Add type checks to Concatenation

In particular, this lets the undefined expression `Concatenation( [ 1 ] )` throw an error instead of returning `1`.
gap-system · Apr 2, 2023 · 6220a99 · 6220a99
1 parent a78e3d2
commit 6220a99
Show file tree

Hide file tree

Showing 2 changed files with 24 additions and 0 deletions.
diff --git a/lib/list.gi b/lib/list.gi
@@ -2084,8 +2084,14 @@ InstallGlobalFunction( Concatenation, function ( arg )
     if Length( arg ) = 0  then
         return [  ];
     fi;
+    if not IsList( arg[1] ) then
+        Error( "Concatenation: arguments must be lists" );
+    fi;
     res := ShallowCopy( arg[1] );
     for i  in [ 2 .. Length( arg ) ]  do
+        if not IsList( arg[i] ) then
+            Error( "Concatenation: arguments must be lists" );
+        fi;
         Append( res, arg[i] );
     od;
     return res;

diff --git a/tst/testinstall/opers/Concatenation.tst b/tst/testinstall/opers/Concatenation.tst
@@ -0,0 +1,18 @@
+gap> START_TEST("Concatenation.tst");
+
+#
+gap> Concatenation( );
+[  ]
+gap> Concatenation( [ ] );
+[  ]
+gap> Concatenation( [ 1 ] );
+Error, Concatenation: arguments must be lists
+gap> Concatenation( [ [ 1, 2 ] ] );
+[ 1, 2 ]
+gap> Concatenation( [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ] ] );
+[ 1, 2, 3, 4, 5, 6 ]
+gap> Concatenation( [ 1, 2 ], [ 3, 4 ], [ 5, 6 ] );
+[ 1, 2, 3, 4, 5, 6 ]
+
+#
+gap> STOP_TEST("Concatenation.tst", 1);