x.json2: fix decoding of float values in scientific notation (fix #26043) (fix #26062) (#26060)

Author: kbkpbot

vlib/x/json2/encode.v

@@ -217,7 +217,10 @@ fn (mut encoder Encoder) encode_boolean(val bool) {
 fn (mut encoder Encoder) encode_number[T](val T) {
 	integer_val := val.str()
 	$if T is $float {
-		if integer_val[integer_val.len - 1] == `0` { // ends in .0
+		if integer_val.len > 2 && integer_val[integer_val.len - 2] == `.`
+			&& integer_val[integer_val.len - 1] == `0` { // ends in .0
+			// `2.0` = > `2`
+			// but skip float in scientific notation, `1e+10`
 			unsafe {
 				integer_val.len -= 2
 			}

vlib/x/json2/tests/encoder_test.v

@@ -177,3 +177,15 @@ fn test_encode_time() {
 
 	assert json.encode(time.Time{}) == '"0000-00-00T00:00:00.000Z"'
 }
+
+fn test_encode_float() {
+	// remove ending `.0`
+	assert json.encode(1.0) == '1'
+
+	// TODO: better generate `1e10` instead of `1e+10`
+	assert json.encode(1.0e+10) == '1e+10'
+	assert json.encode(1.0e10) == '1e+10'
+	assert json.encode(1.e10) == '1e+10'
+	assert json.encode(1.0e-10) == '1e-10'
+	assert json.encode(1.1e10) == '1.1e+10'
+}