\n$2" % [escape(parameter), message]))
-
 
 proc parse_parameter(quit_on_failure: bool, param, value: string,
     param_kind: Tparam_kind): Tparsed_parameter =
diff --git a/tests/system/tnilconcats.nim b/tests/system/tnilconcats.nim
new file mode 100644
index 0000000000..ce059b7b0e
--- /dev/null
+++ b/tests/system/tnilconcats.nim
@@ -0,0 +1,25 @@
+discard """
+  output: '''@[nil, nil, nil, nil, nil, nil, nil, "meh"]'''
+  exitcode: "0"
+"""
+
+when true:
+  var ab: string
+  ab &= "more"
+
+  doAssert ab == "more"
+
+  var x: seq[string]
+
+  setLen(x, 7)
+
+  x.add "meh"
+
+  var s: string
+  var z = "abc"
+  var zz: string
+  s &= "foo" & z & zz
+
+  doAssert s == "fooabc"
+
+  echo x
diff --git a/tests/system/toString.nim b/tests/system/toString.nim
index ea9d6b05b8..37c678a748 100644
--- a/tests/system/toString.nim
+++ b/tests/system/toString.nim
@@ -51,3 +51,59 @@ import strutils
 let arr = ['H','e','l','l','o',' ','W','o','r','l','d','!','\0']
 doAssert $arr == "['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd', '!', '\\x00']"
 doAssert $cstring(unsafeAddr arr) == "Hello World!"
+
+proc takes(c: cstring) =
+  doAssert c == ""
+
+proc testm() =
+  var x: string
+  # nil is mapped to "":
+  takes(x)
+
+testm()
+
+# nil tests
+var xx: seq[string]
+var yy: string
+doAssert xx == @[]
+doAssert yy == ""
+
+proc bar(arg: cstring): void =
+  doAssert arg[0] == '\0'
+
+proc baz(arg: openarray[char]): void =
+  doAssert arg.len == 0
+
+proc stringCompare(): void =
+  var a,b,c,d,e,f,g: string
+  a.add 'a'
+  doAssert a == "a"
+  b.add "bee"
+  doAssert b == "bee"
+  b.add g
+  doAssert b == "bee"
+  c.add 123.456
+  doAssert c == "123.456"
+  d.add 123456
+  doAssert d == "123456"
+
+  doAssert e == ""
+  doAssert "" == e
+  doAssert nil == e
+  doAssert e == nil
+  doAssert f == g
+  doAssert "" == ""
+  doAssert "" == nil
+  doAssert nil == ""
+
+  g.setLen(10)
+  doAssert g == "\0\0\0\0\0\0\0\0\0\0"
+  doAssert "" != "\0\0\0\0\0\0\0\0\0\0"
+
+  var nilstring: string
+  bar(nilstring)
+  baz(nilstring)
+
+stringCompare()
+static:
+  stringCompare()
\ No newline at end of file
diff --git a/tests/typerel/t7600_1.nim b/tests/typerel/t7600_1.nim
new file mode 100644
index 0000000000..e3a5fefa2c
--- /dev/null
+++ b/tests/typerel/t7600_1.nim
@@ -0,0 +1,18 @@
+discard """
+errormsg: "type mismatch: got <Thin[system.int]>"
+nimout: '''t7600_1.nim(18, 6) Error: type mismatch: got <Thin[system.int]>
+but expected one of:
+proc test[T](x: Paper[T])
+
+expression: test tn'''
+"""
+
+type
+  Paper[T] = ref object of RootObj
+    thickness: T
+  Thin[T]  = object of Paper[T]
+
+proc test[T](x: Paper[T]) = discard
+
+var tn = Thin[int]()
+test tn
diff --git a/tests/typerel/t7600_2.nim b/tests/typerel/t7600_2.nim
new file mode 100644
index 0000000000..7badb69cfb
--- /dev/null
+++ b/tests/typerel/t7600_2.nim
@@ -0,0 +1,17 @@
+discard """
+errormsg: "type mismatch: got <Thin>"
+nimout: '''t7600_2.nim(17, 6) Error: type mismatch: got <Thin>
+but expected one of:
+proc test(x: Paper)
+
+expression: test tn'''
+"""
+
+type
+  Paper = ref object of RootObj
+  Thin  = object of Paper
+
+proc test(x: Paper) = discard
+
+var tn = Thin()
+test tn
diff --git a/tools/nimgrep.nim b/tools/nimgrep.nim
index 4cfcbe9bc2..9cfd7a86f6 100644
--- a/tools/nimgrep.nim
+++ b/tools/nimgrep.nim
@@ -128,7 +128,7 @@ proc highlight(s, match, repl: string, t: tuple[first, last: int],
     stdout.write("\n")
     stdout.flushFile()
 
-proc processFile(pattern; filename: string) =
+proc processFile(pattern; filename: string; counter: var int) =
   var filenameShown = false
   template beforeHighlight =
     if not filenameShown and optVerbose notin options and not oneline:
@@ -166,6 +166,7 @@ proc processFile(pattern; filename: string) =
     var wholeMatch = buffer.substr(t.first, t.last)
 
     beforeHighlight()
+    inc counter
     if optReplace notin options:
       highlight(buffer, wholeMatch, "", t, filename, line, showRepl=false)
     else:
@@ -241,17 +242,17 @@ proc styleInsensitive(s: string): string =
         addx()
     else: addx()
 
-proc walker(pattern; dir: string) =
+proc walker(pattern; dir: string; counter: var int) =
   for kind, path in walkDir(dir):
     case kind
     of pcFile:
       if extensions.len == 0 or path.hasRightExt(extensions):
-        processFile(pattern, path)
+        processFile(pattern, path, counter)
     of pcDir:
       if optRecursive in options:
-        walker(pattern, path)
+        walker(pattern, path, counter)
     else: discard
-  if existsFile(dir): processFile(pattern, dir)
+  if existsFile(dir): processFile(pattern, dir, counter)
 
 proc writeHelp() =
   stdout.write(Usage)
@@ -321,6 +322,7 @@ if optStdin in options:
 if pattern.len == 0:
   writeHelp()
 else:
+  var counter = 0
   if filenames.len == 0:
     filenames.add(os.getCurrentDir())
   if optRegex notin options:
@@ -332,7 +334,7 @@ else:
       pattern = "\\i " & pattern
     let pegp = peg(pattern)
     for f in items(filenames):
-      walker(pegp, f)
+      walker(pegp, f, counter)
   else:
     var reflags = {reStudy, reExtended}
     if optIgnoreStyle in options:
@@ -343,5 +345,6 @@ else:
       reflags.incl reIgnoreCase
     let rep = re(pattern, reflags)
     for f in items(filenames):
-      walker(rep, f)
-
+      walker(rep, f, counter)
+  if not oneline:
+    stdout.write($counter & " matches\n")