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..89dba6167462ff8a7de0e2683f2abedd6716a3ab 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 +122,42 @@ 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
+    DWORD size_needed =
+        MultiByteToWideChar(CP_UTF8, 0, filename.data(), -1, nullptr, 0);
+    std::wstring utf16(size_needed, 0);

[dcheng, 2016/09/09 18:57:29]

Nit: '\0' maybe, for slightly better clarity?

[Nico, 2016/09/09 19:06:33]

meh, it's overwritten below anyways. And wouldn't it have to be L'\0'?

[dcheng, 2016/09/09 19:09:48]

I think '\0' should work fine here: the L prefix is only a problem for string
literals since the pointer types aren't convertible.

(It's just a visual hint to the reader that the first parameter is the count:
even though we're passing a named variable as the count, there's still a bare 0
integer literal right next to it, so it takes me a little extra mental energy to
remember that this is a character, not NULL or a count of some other sort)

+    MultiByteToWideChar(CP_UTF8, 0, filename.data(), -1,
+                        &utf16[0], size_needed);
+
+    size_needed = GetFullPathName(utf16.data(), 0, nullptr, nullptr) + 1; // nul

[dcheng, 2016/09/09 18:57:29]

Nit: let's be consistent about calling the W versions.

[dcheng, 2016/09/09 18:57:29]

Also:

If the lpBuffer buffer is too small to contain the path, the return value is the
size, in TCHARs, of the buffer that is required to hold the path and the
terminating null character.

So I think this already includes the terminating null.

[Nico, 2016/09/09 19:06:33]

Oh oops, done, thanks!

[Nico, 2016/09/09 19:06:33]

You're right, I misread the docs. Done.

+    std::wstring full_utf16(size_needed, 0);
+    GetFullPathNameW(utf16.data(), full_utf16.size(), &full_utf16[0], nullptr);
+
+    size_needed = WideCharToMultiByte(CP_UTF8, 0, full_utf16.data(), -1,
+                                      nullptr, 0, nullptr, nullptr);
+    filename.resize(size_needed);
+    WideCharToMultiByte(CP_UTF8, 0, full_utf16.data(), -1, &filename[0],
+                        size_needed, nullptr, nullptr);
+  }
 
-  // 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_) {