prepare for #3898

compiler/parser.nim

@@ -686,11 +686,19 @@ proc primarySuffix(p: var TParser, r: PNode, baseIndent: int): PNode =
   #|       | '{' optInd indexExprList optPar '}'
   #|       | &( '`'|IDENT|literal|'cast'|'addr'|'type') expr # command syntax
   result = r
+
+  template somePar() =
+    if p.tok.strongSpaceA > 0:
+      if p.strongSpaces:
+        break
+      else:
+        parMessage(p, warnDeprecated,
+          "a [b] will be parsed as command syntax; spacing")
   while p.tok.indent < 0 or
        (p.tok.tokType == tkDot and p.tok.indent >= baseIndent):
     case p.tok.tokType
     of tkParLe:
-      if p.strongSpaces and p.tok.strongSpaceA > 0: break
+      somePar()
       result = namedParams(p, result, nkCall, tkParRi)
       if result.len > 1 and result.sons[1].kind == nkExprColonExpr:
         result.kind = nkObjConstr
@@ -705,10 +713,10 @@ proc primarySuffix(p: var TParser, r: PNode, baseIndent: int): PNode =
       result = dotExpr(p, result)
       result = parseGStrLit(p, result)
     of tkBracketLe:
-      if p.strongSpaces and p.tok.strongSpaceA > 0: break
+      somePar()
       result = namedParams(p, result, nkBracketExpr, tkBracketRi)
     of tkCurlyLe:
-      if p.strongSpaces and p.tok.strongSpaceA > 0: break
+      somePar()
       result = namedParams(p, result, nkCurlyExpr, tkCurlyRi)
     of tkSymbol, tkAccent, tkIntLit..tkCharLit, tkNil, tkCast, tkAddr, tkType:
       if p.inPragma == 0: