Implement system dependency checking plugin to fix terrible SwiftPM e…

…rrors for missing system dependencies

Package.swift

@@ -77,7 +77,8 @@ let package = Package(
         .target(name: "AppKitBackend", dependencies: ["SwiftCrossUI"]),
         .target(
             name: "QtBackend",
-            dependencies: ["SwiftCrossUI", .product(name: "Qlift", package: "qlift")]
+            dependencies: ["SwiftCrossUI", .product(name: "Qlift", package: "qlift")],
+            plugins: ["DependencyCheckingPlugin"]
         ),
         .target(
             name: "CursesBackend",
@@ -91,7 +92,11 @@ let package = Package(
                 .product(name: "CLVGL", package: "LVGLSwift"),
             ]
         ),
-        .target(name: "GtkBackend", dependencies: ["SwiftCrossUI", "Gtk", "CGtk"]),
+        .target(
+            name: "GtkBackend",
+            dependencies: ["SwiftCrossUI", "Gtk", "CGtk"],
+            plugins: ["DependencyCheckingPlugin"]
+        ),
         .systemLibrary(
             name: "CGtk",
             pkgConfig: "gtk4",
@@ -112,6 +117,10 @@ let package = Package(
                 "XMLCoder", .product(name: "SwiftSyntaxBuilder", package: "swift-syntax"),
             ]
         ),
+        .plugin(
+            name: "DependencyCheckingPlugin",
+            capability: .buildTool()
+        ),
     ]
 )
 

Plugins/DependencyCheckingPlugin/DependencyCheckingPlugin.swift

@@ -0,0 +1,98 @@
+import Foundation
+import PackagePlugin
+
+enum DependencyError: Error, CustomStringConvertible {
+    case missingSystemDependency(String)
+
+    var description: String {
+        switch self {
+            case .missingSystemDependency(let name):
+                Diagnostics.error("Missing '\(name)' system dependency.")
+
+                #if os(Windows)
+                    return "No installation instructions for Windows."
+                #else
+                    let installationInstructions: String?
+                    let packageManager: String
+                    #if os(macOS)
+                        packageManager = "brew"
+                        switch name {
+                            case "CGtk":
+                                installationInstructions = "brew install gtk4"
+                            case "Qt5Widgets":
+                                installationInstructions = "brew install qt@5 && brew link qt@5"
+                            default:
+                                installationInstructions = nil
+                        }
+                    #elseif os(Linux)
+                        packageManager = "apt"
+                        switch name {
+                            case "CGtk":
+                                installationInstructions = "apt install libgtk-4-dev clang"
+                            case "Qt5Widgets":
+                                installationInstructions = "apt install qt5-default"
+                            default:
+                                installationInstructions = nil
+                        }
+                    #endif
+
+                    let instructions =
+                        installationInstructions
+                        ?? "Missing installation instructions for '\(name)', please open an issue at https://github.com/stackotter/swift-cross-ui"
+                    return "To install with \(packageManager): \(instructions)"
+                #endif
+        }
+    }
+}
+
+@main
+struct DependencyCheckingPlugin: BuildToolPlugin {
+    func createBuildCommands(context: PluginContext, target: Target) throws -> [Command] {
+        if ProcessInfo.processInfo.environment["SWIFTCROSSUI_SKIP_DEP_CHECK"] == "1" {
+            return []
+        }
+
+        #if os(Windows)
+            Diagnostics.warning(
+                "Dependency checking not implemented on Windows. Set SWIFTCROSSUI_SKIP_DEP_CHECK=1 to disable this warning"
+            )
+            return []
+        #endif
+
+        for dependency in target.recursiveTargetDependencies {
+            try check(dependency)
+        }
+
+        return []
+    }
+
+    func check(_ target: Target) throws {
+        // TODO: Add hardcoded checks for curses and lvgl
+        if let systemDependency = target as? SystemLibraryTarget {
+            guard let pkgConfigName = systemDependency.pkgConfig else {
+                Diagnostics.warning(
+                    "Dependency checking not implemented for system libraries without pkgConfig names, manually implement a check for '\(systemDependency.name)'"
+                )
+                return
+            }
+
+            try checkPkgConfig(pkgConfigName)
+        }
+    }
+
+    func checkPkgConfig(_ name: String) throws {
+        let process = Process()
+        process.executableURL = URL(fileURLWithPath: "/usr/bin/env")
+        process.arguments = [
+            "pkg-config",
+            name,
+        ]
+
+        try process.run()
+        process.waitUntilExit()
+
+        if process.terminationStatus != 0 {
+            throw DependencyError.missingSystemDependency(name)
+        }
+    }
+}

format_and_lint.sh

@@ -1,2 +1,2 @@
-swift format format --in-place --recursive --configuration .swift-format Sources Examples
+swift format format --in-place --recursive --configuration .swift-format Sources Examples/Sources Plugins
 swiftlint lint --quiet