Improve the instructions for enabling strict concurrency in SwiftPM.

Author: hborla

documentation/concurrency/index.md

@@ -8,29 +8,52 @@ Data-race safety in the Swift 6 language mode is designed for incremental migrat
 
 Complete data-race safety checking can be enabled as warnings in the Swift 5 language mode using the `-strict-concurrency` compiler flag.
 
-## At the command line
+## Using the Swift compiler
 
 To enable complete concurrency checking when running `swift` or `swiftc` directly at the command line, pass `-strict-concurrency=complete`:
 
 ```
 ~ swift -strict-concurrency=complete main.swift
 ```
 
-## In a Swift package manifest
+## Using SwiftPM
+
+### In a SwiftPM command-line invocation
+
+`-strict-concurrency=complete` can be passed in a Swift package manager command-line invocation using the `-Xswiftc` flag:
+
+```
+~ swift build -Xswiftc -strict-concurrency=complete
+~ swift test -Xswiftc -strict-concurrency=complete
+```
+
+This can be useful to gauge the amount of concurrency warnings before adding the flag permanently in the package manifest as described in the following section.
+
+### In a SwiftPM package manifest
 
 To enable complete concurrency checking for a target in a Swift package using Swift 5.9 or Swift 5.10 tools, use [`SwiftSetting.enableExperimentalFeature`](https://developer.apple.com/documentation/packagedescription/swiftsetting/enableexperimentalfeature(_:_:)) in the Swift settings for the given target:
 
 ```swift
-swiftSettings: [.enableExperimentalFeature("StrictConcurrency")]
+.target(
+  name: "MyTarget",
+  swiftSettings: [
+    .enableExperimentalFeature("StrictConcurrency")
+  ]
+)
 ```
 
 When using Swift 6.0 tools or later, use [`SwiftSetting.enableUpcomingFeature`](https://developer.apple.com/documentation/packagedescription/swiftsetting/enableupcomingfeature(_:_:)) in the Swift settings for the given target:
 
 ```swift
-swiftSettings: [.enableUpcomingFeature("StrictConcurrency")]
+.target(
+  name: "MyTarget",
+  swiftSettings: [
+    .enableUpcomingFeature("StrictConcurrency")
+  ]
+)
 ```
 
-## In Xcode
+## Using Xcode
 
 To enable complete concurrency checking in an Xcode project, set the "Swift Strict Concurrency" setting to "Complete" in the Xcode build settings. Alternatively, you can set `SWIFT_STRICT_CONCURRENCY` to `complete` in an xcconfig file: