clang plugin: Compute absolute paths on Windows as well.

tools/clang/plugins/ChromeClassTester.cpp

Index: tools/clang/plugins/ChromeClassTester.cpp
diff --git a/tools/clang/plugins/ChromeClassTester.cpp b/tools/clang/plugins/ChromeClassTester.cpp
index cd508068e111399c0319dbebc49e707bd94fcea4..080cb96514a75c2afb7e93c4eacfbcd1b1af275b 100644
--- a/tools/clang/plugins/ChromeClassTester.cpp
+++ b/tools/clang/plugins/ChromeClassTester.cpp
@@ -16,6 +16,9 @@
 #ifdef LLVM_ON_UNIX
 #include <sys/param.h>
 #endif
+#if defined(LLVM_ON_WIN32)
+#include <windows.h>
+#endif
 
 using namespace clang;
 using chrome_checker::Options;
@@ -119,27 +122,46 @@ bool ChromeClassTester::InBannedDirectory(SourceLocation loc) {
 
 #if defined(LLVM_ON_UNIX)
   // Resolve the symlinktastic relative path and make it absolute.
-  char resolvedPath[MAXPATHLEN];
   if (options_.no_realpath) {
     // Same reason as windows below, but we don't need to do
     // the '\\' manipulation on linux.
     filename.insert(filename.begin(), '/');
   } else if (realpath(filename.c_str(), resolvedPath)) {
+    char resolvedPath[MAXPATHLEN];
     filename = resolvedPath;
   }
 #endif
 
 #if defined(LLVM_ON_WIN32)
-  std::replace(filename.begin(), filename.end(), '\\', '/');
+  // Make path absolute.
+  if (options_.no_realpath) {
+    // This turns e.g. "gen/dir/file.cc" to "/gen/dir/file.cc" which lets the
+    // "/gen/" banned_dir work.
+    filename.insert(filename.begin(), '/');
+  } else {
+    // The Windows dance: Convert to UTF-16, call GetFullPathNameW, convert back
+    // Use vector instead of string because string doesn't guarantee continuous

[dcheng, 2016/09/09 17:20:57]

According to my thorough scientific research of Google results, C++11 requires
contiguous storage for string.

[Nico, 2016/09/09 17:52:14]

Done. (Why didn't the make data() return non-const char*? :-/)

+    // storage in theory.
+    DWORD size_needed =
+        MultiByteToWideChar(CP_UTF8, 0, filename.data(), -1, nullptr, 0);
+    std::vector<WCHAR> utf16(size_needed);
+    MultiByteToWideChar(CP_UTF8, 0, filename.data(), -1,
+                        utf16.data(), size_needed);
+
+    size_needed = GetFullPathName(utf16.data(), 0, nullptr, nullptr) + 1; // nul
+    std::vector<WCHAR> full_utf16(size_needed, 0);
+    GetFullPathNameW(utf16.data(), full_utf16.size(), full_utf16.data(),
+                     nullptr);
+
+    size_needed = WideCharToMultiByte(CP_UTF8, 0, full_utf16.data(), -1,
+                                      nullptr, 0, nullptr, nullptr);
+    std::vector<char> utf8(size_needed);
+    WideCharToMultiByte(CP_UTF8, 0, full_utf16.data(), -1, utf8.data(),
+                        size_needed, nullptr, nullptr);
+    filename.assign(utf8.begin(), utf8.end());
+  }
 
-  // On Posix, realpath() has made the path absolute.  On Windows, this isn't
-  // necessarily true, so prepend a '/' to the path to make sure the
-  // banned_directories_ loop below works correctly.
-  // This turns e.g. "gen/dir/file.cc" to "/gen/dir/file.cc" which lets the
-  // "/gen/" banned_dir work.
-  // This seems simpler than converting to utf16, calling GetFullPathNameW(),
-  // and converting back to utf8.
-  filename.insert(filename.begin(), '/');
+  std::replace(filename.begin(), filename.end(), '\\', '/');
 #endif
 
   for (const std::string& allowed_dir : allowed_directories_) {