Changes

Swift version support

This release drops support for Swift 5.0.

Swift 5.1+ remain supported for the time being.

Logger.MetadataProvider

This release introduces metadata providers!

They are an additional way to add metadata to your log statements automatically whenever a log statement is about to be made. This works extremely well with systems like distributed tracing, that may pick up trace identifiers and other information from the task-local context from where the log statement is being made.

The feature came with a swift evolution style proposal introduction to the "why?" and "how?" of this feature you may find interesting.

Metadata providers are used like this:

import Logging

enum Namespace { 
  @TaskLocal static var simpleTraceID: String?
}

let simpleTraceIDMetadataProvider = Logger.MetadataProvider { 
    guard let traceID = Namespace.simpleTraceID else {
        return [:]
    }
    return ["simple-trace-id": .string(traceID)]
 }

LoggingSystem.bootstrap({ label, metadataProvider in
    myCoolLogHandler(label: label, metadataProvider: metadataProvider)
}, metadataProvider: simpleTraceIDMetadataProvider)

which in turn makes every Logger on this LoggingSystem add this contextual metadata to log statements automatically:

let log = Logger(label: "hello")

Namespace.$simpleTraceID.withValue("1234-5678") {
  test()
}

func test() {
  log.info("test log statement")
}

// [info] [simple-trace-id: 1234-5678] test log statement

Adoption in LogHandlers

In order to support this new feature in your log handlers, please make it accept a MetadataProvider? at creation, and store it as:

struct MyHandler: LogHandler {
    // ... 
    public var metadataProvider: Logger.MetadataProvider?
    // ...
}

What's Changed

Highlight

• Metadata Providers (e.g. for Distributed Tracing) in LogHandlers by @ktoso in https://github.com/apple/swift-log/pull/238

Other changes

• [docs] Minimal docc setup and landing page by @ktoso in https://github.com/apple/swift-log/pull/226
• =docc Make docs use symbol references by @ktoso in https://github.com/apple/swift-log/pull/230
• =docc Move to multiple Package.swift files by @ktoso in https://github.com/apple/swift-log/pull/231
• Undo 5.7 package files, not needed yet by @ktoso in https://github.com/apple/swift-log/pull/232
• Update README: Add missing Source param by @Rusik in https://github.com/apple/swift-log/pull/233
• Fix build for wasm by @ahti in https://github.com/apple/swift-log/pull/236
• Add .spi.yml for Swift Package Index DocC support by @yim-lee in https://github.com/apple/swift-log/pull/240
• Fixes link to Supabase repository in README.md by @timobollwerk in https://github.com/apple/swift-log/pull/245

New Contributors

• @Rusik made their first contribution in https://github.com/apple/swift-log/pull/233
• @ahti made their first contribution in https://github.com/apple/swift-log/pull/236
• @timobollwerk made their first contribution in https://github.com/apple/swift-log/pull/245

Full Changelog: https://github.com/apple/swift-log/compare/1.4.4...1.5.0