[GN] Add support to rebase_path to resolve paths above the source root.

tools/gn/filesystem_utils_unittest.cc

Index: tools/gn/filesystem_utils_unittest.cc
diff --git a/tools/gn/filesystem_utils_unittest.cc b/tools/gn/filesystem_utils_unittest.cc
index 9f89512cfa29f1260d20488e9a67a6feaed4e448..27ccab2ea4d0db453c217d1921db71729de58aac 100644
--- a/tools/gn/filesystem_utils_unittest.cc
+++ b/tools/gn/filesystem_utils_unittest.cc
@@ -204,7 +204,7 @@ TEST(FilesystemUtils, NormalizePath) {
   NormalizePath(&input);
   EXPECT_EQ("../bar", input);
 
-  input = "/../foo";  // Don't go aboe the root dir.
+  input = "/../foo";  // Don't go above the root dir.
   NormalizePath(&input);
   EXPECT_EQ("/foo", input);
 
@@ -241,6 +241,134 @@ TEST(FilesystemUtils, NormalizePath) {
   input = "//foo/bar/";
   NormalizePath(&input);
   EXPECT_EQ("//foo/bar/", input);
+
+#if defined(OS_WIN)
+  // Go above and outside of the source root.
+  input = "//../foo";
+  NormalizePath(&input, "/C:/source/root");
+  EXPECT_EQ("/C:/source/foo", input);
+
+  input = "//../foo";
+  NormalizePath(&input, "C:\\source\\root");
+  EXPECT_EQ("/C:/source/foo", input);
+
+  input = "//../";
+  NormalizePath(&input, "/C:/source/root");
+  EXPECT_EQ("/C:/source/", input);
+
+  input = "//../foo.txt";
+  NormalizePath(&input, "/C:/source/root");
+  EXPECT_EQ("/C:/source/foo.txt", input);
+
+  input = "//../foo/bar/";
+  NormalizePath(&input, "/C:/source/root");
+  EXPECT_EQ("/C:/source/foo/bar/", input);
+
+  // Go above and back into the source root. This should return a system-
+  // absolute path. We could arguably return this as a source-absolute path,
+  // but that would require additional handling to account for a rare edge
+  // case.
+  input = "//../root/foo";
+  NormalizePath(&input, "/C:/source/root");
+  EXPECT_EQ("/C:/source/root/foo", input);
+
+  input = "//../root/foo/bar/";
+  NormalizePath(&input, "/C:/source/root");
+  EXPECT_EQ("/C:/source/root/foo/bar/", input);
+
+  // Stay inside the source root
+  input = "//foo/bar";
+  NormalizePath(&input, "/C:/source/root");
+  EXPECT_EQ("//foo/bar", input);
+
+  input = "//foo/bar/";
+  NormalizePath(&input, "/C:/source/root");
+  EXPECT_EQ("//foo/bar/", input);
+
+  // The path should not go above the system root. Note that on Windows, this
+  // will consume the drive (C:).
+  input = "//../../../../../foo/bar";
+  NormalizePath(&input, "/C:/source/root");
+  EXPECT_EQ("/foo/bar", input);
+
+  // Test when the source root is the letter drive.
+  input = "//../foo";
+  NormalizePath(&input, "/C:");
+  EXPECT_EQ("/foo", input);
+
+  input = "//../foo";
+  NormalizePath(&input, "C:");
+  EXPECT_EQ("/foo", input);
+
+  input = "//../foo";
+  NormalizePath(&input, "/");
+  EXPECT_EQ("/foo", input);
+
+  input = "//../";
+  NormalizePath(&input, "\\C:");
+  EXPECT_EQ("/", input);
+
+  input = "//../foo.txt";
+  NormalizePath(&input, "/C:");
+  EXPECT_EQ("/foo.txt", input);
+#else
+  // Go above and outside of the source root.
+  input = "//../foo";
+  NormalizePath(&input, "/source/root");
+  EXPECT_EQ("/source/foo", input);
+
+  input = "//../";
+  NormalizePath(&input, "/source/root");
+  EXPECT_EQ("/source/", input);
+
+  input = "//../foo.txt";
+  NormalizePath(&input, "/source/root");
+  EXPECT_EQ("/source/foo.txt", input);
+
+  input = "//../foo/bar/";
+  NormalizePath(&input, "/source/root");
+  EXPECT_EQ("/source/foo/bar/", input);
+
+  // Go above and back into the source root. This should return a system-
+  // absolute path. We could arguably return this as a source-absolute path,
+  // but that would require additional handling to account for a rare edge
+  // case.
+  input = "//../root/foo";
+  NormalizePath(&input, "/source/root");
+  EXPECT_EQ("/source/root/foo", input);
+
+  input = "//../root/foo/bar/";
+  NormalizePath(&input, "/source/root");
+  EXPECT_EQ("/source/root/foo/bar/", input);
+
+  // Stay inside the source root
+  input = "//foo/bar";
+  NormalizePath(&input, "/source/root");
+  EXPECT_EQ("//foo/bar", input);
+
+  input = "//foo/bar/";
+  NormalizePath(&input, "/source/root");
+  EXPECT_EQ("//foo/bar/", input);
+
+  // The path should not go above the system root.
+  input = "//../../../../../foo/bar";
+  NormalizePath(&input, "/source/root");
+  EXPECT_EQ("/foo/bar", input);
+
+  // Test when the source root is the system root.
+  input = "//../foo/bar/";
+  NormalizePath(&input, "/");
+  EXPECT_EQ("/foo/bar/", input);
+
+  input = "//../";
+  NormalizePath(&input, "/");
+  EXPECT_EQ("/", input);
+
+  input = "//../foo.txt";
+  NormalizePath(&input, "/");
+  EXPECT_EQ("/foo.txt", input);
+
+#endif
 }
 
 TEST(FilesystemUtils, RebasePath) {