[sensslen]

Replaces the gzipped JSON embedded resource with a source generator that encodes data.json into a byte array, which TimeZoneData.Load() decodes into the same dictionaries. The first call into TZNames no longer decompresses and parses 10 MB of JSON.

• A byte array initializer compiles to a data blob rather than IL, so the JIT has nothing large to compile. Strings are pooled, so each distinct string is allocated once instead of once per occurrence.
• The generator uses Newtonsoft.Json rather than System.Text.Json, whose dependency chain is awkward to load inside the compiler. It ships next to the generator and never reaches consumers.
• With the resource gone, the package no longer depends on System.Text.Json on netstandard2.0, netstandard2.1 and net462.
• data.json is committed uncompressed because additional files reach a generator as text. The data itself is unchanged: it is the old data.json.gz decompressed. The DataBuilder now writes data.json.
• ThresholdUtc is now always DateTimeKind.Utc. The DateTime.MaxValue thresholds used to load as Unspecified; the comparison ignores the kind, so results are unchanged.
• Adds net10.0 to the library and tests (net8.0 and net9.0 to tests), and moves global.json and the DataBuilder to the .NET 10 SDK.

Measurements

First TZNames.GetDisplayNames("en-US") in a fresh .NET 9 process on Windows, Release, median of 15 runs.

	main	this PR
First call	200 ms	30 ms
Allocated during the call	30.9 MB	17.1 MB
GC heap after a full collection	20.6 MB	12.4 MB
Private bytes	42.6 MB	20.6 MB
Working set	66.5 MB	43.8 MB
TimeZoneNames.dll (net9.0)	1.75 MB	3.85 MB

NativeAOT is not measured.

Can_Get_DisplayNames_For_OS_Culture fails on my machine both before and after this change, so it is unrelated.

🤖 Generated with Claude Code

[jnyrup]

Preamble: I'm just another consumer of TimeZoneNames, i.e. I have no authority here.

That's a clever use of a source-generator!

I tried getting some numbers to see the pros/cons of this approach.

file size of nupkg:

• main: 9857 kb
• PR: 9901 kb

file size of net462 TimeZoneNames.dll

• main: 2mb
• PR: 6 mb

A NativeAOT ConsoleApp that references TimeZoneNames and calls each public API.
I measured the file size of the published .exe file and the runtime by using Measure-Command

• main:
  • 4675 kb
  • 235 ms
• PR:
  • 13763 kb
  • 168 ms

Some suggestions:
Can the capacity of the dictionaries be set to avoid dynamic resizing and over-allocation?

There are +700 empty dictionaries, can we use a few shared empty instances instead?
This of course now assumes that dictionaries can not be mutated by consumers, but as far as I can tell the dictionary instances aren't exposed to consumers today.

I noticed that ThresholdUtc is sometimes has DateTimeKind.Unspecified and sometimes DateTimeKind.Utc
Should it consistently be DateTimeKind.Utc?

[sensslen]

Thanks for measuring. The rework in c3458d7 now generates a byte array instead of one huge initializer, because on the JIT the original approach was slower than main: about 500 ms of the first call was the JIT compiling the generated IL. The updated numbers are in the description. I haven't measured NativeAOT again.

• Capacity: every dictionary is now created at its final size.
• Empty dictionaries: I left them unshared. An empty Dictionary allocates no buckets, so 743 of them come to about 60 KB.
• ThresholdUtc: it's now always DateTimeKind.Utc. The Unspecified ones were the DateTime.MaxValue entries, which main loads the same way. The comparison ignores the kind, so results don't change.

[jnyrup]

With the new commit, the NativeAOT console app had these numbers:

• 5872 kb
• 198 ms

Here's the code project I used to measure NativeAOT.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net10.0</TargetFramework>
    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
    <PublishAot>true</PublishAot>
    <InvariantGlobalization>false</InvariantGlobalization>
  </PropertyGroup>
  <ItemGroup>
    <ProjectReference Include="..\src\TimeZoneNames\TimeZoneNames.csproj" />
  </ItemGroup>
</Project>

using TimeZoneNames;

const string countryCode = "US";
const string languageCode = "en-US";
const string timeZoneId = "America/New_York";
var threshold = new DateTimeOffset(2020, 1, 1, 0, 0, 0, TimeSpan.Zero);

Console.WriteLine("GetTimeZoneIdsForCountry: " + TZNames.GetTimeZoneIdsForCountry(countryCode).Length);
Console.WriteLine("GetTimeZoneIdsForCountry with threshold: " + TZNames.GetTimeZoneIdsForCountry(countryCode, threshold).Length);
Console.WriteLine("GetTimeZonesForCountry: " + TZNames.GetTimeZonesForCountry(countryCode, languageCode).Count);
Console.WriteLine("GetTimeZonesForCountry with threshold: " + TZNames.GetTimeZonesForCountry(countryCode, languageCode, threshold).Count);
Console.WriteLine("GetFixedTimeZoneIds: " + TZNames.GetFixedTimeZoneIds().Count);
Console.WriteLine("GetFixedTimeZoneNames: " + TZNames.GetFixedTimeZoneNames(languageCode).Count);
Console.WriteLine("GetFixedTimeZoneAbbreviations: " + TZNames.GetFixedTimeZoneAbbreviations().Count);
Console.WriteLine("GetNamesForTimeZone: " + TZNames.GetNamesForTimeZone(timeZoneId, languageCode).Generic);
Console.WriteLine("GetCountryNames: " + TZNames.GetCountryNames(languageCode).Count);
Console.WriteLine("GetDisplayNameForTimeZone: " + TZNames.GetDisplayNameForTimeZone(timeZoneId, languageCode));
Console.WriteLine("GetDisplayNames: " + TZNames.GetDisplayNames(languageCode).Count);
Console.WriteLine("GetDisplayNames with IANA Zone IDs: " + TZNames.GetDisplayNames(languageCode, useIanaZoneIds: true).Count);
Console.WriteLine("GetLanguageCodes: " + TZNames.GetLanguageCodes().Count);
Console.WriteLine("GetLanguageCodes forDisplayNames false: " + TZNames.GetLanguageCodes(forDisplayNames: false).Count);
Console.WriteLine("GetLanguageCodes forDisplayNames true: " + TZNames.GetLanguageCodes(forDisplayNames: true).Count);

// Exercise obsolete APIs too so the NativeAOT smoke test covers the entire public API.
#pragma warning disable CS0618
Console.WriteLine("GetFixedTimeZoneAbbreviations: " + TZNames.GetFixedTimeZoneAbbreviations(languageCode).Count);
Console.WriteLine("GetAbbreviationsForTimeZone: " + TZNames.GetAbbreviationsForTimeZone(timeZoneId, languageCode).Generic);
#pragma warning restore CS0618