expression: fix charset conversion warning and error behavior (#51191)

close #50295

pkg/expression/builtin.go

@@ -193,7 +193,7 @@ func newBaseBuiltinFuncWithTp(ctx BuildContext, funcName string, args []Expressi
 			args[i] = WrapWithCastAsDecimal(ctx, args[i])
 		case types.ETString:
 			args[i] = WrapWithCastAsString(ctx, args[i])
-			args[i] = HandleBinaryLiteral(ctx, args[i], ec, funcName)
+			args[i] = HandleBinaryLiteral(ctx, args[i], ec, funcName, false)
 		case types.ETDatetime:
 			args[i] = WrapWithCastAsTime(ctx, args[i], types.NewFieldType(mysql.TypeDatetime))
 		case types.ETTimestamp:
@@ -253,7 +253,7 @@ func newBaseBuiltinFuncWithFieldTypes(ctx BuildContext, funcName string, args []
 			args[i] = WrapWithCastAsReal(ctx, args[i])
 		case types.ETString:
 			args[i] = WrapWithCastAsString(ctx, args[i])
-			args[i] = HandleBinaryLiteral(ctx, args[i], ec, funcName)
+			args[i] = HandleBinaryLiteral(ctx, args[i], ec, funcName, false)
 		case types.ETJson:
 			args[i] = WrapWithCastAsJSON(ctx, args[i])
 		// https://github.com/pingcap/tidb/issues/44196

pkg/expression/builtin_cast.go

@@ -329,7 +329,7 @@ func (c *castAsStringFunctionClass) getFunction(ctx BuildContext, args []Express
 	case types.ETString:
 		// When cast from binary to some other charsets, we should check if the binary is valid or not.
 		// so we build a from_binary function to do this check.
-		bf.args[0] = HandleBinaryLiteral(ctx, args[0], &ExprCollation{Charset: c.tp.GetCharset(), Collation: c.tp.GetCollate()}, c.funcName)
+		bf.args[0] = HandleBinaryLiteral(ctx, args[0], &ExprCollation{Charset: c.tp.GetCharset(), Collation: c.tp.GetCollate()}, c.funcName, true)
 		sig = &builtinCastStringAsStringSig{bf}
 		sig.setPbCode(tipb.ScalarFuncSig_CastStringAsString)
 	default:

pkg/expression/builtin_cast_test.go

@@ -1448,7 +1448,7 @@ func TestWrapWithCastAsString(t *testing.T) {
 
 	cases := []struct {
 		expr Expression
-		err  bool
+		warn bool
 		ret  string
 	}{
 		{
@@ -1487,11 +1487,14 @@ func TestWrapWithCastAsString(t *testing.T) {
 			"-127",
 		},
 	}
+	lastWarningLen := 0
 	for _, c := range cases {
 		expr := BuildCastFunction(ctx, c.expr, types.NewFieldType(mysql.TypeVarString))
-		res, _, err := expr.EvalString(ctx, chunk.Row{})
-		if c.err {
-			require.Error(t, err)
+		res, _, _ := expr.EvalString(ctx, chunk.Row{})
+		if c.warn {
+			warns := ctx.GetSessionVars().StmtCtx.GetWarnings()
+			require.Greater(t, len(warns), lastWarningLen)
+			lastWarningLen = len(warns)
 		} else {
 			require.Equal(t, c.ret, res)
 		}

pkg/expression/builtin_convert_charset.go

@@ -134,7 +134,8 @@ func (b *builtinInternalToBinarySig) vecEvalString(ctx EvalContext, input *chunk
 type tidbFromBinaryFunctionClass struct {
 	baseFunctionClass
 
-	tp *types.FieldType
+	tp                           *types.FieldType
+	cannotConvertStringAsWarning bool
 }
 
 func (c *tidbFromBinaryFunctionClass) getFunction(ctx BuildContext, args []Expression) (builtinFunc, error) {
@@ -150,7 +151,7 @@ func (c *tidbFromBinaryFunctionClass) getFunction(ctx BuildContext, args []Expre
 			return nil, err
 		}
 		bf.tp = c.tp
-		sig = &builtinInternalFromBinarySig{bf}
+		sig = &builtinInternalFromBinarySig{bf, c.cannotConvertStringAsWarning}
 		sig.setPbCode(tipb.ScalarFuncSig_FromBinary)
 	default:
 		return nil, fmt.Errorf("unexpected argTp: %d", argTp)
@@ -160,6 +161,9 @@ func (c *tidbFromBinaryFunctionClass) getFunction(ctx BuildContext, args []Expre
 
 type builtinInternalFromBinarySig struct {
 	baseBuiltinFunc
+
+	// TODO: also pass this field when pushing down this function. The behavior of TiDB and TiKV is different on this function now.
+	cannotConvertStringAsWarning bool
 }
 
 func (b *builtinInternalFromBinarySig) Clone() builtinFunc {
@@ -179,8 +183,20 @@ func (b *builtinInternalFromBinarySig) evalString(ctx EvalContext, row chunk.Row
 	if err != nil {
 		strHex := formatInvalidChars(valBytes)
 		err = errCannotConvertString.GenWithStackByArgs(strHex, charset.CharsetBin, b.tp.GetCharset())
+
+		if b.cannotConvertStringAsWarning {
+			tc := typeCtx(ctx)
+			tc.AppendWarning(err)
+			if sqlMode(ctx).HasStrictMode() {
+				return "", true, nil
+			}
+
+			return string(ret), false, nil
+		}
+
+		return "", false, err
 	}
-	return string(ret), false, err
+	return string(ret), false, nil
 }
 
 func (b *builtinInternalFromBinarySig) vectorized() bool {
@@ -209,7 +225,21 @@ func (b *builtinInternalFromBinarySig) vecEvalString(ctx EvalContext, input *chu
 		val, err := enc.Transform(encodedBuf, str, charset.OpDecode)
 		if err != nil {
 			strHex := formatInvalidChars(str)
-			return errCannotConvertString.GenWithStackByArgs(strHex, charset.CharsetBin, b.tp.GetCharset())
+			err = errCannotConvertString.GenWithStackByArgs(strHex, charset.CharsetBin, b.tp.GetCharset())
+
+			if b.cannotConvertStringAsWarning {
+				tc := typeCtx(ctx)
+				tc.AppendWarning(err)
+				if sqlMode(ctx).HasStrictMode() {
+					result.AppendNull()
+					continue
+				}
+
+				result.AppendBytes(str)
+				continue
+			}
+
+			return err
 		}
 		result.AppendBytes(val)
 	}
@@ -232,8 +262,8 @@ func BuildToBinaryFunction(ctx BuildContext, expr Expression) (res Expression) {
 }
 
 // BuildFromBinaryFunction builds from_binary function.
-func BuildFromBinaryFunction(ctx BuildContext, expr Expression, tp *types.FieldType) (res Expression) {
-	fc := &tidbFromBinaryFunctionClass{baseFunctionClass{InternalFuncFromBinary, 1, 1}, tp}
+func BuildFromBinaryFunction(ctx BuildContext, expr Expression, tp *types.FieldType, cannotConvertStringAsWarning bool) (res Expression) {
+	fc := &tidbFromBinaryFunctionClass{baseFunctionClass{InternalFuncFromBinary, 1, 1}, tp, cannotConvertStringAsWarning}
 	f, err := fc.getFunction(ctx, []Expression{expr})
 	if err != nil {
 		return expr
@@ -305,7 +335,7 @@ func init() {
 }
 
 // HandleBinaryLiteral wraps `expr` with to_binary or from_binary sig.
-func HandleBinaryLiteral(ctx BuildContext, expr Expression, ec *ExprCollation, funcName string) Expression {
+func HandleBinaryLiteral(ctx BuildContext, expr Expression, ec *ExprCollation, funcName string, explicitCast bool) Expression {
 	argChs, dstChs := expr.GetType().GetCharset(), ec.Charset
 	switch convertFuncsMap[funcName] {
 	case funcPropNone:
@@ -326,7 +356,7 @@ func HandleBinaryLiteral(ctx BuildContext, expr Expression, ec *ExprCollation, f
 			ft := expr.GetType().Clone()
 			ft.SetCharset(ec.Charset)
 			ft.SetCollate(ec.Collation)
-			return BuildFromBinaryFunction(ctx, expr, ft)
+			return BuildFromBinaryFunction(ctx, expr, ft, explicitCast)
 		}
 	}
 	return expr

pkg/expression/distsql_builtin.go

@@ -1074,7 +1074,8 @@ func getSignatureByPB(ctx BuildContext, sigCode tipb.ScalarFuncSig, tp *tipb.Fie
 	case tipb.ScalarFuncSig_ToBinary:
 		f = &builtinInternalToBinarySig{base}
 	case tipb.ScalarFuncSig_FromBinary:
-		f = &builtinInternalFromBinarySig{base}
+		// TODO: set the `cannotConvertStringAsWarning` accordingly
+		f = &builtinInternalFromBinarySig{base, false}
 
 	default:
 		e = ErrFunctionNotExists.GenWithStackByArgs("FUNCTION", sigCode)

pkg/expression/scalar_function.go

@@ -201,7 +201,7 @@ func newFunctionImpl(ctx BuildContext, fold int, funcName string, retType *types
 	case ast.GetVar:
 		return BuildGetVarFunction(ctx, args[0], retType)
 	case InternalFuncFromBinary:
-		return BuildFromBinaryFunction(ctx, args[0], retType), nil
+		return BuildFromBinaryFunction(ctx, args[0], retType, false), nil
 	case InternalFuncToBinary:
 		return BuildToBinaryFunction(ctx, args[0]), nil
 	case ast.Sysdate:

tests/integrationtest/r/expression/charset_and_collation.result

@@ -2056,3 +2056,15 @@ select export_set(3,cast('[]' as json),'2','-',8) between 'W' and 'm';
 export_set(3,cast('[]' as json),'2','-',8) between 'W' and 'm'
 1
 set names default;
+select cast(compress('b') as char);
+cast(compress('b') as char)
+NULL
+Level	Code	Message
+Warning	3854	Cannot convert string '
x\x9C...' from binary to utf8mb4
+set sql_mode='';
+select cast(compress('b') as char);
+cast(compress('b') as char)
+
x
+Level	Code	Message
+Warning	3854	Cannot convert string '
x\x9C...' from binary to utf8mb4
+set sql_mode=DEFAULT;

tests/integrationtest/t/expression/charset_and_collation.test

@@ -838,4 +838,13 @@ select insert('[]', 0, 100, cast('[]' as json)) between 'W' and 'm';
 select substr(cast('[]' as json), 1) between 'W' and 'm';
 select repeat(cast('[]' as json), 10) between 'W' and 'm';
 select export_set(3,cast('[]' as json),'2','-',8) between 'W' and 'm';
-set names default;
+set names default;
+
+
+# TestConvertCharsetFromBinary
+--enable_warnings
+select cast(compress('b') as char);
+set sql_mode='';
+select cast(compress('b') as char);
+--disable_warnings
+set sql_mode=DEFAULT;