From 82bd4dd9a6d4059d741869be564f3f2a47c3ce2c Mon Sep 17 00:00:00 2001
From: Wilf Wilson <wilf@wilf-wilson.net>
Date: Sat, 5 Oct 2019 22:49:41 +0200
Subject: [PATCH] oper: reinstate 3-arg DigraphAddVertices

---
 doc/oper.xml          |  2 ++
 gap/oper.gd           |  2 ++
 gap/oper.gi           | 13 +++++++++++++
 tst/standard/oper.tst | 12 ++++++++++++
 4 files changed, 29 insertions(+)

diff --git a/doc/oper.xml b/doc/oper.xml
index b77ebcc74..35f20f02b 100644
--- a/doc/oper.xml
+++ b/doc/oper.xml
@@ -304,6 +304,8 @@ true
     Label="for a digraph and an integer"/>
   <Oper Name="DigraphAddVertices" Arg="digraph, labels"
     Label="for a digraph and a list of labels"/>
+  <!-- The 3-argument version is deliberately undocumented. It is redundant,
+       but it is included for backwards compatibility. -->
   <Returns>A digraph.</Returns>
   <Description>
     For a non-negative integer <A>m</A>, this operation returns a digraph
diff --git a/gap/oper.gd b/gap/oper.gd
index ab7815597..2e2623b82 100644
--- a/gap/oper.gd
+++ b/gap/oper.gd
@@ -13,6 +13,8 @@ DeclareOperation("DigraphAddVertex", [IsDigraph]);
 DeclareOperation("DigraphAddVertex", [IsDigraph, IsObject]);
 DeclareOperation("DigraphAddVertices", [IsDigraph, IsInt]);
 DeclareOperation("DigraphAddVertices", [IsDigraph, IsList]);
+# 3-arg version of DigraphAddVertices is included for backwards compatibility.
+DeclareOperation("DigraphAddVertices", [IsDigraph, IsInt, IsList]);
 
 DeclareOperation("DigraphRemoveVertex", [IsDigraph, IsPosInt]);
 DeclareOperation("DigraphRemoveVertices", [IsDigraph, IsList]);
diff --git a/gap/oper.gi b/gap/oper.gi
index 5d5019178..114668ec8 100644
--- a/gap/oper.gi
+++ b/gap/oper.gi
@@ -81,6 +81,19 @@ InstallMethod(DigraphAddVertices, "for an immutable digraph and an integer",
 [IsImmutableDigraph, IsInt],
 {D, m} -> MakeImmutable(DigraphAddVertices(DigraphMutableCopy(D), m)));
 
+# Included for backwards compatibility, even though the 2nd arg is redundant.
+# See https://github.com/gap-packages/Digraphs/issues/264
+# This is deliberately kept undocumented.
+InstallMethod(DigraphAddVertices, "for a digraph, an integer, and a list",
+[IsDigraph, IsInt, IsList],
+function(D, m, labels)
+  if m <> Length(labels) then
+    ErrorNoReturn("the list <labels> (3rd argument) must have length <m> ",
+                  "(2nd argument),");
+  fi;
+  return DigraphAddVertices(D, labels);
+end);
+
 InstallMethod(DigraphRemoveVertex,
 "for a mutable digraph by out-neighbours and positive integer",
 [IsMutableDigraph and IsDigraphByOutNeighboursRep, IsPosInt],
diff --git a/tst/standard/oper.tst b/tst/standard/oper.tst
index bb3796162..986ecfc7c 100644
--- a/tst/standard/oper.tst
+++ b/tst/standard/oper.tst
@@ -630,6 +630,18 @@ false
 gap> gr2 = gr3;
 true
 
+#  DigraphAddVertices (redundant three-argument version)
+gap> D := Digraph([[1]]);
+<immutable digraph with 1 vertex, 1 edge>
+gap> DigraphVertexLabels(D);
+[ 1 ]
+gap> DigraphAddVertices(D, 2, [fail]);
+Error, the list <labels> (3rd argument) must have length <m> (2nd argument),
+gap> D := DigraphAddVertices(D, 2, [fail, true]);
+<immutable digraph with 3 vertices, 1 edge>
+gap> DigraphVertexLabels(D);
+[ 1, fail, true ]
+
 #  DigraphAddVertex
 gap> gr := CompleteDigraph(1);
 <immutable empty digraph with 1 vertex>