SR-12050: lldb error: could not build C module 'CNIOBoringSSLShims' (Linux 5.1.3) when debugging (#3215)

When invoking the Swift compiler, SwiftPM was passing search paths to C headers as "-I" arguments.  But it wasn't prefixing them with "-Xcc" so they were being interpreted by the Swift driver and not Clang.  This meant that they weren't recorded as serialized import paths in the AST.  It isn't fully clear why they are needed when building the module in response to the debugger or REPL but not when building using the compiler, but it is clear that these are C header search paths and not Swift module search paths, so they should indeed be passed using "-Xcc" prefixes.

rdar://58709835

Author: abertelrud

Sources/Build/BuildPlan.swift

@@ -1668,15 +1668,15 @@ public class BuildPlan {
                 guard let moduleMap = target.moduleMap else { break }
                 swiftTarget.additionalFlags += [
                     "-Xcc", "-fmodule-map-file=\(moduleMap.pathString)",
-                    "-I", target.clangTarget.includeDir.pathString,
+                    "-Xcc", "-I", "-Xcc", target.clangTarget.includeDir.pathString,
                 ]
             case let target as SystemLibraryTarget:
                 swiftTarget.additionalFlags += ["-Xcc", "-fmodule-map-file=\(target.moduleMapPath.pathString)"]
                 swiftTarget.additionalFlags += pkgConfig(for: target).cFlags
             case let target as BinaryTarget:
                 if let library = xcFrameworkLibrary(for: target) {
                     if let headersPath = library.headersPath {
-                        swiftTarget.additionalFlags += ["-I", headersPath.pathString]
+                        swiftTarget.additionalFlags += ["-Xcc", "-I", "-Xcc", headersPath.pathString]
                     }
                     swiftTarget.libraryBinaryPaths.insert(library.binaryPath)
                 }

Tests/BuildTests/BuildPlanTests.swift

@@ -774,7 +774,7 @@ final class BuildPlanTests: XCTestCase {
         XCTAssertEqual(lib.moduleMap, AbsolutePath("/path/to/build/debug/lib.build/module.modulemap"))
 
         let exe = try result.target(for: "exe").swiftTarget().compileArguments()
-        XCTAssertMatch(exe, ["-swift-version", "4", "-enable-batch-mode", "-Onone", "-enable-testing", "-g", .equal(j), "-DSWIFT_PACKAGE", "-DDEBUG","-Xcc", "-fmodule-map-file=/path/to/build/debug/lib.build/module.modulemap", "-I", "/Pkg/Sources/lib/include", "-module-cache-path", "/path/to/build/debug/ModuleCache", .anySequence])
+        XCTAssertMatch(exe, ["-swift-version", "4", "-enable-batch-mode", "-Onone", "-enable-testing", "-g", .equal(j), "-DSWIFT_PACKAGE", "-DDEBUG","-Xcc", "-fmodule-map-file=/path/to/build/debug/lib.build/module.modulemap", "-Xcc", "-I", "-Xcc", "/Pkg/Sources/lib/include", "-module-cache-path", "/path/to/build/debug/ModuleCache", .anySequence])
 
       #if os(macOS)
         XCTAssertEqual(try result.buildProduct(for: "exe").linkArguments(), [
@@ -1610,7 +1610,7 @@ final class BuildPlanTests: XCTestCase {
         XCTAssertEqual(lib.moduleMap, AbsolutePath("/path/to/build/debug/lib.build/module.modulemap"))
 
         let exe = try result.target(for: "exe").swiftTarget().compileArguments()
-        XCTAssertMatch(exe, ["-swift-version", "4", "-enable-batch-mode", "-Onone", "-enable-testing", "-g", .equal(j), "-DSWIFT_PACKAGE", "-DDEBUG","-Xcc", "-fmodule-map-file=/path/to/build/debug/lib.build/module.modulemap", "-I", "/Pkg/Sources/lib/include", "-module-cache-path", "/path/to/build/debug/ModuleCache", .anySequence])
+        XCTAssertMatch(exe, ["-swift-version", "4", "-enable-batch-mode", "-Onone", "-enable-testing", "-g", .equal(j), "-DSWIFT_PACKAGE", "-DDEBUG","-Xcc", "-fmodule-map-file=/path/to/build/debug/lib.build/module.modulemap", "-Xcc", "-I", "-Xcc", "/Pkg/Sources/lib/include", "-module-cache-path", "/path/to/build/debug/ModuleCache", .anySequence])
 
         XCTAssertEqual(try result.buildProduct(for: "exe").linkArguments(), [
             "/fake/path/to/swiftc",
@@ -1681,7 +1681,7 @@ final class BuildPlanTests: XCTestCase {
                 "-swift-version", "4", "-enable-batch-mode", "-Onone", "-enable-testing", "-g",
                 .equal(j), "-DSWIFT_PACKAGE", "-DDEBUG","-Xcc",
                 "-fmodule-map-file=/path/to/build/debug/lib.build/module.modulemap",
-                "-I", "/Pkg/Sources/lib/include",
+                "-Xcc", "-I", "-Xcc", "/Pkg/Sources/lib/include",
                 "-module-cache-path", "/path/to/build/debug/ModuleCache", .anySequence
             ]
         )