Parse the full ISO 8601 grammar in fromdateiso8601 (#3617)

`fromdateiso8601` was `strptime("%Y-%m-%dT%H:%M:%SZ") | mktime`, which
accepts only one of the many representations ISO 8601 permits. strptime
cannot be extended to cover the rest portably, since it has no specifier
for fractional seconds and glibc discards `%G` and `%V`.

Replace it with a parser in src/iso8601.c that handles basic and extended
representations, ordinal and week dates, fractional seconds, offsets and
date-only input. It uses integer arithmetic instead of `time_t`, so the
results no longer depend on the platform.

This is stricter than before. Impossible dates like `2015-02-30`, which
`mktime` used to normalize into March, and unpadded components like
`2015-3-5T6:00:00Z` are now errors. So is any trailing input, including
whitespace. Leading whitespace is rejected too; before, glibc skipped it
and macOS did not. A leap second now maps to the second before it rather
than the next minute. The error message has changed, and the result can
now be non-integer.

tests/jq.test

@@ -1921,6 +1921,111 @@ last(range(365 * 67)|("1970-03-01T01:02:03Z"|strptime("%Y-%m-%dT%H:%M:%SZ")|mkti
 null
 [2037,1,11,1,2,3,3,41]
 
+# fromdateiso8601 accepts the calendar, ordinal and week date forms,
+# in both the extended and the basic representation
+[("2015-03-05T23:51:47Z", "20150305T235147Z", "2015-064T23:51:47Z", "2015064T235147Z", "2015-W10-4T23:51:47Z", "2015W104T235147Z") | fromdateiso8601]
+null
+[1425599507,1425599507,1425599507,1425599507,1425599507,1425599507]
+
+# fractional seconds, with either decimal sign
+[("2015-03-05T23:51:47.25Z", "2015-03-05T23:51:47,25Z", "20150305T235147.25Z") | fromdateiso8601]
+null
+[1425599507.25,1425599507.25,1425599507.25]
+
+# UTC offsets; an absent offset means UTC
+[("2015-03-06T08:51:47+09:00", "2015-03-06T08:51:47+0900", "2015-03-06T08:51:47+09", "2015-03-05T18:21:47-05:30", "2015-03-05T23:51:47z", "2015-03-05T23:51:47") | fromdateiso8601]
+null
+[1425599507,1425599507,1425599507,1425599507,1425599507,1425599507]
+
+# the date and the time may be separated by "T", "t" or a space
+[("2015-03-05t23:51:47Z", "2015-03-05 23:51:47Z") | fromdateiso8601]
+null
+[1425599507,1425599507]
+
+# the W, T and Z designators may be written in lower case
+[("2015-w10-4t23:51:47z", "2015w104t235147z", "2015-03-05t23:51:47z") | fromdateiso8601]
+null
+[1425599507,1425599507,1425599507]
+
+# expanded years carry a sign and exactly six digits
+[("+012015-03-05T23:51:47Z", "-000001-01-01T00:00:00Z", "+0020150305T235147Z", "+2025-03-05", "+02025-03-05", "+0002025-03-05") | try fromdateiso8601 catch "ERR"]
+null
+[316995119507,-62198755200,1425599507,"ERR","ERR","ERR"]
+
+# "24:00:00" is midnight of the following day, at any precision
+[("2015-03-05T24:00:00Z", "2015-03-05T24:00Z", "2015-03-05T24Z") | fromdateiso8601 | todate]
+null
+["2015-03-06T00:00:00Z","2015-03-06T00:00:00Z","2015-03-06T00:00:00Z"]
+
+# leap seconds are dropped rather than rejected
+"2015-06-30T23:59:60Z" | fromdateiso8601 | todate
+null
+"2015-06-30T23:59:59Z"
+
+# 2015 starts on a Thursday, so it has 53 ISO weeks
+"2015-W53-1T00:00:00Z" | fromdateiso8601 | todate
+null
+"2015-12-28T00:00:00Z"
+
+# 2016 is a leap year starting on a Friday: 366 days, but only 52 ISO weeks
+[("2016-366T00:00:00Z", "2016-W52-7T00:00:00Z") | fromdateiso8601 | todate]
+null
+["2016-12-31T00:00:00Z","2017-01-01T00:00:00Z"]
+
+# fromdateiso8601 is not limited by the range of a 32-bit time_t (#3276)
+fromdate
+"2038-01-19T03:14:08Z"
+2147483648
+
+# the time may drop its seconds, or its minutes and seconds
+[("2015-03-05T23:51Z", "2015-03-05T23Z", "20150305T2351Z", "20150305T23Z") | fromdateiso8601]
+null
+[1425599460,1425596400,1425599460,1425596400]
+
+# a decimal fraction belongs to the lowest component present
+[("2015-03-05T23:51:47,5Z", "2015-03-05T23:51,5Z", "2015-03-05T23,5Z") | fromdateiso8601]
+null
+[1425599507.5,1425599490,1425598200]
+
+# a date on its own is midnight UTC
+[("2015-03-05", "20150305", "2015-064", "2015064", "2015-W10-4", "2015W104") | fromdateiso8601]
+null
+[1425513600,1425513600,1425513600,1425513600,1425513600,1425513600]
+
+# the zone designator belongs to the time, so a bare date cannot carry one
+[("2015-03-05Z", "2015-03-05+09:00", "2015-03-05T") | try fromdateiso8601 catch "ERR"]
+null
+["ERR","ERR","ERR"]
+
+# the date must be complete, and a time must not be empty
+[("2015", "2015-03", "2015-W10", "2015-03T00:00:00Z", "T23:51:47Z", "T23:51:47", "23:51:47", "") | try fromdateiso8601 catch "ERR"]
+null
+["ERR","ERR","ERR","ERR","ERR","ERR","ERR","ERR"]
+
+# the date and the time must agree on whether separators are used,
+# and "YYYYMM" is ambiguous with "YYMMDD"
+[("2015-03-05T235147Z", "20150305T23:51:47Z", "201503T00:00:00Z", "2015-03-05T2351Z", "20150305T23:51Z", "20150305T23205Z") | try fromdateiso8601 catch "ERR"]
+null
+["ERR","ERR","ERR","ERR","ERR","ERR"]
+
+# out-of-range components are rejected
+[("2015-02-30T00:00:00Z", "2015-13-01T00:00:00Z", "2015-00-01T00:00:00Z", "2015-366T00:00:00Z", "2016-W53-1T00:00:00Z", "2015-W10-8T00:00:00Z", "2015-W00-1T00:00:00Z", "2015-03-05T25:00:00Z", "2015-03-05T24:00:01Z", "2015-03-05T24:01Z", "2015-03-05T23:60:00Z", "2015-03-05T23:51:47+24:00", "2015-03-05T23:51:47+09:") | try fromdateiso8601 catch "ERR"]
+null
+["ERR","ERR","ERR","ERR","ERR","ERR","ERR","ERR","ERR","ERR","ERR","ERR","ERR"]
+
+# the input must be exactly a datetime: no surrounding whitespace
+[(" 2015-03-05T23:51:47Z", "2015-03-05T23:51:47Z ") | try fromdateiso8601 catch "ERR"]
+null
+["ERR","ERR"]
+
+try fromdateiso8601 catch .
+123
+"fromdateiso8601 requires string inputs"
+
+try fromdateiso8601 catch .
+"not a date"
+"date \"not a date\" is not a valid ISO 8601 datetime"
+
 # module system
 import "a" as foo; import "b" as bar; def fooa: foo::a; [fooa, bar::a, bar::b, foo::a]
 null