evalengine: Implement LAST_DAY

Signed-off-by: Noble Mittal <[email protected]>

go/vt/vtgate/evalengine/compiler_asm.go

@@ -3778,6 +3778,22 @@ func (asm *assembler) Fn_MONTHNAME(col collations.TypedCollation) {
 	}, "FN MONTHNAME DATE(SP-1)")
 }
 
+func (asm *assembler) Fn_LAST_DAY() {
+	asm.emit(func(env *ExpressionEnv) int {
+		if env.vm.stack[env.vm.sp-1] == nil {
+			return 1
+		}
+		arg := env.vm.stack[env.vm.sp-1].(*evalTemporal)
+		d, ok := lastDay(arg.dt)
+		if !ok {
+			env.vm.stack[env.vm.sp-1] = nil
+			return 1
+		}
+		env.vm.stack[env.vm.sp-1] = env.vm.arena.newEvalDate(d)
+		return 1
+	}, "FN LAST_DAY DATETIME(SP-1)")
+}
+
 func (asm *assembler) Fn_QUARTER() {
 	asm.emit(func(env *ExpressionEnv) int {
 		if env.vm.stack[env.vm.sp-1] == nil {

go/vt/vtgate/evalengine/fn_time.go

@@ -107,6 +107,10 @@ type (
 		collate collations.ID
 	}
 
+	builtinLastDay struct {
+		CallExpr
+	}
+
 	builtinQuarter struct {
 		CallExpr
 	}
@@ -168,6 +172,7 @@ var _ IR = (*builtinMicrosecond)(nil)
 var _ IR = (*builtinMinute)(nil)
 var _ IR = (*builtinMonth)(nil)
 var _ IR = (*builtinMonthName)(nil)
+var _ IR = (*builtinLastDay)(nil)
 var _ IR = (*builtinQuarter)(nil)
 var _ IR = (*builtinSecond)(nil)
 var _ IR = (*builtinTime)(nil)
@@ -1200,6 +1205,54 @@ func (call *builtinMonthName) compile(c *compiler) (ctype, error) {
 	return ctype{Type: sqltypes.VarChar, Col: col, Flag: arg.Flag | flagNullable}, nil
 }
 
+func lastDay(dt datetime.DateTime) (datetime.Date, bool) {
+	ts := dt.Date.ToStdTime(time.Local)
+	firstDayOfNextMonth := time.Date(ts.Year(), ts.Month()+1, 1, 0, 0, 0, 0, time.Local)
+	lastDayOfMonth := firstDayOfNextMonth.AddDate(0, 0, -1)
+
+	date := datetime.NewDateFromStd(lastDayOfMonth)
+	return date, true
+}
+
+func (b *builtinLastDay) eval(env *ExpressionEnv) (eval, error) {
+	date, err := b.arg1(env)
+	if err != nil {
+		return nil, err
+	}
+	if date == nil {
+		return nil, nil
+	}
+	dt := evalToDateTime(date, -1, env.now, env.sqlmode.AllowZeroDate())
+	if dt == nil || dt.isZero() {
+		return nil, nil
+	}
+
+	d, ok := lastDay(dt.dt)
+	if !ok {
+		return nil, nil
+	}
+
+	return newEvalDate(d, env.sqlmode.AllowZeroDate()), nil
+}
+
+func (call *builtinLastDay) compile(c *compiler) (ctype, error) {
+	arg, err := call.Arguments[0].compile(c)
+	if err != nil {
+		return ctype{}, err
+	}
+
+	skip := c.compileNullCheck1(arg)
+
+	switch arg.Type {
+	case sqltypes.Date, sqltypes.Datetime:
+	default:
+		c.asm.Convert_xD(1, c.sqlmode.AllowZeroDate())
+	}
+	c.asm.Fn_LAST_DAY()
+	c.asm.jumpDestination(skip)
+	return ctype{Type: sqltypes.Date, Flag: arg.Flag | flagNullable}, nil
+}
+
 func (b *builtinQuarter) eval(env *ExpressionEnv) (eval, error) {
 	date, err := b.arg1(env)
 	if err != nil {

go/vt/vtgate/evalengine/testcases/cases.go

@@ -130,6 +130,7 @@ var Cases = []TestCase{
 	{Run: FnMinute},
 	{Run: FnMonth},
 	{Run: FnMonthName},
+	{Run: FnLastDay},
 	{Run: FnQuarter},
 	{Run: FnSecond},
 	{Run: FnTime},
@@ -1742,6 +1743,12 @@ func FnMonthName(yield Query) {
 	}
 }
 
+func FnLastDay(yield Query) {
+	for _, d := range inputConversions {
+		yield(fmt.Sprintf("LAST_DAY(%s)", d), nil)
+	}
+}
+
 func FnQuarter(yield Query) {
 	for _, d := range inputConversions {
 		yield(fmt.Sprintf("QUARTER(%s)", d), nil)

go/vt/vtgate/evalengine/translate_builtin.go

@@ -414,6 +414,11 @@ func (ast *astCompiler) translateFuncExpr(fn *sqlparser.FuncExpr) (IR, error) {
 			return nil, argError(method)
 		}
 		return &builtinMonthName{CallExpr: call, collate: ast.cfg.Collation}, nil
+	case "last_day":
+		if len(args) != 1 {
+			return nil, argError(method)
+		}
+		return &builtinLastDay{CallExpr: call}, nil
 	case "quarter":
 		if len(args) != 1 {
 			return nil, argError(method)