--nilseqs is now a deprecated noop (#17211)

* --nilseqs is now a deprecated noop

* fix tests; fix: future => sugar

compiler/ccgexprs.nim

@@ -85,10 +85,9 @@ proc genLiteral(p: BProc, n: PNode, ty: PType): Rope =
     of tyNil:
       result = genNilStringLiteral(p.module, n.info)
     of tyString:
-      # with the new semantics for 'nil' strings, we can map "" to nil and
+      # with the new semantics for not 'nil' strings, we can map "" to nil and
       # save tons of allocations:
-      if n.strVal.len == 0 and optNilSeqs notin p.options and
-          optSeqDestructors notin p.config.globalOptions:
+      if n.strVal.len == 0 and optSeqDestructors notin p.config.globalOptions:
         result = genNilStringLiteral(p.module, n.info)
       else:
         result = genStringLiteral(p.module, n)
@@ -176,8 +175,7 @@ proc canMove(p: BProc, n: PNode; dest: TLoc): bool =
     if not isDeepConstExpr(n) or n.len == 0:
       if skipTypes(n.typ, abstractVarRange).kind == tySequence:
         return true
-  elif optNilSeqs notin p.options and
-    n.kind in nkStrKinds and n.strVal.len == 0:
+  elif n.kind in nkStrKinds and n.strVal.len == 0:
     # Empty strings are codegen'd as NIM_NIL so it's just a pointer copy
     return true
   result = n.kind in nkCallKinds
@@ -1371,8 +1369,7 @@ proc genNewSeq(p: BProc, e: PNode) =
        getTypeDesc(p.module, seqtype.lastSon),
        getSeqPayloadType(p.module, seqtype)])
   else:
-    let lenIsZero = optNilSeqs notin p.options and
-      e[2].kind == nkIntLit and e[2].intVal == 0
+    let lenIsZero = e[2].kind == nkIntLit and e[2].intVal == 0
     genNewSeqAux(p, a, b.rdLoc, lenIsZero)
     gcUsage(p.config, e)
 
@@ -1497,8 +1494,7 @@ proc genSeqConstr(p: BProc, n: PNode, d: var TLoc) =
       getSeqPayloadType(p.module, seqtype)])
   else:
     # generate call to newSeq before adding the elements per hand:
-    genNewSeqAux(p, dest[], l,
-      optNilSeqs notin p.options and n.len == 0)
+    genNewSeqAux(p, dest[], l, n.len == 0)
   for i in 0..<n.len:
     initLoc(arr, locExpr, n[i], OnHeap)
     arr.r = ropecg(p.module, "$1$3[$2]", [rdLoc(dest[]), intLiteral(i), dataField(p)])
@@ -1527,7 +1523,7 @@ proc genArrToSeq(p: BProc, n: PNode, d: var TLoc) =
       [rdLoc d, L, getTypeDesc(p.module, seqtype.lastSon),
       getSeqPayloadType(p.module, seqtype)])
   else:
-    genNewSeqAux(p, d, intLiteral(L), optNilSeqs notin p.options and L == 0)
+    genNewSeqAux(p, d, intLiteral(L), L == 0)
   initLocExpr(p, n[1], a)
   # bug #5007; do not produce excessive C source code:
   if L < 10:

compiler/commands.nim

@@ -318,7 +318,9 @@ proc testCompileOption*(conf: ConfigRef; switch: string, info: TLineInfo): bool
   of "implicitstatic": result = contains(conf.options, optImplicitStatic)
   of "patterns", "trmacros": result = contains(conf.options, optTrMacros)
   of "excessivestacktrace": result = contains(conf.globalOptions, optExcessiveStackTrace)
-  of "nilseqs": result = contains(conf.options, optNilSeqs)
+  of "nilseqs":
+    warningDeprecated(conf, info, "nilseqs is a deprecated noop")
+    result = false
   else: invalidCmdLineOption(conf, passCmd1, switch, info)
 
 proc processPath(conf: ConfigRef; path: string, info: TLineInfo,
@@ -650,7 +652,7 @@ proc processSwitch*(switch, arg: string, pass: TCmdLinePass, info: TLineInfo;
     else:
       undefSymbol(conf.symbols, "hotcodereloading")
       undefSymbol(conf.symbols, "useNimRtl")
-  of "nilseqs": processOnOffSwitch(conf, {optNilSeqs}, arg, pass, info)
+  of "nilseqs": warningDeprecated(conf, info, "nilseqs is a deprecated noop")
   of "checks", "x": processOnOffSwitch(conf, ChecksOptions, arg, pass, info)
   of "floatchecks":
     processOnOffSwitch(conf, {optNaNCheck, optInfCheck}, arg, pass, info)

compiler/msgs.nim

@@ -590,6 +590,9 @@ template localError*(conf: ConfigRef; info: TLineInfo, format: string, params: o
 template message*(conf: ConfigRef; info: TLineInfo, msg: TMsgKind, arg = "") =
   liMessage(conf, info, msg, arg, doNothing, instLoc())
 
+proc warningDeprecated*(conf: ConfigRef, info: TLineInfo = gCmdLineInfo, msg = "") {.inline.} =
+  message(conf, info, warnDeprecated, msg)
+
 proc internalErrorImpl(conf: ConfigRef; info: TLineInfo, errMsg: string, info2: InstantiationInfo) =
   if conf.cmd == cmdIdeTools and conf.structuredErrorHook.isNil: return
   writeContext(conf, info)

compiler/options.nim

@@ -39,7 +39,6 @@ type                          # please make sure we have under 32 options
                               # evaluation
     optTrMacros,              # en/disable pattern matching
     optMemTracker,
-    optNilSeqs,
     optSinkInference          # 'sink T' inference
     optCursorInference
 

compiler/sigmatch.nim

@@ -556,12 +556,6 @@ proc recordRel(c: var TCandidate, f, a: PType): TTypeRelation =
 proc allowsNil(f: PType): TTypeRelation {.inline.} =
   result = if tfNotNil notin f.flags: isSubtype else: isNone
 
-proc allowsNilDeprecated(c: TCandidate, f: PType): TTypeRelation =
-  if optNilSeqs in c.c.config.options:
-    result = allowsNil(f)
-  else:
-    result = isNone
-
 proc inconsistentVarTypes(f, a: PType): bool {.inline.} =
   result = f.kind != a.kind and
     (f.kind in {tyVar, tyLent, tySink} or a.kind in {tyVar, tyLent, tySink})
@@ -1300,7 +1294,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
             result = isNone
         elif tfNotNil in f.flags and tfNotNil notin a.flags:
           result = isNilConversion
-    of tyNil: result = allowsNilDeprecated(c, f)
+    of tyNil: result = isNone
     else: discard
   of tyOrdinal:
     if isOrdinalType(a, allowEnumWithHoles = optNimV1Emulation in c.c.config.globalOptions):
@@ -1396,7 +1390,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
         result = isNilConversion
       else:
         result = isEqual
-    of tyNil: result = allowsNilDeprecated(c, f)
+    of tyNil: result = isNone
     else: discard
   of tyCString:
     # conversion from string to cstring is automatic: