[Explicit Module Builds] Move generation of explicit auto-link flags to a toolchain-specific method

This way we can adopt a feature of a specific platform's linker separately from the others

Author: artemcm

Sources/SwiftDriver/ExplicitModuleBuilds/ExplicitDependencyBuildPlanner.swift

@@ -421,17 +421,7 @@ public typealias ExternalTargetModuleDetailsMap = [ModuleDependencyId: ExternalT
         allLinkLibraries.append(linkLibrary)
       }
     }
-
-    for linkLibrary in allLinkLibraries {
-      if !linkLibrary.isFramework {
-        commandLine.appendFlag("-l\(linkLibrary.linkName)")
-      } else {
-        commandLine.appendFlag(.Xlinker)
-        commandLine.appendFlag("-framework")
-        commandLine.appendFlag(.Xlinker)
-        commandLine.appendFlag(linkLibrary.linkName)
-      }
-    }
+    toolchain.addAutoLinkFlags(for: allLinkLibraries, to: &commandLine)
   }
 
   /// Resolve all module dependencies of the main module and add them to the lists of

Sources/SwiftDriver/Toolchains/DarwinToolchain.swift

@@ -114,6 +114,20 @@ public final class DarwinToolchain: Toolchain {
     }
   }
 
+  public func addAutoLinkFlags(for linkLibraries: [LinkLibraryInfo], to commandLine: inout [Job.ArgTemplate]) {
+    for linkLibrary in linkLibraries {
+      if !linkLibrary.isFramework {
+        commandLine.appendFlag(.Xlinker)
+        commandLine.appendFlag("-possible-l\(linkLibrary.linkName)")
+      } else {
+        commandLine.appendFlag(.Xlinker)
+        commandLine.appendFlag("-possible_framework")
+        commandLine.appendFlag(.Xlinker)
+        commandLine.appendFlag(linkLibrary.linkName)
+      }
+    }
+  }
+
   public func defaultSDKPath(_ target: Triple?) throws -> AbsolutePath? {
     let hostIsMacOS: Bool
     #if os(macOS)

Sources/SwiftDriver/Toolchains/GenericUnixToolchain.swift

@@ -78,6 +78,12 @@ public final class GenericUnixToolchain: Toolchain {
     }
   }
 
+  public func addAutoLinkFlags(for linkLibraries: [LinkLibraryInfo], to commandLine: inout [Job.ArgTemplate]) {
+    for linkLibrary in linkLibraries {
+      commandLine.appendFlag("-l\(linkLibrary.linkName)")
+    }
+  }
+
   /// Retrieve the absolute path for a given tool.
   public func getToolPath(_ tool: Tool) throws -> AbsolutePath {
     // Check the cache

Sources/SwiftDriver/Toolchains/Toolchain.swift

@@ -115,6 +115,9 @@ public protocol Toolchain {
   /// Constructs a proper output file name for a linker product.
   func makeLinkerOutputFilename(moduleName: String, type: LinkOutputType) -> String
 
+  /// Adds linker flags corresponding to the specified set of link libraries
+  func addAutoLinkFlags(for linkLibraries: [LinkLibraryInfo], to commandLine: inout [Job.ArgTemplate])
+
   /// Perform platform-specific argument validation.
   func validateArgs(_ parsedOptions: inout ParsedOptions,
                     targetTriple: Triple,

Sources/SwiftDriver/Toolchains/WebAssemblyToolchain.swift

@@ -79,6 +79,12 @@ public final class WebAssemblyToolchain: Toolchain {
     }
   }
 
+  public func addAutoLinkFlags(for linkLibraries: [LinkLibraryInfo], to commandLine: inout [Job.ArgTemplate]) {
+    for linkLibrary in linkLibraries {
+      commandLine.appendFlag("-l\(linkLibrary.linkName)")
+    }
+  }
+
   /// Retrieve the absolute path for a given tool.
   public func getToolPath(_ tool: Tool) throws -> AbsolutePath {
     // Check the cache

Sources/SwiftDriver/Toolchains/WindowsToolchain.swift

@@ -113,6 +113,12 @@ extension WindowsToolchain.ToolchainValidationError {
     }
   }
 
+  public func addAutoLinkFlags(for linkLibraries: [LinkLibraryInfo], to commandLine: inout [Job.ArgTemplate]) {
+    for linkLibrary in linkLibraries {
+      commandLine.appendFlag("-l\(linkLibrary.linkName)")
+    }
+  }
+
   public func defaultSDKPath(_ target: Triple?) throws -> AbsolutePath? {
     // TODO(compnerd): replicate the SPM processing of the SDKInfo.plist
     if let SDKROOT = env["SDKROOT"] {

Tests/SwiftDriverTests/ExplicitModuleBuildTests.swift

@@ -500,6 +500,61 @@ final class ExplicitModuleBuildTests: XCTestCase {
     }
   }
 
+  func testExplicitLinkFlags() throws {
+    try withTemporaryDirectory { path in
+      let (_, _, toolchain, _) = try getDriverArtifactsForScanning()
+
+      let main = path.appending(component: "testExplicitLinkLibraries.swift")
+      try localFileSystem.writeFileContents(main, bytes:
+        """
+        import C;import E;import G;
+        """
+      )
+
+      let cHeadersPath: AbsolutePath =
+      try testInputsPath.appending(component: "ExplicitModuleBuilds")
+        .appending(component: "CHeaders")
+      let bridgingHeaderpath: AbsolutePath =
+      cHeadersPath.appending(component: "Bridging.h")
+      let swiftModuleInterfacesPath: AbsolutePath =
+      try testInputsPath.appending(component: "ExplicitModuleBuilds")
+        .appending(component: "Swift")
+      let sdkArgumentsForTesting = (try? Driver.sdkArgumentsForTesting()) ?? []
+
+      // Verify the dependency scanner supports link library reporting
+      let dependencyOracle = InterModuleDependencyOracle()
+      let scanLibPath = try XCTUnwrap(toolchain.lookupSwiftScanLib())
+      try dependencyOracle.verifyOrCreateScannerInstance(swiftScanLibPath: scanLibPath)
+      guard try dependencyOracle.supportsLinkLibraries() else {
+        throw XCTSkip("libSwiftScan does not support link library reporting.")
+      }
+
+      let args = ["swiftc",
+                  "-I", cHeadersPath.nativePathString(escaped: true),
+                  "-I", swiftModuleInterfacesPath.nativePathString(escaped: true),
+                  "-explicit-module-build", "-explicit-auto-linking",
+                  "-import-objc-header", bridgingHeaderpath.nativePathString(escaped: true),
+                  main.nativePathString(escaped: true)] + sdkArgumentsForTesting
+      var driver = try Driver(args: args)
+      let jobs = try driver.planBuild()
+
+      let linkJob = try jobs.findJob(.link)
+      if driver.targetTriple.isDarwin {
+        XCTAssertTrue(linkJob.commandLine.contains("-possible-lswiftCore"))
+        XCTAssertTrue(linkJob.commandLine.contains("-possible-lswift_StringProcessing"))
+        XCTAssertTrue(linkJob.commandLine.contains("-possible-lobjc"))
+        XCTAssertTrue(linkJob.commandLine.contains("-possible-lswift_Concurrency"))
+        XCTAssertTrue(linkJob.commandLine.contains("-possible-lswiftSwiftOnoneSupport"))
+      } else {
+        XCTAssertTrue(linkJob.commandLine.contains("-lswiftCore"))
+        XCTAssertTrue(linkJob.commandLine.contains("-lswift_StringProcessing"))
+        XCTAssertTrue(linkJob.commandLine.contains("-lobjc"))
+        XCTAssertTrue(linkJob.commandLine.contains("-lswift_Concurrency"))
+        XCTAssertTrue(linkJob.commandLine.contains("-lswiftSwiftOnoneSupport"))
+      }
+    }
+  }
+
   func testExplicitLinkLibraries() throws {
     try withTemporaryDirectory { path in
       let (_, _, toolchain, _) = try getDriverArtifactsForScanning()