Restrict SetDimension method to IsFreeLeftModule (gap-system#5520)

dev/ci-download-pkgs.sh

@@ -5,6 +5,7 @@ SRCDIR=${SRCDIR:-$PWD}
 
 # change into BUILDDIR
 [[ -n "$BUILDDIR" ]] && cd "$BUILDDIR"
+BUILDDIR=$PWD
 
 # if requested, bootstrap with minimal set of packages
 if [[ $BOOTSTRAP_MINIMAL = yes ]]
@@ -29,3 +30,16 @@ fi
 
 echo "ls $SRCDIR/pkg"
 ls $SRCDIR/pkg
+
+# reset CFLAGS, CXXFLAGS, LDFLAGS before compiling packages, to prevent
+# them from being compiled with coverage gathering, because
+# otherwise gcov may confuse IO's src/io.c, or anupq's src/read.c,
+# with GAP kernel files with the same name
+unset CFLAGS
+unset CXXFLAGS
+unset LDFLAGS
+
+# compile a few packages useful for some tests, e.g. in testbugfix
+pushd "$SRCDIR/pkg"
+"$SRCDIR/bin/BuildPackages.sh" --strict --with-gaproot="$BUILDDIR" io* cvec*
+popd

lib/coll.gi

@@ -3105,6 +3105,7 @@ local filt;
 
   # some sanity checks
   Assert(0, not HasIsEmpty(obj) or (IsEmpty(obj) = (sz=0)));
+  Assert(0, not HasIsNonTrivial(obj) or (IsNonTrivial(obj) = (sz<>1)));
   Assert(0, not HasIsTrivial(obj) or (IsTrivial(obj) = (sz=1)));
   Assert(0, not HasIsFinite(obj) or (IsFinite(obj) = (sz<>infinity)));
 

lib/module.gi

@@ -410,7 +410,7 @@ InstallMethod( DimensionOfVectors,
 # multiple immediate methods, several of which could apply and each changing
 # the type of the object. Doing so can be costly and thus should be
 # avoided.
-InstallOtherMethod(SetDimension,true,[IsObject and IsAttributeStoringRep,IsObject],
+InstallOtherMethod(SetDimension,true,[IsFreeLeftModule and IsAttributeStoringRep,IsObject],
   100, # override system setter
 function(obj,dim)
 local filt;

tst/testbugfix/2023-10-18-SetDimension.tst

@@ -0,0 +1,13 @@
+# issue reported by Michel Lavrauw on 18 October 2023
+gap> LoadPackage("fining",false);
+true
+gap> G:=ProjectivityGroup(PG(8,2));
+The FinInG projectivity group PGL(9,2)
+gap> H:=Group(Identity(G));
+<projective collineation group with 1 generators>
+gap> Size(H); # this used to run into an error
+1
+gap> IsTrivial(H);
+true
+gap> IsNonTrivial(H); # this used to return "true"
+false