[clang-doc] Fix assert on startup

[brettw]

Summary

When using clang-doc --format=html it will crash on startup because of an assertion doing a self-assignment of a SmallString. This patch removes the self-assignment by creating an intermediate copy.

[paulkirth]

This is LGTM, but can you add a tag to the summary title/commit message? ie. [clang-doc] Fix assert on startup in clang-doc

[brettw]

In D131793#3719619, @paulkirth wrote:

This is LGTM, but can you add a tag to the summary title/commit message? ie. [clang-doc] Fix assert on startup in clang-doc

Done

clang-tools-extra/clang-doc/tool/ClangDocMain.cpp

clang::doc::ClangDocContext CDCtx = {
       SourceRoot,
       RepositoryUrl,
       {UserStylesheets.begin(), UserStylesheets.end()},
       {"index.js", "index_json.js"}};
 
   if (Format == "html") {
     void *MainAddr = (void *)(intptr_t)GetExecutablePath;
     std::string ClangDocPath = GetExecutablePath(argv[0], MainAddr);
+    llvm::SmallString<128> NativeClangDocPath;
+    llvm::sys::path::native(ClangDocPath, NativeClangDocPath);
     llvm::SmallString<128> AssetsPath;
-    llvm::sys::path::native(ClangDocPath, AssetsPath);
-    AssetsPath = llvm::sys::path::parent_path(AssetsPath);
+    AssetsPath = llvm::sys::path::parent_path(NativeClangDocPath);
     llvm::sys::path::append(AssetsPath, "..", "share", "clang");
     llvm::SmallString<128> DefaultStylesheet;
     llvm::sys::path::native(AssetsPath, DefaultStylesheet);
     llvm::sys::path::append(DefaultStylesheet,
                             "clang-doc-default-stylesheet.css");
     llvm::SmallString<128> IndexJS;
     llvm::sys::path::native(AssetsPath, IndexJS);
     llvm::sys::path::append(IndexJS, "index.js");