Add global RuntimeConfiguration (#6)

# Add global RuntimeConfiguration

## ♻️ Current situation & Problem
Within the `SpeziChat` project, we discovered the need for a global
runtime configuration object that holds certain testing support
variables (e.g. about the debug mode).


## ⚙️ Release Notes 
- Add global `RuntimeConfiguration` accessible via the `TestingSupport`
SPI target.


## 📚 Documentation
Added proper documentation


## ✅ Testing
No new test cases written


## 📝 Code of Conduct & Contributing Guidelines 

By submitting creating this pull request, you agree to follow our [Code
of
Conduct](https://github.com/StanfordSpezi/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/StanfordSpezi/.github/blob/main/CONTRIBUTING.md):
- [x] I agree to follow the [Code of
Conduct](https://github.com/StanfordSpezi/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/StanfordSpezi/.github/blob/main/CONTRIBUTING.md).

CITATION.cff

@@ -15,6 +15,9 @@ authors:
 - family-names: "Bauer"
   given-names: "Andreas"
   orcid: "https://orcid.org/0000-0002-1680-237X"
+- family-names: "Zagar"
+  given-names: "Philipp"
+  orcid: "https://orcid.org/0009-0001-5934-2078"
 title: "SpeziFoundation"
 doi: 10.5281/zenodo.10077558
 url: "https://github.com/StanfordSpezi/SpeziFoundation"

CONTRIBUTORS.md

@@ -15,3 +15,4 @@ SpeziFoundation contributors
 
 * [Paul Schmiedmayer](https://github.com/PSchmiedmayer)
 * [Andreas Bauer](https://github.com/Supereg)
+* [Philipp Zagar](https://github.com/philippzagar)

Package.swift

@@ -25,7 +25,10 @@ let package = Package(
     ],
     targets: [
         .target(
-            name: "SpeziFoundation"
+            name: "SpeziFoundation",
+            swiftSettings: [
+                .enableExperimentalFeature("StrictConcurrency")
+            ]
         ),
         .testTarget(
             name: "SpeziFoundationTests",

Sources/SpeziFoundation/RuntimeConfig/RuntimeConfig.swift

@@ -0,0 +1,42 @@
+//
+// This source file is part of the Stanford Spezi open-source project
+//
+// SPDX-FileCopyrightText: 2023 Stanford University and the project authors (see CONTRIBUTORS.md)
+//
+// SPDX-License-Identifier: MIT
+//
+
+import Foundation
+
+
+/// Holds globally accessible runtime testing support configurations.
+///
+/// The ``RuntimeConfig`` stores configurations of the current runtime environment for testing support.
+/// 
+/// - Important: ``RuntimeConfig`` is only exposed as the [System Programming Interface (SPI)](https://blog.eidinger.info/system-programming-interfaces-spi-in-swift-explained)
+/// target `TestingSupport`, therefore requiring to state the SPI target upon importing the `SpeziFoundation` target via `@_spi(TestingSupport)`.
+///
+/// ### Usage
+///
+/// One is able to access the ``RuntimeConfig`` from the `TestingSupport` SPI target as shown below.
+///
+/// ```swift
+/// // Import the entire target, including the `TestingSupport` SPI target.
+/// @_spi(TestingSupport) import SpeziFoundation
+///
+/// if RuntimeConfig.testMode { /* ... */ }
+/// ```
+///
+/// As of Swift 5.8, one is able to only import the SPI target, without any other parts of the overall SPM target,
+/// by setting the `-experimental-spi-only-imports` Swift compiler flag and using the `@_spiOnly` notation upon target import.
+///
+/// ```swift
+/// // Import only the `TestingSupport` SPI target.
+/// @_spiOnly import SpeziFoundation
+///
+/// if RuntimeConfig.testMode { /* ... */ }
+/// ```
+@_spi(TestingSupport)
+public struct RuntimeConfig: Sendable {
+    public static let testMode: Bool = ProcessInfo.processInfo.arguments.contains("--testMode")
+}

Sources/SpeziFoundation/SpeziFoundation.docc/SpeziFoundation.md

@@ -22,3 +22,7 @@ Spezi Foundation provides a base layer of functionality useful in many applicati
 
 - ``AnyArray``
 - ``AnyOptional``
+
+### Runtime Configuration
+
+- `RuntimeConfig` (exposed via the `TestingSupport` SPI target)