[Build] Emit BuildPlan diagnostics to DiagnosticsEngine

<rdar://problem/41342798> SwiftPM is not warning about non whitelisted flags
<rdar://problem/40260898> [SR-7690]: SwiftPM does not print any warnings which is must be emitted at all during `build plan` including message about pkg-config provider hinting feature

Author: aciidgh

Sources/Build/BuildPlan.swift

@@ -524,13 +524,6 @@ public final class ProductBuildDescription {
     }
 }
 
-/// The delegate interface used by the build plan to report status information.
-public protocol BuildPlanDelegate: class {
-
-    /// The build plan emitted this warning.
-    func warning(message: String)
-}
-
 /// A build plan for a package graph.
 public class BuildPlan {
 
@@ -573,9 +566,6 @@ public class BuildPlan {
         return AnySequence(productMap.values)
     }
 
-    /// Build plan delegate.
-    public let delegate: BuildPlanDelegate?
-
     /// The filesystem to operate on.
     let fileSystem: FileSystem
 
@@ -587,13 +577,11 @@ public class BuildPlan {
         buildParameters: BuildParameters,
         graph: PackageGraph,
         diagnostics: DiagnosticsEngine,
-        delegate: BuildPlanDelegate? = nil,
         fileSystem: FileSystem = localFileSystem
     ) throws {
         self.buildParameters = buildParameters
         self.graph = graph
         self.diagnostics = diagnostics
-        self.delegate = delegate
         self.fileSystem = fileSystem
 
         // Create build target description for each target which we need to plan.
@@ -828,10 +816,9 @@ public class BuildPlan {
         }
         // If there is no pc file on system and we have an available provider, emit a warning.
         if let provider = result.provider, result.couldNotFindConfigFile {
-            delegate?.warning(message: "you may be able to install \(result.pkgConfigName) using your system-packager:")
-            delegate?.warning(message: provider.installText)
+            diagnostics.emit(data: PkgConfigHintDiagnostic(pkgConfigName: result.pkgConfigName, installText: provider.installText))
         } else if let error = result.error {
-            delegate?.warning(message: "error while trying to use pkgConfig flags for \(target.name): \(error)")
+            diagnostics.emit(error)
         }
         pkgConfigCache[target] = (result.cFlags, result.libs)
         return pkgConfigCache[target]!
@@ -840,3 +827,18 @@ public class BuildPlan {
     /// Cache for pkgConfig flags.
     private var pkgConfigCache = [SystemLibraryTarget: (cFlags: [String], libs: [String])]()
 }
+
+public struct PkgConfigHintDiagnostic: DiagnosticData {
+    public static let id = DiagnosticID(
+        type: PkgConfigHintDiagnostic.self,
+        name: "org.swift.diags.pkg-config-hint",
+        defaultBehavior: .warning,
+        description: {
+            $0 <<< "you may be able to install" <<< { $0.pkgConfigName } <<< "using your system-packager:\n"
+            $0 <<< { $0.installText }
+        }
+    )
+
+    let pkgConfigName: String
+    let installText: String
+}

Sources/Commands/SwiftTestTool.swift

@@ -30,6 +30,17 @@ struct SpecifierDeprecatedDiagnostic: DiagnosticData {
     )
 }
 
+struct LinuxTestDiscoveryDiagnostic: DiagnosticData {
+    static let id = DiagnosticID(
+        type: LinuxTestDiscoveryDiagnostic.self,
+        name: "org.swift.diags.linux-test-discovery",
+        defaultBehavior: .warning,
+        description: {
+            $0 <<< "can't discover tests on Linux; please use this option on macOS instead"
+        }
+    )
+}
+
 /// Diagnostic data for zero --filter matches.
 struct NoMatchingTestsWarning: DiagnosticData {
     static let id = DiagnosticID(
@@ -185,7 +196,7 @@ public class SwiftTestTool: SwiftTool<TestToolOptions> {
 
         case .generateLinuxMain:
           #if os(Linux)
-            warning(message: "can't discover new tests on Linux; please use this option on macOS instead")
+            diagnostics.emit(data: LinuxTestDiscoveryDiagnostic())
           #endif
             let graph = try loadPackageGraph()
             let testPath = try buildTestsIfNeeded(options, graph: graph)

Sources/Commands/SwiftTool.swift

@@ -572,11 +572,6 @@ public class SwiftTool<Options: ToolOptions> {
 
     /// Build a subset of products and targets using swift-build-tool.
     func build(plan: BuildPlan, subset: BuildSubset) throws {
-        guard !plan.graph.rootPackages[0].targets.isEmpty else {
-            warning(message: "no targets to build in package")
-            return
-        }
-
         guard let llbuildTargetName = subset.llbuildTargetName(for: plan.graph, diagnostics: diagnostics) else {
             return
         }
@@ -738,13 +733,6 @@ enum BuildSubset {
     case target(String)
 }
 
-extension SwiftTool: BuildPlanDelegate {
-    public func warning(message: String) {
-        // FIXME: Coloring would be nice.
-        print("warning: " + message)
-    }
-}
-
 extension BuildSubset {
     /// Returns the name of the llbuild target that corresponds to the build subset.
     func llbuildTargetName(for graph: PackageGraph, diagnostics: DiagnosticsEngine) -> String? {

Tests/BuildTests/BuildPlanTests.swift

@@ -827,6 +827,40 @@ final class BuildPlanTests: XCTestCase {
                 graph: graph, diagnostics: diagnostics, fileSystem: fs)
         }
     }
+
+    func testPkgConfigError() throws {
+        let fileSystem = InMemoryFileSystem(emptyFiles:
+            "/A/Sources/ATarget/foo.swift",
+            "/A/Sources/BTarget/module.modulemap"
+        )
+
+        let diagnostics = DiagnosticsEngine()
+        let graph = loadPackageGraph(root: "/A", fs: fileSystem, diagnostics: diagnostics,
+            manifests: [
+                Manifest.createV4Manifest(
+                    name: "A",
+                    path: "/A",
+                    url: "/A",
+                    targets: [
+                        TargetDescription(name: "ATarget", dependencies: ["BTarget"]),
+                        TargetDescription(
+                            name: "BTarget",
+                            type: .system,
+                            pkgConfig: "BTarget",
+                            providers: [
+                                .brew(["BTarget"]),
+                                .apt(["BTarget"]),
+                            ]
+                        )
+                    ]),
+            ]
+        )
+
+        _ = try BuildPlan(buildParameters: mockBuildParameters(),
+            graph: graph, diagnostics: diagnostics, fileSystem: fileSystem)
+
+        XCTAssertTrue(diagnostics.diagnostics.contains(where: { ($0.data is PkgConfigHintDiagnostic) }))
+    }
 }
 
 // MARK:- Test Helpers

Tests/BuildTests/XCTestManifests.swift

@@ -14,6 +14,7 @@ extension BuildPlanTests {
         ("testDynamicProducts", testDynamicProducts),
         ("testExecAsDependency", testExecAsDependency),
         ("testNonReachableProductsAndTargets", testNonReachableProductsAndTargets),
+        ("testPkgConfigError", testPkgConfigError),
         ("testSwiftCMixed", testSwiftCMixed),
         ("testSystemPackageBuildPlan", testSystemPackageBuildPlan),
         ("testTestModule", testTestModule),