This is an automated cherry-pick of #57484

Signed-off-by: ti-chi-bot <ti-community-prow-bot@tidb.io>

expression/builtin_cast.go

@@ -281,10 +281,27 @@ func (c *castAsStringFunctionClass) getFunction(ctx sessionctx.Context, args []E
 	if err != nil {
 		return nil, err
 	}
+<<<<<<< HEAD:expression/builtin_cast.go
 	if args[0].GetType().Hybrid() {
 		sig = &builtinCastStringAsStringSig{bf}
 		sig.setPbCode(tipb.ScalarFuncSig_CastStringAsString)
 		return sig, nil
+=======
+	if ft := args[0].GetType(ctx.GetEvalCtx()); ft.Hybrid() {
+		castBitAsUnBinary := ft.GetType() == mysql.TypeBit && c.tp.GetCharset() != charset.CharsetBin
+		if !castBitAsUnBinary {
+			sig = &builtinCastStringAsStringSig{bf}
+			sig.setPbCode(tipb.ScalarFuncSig_CastStringAsString)
+			return sig, nil
+		}
+		// for type BIT, it maybe an invalid value for the specified charset, we need to convert it to binary first,
+		// and then convert it to the specified charset with `HandleBinaryLiteral` in the following code.
+		tp := types.NewFieldType(mysql.TypeString)
+		tp.SetCharset(charset.CharsetBin)
+		tp.SetCollate(charset.CollationBin)
+		tp.AddFlag(mysql.BinaryFlag)
+		args[0] = BuildCastFunction(ctx, args[0], tp)
+>>>>>>> 38104f4f328 (expression: fix tikv crash when `bool like cast(bit as char)` (#57484)):pkg/expression/builtin_cast.go
 	}
 	argTp := args[0].GetType().EvalType()
 	switch argTp {

expression/builtin_convert_charset.go

@@ -166,6 +166,7 @@ type builtinInternalFromBinarySig struct {
 func (b *builtinInternalFromBinarySig) Clone() builtinFunc {
 	newSig := &builtinInternalFromBinarySig{}
 	newSig.cloneFrom(&b.baseBuiltinFunc)
+	newSig.cannotConvertStringAsWarning = b.cannotConvertStringAsWarning
 	return newSig
 }
 

expression/expr_to_pb_test.go

@@ -1439,7 +1439,37 @@ func TestExprPushDownToTiKV(t *testing.T) {
 	require.NoError(t, err)
 	exprs = append(exprs, function)
 
+<<<<<<< HEAD:expression/expr_to_pb_test.go
 	pushed, remained := PushDownExprs(sc, exprs, client, kv.TiKV)
+=======
+	ctx := mock.NewContext()
+	pushDownCtx := NewPushDownContextFromSessionVars(ctx, ctx.GetSessionVars(), client)
+	pushed, remained := PushDownExprs(pushDownCtx, exprs, kv.TiKV)
+	require.Len(t, pushed, 0)
+	require.Len(t, remained, len(exprs))
+
+	// Test Conv function, `conv` function for a BIT column should not be pushed down for its special behavior which
+	// is only handled in TiDB currently.
+	// see issue: https://github.com/pingcap/tidb/issues/51877
+	exprs = exprs[:0]
+	function, err = NewFunction(mock.NewContext(), ast.Conv, types.NewFieldType(mysql.TypeString), stringColumn, intColumn, intColumn)
+	require.NoError(t, err)
+	exprs = append(exprs, function)
+	pushed, remained = PushDownExprs(pushDownCtx, exprs, kv.TiKV)
+	require.Len(t, pushed, len(exprs))
+	require.Len(t, remained, 0)
+	exprs = exprs[:0]
+	// when conv a column with type BIT, a cast function will be used to cast bit to a binary string
+	castTp := types.NewFieldType(mysql.TypeString)
+	castTp.SetCharset(charset.CharsetBin)
+	castTp.SetCollate(charset.CollationBin)
+	castByteAsStringFunc, err := NewFunction(mock.NewContext(), ast.Cast, castTp, byteColumn)
+	require.NoError(t, err)
+	function, err = NewFunction(mock.NewContext(), ast.Conv, types.NewFieldType(mysql.TypeString), castByteAsStringFunc, intColumn, intColumn)
+	require.NoError(t, err)
+	exprs = append(exprs, function)
+	pushed, remained = PushDownExprs(pushDownCtx, exprs, kv.TiKV)
+>>>>>>> 38104f4f328 (expression: fix tikv crash when `bool like cast(bit as char)` (#57484)):pkg/expression/expr_to_pb_test.go
 	require.Len(t, pushed, 0)
 	require.Len(t, remained, len(exprs))