strconv: fix remove_tail_zeros bug (fix #22421) (#22422)

Author: kbkpbot

vlib/strconv/format_mem.c.v

@@ -491,13 +491,17 @@ pub fn remove_tail_zeros(s string) string {
 		if i_s < s.len && s[i_s] == `.` {
 			mut i_s1 := i_s + 1
 			mut sum := 0
+			mut i_s2 := i_s1 // last non-zero index after `.`
 			for i_s1 < s.len && s[i_s1] >= `0` && s[i_s1] <= `9` {
 				sum += s[i_s1] - u8(`0`)
+				if s[i_s1] != `0` {
+					i_s2 = i_s1
+				}
 				i_s1++
 			}
 			// decimal part must be copied
 			if sum > 0 {
-				for c_i in i_s .. i_s1 {
+				for c_i in i_s .. i_s2 + 1 {
 					buf[i_d] = s[c_i]
 					i_d++
 				}

vlib/strconv/format_test.v

@@ -119,3 +119,10 @@ fn test_sprintf_with_escape() {
 	s := unsafe { strconv.v_sprintf('%d is 100%% awesome', n) }
 	assert s == '69 is 100% awesome'
 }
+
+fn test_remove_tail_zeros() {
+	assert strconv.remove_tail_zeros('1.234000000000') == '1.234'
+	assert strconv.remove_tail_zeros('1.0000000') == '1'
+	assert strconv.remove_tail_zeros('1234') == '1234'
+	assert strconv.remove_tail_zeros('1.00000000007') == '1.00000000007'
+}

vlib/v/tests/builtin_strings_and_interpolation/string_interpolation_float_fmt_test.v

@@ -1,13 +1,13 @@
 fn test_string_interpolation_float_fmt() {
 	mut a := 76.295
 	eprintln('${a:8.2}')
-	assert '${a:8.2}' == '   76.30'
+	assert '${a:8.2}' == '    76.3'
 	eprintln('${a:8.2f}')
 	assert '${a:8.2f}' == '   76.30'
 
 	a = 76.296
 	eprintln('${a:8.2}')
-	assert '${a:8.2}' == '   76.30'
+	assert '${a:8.2}' == '    76.3'
 	eprintln('${a:8.2f}')
 	assert '${a:8.2f}' == '   76.30'
 }

vlib/v/tests/casts/cast_to_empty_interface_test.v

@@ -22,8 +22,8 @@ fn test_cast_to_empty_interface() {
 	assert ret_strings[1] == 'int               22'
 	assert ret_strings[2] == 'int             8888'
 	assert ret_strings[3] == 'int             9999'
-	assert ret_strings[4] == 'f64               1.110'
-	assert ret_strings[5] == 'f64               2.220'
-	assert ret_strings[6] == 'f64               8.880'
-	assert ret_strings[7] == 'f64               9.990'
+	assert ret_strings[4] == 'f64                1.11'
+	assert ret_strings[5] == 'f64                2.22'
+	assert ret_strings[6] == 'f64                8.88'
+	assert ret_strings[7] == 'f64                9.99'
 }