Duration format with precision: "second"

[FrankYFTang]

I think I find a bug when I try to fix my v8 implementaiton of broken test
built-ins/Temporal/Duration/prototype/toString/smallestunit-valid-units.js

what should be the result of
const duration = new Temporal.Duration(1, 2, 3, 4, 5, 6, 7, 987, 654, 321);
duration.toString({ smallestUnit: "second" })

The test said it should be "P1Y2M3W4DT5H6M7S"
but my implementation output "P1Y2M3W4DT5H6M7.000000000S"

Here is why, in

7.3.22 Temporal.Duration.prototype.toString ( [ options ] )

after

4. Let precision be ? ToSecondsStringPrecision(options).

precision is { [[Precision]]: 0, [[Unit]]: "second", [[Increment]]: 1 }.

and then

Return ! TemporalDurationToString(result.[[Years]], result.[[Months]], result.[[Weeks]], result.[[Days]], result.[[Hours]], result.[[Minutes]], result.[[Seconds]], result.[[Milliseconds]], result.[[Microseconds]], result.[[Nanoseconds]], precision.[[Precision]]).

now the values of the last 5 args are

result.[[Seconds]] = 7
result.[[Milliseconds]] = 0
result.[[Microseconds]] = 0 
result.[[Nanoseconds]] = 0
precision.[[Precision]] = 0

Now, in https://tc39.es/proposal-temporal/#sec-temporal-temporaldurationtostring

21. If any of seconds, milliseconds, microseconds, and nanoseconds are not 0; or years, months, weeks, days, hours, and minutes are all 0, then

since seconds is 7, it will get into the block:

after

a. Let fraction be abs(milliseconds) × 106 + abs(microseconds) × 103 + abs(nanoseconds).
b. Let decimalPart be fraction formatted as a nine-digit decimal number, padded to the left with zeroes if necessary.

so fraction is 0 and decimalPart is "000000000"

c. If precision is "auto", then
i. Set decimalPart to the longest possible substring of decimalPart starting at position 0 and not ending with the code unit 0x0030 (DIGIT ZERO).
d. Else if precision ≠ 0, then
  i. Set decimalPart to the substring of decimalPart from 0 to precision.

Since precision is 0, it will not get into either c-i nor d-i and therefore decimalPart is still "000000000"

e. Let secondsPart be abs(seconds) formatted as a decimal number.

now secondsPart = "7"

f. If decimalPart is not "", then
i. Set secondsPart to the string-concatenation of secondsPart, the code unit 0x002E (FULL STOP), and decimalPart.

since decimalPart is "000000000" it will get into f-i block and secondsPart will now = "7.000000000"

I think the problem is we need to change d to

d. Else if precision = 0, then
  i. Set decimalPart to "".
e. Else
  i. Set decimalPart to the substring of decimalPart from 0 to precision.

[FrankYFTang]

@ptomato @Ms2ger @ljharb @justingrant @ryzokuken

[FrankYFTang]

Similar issue with test/test262/data/test/built-ins/Temporal/Duration/prototype/toString/blank-duration-precision.js
const blank = new Temporal.Duration();
blank.toString({ fractionalSecondDigits: "auto" })

Following the current spec text will output "PT0.000000000S" not "PT0S" for the same reason

[FrankYFTang]

Also test/built-ins/Temporal/Duration/prototype/toString/roundingmode-undefined.js
const duration = new Temporal.Duration(0, 0, 0, 0, 12, 34, 56, 123, 987, 500);

duration.toString({ smallestUnit: "second", roundingMode: undefined })
and
duration.toString({ smallestUnit: "second" })
by the current spec text will both produce "PT12H34M56.000000000S" but not "PT12H34M56S"

[ptomato]

This was closed by #1860.