From fa5444760e3a16de3380e856b1f620f506e007c7 Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Tue, 14 Aug 2018 14:05:35 +0200
Subject: [PATCH] Forbid constructors with 0 arguments

Constructors with 0 arguments make no sense. Thus, forbid creating such
constructors, and also forbid installing zero argument methods for
constructors.
---
 lib/oper.g                      |  7 ++-
 lib/oper1.g                     |  5 +-
 src/c_oper1.c                   | 95 ++++++++++++++++++---------------
 src/hpc/c_oper1.c               | 95 ++++++++++++++++++---------------
 src/opers.c                     | 40 +++++++-------
 tst/testinstall/constructor.tst | 27 ++++++++++
 tst/testinstall/varargs.tst     |  2 +-
 tst/testspecial/trace.g         |  6 +--
 tst/testspecial/trace.g.out     | 24 ++++-----
 9 files changed, 173 insertions(+), 128 deletions(-)
 create mode 100644 tst/testinstall/constructor.tst

diff --git a/lib/oper.g b/lib/oper.g
index b642d809ce..0623169370 100644
--- a/lib/oper.g
+++ b/lib/oper.g
@@ -773,6 +773,9 @@ end );
 BIND_GLOBAL( "NewConstructor", function ( name, filters )
     local   oper,  filt,  filter;
 
+    if LEN_LIST( filters ) = 0 then
+      Error( "constructors must have at least one argument" );
+    fi;
     if GAPInfo.MaxNrArgsMethod < LEN_LIST( filters ) then
       Error( "methods can have at most ", GAPInfo.MaxNrArgsMethod,
              " arguments" );
@@ -944,7 +947,9 @@ BIND_GLOBAL( "DeclareConstructor", function ( name, filters )
 
     local gvar, req, filt, filter;
 
-    if GAPInfo.MaxNrArgsMethod < LEN_LIST( filters ) then
+    if LEN_LIST( filters ) = 0 then
+      Error( "constructors must have at least one argument" );
+    elif GAPInfo.MaxNrArgsMethod < LEN_LIST( filters ) then
       Error( "methods can have at most ", GAPInfo.MaxNrArgsMethod,
              " arguments" );
     elif ISB_GVAR( name ) then
diff --git a/lib/oper1.g b/lib/oper1.g
index 5ae4ecd52f..71067774e0 100644
--- a/lib/oper1.g
+++ b/lib/oper1.g
@@ -153,9 +153,10 @@ BIND_GLOBAL( "INSTALL_METHOD_FLAGS",
     fi;
     # add the number of filters required for each argument
     if IS_CONSTRUCTOR(opr) then
-        if 0 < LEN_LIST(flags)  then
-            rank := rank - RankFilter( flags[ 1 ] );
+        if 0 = LEN_LIST(flags)  then
+            Error(NAME_FUNC(opr),": constructors must have at least one argument");
         fi;
+        rank := rank - RankFilter( flags[ 1 ] );
     else
         for i  in flags  do
             rank := rank + RankFilter( i );
diff --git a/src/c_oper1.c b/src/c_oper1.c
index 35886bdeb8..aeb413b27f 100644
--- a/src/c_oper1.c
+++ b/src/c_oper1.c
@@ -1,7 +1,7 @@
 #ifndef AVOID_PRECOMPILED
 /* C file produced by GAC */
 #include "compiled.h"
-#define FILE_CRC  "93694864"
+#define FILE_CRC  "32938550"
 
 /* global variables used in handlers */
 static GVar G_REREADING;
@@ -646,24 +646,32 @@ static Obj  HdlrFunc3 (
  t_1 = (Obj)(UInt)(t_2 != False);
  if ( t_1 ) {
   
-  /* if 0 < LEN_LIST( flags ) then */
+  /* if 0 = LEN_LIST( flags ) then */
   t_3 = GF_LEN__LIST;
   t_2 = CALL_1ARGS( t_3, a_flags );
   CHECK_FUNC_RESULT( t_2 )
-  t_1 = (Obj)(UInt)(LT( INTOBJ_INT(0), t_2 ));
+  t_1 = (Obj)(UInt)(EQ( INTOBJ_INT(0), t_2 ));
   if ( t_1 ) {
    
-   /* rank := rank - RankFilter( flags[1] ); */
-   t_3 = GF_RankFilter;
-   C_ELM_LIST_FPL( t_4, a_flags, INTOBJ_INT(1) )
-   t_2 = CALL_1ARGS( t_3, t_4 );
+   /* Error( NAME_FUNC( opr ), ": constructors must have at least one argument" ); */
+   t_1 = GF_Error;
+   t_3 = GF_NAME__FUNC;
+   t_2 = CALL_1ARGS( t_3, a_opr );
    CHECK_FUNC_RESULT( t_2 )
-   C_DIFF_FIA( t_1, a_rank, t_2 )
-   a_rank = t_1;
+   t_3 = MakeString( ": constructors must have at least one argument" );
+   CALL_2ARGS( t_1, t_2, t_3 );
    
   }
   /* fi */
   
+  /* rank := rank - RankFilter( flags[1] ); */
+  t_3 = GF_RankFilter;
+  C_ELM_LIST_FPL( t_4, a_flags, INTOBJ_INT(1) )
+  t_2 = CALL_1ARGS( t_3, t_4 );
+  CHECK_FUNC_RESULT( t_2 )
+  C_DIFF_FIA( t_1, a_rank, t_2 )
+  a_rank = t_1;
+  
  }
  
  /* else */
@@ -2685,8 +2693,8 @@ static Obj  HdlrFunc7 (
    t_6 = NewFunction( NameFunc[8], 1, 0, HdlrFunc8 );
    SET_ENVI_FUNC( t_6, STATE(CurrLVars) );
    t_7 = NewBag( T_BODY, sizeof(BodyHeader) );
-   SET_STARTLINE_BODY(t_7, 651);
-   SET_ENDLINE_BODY(t_7, 669);
+   SET_STARTLINE_BODY(t_7, 652);
+   SET_ENDLINE_BODY(t_7, 670);
    SET_FILENAME_BODY(t_7, FileName);
    SET_BODY_FUNC(t_6, t_7);
    CHANGED_BAG( STATE(CurrLVars) );
@@ -3289,8 +3297,8 @@ static Obj  HdlrFunc11 (
   t_1 = NewFunction( NameFunc[12], 1, 0, HdlrFunc12 );
   SET_ENVI_FUNC( t_1, STATE(CurrLVars) );
   t_2 = NewBag( T_BODY, sizeof(BodyHeader) );
-  SET_STARTLINE_BODY(t_2, 848);
-  SET_ENDLINE_BODY(t_2, 852);
+  SET_STARTLINE_BODY(t_2, 849);
+  SET_ENDLINE_BODY(t_2, 853);
   SET_FILENAME_BODY(t_2, FileName);
   SET_BODY_FUNC(t_1, t_2);
   CHANGED_BAG( STATE(CurrLVars) );
@@ -3369,8 +3377,8 @@ static Obj  HdlrFunc11 (
  t_6 = NewFunction( NameFunc[13], 1, 0, HdlrFunc13 );
  SET_ENVI_FUNC( t_6, STATE(CurrLVars) );
  t_7 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_7, 869);
- SET_ENDLINE_BODY(t_7, 869);
+ SET_STARTLINE_BODY(t_7, 870);
+ SET_ENDLINE_BODY(t_7, 870);
  SET_FILENAME_BODY(t_7, FileName);
  SET_BODY_FUNC(t_6, t_7);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -3432,8 +3440,8 @@ static Obj  HdlrFunc11 (
  t_6 = NewFunction( NameFunc[14], 2, 0, HdlrFunc14 );
  SET_ENVI_FUNC( t_6, STATE(CurrLVars) );
  t_7 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_7, 891);
- SET_ENDLINE_BODY(t_7, 914);
+ SET_STARTLINE_BODY(t_7, 892);
+ SET_ENDLINE_BODY(t_7, 915);
  SET_FILENAME_BODY(t_7, FileName);
  SET_BODY_FUNC(t_6, t_7);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -3481,8 +3489,8 @@ static Obj  HdlrFunc11 (
  t_6 = NewFunction( NameFunc[15], 2, 0, HdlrFunc15 );
  SET_ENVI_FUNC( t_6, STATE(CurrLVars) );
  t_7 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_7, 924);
- SET_ENDLINE_BODY(t_7, 932);
+ SET_STARTLINE_BODY(t_7, 925);
+ SET_ENDLINE_BODY(t_7, 933);
  SET_FILENAME_BODY(t_7, FileName);
  SET_BODY_FUNC(t_6, t_7);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -3543,8 +3551,8 @@ static Obj  HdlrFunc11 (
  t_6 = NewFunction( NameFunc[16], 3, 0, HdlrFunc16 );
  SET_ENVI_FUNC( t_6, STATE(CurrLVars) );
  t_7 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_7, 941);
- SET_ENDLINE_BODY(t_7, 954);
+ SET_STARTLINE_BODY(t_7, 942);
+ SET_ENDLINE_BODY(t_7, 955);
  SET_FILENAME_BODY(t_7, FileName);
  SET_BODY_FUNC(t_6, t_7);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -3917,8 +3925,8 @@ static Obj  HdlrFunc17 (
  t_4 = NewFunction( NameFunc[18], -1, 0, HdlrFunc18 );
  SET_ENVI_FUNC( t_4, STATE(CurrLVars) );
  t_5 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_5, 1020);
- SET_ENDLINE_BODY(t_5, 1036);
+ SET_STARTLINE_BODY(t_5, 1021);
+ SET_ENDLINE_BODY(t_5, 1037);
  SET_FILENAME_BODY(t_5, FileName);
  SET_BODY_FUNC(t_4, t_5);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4030,9 +4038,10 @@ static Obj  HdlrFunc1 (
       local methods, narg, i, k, tmp, replace, match, j, lk;
       ;
       if IS_CONSTRUCTOR( opr ) then
-          if 0 < LEN_LIST( flags ) then
-              rank := rank - RankFilter( flags[1] );
+          if 0 = LEN_LIST( flags ) then
+              Error( NAME_FUNC( opr ), ": constructors must have at least one argument" );
           fi;
+          rank := rank - RankFilter( flags[1] );
       else
           for i in flags do
               rank := rank + RankFilter( i );
@@ -4122,7 +4131,7 @@ static Obj  HdlrFunc1 (
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
  SET_STARTLINE_BODY(t_4, 146);
- SET_ENDLINE_BODY(t_4, 273);
+ SET_ENDLINE_BODY(t_4, 274);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4137,8 +4146,8 @@ static Obj  HdlrFunc1 (
  t_3 = NewFunction( NameFunc[4], -1, 0, HdlrFunc4 );
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_4, 320);
- SET_ENDLINE_BODY(t_4, 322);
+ SET_STARTLINE_BODY(t_4, 321);
+ SET_ENDLINE_BODY(t_4, 323);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4153,8 +4162,8 @@ static Obj  HdlrFunc1 (
  t_3 = NewFunction( NameFunc[5], -1, 0, HdlrFunc5 );
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_4, 347);
- SET_ENDLINE_BODY(t_4, 349);
+ SET_STARTLINE_BODY(t_4, 348);
+ SET_ENDLINE_BODY(t_4, 350);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4323,8 +4332,8 @@ static Obj  HdlrFunc1 (
  t_3 = NewFunction( NameFunc[6], 2, 0, HdlrFunc6 );
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_4, 360);
- SET_ENDLINE_BODY(t_4, 590);
+ SET_STARTLINE_BODY(t_4, 361);
+ SET_ENDLINE_BODY(t_4, 591);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4382,8 +4391,8 @@ static Obj  HdlrFunc1 (
  t_2 = NewFunction( NameFunc[7], 6, 0, HdlrFunc7 );
  SET_ENVI_FUNC( t_2, STATE(CurrLVars) );
  t_3 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_3, 609);
- SET_ENDLINE_BODY(t_3, 673);
+ SET_STARTLINE_BODY(t_3, 610);
+ SET_ENDLINE_BODY(t_3, 674);
  SET_FILENAME_BODY(t_3, FileName);
  SET_BODY_FUNC(t_2, t_3);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4397,8 +4406,8 @@ static Obj  HdlrFunc1 (
  t_2 = NewFunction( NameFunc[9], 6, 0, HdlrFunc9 );
  SET_ENVI_FUNC( t_2, STATE(CurrLVars) );
  t_3 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_3, 676);
- SET_ENDLINE_BODY(t_3, 682);
+ SET_STARTLINE_BODY(t_3, 677);
+ SET_ENDLINE_BODY(t_3, 683);
  SET_FILENAME_BODY(t_3, FileName);
  SET_BODY_FUNC(t_2, t_3);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4426,8 +4435,8 @@ static Obj  HdlrFunc1 (
  t_3 = NewFunction( NameFunc[10], 2, 0, HdlrFunc10 );
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_4, 695);
- SET_ENDLINE_BODY(t_4, 719);
+ SET_STARTLINE_BODY(t_4, 696);
+ SET_ENDLINE_BODY(t_4, 720);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4511,8 +4520,8 @@ static Obj  HdlrFunc1 (
  t_3 = NewFunction( NameFunc[11], 4, 0, HdlrFunc11 );
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_4, 844);
- SET_ENDLINE_BODY(t_4, 955);
+ SET_STARTLINE_BODY(t_4, 845);
+ SET_ENDLINE_BODY(t_4, 956);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4563,8 +4572,8 @@ static Obj  HdlrFunc1 (
  t_3 = NewFunction( NameFunc[17], -1, 0, HdlrFunc17 );
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_4, 990);
- SET_ENDLINE_BODY(t_4, 1037);
+ SET_STARTLINE_BODY(t_4, 991);
+ SET_ENDLINE_BODY(t_4, 1038);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4871,7 +4880,7 @@ static Int InitLibrary ( StructInitInfo * module )
 static StructInitInfo module = {
  .type        = MODULE_STATIC,
  .name        = "GAPROOT/lib/oper1.g",
- .crc         = 93694864,
+ .crc         = 32938550,
  .initKernel  = InitKernel,
  .initLibrary = InitLibrary,
  .postRestore = PostRestore,
diff --git a/src/hpc/c_oper1.c b/src/hpc/c_oper1.c
index d9962694e9..1c5ef2b2ab 100644
--- a/src/hpc/c_oper1.c
+++ b/src/hpc/c_oper1.c
@@ -1,7 +1,7 @@
 #ifndef AVOID_PRECOMPILED
 /* C file produced by GAC */
 #include "compiled.h"
-#define FILE_CRC  "93694864"
+#define FILE_CRC  "32938550"
 
 /* global variables used in handlers */
 static GVar G_REREADING;
@@ -670,24 +670,32 @@ static Obj  HdlrFunc3 (
  t_1 = (Obj)(UInt)(t_2 != False);
  if ( t_1 ) {
   
-  /* if 0 < LEN_LIST( flags ) then */
+  /* if 0 = LEN_LIST( flags ) then */
   t_3 = GF_LEN__LIST;
   t_2 = CALL_1ARGS( t_3, a_flags );
   CHECK_FUNC_RESULT( t_2 )
-  t_1 = (Obj)(UInt)(LT( INTOBJ_INT(0), t_2 ));
+  t_1 = (Obj)(UInt)(EQ( INTOBJ_INT(0), t_2 ));
   if ( t_1 ) {
    
-   /* rank := rank - RankFilter( flags[1] ); */
-   t_3 = GF_RankFilter;
-   C_ELM_LIST_FPL( t_4, a_flags, INTOBJ_INT(1) )
-   t_2 = CALL_1ARGS( t_3, t_4 );
+   /* Error( NAME_FUNC( opr ), ": constructors must have at least one argument" ); */
+   t_1 = GF_Error;
+   t_3 = GF_NAME__FUNC;
+   t_2 = CALL_1ARGS( t_3, a_opr );
    CHECK_FUNC_RESULT( t_2 )
-   C_DIFF_FIA( t_1, a_rank, t_2 )
-   a_rank = t_1;
+   t_3 = MakeString( ": constructors must have at least one argument" );
+   CALL_2ARGS( t_1, t_2, t_3 );
    
   }
   /* fi */
   
+  /* rank := rank - RankFilter( flags[1] ); */
+  t_3 = GF_RankFilter;
+  C_ELM_LIST_FPL( t_4, a_flags, INTOBJ_INT(1) )
+  t_2 = CALL_1ARGS( t_3, t_4 );
+  CHECK_FUNC_RESULT( t_2 )
+  C_DIFF_FIA( t_1, a_rank, t_2 )
+  a_rank = t_1;
+  
  }
  
  /* else */
@@ -2748,8 +2756,8 @@ static Obj  HdlrFunc7 (
    t_6 = NewFunction( NameFunc[8], 1, 0, HdlrFunc8 );
    SET_ENVI_FUNC( t_6, STATE(CurrLVars) );
    t_7 = NewBag( T_BODY, sizeof(BodyHeader) );
-   SET_STARTLINE_BODY(t_7, 651);
-   SET_ENDLINE_BODY(t_7, 669);
+   SET_STARTLINE_BODY(t_7, 652);
+   SET_ENDLINE_BODY(t_7, 670);
    SET_FILENAME_BODY(t_7, FileName);
    SET_BODY_FUNC(t_6, t_7);
    CHANGED_BAG( STATE(CurrLVars) );
@@ -3352,8 +3360,8 @@ static Obj  HdlrFunc11 (
   t_1 = NewFunction( NameFunc[12], 1, 0, HdlrFunc12 );
   SET_ENVI_FUNC( t_1, STATE(CurrLVars) );
   t_2 = NewBag( T_BODY, sizeof(BodyHeader) );
-  SET_STARTLINE_BODY(t_2, 848);
-  SET_ENDLINE_BODY(t_2, 852);
+  SET_STARTLINE_BODY(t_2, 849);
+  SET_ENDLINE_BODY(t_2, 853);
   SET_FILENAME_BODY(t_2, FileName);
   SET_BODY_FUNC(t_1, t_2);
   CHANGED_BAG( STATE(CurrLVars) );
@@ -3432,8 +3440,8 @@ static Obj  HdlrFunc11 (
  t_6 = NewFunction( NameFunc[13], 1, 0, HdlrFunc13 );
  SET_ENVI_FUNC( t_6, STATE(CurrLVars) );
  t_7 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_7, 869);
- SET_ENDLINE_BODY(t_7, 869);
+ SET_STARTLINE_BODY(t_7, 870);
+ SET_ENDLINE_BODY(t_7, 870);
  SET_FILENAME_BODY(t_7, FileName);
  SET_BODY_FUNC(t_6, t_7);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -3507,8 +3515,8 @@ static Obj  HdlrFunc11 (
  t_6 = NewFunction( NameFunc[14], 2, 0, HdlrFunc14 );
  SET_ENVI_FUNC( t_6, STATE(CurrLVars) );
  t_7 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_7, 891);
- SET_ENDLINE_BODY(t_7, 914);
+ SET_STARTLINE_BODY(t_7, 892);
+ SET_ENDLINE_BODY(t_7, 915);
  SET_FILENAME_BODY(t_7, FileName);
  SET_BODY_FUNC(t_6, t_7);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -3556,8 +3564,8 @@ static Obj  HdlrFunc11 (
  t_6 = NewFunction( NameFunc[15], 2, 0, HdlrFunc15 );
  SET_ENVI_FUNC( t_6, STATE(CurrLVars) );
  t_7 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_7, 924);
- SET_ENDLINE_BODY(t_7, 932);
+ SET_STARTLINE_BODY(t_7, 925);
+ SET_ENDLINE_BODY(t_7, 933);
  SET_FILENAME_BODY(t_7, FileName);
  SET_BODY_FUNC(t_6, t_7);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -3618,8 +3626,8 @@ static Obj  HdlrFunc11 (
  t_6 = NewFunction( NameFunc[16], 3, 0, HdlrFunc16 );
  SET_ENVI_FUNC( t_6, STATE(CurrLVars) );
  t_7 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_7, 941);
- SET_ENDLINE_BODY(t_7, 954);
+ SET_STARTLINE_BODY(t_7, 942);
+ SET_ENDLINE_BODY(t_7, 955);
  SET_FILENAME_BODY(t_7, FileName);
  SET_BODY_FUNC(t_6, t_7);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -3992,8 +4000,8 @@ static Obj  HdlrFunc17 (
  t_4 = NewFunction( NameFunc[18], -1, 0, HdlrFunc18 );
  SET_ENVI_FUNC( t_4, STATE(CurrLVars) );
  t_5 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_5, 1020);
- SET_ENDLINE_BODY(t_5, 1036);
+ SET_STARTLINE_BODY(t_5, 1021);
+ SET_ENDLINE_BODY(t_5, 1037);
  SET_FILENAME_BODY(t_5, FileName);
  SET_BODY_FUNC(t_4, t_5);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4114,9 +4122,10 @@ static Obj  HdlrFunc1 (
       local methods, narg, i, k, tmp, replace, match, j, lk;
       lk := WRITE_LOCK( METHODS_OPERATION_REGION );
       if IS_CONSTRUCTOR( opr ) then
-          if 0 < LEN_LIST( flags ) then
-              rank := rank - RankFilter( flags[1] );
+          if 0 = LEN_LIST( flags ) then
+              Error( NAME_FUNC( opr ), ": constructors must have at least one argument" );
           fi;
+          rank := rank - RankFilter( flags[1] );
       else
           for i in flags do
               rank := rank + RankFilter( i );
@@ -4207,7 +4216,7 @@ static Obj  HdlrFunc1 (
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
  SET_STARTLINE_BODY(t_4, 146);
- SET_ENDLINE_BODY(t_4, 273);
+ SET_ENDLINE_BODY(t_4, 274);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4222,8 +4231,8 @@ static Obj  HdlrFunc1 (
  t_3 = NewFunction( NameFunc[4], -1, 0, HdlrFunc4 );
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_4, 320);
- SET_ENDLINE_BODY(t_4, 322);
+ SET_STARTLINE_BODY(t_4, 321);
+ SET_ENDLINE_BODY(t_4, 323);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4238,8 +4247,8 @@ static Obj  HdlrFunc1 (
  t_3 = NewFunction( NameFunc[5], -1, 0, HdlrFunc5 );
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_4, 347);
- SET_ENDLINE_BODY(t_4, 349);
+ SET_STARTLINE_BODY(t_4, 348);
+ SET_ENDLINE_BODY(t_4, 350);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4408,8 +4417,8 @@ static Obj  HdlrFunc1 (
  t_3 = NewFunction( NameFunc[6], 2, 0, HdlrFunc6 );
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_4, 360);
- SET_ENDLINE_BODY(t_4, 590);
+ SET_STARTLINE_BODY(t_4, 361);
+ SET_ENDLINE_BODY(t_4, 591);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4467,8 +4476,8 @@ static Obj  HdlrFunc1 (
  t_2 = NewFunction( NameFunc[7], 6, 0, HdlrFunc7 );
  SET_ENVI_FUNC( t_2, STATE(CurrLVars) );
  t_3 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_3, 609);
- SET_ENDLINE_BODY(t_3, 673);
+ SET_STARTLINE_BODY(t_3, 610);
+ SET_ENDLINE_BODY(t_3, 674);
  SET_FILENAME_BODY(t_3, FileName);
  SET_BODY_FUNC(t_2, t_3);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4482,8 +4491,8 @@ static Obj  HdlrFunc1 (
  t_2 = NewFunction( NameFunc[9], 6, 0, HdlrFunc9 );
  SET_ENVI_FUNC( t_2, STATE(CurrLVars) );
  t_3 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_3, 676);
- SET_ENDLINE_BODY(t_3, 682);
+ SET_STARTLINE_BODY(t_3, 677);
+ SET_ENDLINE_BODY(t_3, 683);
  SET_FILENAME_BODY(t_3, FileName);
  SET_BODY_FUNC(t_2, t_3);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4511,8 +4520,8 @@ static Obj  HdlrFunc1 (
  t_3 = NewFunction( NameFunc[10], 2, 0, HdlrFunc10 );
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_4, 695);
- SET_ENDLINE_BODY(t_4, 719);
+ SET_STARTLINE_BODY(t_4, 696);
+ SET_ENDLINE_BODY(t_4, 720);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4596,8 +4605,8 @@ static Obj  HdlrFunc1 (
  t_3 = NewFunction( NameFunc[11], 4, 0, HdlrFunc11 );
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_4, 844);
- SET_ENDLINE_BODY(t_4, 955);
+ SET_STARTLINE_BODY(t_4, 845);
+ SET_ENDLINE_BODY(t_4, 956);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4648,8 +4657,8 @@ static Obj  HdlrFunc1 (
  t_3 = NewFunction( NameFunc[17], -1, 0, HdlrFunc17 );
  SET_ENVI_FUNC( t_3, STATE(CurrLVars) );
  t_4 = NewBag( T_BODY, sizeof(BodyHeader) );
- SET_STARTLINE_BODY(t_4, 990);
- SET_ENDLINE_BODY(t_4, 1037);
+ SET_STARTLINE_BODY(t_4, 991);
+ SET_ENDLINE_BODY(t_4, 1038);
  SET_FILENAME_BODY(t_4, FileName);
  SET_BODY_FUNC(t_3, t_4);
  CHANGED_BAG( STATE(CurrLVars) );
@@ -4972,7 +4981,7 @@ static Int InitLibrary ( StructInitInfo * module )
 static StructInitInfo module = {
  .type        = MODULE_STATIC,
  .name        = "GAPROOT/lib/oper1.g",
- .crc         = 93694864,
+ .crc         = 32938550,
  .initKernel  = InitKernel,
  .initLibrary = InitLibrary,
  .postRestore = PostRestore,
diff --git a/src/opers.c b/src/opers.c
index 2e42d27847..b585fbbd93 100644
--- a/src/opers.c
+++ b/src/opers.c
@@ -2341,16 +2341,20 @@ Obj NewOperation(Obj name, Int narg, Obj nams, ObjFunc hdlr)
 
 /****************************************************************************
 **
-**  DoConstructor0Args( <oper> )
-**
-** I'm not sure if this makes any sense at all
+*F  DoConstructor0Args( <oper> )
+*F  DoConstructor1Args( <oper> )
+*F  DoConstructor2Args( <oper> )
+*F  DoConstructor3Args( <oper> )
+*F  DoConstructor4Args( <oper> )
+*F  DoConstructor5Args( <oper> )
+*F  DoConstructor6Args( <oper> )
+*F  DoConstructorXArgs( <oper> )
 */
 
-
 Obj DoConstructor0Args(Obj oper)
 {
-    return DoOperationNArgs(oper, 0, 0, 1, 0, 0, 0, 0,
-                            0, 0);
+    ErrorQuit("constructors must have at least one argument", 0L, 0L);
+    return 0;
 }
 
 Obj DoConstructor1Args(Obj oper, Obj arg1)
@@ -2391,26 +2395,29 @@ Obj DoConstructor6Args(
                             arg3, arg4, arg5, arg6);
 }
 
-
-/****************************************************************************
-**
-**  DoConstructorXArgs( <oper>, ... )
-*/
 Obj DoConstructorXArgs(Obj self, Obj args)
 {
     ErrorQuit("sorry: cannot yet have X argument constructors", 0L, 0L);
     return 0;
 }
 
+
 /****************************************************************************
 **
-**  DoVerboseConstructor0Args( <oper> )
+*F  DoVerboseConstructor0Args( <oper> )
+*F  DoVerboseConstructor1Args( <oper> )
+*F  DoVerboseConstructor2Args( <oper> )
+*F  DoVerboseConstructor3Args( <oper> )
+*F  DoVerboseConstructor4Args( <oper> )
+*F  DoVerboseConstructor5Args( <oper> )
+*F  DoVerboseConstructor6Args( <oper> )
+*F  DoVerboseConstructorXArgs( <oper> )
 */
 
 Obj DoVerboseConstructor0Args(Obj oper)
 {
-    return DoOperationNArgs(oper, 0, 1, 1, 0, 0,
-                            0, 0, 0, 0);
+    ErrorQuit("constructors must have at least one argument", 0L, 0L);
+    return 0;
 }
 
 Obj DoVerboseConstructor1Args(Obj oper, Obj arg1)
@@ -2452,11 +2459,6 @@ Obj DoVerboseConstructor6Args(
                             arg2, arg3, arg4, arg5, arg6);
 }
 
-
-/****************************************************************************
-**
-**  DoVerboseConstructorXArgs( <oper>, ... )
-*/
 Obj DoVerboseConstructorXArgs(Obj self, Obj args)
 {
     ErrorQuit("sorry: cannot yet have X argument constructors", 0L, 0L);
diff --git a/tst/testinstall/constructor.tst b/tst/testinstall/constructor.tst
new file mode 100644
index 0000000000..e711616bc8
--- /dev/null
+++ b/tst/testinstall/constructor.tst
@@ -0,0 +1,27 @@
+# constructors with zero arguments cannot be created
+gap> DeclareConstructor("foobar",[]);
+Error, constructors must have at least one argument
+gap> NewConstructor("foobar",[]);
+Error, constructors must have at least one argument
+
+#
+gap> c := NewConstructor("foobar",[IsObject]);
+<Constructor "foobar">
+gap> c(1);
+Error, Constructor: the first argument must be a filter not a integer
+gap> c(IsInt);
+Error, no method found! For debugging hints type ?Recovery from NoMethodFound
+Error, no 1st choice method found for `foobar' on 1 arguments
+gap> InstallMethod(c,[IsInt],x->x);
+gap> c(IsInt);
+<Category "IsInt">
+gap> InstallOtherMethod(c,[IsInt,IsObject],{x,y}->[x,y]);
+gap> c(IsInt, 0);
+[ <Category "IsInt">, 0 ]
+
+# constructors must not have methods with zero arguments, nor is it ever legal
+# to invoke a constructor with zero arguments
+gap> InstallOtherMethod(c,[],{}->[]);
+Error, foobar: constructors must have at least one argument
+gap> c();
+Error, constructors must have at least one argument
diff --git a/tst/testinstall/varargs.tst b/tst/testinstall/varargs.tst
index 1038e5db22..f31c64b2ac 100644
--- a/tst/testinstall/varargs.tst
+++ b/tst/testinstall/varargs.tst
@@ -87,7 +87,7 @@ function ( <<arg-1>>, <<arg-2>>, <<arg-3>>, <<arg-4>>, <<arg-5>>, <<arg-6>> )
 end
 gap> Display(InstallMethod);
 function ( <<arg-1>>... )
-    <<compiled GAP code from GAPROOT/lib/oper1.g:320>>
+    <<compiled GAP code from GAPROOT/lib/oper1.g:321>>
 end
 gap> [1..2];
 [ 1, 2 ]
diff --git a/tst/testspecial/trace.g b/tst/testspecial/trace.g
index 39dcf5992e..62a47b251a 100644
--- a/tst/testspecial/trace.g
+++ b/tst/testspecial/trace.g
@@ -50,8 +50,7 @@ o(1,2,3,4,5,6,7); # not (yet?) supported
 #
 
 # create a dummy constructor
-o:=NewConstructor("foobar",[]);
-InstallOtherMethod(o,[],{}->[]);
+o:=NewConstructor("foobar",[IsObject]);
 InstallOtherMethod(o,[IsInt],{arg...}->arg);
 InstallOtherMethod(o,[IsInt,IsInt],{arg...}->arg);
 InstallOtherMethod(o,[IsInt,IsInt],{arg...}->arg);
@@ -61,7 +60,6 @@ InstallOtherMethod(o,[IsInt,IsInt,IsInt,IsInt,IsInt],{arg...}->arg);
 InstallOtherMethod(o,[IsInt,IsInt,IsInt,IsInt,IsInt,IsInt],{arg...}->arg);
 
 # without tracing
-#o(); # ???
 o(IsInt);
 o(IsInt,2);
 o(IsInt,2,3);
@@ -72,7 +70,6 @@ o(IsInt,2,3,4,5,6,7); # not (yet?) supported
 
 # with tracing
 TraceMethods( o );
-#o(); # ???
 o(IsInt);
 o(IsInt,2);
 o(IsInt,2,3);
@@ -83,7 +80,6 @@ o(IsInt,2,3,4,5,6,7); # not (yet?) supported
 UntraceMethods( o );
 
 # again without tracing
-#o(); # ???
 o(IsInt);
 o(IsInt,2);
 o(IsInt,2,3);
diff --git a/tst/testspecial/trace.g.out b/tst/testspecial/trace.g.out
index 06f37aeb4a..844962b4d0 100644
--- a/tst/testspecial/trace.g.out
+++ b/tst/testspecial/trace.g.out
@@ -85,9 +85,8 @@ gap> # tracing of constructors
 gap> #
 gap> 
 gap> # create a dummy constructor
-gap> o:=NewConstructor("foobar",[]);
+gap> o:=NewConstructor("foobar",[IsObject]);
 <Constructor "foobar">
-gap> InstallOtherMethod(o,[],{}->[]);
 gap> InstallOtherMethod(o,[IsInt],{arg...}->arg);
 gap> InstallOtherMethod(o,[IsInt,IsInt],{arg...}->arg);
 gap> InstallOtherMethod(o,[IsInt,IsInt],{arg...}->arg);
@@ -97,7 +96,6 @@ gap> InstallOtherMethod(o,[IsInt,IsInt,IsInt,IsInt,IsInt],{arg...}->arg);
 gap> InstallOtherMethod(o,[IsInt,IsInt,IsInt,IsInt,IsInt,IsInt],{arg...}->arg);
 gap> 
 gap> # without tracing
-gap> #o(); # ???
 gap> o(IsInt);
 [ <Category "IsInt"> ]
 gap> o(IsInt,2);
@@ -112,36 +110,34 @@ gap> o(IsInt,2,3,4,5,6);
 [ <Category "IsInt">, 2, 3, 4, 5, 6 ]
 gap> o(IsInt,2,3,4,5,6,7); # not (yet?) supported
 Error, sorry: cannot yet have X argument constructors
-not in any function at *stdin*:72
+not in any function at *stdin*:70
 gap> 
 gap> # with tracing
 gap> TraceMethods( o );
-gap> #o(); # ???
 gap> o(IsInt);
-#I  foobar at *stdin*:56
+#I  foobar at *stdin*:55
 [ <Category "IsInt"> ]
 gap> o(IsInt,2);
-#I  foobar at *stdin*:58
+#I  foobar at *stdin*:57
 [ <Category "IsInt">, 2 ]
 gap> o(IsInt,2,3);
-#I  foobar at *stdin*:59
+#I  foobar at *stdin*:58
 [ <Category "IsInt">, 2, 3 ]
 gap> o(IsInt,2,3,4);
-#I  foobar at *stdin*:60
+#I  foobar at *stdin*:59
 [ <Category "IsInt">, 2, 3, 4 ]
 gap> o(IsInt,2,3,4,5);
-#I  foobar at *stdin*:61
+#I  foobar at *stdin*:60
 [ <Category "IsInt">, 2, 3, 4, 5 ]
 gap> o(IsInt,2,3,4,5,6);
-#I  foobar at *stdin*:62
+#I  foobar at *stdin*:61
 [ <Category "IsInt">, 2, 3, 4, 5, 6 ]
 gap> o(IsInt,2,3,4,5,6,7); # not (yet?) supported
 Error, sorry: cannot yet have X argument constructors
-not in any function at *stdin*:83
+not in any function at *stdin*:80
 gap> UntraceMethods( o );
 gap> 
 gap> # again without tracing
-gap> #o(); # ???
 gap> o(IsInt);
 [ <Category "IsInt"> ]
 gap> o(IsInt,2);
@@ -156,5 +152,5 @@ gap> o(IsInt,2,3,4,5,6);
 [ <Category "IsInt">, 2, 3, 4, 5, 6 ]
 gap> o(IsInt,2,3,4,5,6,7); # not (yet?) supported
 Error, sorry: cannot yet have X argument constructors
-not in any function at *stdin*:94
+not in any function at *stdin*:90
 gap> QUIT;