Dil.Extensions.Localization 0.4.0

Dil

Strongly-typed .NET localization from plain JSON files, generated at build time.

No resx. No .Designer.cs. No stringly-typed lookups. No IDE dependency. Just Strings.Hello.

CultureInfo.CurrentUICulture = new("tr");
Strings.Hello;                  // "Merhaba"
Strings.Greeting.Render("Ada"); // "Merhaba, Ada!"
Strings.Greeting.Template;      // "Merhaba, {name}!"
Strings.Inbox.Render(3);        // "3 okunmamış mesajınız var"

The class name comes from the JSON file's base name, resx-style: Strings.json → Strings, Errors.json → Errors, CustomerResources.json → CustomerResources. Each file group is an independent set, so two sets can use the same key names without clashing.

Why

.resx gives you typed access but drags along XML boilerplate, an IDE-bound designer, and no cross-platform CLI regeneration. Dil keeps the one good part of resx — the typed Strings.Hello accessor that respects the ambient CurrentUICulture — and drops the rest:

• JSON, not XML — readable, diffable, translator-friendly.
• Source generator — the typed classes are regenerated on every dotnet build, on any OS. Nothing checked in.
• Many resource sets — one generated class per file group (Strings, Errors, …), each independent.
• Generic, formattable params — {placeholder} values are generic (Greeting.Render<T>(T name)), so int/string/etc. flow without object?, and IFormattable values render in the current culture.
• Live reload — edits to the JSON files are picked up at runtime (on in Debug builds; toggle with Dil.Loc.LiveReload).
• Translations in IntelliSense — every member's doc comment lists all its translations.
• Lean runtime — multi-targets netstandard2.0, net8.0, net10.0, and net11.0; parses JSON with System.Text.Json (in-box on modern .NET) and assembles formatted strings with Glot's pooled TextBuilder.
• Ambient culture — works exactly like resx: set CultureInfo.CurrentUICulture, read Strings.X.
• Compile-time safety — missing translations are reported as build warnings (DIL001).

Install

dotnet add package Dil

That's it — the package wires the generator and the required MSBuild glue in automatically.

Use

Register one file of each set with <DilResource Include="..." />; the rest of the set on disk is pulled in automatically. The base name becomes the class and the trailing segment is the culture, resx-style: Strings.json is the neutral (culture-free) file of the Strings set, Strings.tr.json is Turkish, Strings.de.json is German, Strings.zh-Hans.json is Simplified Chinese. The neutral file is optional (see Sets without a neutral file).

<ItemGroup>
  <DilResource Include="Resources/Strings.json" /> 
  
  <DilResource Include="Resources/Errors.json" />
</ItemGroup>

A wildcard (Resources/Strings.*.json) or a single culture file (Resources/Strings.en.json) works just as well.

// Resources/Strings.json  (neutral — defines the keys and is the fallback)
{ "hello": "Hello", "greeting": "Hello, {name}!" }

// Resources/Strings.tr.json
{ "hello": "Merhaba", "greeting": "Merhaba, {name}!" }

Build, then use the generated classes (they land in your project's RootNamespace):

using YourRootNamespace;

Console.WriteLine(Strings.Hello);
Console.WriteLine(Strings.Greeting.Render("Ada"));   // generic param: Render<T>(T name)
Console.WriteLine(Strings.Greeting.Template);        // "Hello, {name}!" — the raw template
Console.WriteLine(Errors.NotFound.Render("a.json")); // a separate set

Plain values become string properties. A value with {placeholder} tokens becomes a property returning a small generated struct with two members:

• Render(...) fills in the placeholders. Each token becomes a generic method parameter.
• Template returns the raw value for the current UI culture with the tokens left in, for callers that do their own formatting (for example, an error model that returns both the template and the message).

Both resolve through the same culture fallback as everything else. The struct is an empty readonly struct, so the property allocates nothing and Strings.Greeting.Render(...) costs the same as a plain method call. Its type is named <Member>Template (e.g. Strings.GreetingTemplate); if that clashes with a key's member, the key keeps its name and the struct gets a number (GreetingTemplate2).

Add a type to pin a parameter: {name:string} generates string name, {count:int} generates int count. Bare and typed placeholders can mix in one string (Items.Render<T>(int count, T thing)).

{ "greet": "Hello, {name:string}!", "items": "{count:int} items" }
// -> Greet.Render(string name);  Items.Render(int count);

Any C# type works as a typed parameter — including your own ({total:Money} → Money total), rendered via IFormattable/ToString(). The type must be resolvable in your RootNamespace, or fully-qualified ({total:global::MyApp.Money}). The bare {total} form is generic, so it accepts any type without that.

Sets without a neutral file

A set doesn't need a neutral file. One file per language, each named after its language, is a set too:

// Resources/Strings.en.json
{ "hello": "Hello" }

// Resources/Strings.tr.json
{ "hello": "Merhaba" }

Without a neutral file, the set's keys are all the keys found across its culture files, and DIL001 reports any culture file that's missing one of them. If neither the current UI culture nor its parents have a file, a lookup returns the key itself ("hello"), unless the set has a default culture.

Default culture

Name the culture to use when the current one has no value. With en as the default, fr-FR resolves as fr-FR → fr → en → key, instead of going straight to the key:

<PropertyGroup>
  <DilDefaultCulture>en</DilDefaultCulture>                     
</PropertyGroup>

<ItemGroup>
  <DilResource Include="Resources/Strings.en.json" DefaultCulture="en" /> 
</ItemGroup>

The default is per set, like everything else. If a set has both a neutral file and a default culture, the default culture comes first, like resx's NeutralResourcesLanguage. A regional default falls back to its parent (en-US → en). The default culture's file also supplies the <summary> text of the generated members; otherwise it comes from the neutral file.

Class accessibility

Generated classes are internal by default — localization tables are usually an implementation detail of one assembly. Make them public project-wide with the DilAccessibility property, or per resource with Accessibility metadata on the <DilResource> item:

<PropertyGroup>
  
  <DilAccessibility>public</DilAccessibility>
</PropertyGroup>

<ItemGroup>
  
  <DilResource Include="Resources/Strings.json" Accessibility="internal" />
</ItemGroup>

A set spans several files (neutral + cultures) but produces one class, so one file decides the set's accessibility: the neutral (cultureless) file, or without one, the default culture's file. Files pulled in automatically take the Accessibility and DefaultCulture of the file you registered. The members themselves stay public static — their visibility is already capped by the class.

How file selection works

The generator only ever sees files you register with <DilResource> — a source generator cannot read arbitrary files, only those passed to it as AdditionalFiles (which <DilResource> becomes under the hood). Your appsettings.json, package.json, and every other JSON file are invisible to it. There is no folder scan and no magic filename.

As a convenience, registering a file also pulls in the rest of its set on disk — the build drops the culture from the registered name and adds <dir>/<stem>.json and every <dir>/<stem>.<culture>.json next to it. So registering Strings.json or Strings.en.json also picks up Strings.tr.json, Strings.de.json, and so on; you don't list each culture. (This is an MSBuild-side expansion, so the files must exist on disk at build time.)

Setting the culture

Dil reads the ambient CultureInfo.CurrentUICulture — set it however your app already does:

• Console / desktop: CultureInfo.CurrentUICulture = new("tr");
• ASP.NET Core: app.UseRequestLocalization(...) sets it per request; Strings.X just works inside the request.

IStringLocalizer interop (optional)

Prefer the typed Strings.Greeting.Render("Ada") API. But when a framework or library expects the Microsoft.Extensions.Localization abstractions, install the optional Dil.Extensions.Localization package — it adapts a Dil resource set to IStringLocalizer, IStringLocalizer<T>, and IStringLocalizerFactory, with a DI extension:

builder.Services.AddDilLocalization();
// optionally: AddDilLocalization(o => { o.BaseDirectory = "..."; o.LiveReload = false; });

public class HomeController(IStringLocalizer<Strings> loc) // T is your generated class -> the "Strings" set
{
    public string Hi() => loc["hello"];          // -> "Merhaba"
    public string Cost() => loc["price", 37.63];  // string.Format positional: "{0:C}" etc.
}

IStringLocalizer<Strings> reads the Strings.json group of the assembly that defines Strings. Note the formatting difference: the IStringLocalizer["key", args] overload uses positional string.Format ({0}, {1:C}) like resx — so author those values positionally. Dil's named {name} placeholders are for the generated typed members; a named template passed through the indexer is returned unformatted (never throws).

Diagnostics

Treat it as an error if you want a hard guarantee that every string is translated:

<PropertyGroup>
  <WarningsAsErrors>$(WarningsAsErrors);DIL001</WarningsAsErrors>
</PropertyGroup>

Notes

• Missing keys fall back: tr-TR → tr → default culture → neutral → the key itself. Fallback is per set.
• Each assembly's resource files are copied to Dil/<AssemblyName>/ in the output (keeping their path in the project), and each set is keyed by its assembly and class name. Two libraries can both have a Strings set, even at the same path, and an app that references both keeps them apart.
• Only string values are used; numbers, objects, and arrays are ignored. Comments and trailing commas are tolerated, so .jsonc works.
• Live reload — editing a resource file is picked up at runtime. It is on for Debug builds and off otherwise, so a published Release app runs no file watchers. Override the build default with <DilLiveReload>true|false</DilLiveReload> in the app project (it reaches the runtime via runtimeconfig.json, so the app must reference Dil directly), or at runtime with Dil.Loc.LiveReload. All sets share one watcher per folder, and a change reloads only the sets that own the changed file — appsettings.json and other JSON files next to them are ignored.
• Dil.Loc.Configure(baseDirectory) overrides where files are loaded from / forces a reload.
• Placeholder values are formatted with the current culture via IFormattable; a null value becomes the empty string.

Build from source

Needs the .NET 11 SDK (pinned in global.json); the tests also run on .NET 10, so have its runtime too.

dotnet build                                    # build everything
dotnet run --project sample/Dil.Sample          # run the demo
dotnet test                                     # run the TUnit tests
dotnet pack Dil.slnx -c Release -o artifacts    # produce both NuGet packages

Project layout

src/Dil/                       runtime (netstandard2.0/net8.0/net10.0/net11.0) + build/ props & targets
src/Dil.Generator/             incremental source generator + DIL001 diagnostics
src/Dil.Extensions.Localization/  optional IStringLocalizer / DI adapter
sample/Dil.Sample/             runnable console demo
sample/Dil.Localization.Sample/  IStringLocalizer + DI demo
tests/                         TUnit tests for the runtime, generator, and the adapter

License

MIT