Tests: simplify, homogenise path computation

Simply construct he path relative to the root.  Previous changes had
caused divergences as the null coalesced value would never be used in
any case.  Furthermore, this cleanup will work better with the new path
canonicalization for relative paths on Windows.

Author: compnerd

Tests/SwiftDriverTests/ParsableMessageTests.swift

@@ -142,8 +142,7 @@ final class ParsableMessageTests: XCTestCase {
         try withHijackedBufferedErrorStream(in: path) { errorBuffer in
           let resolver = try ArgsResolver(fileSystem: localFileSystem)
 
-          let workdir: AbsolutePath =
-                try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/WorkDir", relativeTo: $0) } ?? AbsolutePath(validating: "/WorkDir")
+          let workdir: AbsolutePath = localFileSystem.currentWorkingDirectory!.appending(components: "WorkDir")
 
           var driver = try Driver(args: ["swiftc", "-o", "test.o",
                                          "main.swift", "test1.swift", "test2.swift",
@@ -170,16 +169,21 @@ final class ParsableMessageTests: XCTestCase {
             "name" : "compile",
           """).count - 1, 3)
 
-          /// One per primary
-          XCTAssertTrue(errorOutput.contains(
-          """
-            "pid" : -1000,
-          """))
 #if os(Windows)
           let mainPath: String = workdir.appending(component: "main.swift").nativePathString(escaped: true)
+          let test1Path: String = workdir.appending(component: "test1.swift").nativePathString(escaped: true)
+          let test2Path: String = workdir.appending(component: "test2.swift").nativePathString(escaped: true)
 #else
           let mainPath: String = workdir.appending(component: "main.swift").pathString.replacingOccurrences(of: "/", with: "\\/")
+          let test1Path: String = workdir.appending(component: "test1.swift").pathString.replacingOccurrences(of: "/", with: "\\/")
+          let test2Path: String = workdir.appending(component: "test2.swift").pathString.replacingOccurrences(of: "/", with: "\\/")
 #endif
+
+          /// One per primary
+          XCTAssertTrue(errorOutput.contains(
+          """
+            "pid" : -1000,
+          """))
           XCTAssertTrue(errorOutput.contains(
           """
             \"inputs\" : [
@@ -190,11 +194,6 @@ final class ParsableMessageTests: XCTestCase {
           """
             "pid" : -1001,
           """))
-#if os(Windows)
-          let test1Path: String = workdir.appending(component: "test1.swift").nativePathString(escaped: true)
-#else
-          let test1Path: String = workdir.appending(component: "test1.swift").pathString.replacingOccurrences(of: "/", with: "\\/")
-#endif
           XCTAssertTrue(errorOutput.contains(
           """
             \"inputs\" : [
@@ -205,11 +204,6 @@ final class ParsableMessageTests: XCTestCase {
           """
             "pid" : -1002,
           """))
-#if os(Windows)
-          let test2Path: String = workdir.appending(component: "test2.swift").nativePathString(escaped: true)
-#else
-          let test2Path: String = workdir.appending(component: "test2.swift").pathString.replacingOccurrences(of: "/", with: "\\/")
-#endif
           XCTAssertTrue(errorOutput.contains(
           """
             \"inputs\" : [

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -284,12 +284,8 @@ final class SwiftDriverTests: XCTestCase {
                    [ TypedVirtualPath(file: VirtualPath.relative(RelativePath("a.swift")).intern(), type: .swift),
                      TypedVirtualPath(file: VirtualPath.absolute(AbsolutePath("/tmp/b.swift")).intern(), type: .swift) ])
 
-    let workingDirectory =
-        try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/wobble", relativeTo: $0) }
-                ?? AbsolutePath(validating: "/Foo/Bar")
-    let tempDirectory =
-        try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/tmp", relativeTo: $0) }
-                ?? AbsolutePath(validating: "/Foo/Bar")
+    let workingDirectory = localFileSystem.currentWorkingDirectory!.appending(components: "wobble")
+    let tempDirectory = localFileSystem.currentWorkingDirectory!.appending(components: "tmp")
 
     let driver2 = try Driver(args: ["swiftc", "a.swift", "-working-directory", workingDirectory.pathString, rebase("b.swift", at: tempDirectory)])
     XCTAssertEqual(driver2.inputFiles,
@@ -649,9 +645,7 @@ final class SwiftDriverTests: XCTestCase {
     XCTAssertEqual(plannedJobs[2].outputs.first!.file, VirtualPath.relative(RelativePath(executableName("Test"))))
 
     // Forwarding of arguments.
-    let workingDirectory =
-        try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/tmp", relativeTo: $0) }
-                ?? AbsolutePath(validating: "/Foo/Bar")
+    let workingDirectory = localFileSystem.currentWorkingDirectory!.appending(components: "tmp")
 
     var driver2 = try Driver(args: ["swiftc", "-color-diagnostics", "foo.swift", "bar.swift", "-working-directory", workingDirectory.pathString, "-api-diff-data-file", "diff.txt", "-Xfrontend", "-HI", "-no-color-diagnostics", "-g"])
     let plannedJobs2 = try driver2.planBuild()
@@ -1097,8 +1091,7 @@ final class SwiftDriverTests: XCTestCase {
       ]
     ]
 
-    let root = try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/foo_root", relativeTo: $0) }
-                    ?? AbsolutePath(validating: "/foo_root")
+    let root = localFileSystem.currentWorkingDirectory!.appending(components: "foo_root")
 
     let resolvedStringyEntries: [String: [FileType: String]] = [
       "": [.swiftDeps: root.appending(components: "foo.build", "master.swiftdeps").pathString],
@@ -2749,8 +2742,7 @@ final class SwiftDriverTests: XCTestCase {
     }
 
     do {
-      let root = try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/foo/bar", relativeTo: $0) }
-                    ?? AbsolutePath(validating: "/foo/bar")
+      let root = localFileSystem.currentWorkingDirectory!.appending(components: "foo", "bar")
 
       var driver = try Driver(args: ["swiftc", "foo.swift", "bar.swift", "-module-name", "Test", "-emit-module-path", rebase("Test.swiftmodule", at: root), "-no-emit-module-separately"])
       let plannedJobs = try driver.planBuild()
@@ -2814,8 +2806,7 @@ final class SwiftDriverTests: XCTestCase {
     envVars["SWIFT_DRIVER_LD_EXEC"] = ld.nativePathString(escaped: false)
 
     do {
-      let root = try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/foo/bar", relativeTo: $0) }
-                    ?? AbsolutePath(validating: "/foo/bar")
+      let root = localFileSystem.currentWorkingDirectory!.appending(components: "foo", "bar")
 
       var driver = try Driver(args: ["swiftc", "foo.swift", "bar.swift", "-module-name", "Test", "-emit-module-path", rebase("Test.swiftmodule", at: root), "-emit-symbol-graph", "-emit-symbol-graph-dir", "/foo/bar/", "-experimental-emit-module-separately", "-emit-library"],
                               env: envVars)
@@ -2837,8 +2828,7 @@ final class SwiftDriverTests: XCTestCase {
     }
 
     do {
-      let root = try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/foo/bar", relativeTo: $0) }
-                    ?? AbsolutePath(validating: "/foo/bar")
+      let root = localFileSystem.currentWorkingDirectory!.appending(components: "foo", "bar")
 
       // We don't expect partial jobs when asking only for the swiftmodule with
       // -experimental-emit-module-separately.
@@ -2886,8 +2876,7 @@ final class SwiftDriverTests: XCTestCase {
   func testEmitModuleSeparatelyWMO() throws {
     var envVars = ProcessEnv.vars
     envVars["SWIFT_DRIVER_LD_EXEC"] = ld.nativePathString(escaped: false)
-    let root = try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/foo/bar", relativeTo: $0) }
-                  ?? AbsolutePath(validating: "/foo/bar")
+    let root = localFileSystem.currentWorkingDirectory!.appending(components: "foo", "bar")
 
     do {
       var driver = try Driver(args: ["swiftc", "foo.swift", "bar.swift", "-module-name", "Test", "-emit-module-path", rebase("Test.swiftmodule", at: root), "-emit-symbol-graph", "-emit-symbol-graph-dir", root.pathString, "-emit-library", "-target", "x86_64-apple-macosx10.15", "-wmo", "-emit-module-separately-wmo"],
@@ -4262,9 +4251,7 @@ final class SwiftDriverTests: XCTestCase {
   }
 
   func testLEqualPassedDownToLinkerInvocation() throws {
-    let workingDirectory =
-        try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/Foo/Bar", relativeTo: $0) }
-                ?? AbsolutePath(validating: "/Foo/Bar")
+    let workingDirectory = localFileSystem.currentWorkingDirectory!.appending(components: "Foo", "Bar")
 
     var driver = try Driver(args: [
       "swiftc", "-working-directory", workingDirectory.pathString, "-emit-executable", "test.swift", "-L=.", "-F=."
@@ -4283,9 +4270,7 @@ final class SwiftDriverTests: XCTestCase {
   }
 
   func testWorkingDirectoryForImplicitOutputs() throws {
-    let workingDirectory =
-        try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/Foo/Bar", relativeTo: $0) }
-                ?? AbsolutePath(validating: "/Foo/Bar")
+    let workingDirectory = localFileSystem.currentWorkingDirectory!.appending(components: "Foo", "Bar")
 
     var driver = try Driver(args: [
       "swiftc", "-working-directory", workingDirectory.pathString, "-emit-executable", "-c", "/tmp/main.swift"
@@ -4298,9 +4283,7 @@ final class SwiftDriverTests: XCTestCase {
   }
 
   func testWorkingDirectoryForImplicitModules() throws {
-    let workingDirectory =
-        try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/Foo/Bar", relativeTo: $0) }
-                ?? AbsolutePath(validating: "/Foo/Bar")
+    let workingDirectory = localFileSystem.currentWorkingDirectory!.appending(components: "Foo", "Bar")
 
     var driver = try Driver(args: [
       "swiftc", "-working-directory", workingDirectory.pathString, "-emit-module", "/tmp/main.swift"
@@ -4677,8 +4660,7 @@ final class SwiftDriverTests: XCTestCase {
       // Replace the error stream with one we capture here.
       let errorStream = stderrStream
 
-      let root = try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/build", relativeTo: $0) }
-                    ?? AbsolutePath(validating: "/build")
+      let root = localFileSystem.currentWorkingDirectory!.appending(components: "build")
 
       let errorOutputFile = path.appending(component: "dummy_error_stream")
       TSCBasic.stderrStream = try! ThreadSafeOutputByteStream(LocalFileOutputByteStream(errorOutputFile))
@@ -5903,9 +5885,7 @@ final class SwiftDriverTests: XCTestCase {
 
   func testFrontendTargetInfoWithWorkingDirectory() throws {
     do {
-      let workingDirectory =
-          try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/absolute/path", relativeTo: $0) }
-                  ?? AbsolutePath(validating: "/Foo/Bar")
+      let workingDirectory = localFileSystem.currentWorkingDirectory!.appending(components: "absolute", "path")
 
       var driver = try Driver(args: ["swiftc", "-typecheck", "foo.swift",
                                      "-resource-dir", "resource/dir",
@@ -6320,13 +6300,8 @@ final class SwiftDriverTests: XCTestCase {
 
   func testRegistrarLookup() throws {
 #if os(Windows)
-    let SDKROOT: AbsolutePath =
-        try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/SDKROOT", relativeTo: $0) }
-            ?? AbsolutePath(validating: "/SDKROOT")
-
-    let resourceDir: AbsolutePath =
-        try localFileSystem.currentWorkingDirectory.map { AbsolutePath("/swift/resources", relativeTo: $0) }
-            ?? AbsolutePath(validating: "/swift/resources")
+    let SDKROOT: AbsolutePath = localFileSystem.currentWorkingDirectory!.appending(components: "SDKROOT")
+    let resourceDir: AbsolutePath = localFileSystem.currentWorkingDirectory!.appending(components: "swift", "resources")
 
     let platform: String = "windows"
 #if arch(x86_64)