More updates from code review

* Removed _limit_ parameter from StringSplitToList and adjusted its callsites. * Added editorial note explaining Link resolution complexity. * Minor updates to AvailableNamedTimeZoneIdentifiers.
tc39 · May 27, 2024 · b177cec · b177cec
1 parent 16e86a8
commit b177cec
Showing 1 changed file with 36 additions and 22 deletions.
diff --git a/spec/locales-currencies-tz.html b/spec/locales-currencies-tz.html
@@ -258,7 +258,6 @@ <h1>AvailableNamedTimeZoneIdentifiers ( ): a List of Time Zone Identifier Record
         1. Let _result_ be a new empty List.
         1. For each element _identifier_ of _identifiers_, do
           1. Let _primary_ be _identifier_.
-          1. NOTE: The algorithm steps below are intended to correspond to the behaviour of <code>icu::TimeZone::getIanaID()</code> in the International Components for Unicode (<a href="https://icu.unicode.org/">ICU</a>) and the processes for maintaining time zone identifier data in the Unicode Common Locale Data Repository (<a href="https://cldr.unicode.org">CLDR</a>).
           1. If _identifier_ is a Link name in the IANA Time Zone Database and _identifier_ is not present in the “TZ” column of <code>zone.tab</code> of the IANA Time Zone Database, then
             1. Let _zone_ be the Zone name that _identifier_ resolves to, according to the rules for resolving Link names in the IANA Time Zone Database.
             1. If _zone_ starts with *"Etc/"*, then
@@ -277,15 +276,15 @@ <h1>AvailableNamedTimeZoneIdentifiers ( ): a List of Time Zone Identifier Record
                   1. Let _backzone_ be *undefined*.
                   1. Let _backzoneLinkLines_ be the List of lines in the file <code>backzone</code> of the IANA Time Zone Database that start with either *"Link "* or *"#PACKRATLIST zone.tab Link "*.
                   1. For each element _line_ of _backzoneLinkLines_, do
-                    1. If _line_ starts with *"#PACKRATLIST zone.tab "*, set _line_ to the substring of _line_ from 22.
-                    1. Assert: _line_ starts with *"Link "*.
-                    1. Set _line_ to the substring of _line_ from 5.
-                    1. Let _backzoneAndLink_ be StringSplitToList(_line_, *" "*, 2).
-                    1. Assert: _backzoneAndLink_ has exactly two elements.
+                    1. Let _i_ be StringIndexOf(_line_, *"Link "*, 0).
+                    1. Set _line_ to the substring of _line_ from _i_ + 5.
+                    1. Let _backzoneAndLink_ be StringSplitToList(_line_, *" "*).
+                    1. Assert: _backzoneAndLink_ has at least two elements, and both _backzoneAndLink_[0] and _backzoneAndLink_[1] are available named time zone identifiers.
                     1. If _backzoneAndLink_[1] is _identifier_, then
                       1. Assert: _backzone_ is *undefined*.
-                      1. Set _primary_ to _backzoneAndLink_[0].
+                      1. Set _backzone_ to _backzoneAndLink_[0].
                   1. Assert: _backzone_ is not *undefined*.
+                  1. Set _primary_ to _backzone_.
           1. If _primary_ is one of *"Etc/UTC"*, *"Etc/GMT"*, or *"GMT"*, set _primary_ to *"UTC"*.
           1. If _primary_ is a replacement time zone identifier and its rename waiting period has not concluded, then
             1. Let _renamedIdentifier_ be the renamed time zone identifier that _primary_ replaced.
@@ -296,6 +295,27 @@ <h1>AvailableNamedTimeZoneIdentifiers ( ): a List of Time Zone Identifier Record
         1. Return _result_.
       </emu-alg>
 
+      <emu-note>
+        <p>
+          The algorithm above for resolving Links to primary time zone identifiers is intended to correspond to the behaviour of <code>icu::TimeZone::getIanaID()</code> in the International Components for Unicode (<a href="https://icu.unicode.org/">ICU</a>) and the processes for maintaining time zone identifier data in the Unicode Common Locale Data Repository (<a href="https://cldr.unicode.org">CLDR</a>).
+        </p>
+        <p>
+          This algorithm resolves Links to primary time zone identifiers without crossing the boundaries of ISO 3166-1 Alpha-2 country codes, using data from files <code>zone.tab</code> and <code>backzone</code> of the IANA Time Zone Database.
+          If the country code of a Link has only one line in <code>zone.tab</code>, then that line will determine the primary time zone identifier.
+          However, if that country code has multiple lines in <code>zone.tab</code>, then historical mappings in <code>backzone</code> must be used to identify the correct primary time zone identifier.
+        </p>
+        <p>
+          For example, if "Pacific/Truk" (in country code "FM") is a Link to "Pacific/Port_Moresby" (in country code "PG") with the default build options of the IANA Time Zone Database, then the “country-code” column of <code>zone.tab</code> will be checked for lines corresponding with "FM".
+          If there were only one such line, then the “TZ” column of that line would determine the primary time zone identifier associated with "Pacific/Truk".
+          But "FM" has multiple lines in <code>zone.tab</code>, so <code>backzone</code> must be consulted to find the line "Link Pacific/Chuuk Pacific/Truk", resulting in "Pacific/Chuuk" as the primary time zone identifier.
+        </p>
+        <p>
+          Note that <code>zone.tab</code> is the preferred source of mapping data because <code>backzone</code> mappings may, in rare cases, cross the boundaries of ISO 3166-1 Alpha-2 country codes.
+          For example, "Atlantic/Jan_Mayen" (in country code "SJ") is mapped in <code>backzone</code> to "Europe/Oslo" (in country code "NO").
+          As of the 2024a release of the IANA Time Zone Database, "Atlantic/Jan_Mayen" is the only case where this happens.
+        </p>
+      </emu-note>
+
       <emu-note>
         Time zone identifiers in the IANA Time Zone Database can change over time.
         At a minimum, it is recommended that implementations limit changes to the result of AvailableNamedTimeZoneIdentifiers to the changes allowed by GetAvailableNamedTimeZoneIdentifier, for the lifetime of the surrounding agent.
@@ -352,41 +372,33 @@ <h1>
         <h1>
           StringSplitToList (
             _S_: a String,
-            _separator_: a String that is not the empty String,
-            _limit_: a mathematical value in the range 1 to 2<sup>32</sup> - 1
+            _separator_: a String,
           ): a List of Strings
         </h1>
         <dl class="header">
           <dt>description</dt>
           <dd>
-            The returned List contains substrings of _S_.
-            These substrings are determined by searching from left to right for occurrences of _separator_; these occurrences are not part of any String in the returned List, but serve to divide _S_ into substrings.
-            The output List will contain no more than _limit_ elements; any additional separators and/or substrings present in _S_ will be ignored.
+            The returned List contains all disjoint substrings of _S_ that do not contain _separator_ but are immediately preceded and/or immediately followed by an occurrence of _separator_.
+            Each such <emu-not-ref>substring</emu-not-ref> will be the empty String between adjacent occurrences of _separator_, before a _separator_ at the very start of _S_, or after a _separator_ at the very end of _S_, but otherwise will not be empty.
           </dd>
         </dl>
         <emu-alg>
-          1. If _S_ is the empty String, return « ».
+          1. Assert: _S_ is not the empty String.
+          1. Assert: _separator_ is not the empty String.
           1. Let _separatorLength_ be the length of _separator_.
-          1. Assert: _separatorLength_ is not 0.
           1. Let _substrings_ be a new empty List.
           1. Let _i_ be 0.
           1. Let _j_ be StringIndexOf(_S_, _separator_, 0).
-          1. Repeat, while _j_ ≠ -1,
+          1. Repeat, while _j_ is not ~not-found~,
             1. Let _T_ be the substring of _S_ from _i_ to _j_.
             1. Append _T_ to _substrings_.
-            1. If the number of elements in _substrings_ is _limit_, return _substrings_.
             1. Set _i_ to _j_ + _separatorLength_.
             1. Set _j_ to StringIndexOf(_S_, _separator_, _i_).
           1. Let _T_ be the substring of _S_ from _i_.
           1. Append _T_ to _substrings_.
           1. Return _substrings_.
         </emu-alg>
       </emu-clause>
-      <emu-note>
-        <p>
-          Substrings in the returned List may be the empty String if _S_ starts or ends with _separator_ or if _S_ contains adjacent occurrences of _separator_.
-        </p>
-      </emu-note>
   </emu-clause>
 
   <emu-clause id="sec-measurement-unit-identifiers">
@@ -414,7 +426,9 @@ <h1>
       <emu-alg>
         1. If IsSanctionedSingleUnitIdentifier(_unitIdentifier_) is *true*, then
           1. Return *true*.
-        1. Let _units_ be StringSplitToList(_unitIdentifier_, *"-per-"*, 3).
+        1. If _unitIdentifier_ is the empty String, then
+          1. Return *false*.
+        1. Let _units_ be StringSplitToList(_unitIdentifier_, *"-per-"*).
         1. If the number of elements in _units_ is not 2, then
           1. Return *false*.
         1. If IsSanctionedSingleUnitIdentifier(_units_[0]) and IsSanctionedSingleUnitIdentifier(_units_[1]) are both *true*, then