From f1db43864cdd6470ea213e6a1f8441920f635489 Mon Sep 17 00:00:00 2001
From: Lawrence Forooghian <lawrence@forooghian.com>
Date: Mon, 5 Aug 2024 13:06:06 +0100
Subject: [PATCH] try generating matrices

---
 .github/workflows/check.yaml      | 36 ++++++++++++++-----------------
 Sources/BuildTool/BuildTool.swift | 30 +++++++++++++++++++++++++-
 2 files changed, 45 insertions(+), 21 deletions(-)

diff --git a/.github/workflows/check.yaml b/.github/workflows/check.yaml
index 7b891cf..7ae3ec0 100644
--- a/.github/workflows/check.yaml
+++ b/.github/workflows/check.yaml
@@ -33,17 +33,23 @@ jobs:
       - run: script/format/check
       - run: script/lint/check
 
+  generate-matrices:
+    runs-on: macos-latest
+    outputs:
+      matrix: ${{ steps.generation-step.outputs.matrix }}
+    steps:
+      - uses: actions/checkout@v4
+      - id: generation-step
+        run: swift run BuildTool generate-matrices >> $GITHUB_OUTPUT
+
   check-spm:
     name: SPM (Xcode ${{ matrix.tooling.xcode-version }}, Swift ${{ matrix.tooling.swift-version }})
     runs-on: macos-latest
+    needs: generate-matrices
     strategy:
       fail-fast: false
-      matrix:
-        tooling:
-          - xcode-version: 15.3
-            swift-version: 5
-          - xcode-version: 16-beta
-            swift-version: 6
+      matrix: ${{ fromJson(needs.generate-matrices.outputs.matrix) }}
+
     steps:
       - uses: actions/checkout@v4
       - uses: maxim-lobanov/setup-xcode@v1
@@ -57,16 +63,11 @@ jobs:
   check-xcode:
     name: Library, ${{matrix.platform}} (Xcode ${{ matrix.tooling.xcode-version }}, Swift ${{ matrix.tooling.swift-version }})
     runs-on: macos-latest
+    needs: generate-matrices
 
     strategy:
       fail-fast: false
-      matrix:
-        tooling:
-          - xcode-version: 15.3
-            swift-version: 5
-          - xcode-version: 16-beta
-            swift-version: 6
-        platform: [macOS, iOS, tvOS]
+      matrix: ${{ fromJson(needs.generate-matrices.outputs.matrix) }}
 
     steps:
       - uses: actions/checkout@v4
@@ -80,16 +81,11 @@ jobs:
   check-example-app:
     name: Example app, ${{matrix.platform}} (Xcode ${{ matrix.tooling.xcode-version }}, Swift ${{ matrix.tooling.swift-version }})
     runs-on: macos-latest
+    needs: generate-matrices
 
     strategy:
       fail-fast: false
-      matrix:
-        tooling:
-          - xcode-version: 15.3
-            swift-version: 5
-          - xcode-version: 16-beta
-            swift-version: 6
-        platform: [macOS, iOS, tvOS]
+      matrix: ${{ fromJson(needs.generate-matrices.outputs.matrix) }}
 
     steps:
       - uses: actions/checkout@v4
diff --git a/Sources/BuildTool/BuildTool.swift b/Sources/BuildTool/BuildTool.swift
index 9c219b3..893ce72 100644
--- a/Sources/BuildTool/BuildTool.swift
+++ b/Sources/BuildTool/BuildTool.swift
@@ -67,7 +67,13 @@ enum Error: Swift.Error {
 @main
 @available(macOS 14, *)
 struct BuildTool: ParsableCommand {
-    static let configuration = CommandConfiguration(subcommands: [BuildAndTestLibrary.self, BuildExampleApp.self])
+    static let configuration = CommandConfiguration(
+        subcommands: [
+            BuildAndTestLibrary.self,
+            BuildExampleApp.self,
+            GenerateMatrices.self,
+        ]
+    )
 }
 
 // TODO: Is there a better way to make sure that this script has access to macOS APIs that are more recent than the package’s deployment target?
@@ -91,6 +97,28 @@ struct BuildAndTestLibrary: ParsableCommand {
     }
 }
 
+struct GenerateMatrices: ParsableCommand {
+    mutating func run() throws {
+        let matrix: [String: Any] = [
+            "tooling": [
+                [
+                    "xcode-version": "15.3",
+                    "swift-version": 5,
+                ],
+                [
+                    "xcode-version": "16-beta",
+                    "swift-version": 6,
+                ],
+            ],
+            "platform": Platform.allCases.map(\.rawValue),
+        ]
+
+        // I’m assuming the JSONSerialization output has no newlines
+        let keyValue = try "matrix=\(String(decoding: JSONSerialization.data(withJSONObject: matrix), as: UTF8.self))"
+        print(keyValue)
+    }
+}
+
 @available(macOS 14, *)
 struct BuildExampleApp: ParsableCommand {
     @Option var platform: Platform