[JSC] CET, EET, MET and WET are aliases of their city zones with every tz data

JSTests/BUN-TEST-DIFFERENCES.md

@@ -197,7 +197,7 @@ Not upstream's: a sync neither brings nor changes them. Most are named `stress/b
 | `stress/regexp-image-code-hands-long-searches-over.js` | with `--useRegExpImageMode=1`, in a `jsc` that has the ahead-of-time compiler: the code of a pattern stops after nine turns a unit and 65,537, and the match is made again by the flat programs, which give it up where the JIT does. In a `jsc` without the compiler the option changes nothing, and both runs hold the JIT to the same answers |
 | `stress/switch-string-substring-of-base-widened-by-atomization.js` | a `switch` over strings that reads the characters of a substring in place, in its base, goes by the width that the base has now: atomizing the base may have put an equal 16-bit string in its place since the substring was made (DFG and FTL) |
 | `stress/bun-weak-map-and-set-shrunk-before-eden-collection.js` | the buffer of a `WeakMap` or `WeakSet` counts in the heap's size as it is behind a collection (`WeakMapImpl::reconcileWeakReferencesAtGCEnd`; upstream counts it as the last visit found it), but an eden collection never leaves that size below what the collection before it left: a buffer that shrank stops counting at the next full collection |
-| `stress/intl-timezone-posix-style.js` | `EST5EDT`, `CST6CDT`, `MST7MDT` and `PST8PDT` stay aliases of their `America/*` zones (tc39/ecma402#1103) on every ICU, including those where CLDR treats them as canonical zones (45 and earlier, 49 and later): accepted, kept as written, not in `supportedValuesOf`, same offsets and names as the primary zone, and resolved to it when they are the host's zone |
+| `stress/intl-timezone-posix-style.js` | `EST5EDT`, `CST6CDT`, `MST7MDT` and `PST8PDT` stay aliases of their `America/*` zones (tc39/ecma402#1103) on every ICU, including those where CLDR treats them as canonical zones (45 and earlier, 49 and later): accepted, kept as written, not in `supportedValuesOf`, same offsets and names as the primary zone, and resolved to it when they are the host's zone. `CET`, `EET`, `MET` and `WET` are aliases of `Europe/Brussels`, `Europe/Athens`, `Europe/Brussels` and `Europe/Lisbon` in the same way: tzdata before 2024b has them as zones, and the system ICU of a Mac can have such data |
 | `stress/temporal-calendar-gregory-near-min-date.js` | the `gregory` calendar agrees with the ISO calendar in the first years of Temporal's range: reading fields, building from fields and formatting (`prolepticGregorianChangeDate`, `runtime/JSDateMath.h`) |
 | the fr-CA block of `stress/intl-date-pattern-includes-literal-text.js` (the file is upstream's) | keeps the file's coverage on CLDR 49, where fr's pattern no longer has literal text: an `h` inside literal text is not mistaken for the hour field |
 | the last block of `stress/regexp-test-sticky-first-char-filter.js` (the file is upstream's; nothing of upstream's text changes) | the first-character filter of a sticky `test()` comes from the first sets of the alternatives (`yarr/YarrFirstFollowSets.*`): behind a leading lookbehind, forward reference or lookahead, and in groups nested more than eight deep, a byte that passes the filter still reaches the matcher |

JSTests/stress/intl-timezone-posix-style.js

@@ -12,6 +12,11 @@ const links = [
     ["CST6CDT", "America/Chicago", 300],
     ["MST7MDT", "America/Denver", 360],
     ["PST8PDT", "America/Los_Angeles", 420],
+    // Not part of that issue: tzdata before 2024b has these as zones too, and they are links from 2024b on.
+    ["CET", "Europe/Brussels", -120],
+    ["EET", "Europe/Athens", -180],
+    ["MET", "Europe/Brussels", -120],
+    ["WET", "Europe/Lisbon", -60],
 ];
 
 const supported = Intl.supportedValuesOf("timeZone");

Source/JavaScriptCore/runtime/IntlObject.cpp

@@ -2002,6 +2002,14 @@ static std::optional<ASCIILiteral> mapPOSIXStyleTimeZoneToPrimary(StringView tim
         return "America/Denver"_s;
     if (timeZone == "PST8PDT"_s)
         return "America/Los_Angeles"_s;
+    // Not part of that issue: tzdata before 2024b has these four as zones too, and links them to these zones from
+    // 2024b on. The system ICU of a Mac can have the older data (macOS 15.7.7 has tzdata 2024a).
+    if (timeZone == "CET"_s || timeZone == "MET"_s)
+        return "Europe/Brussels"_s;
+    if (timeZone == "EET"_s)
+        return "Europe/Athens"_s;
+    if (timeZone == "WET"_s)
+        return "Europe/Lisbon"_s;
     return std::nullopt;
 }