[clang] [llvm] [InstallAPI] Add *umbrella-header options (PR #86587)

[Juergen Ributzka via cfe-commits]

================
@@ -424,6 +448,56 @@ InstallAPIContext Options::createContext() {
     if (!Glob->didMatch())
       Diags->Report(diag::warn_glob_did_not_match) << Glob->str();
 
+  // Mark any explicit or inferred umbrella headers. If one exists, move
+  // that to the beginning of the input headers.
+  auto MarkandMoveUmbrellaInHeaders = [&](Regex &Regex,
+                                          HeaderType Type) -> bool {
+    auto It = find_if(Ctx.InputHeaders, [&Regex, Type](const HeaderFile &H) {
+      return (H.getType() == Type) && Regex.match(H.getPath());
+    });
+
+    if (It == Ctx.InputHeaders.end())
+      return false;
+    It->setUmbrellaHeader();
+
+    // Because there can be an umbrella header per header type,
+    // find the first non umbrella header to swap position with.
+    auto BeginPos = find_if(Ctx.InputHeaders, [](const HeaderFile &H) {
+      return !H.isUmbrellaHeader();
+    });
+    if (BeginPos != Ctx.InputHeaders.end() && BeginPos < It)
+      std::swap(*BeginPos, *It);
+    return true;
+  };
+
+  auto FindUmbrellaHeader = [&](StringRef HeaderPath, HeaderType Type) -> bool {
+    if (!HeaderPath.empty()) {
+      auto EscapedString = Regex::escape(HeaderPath);
+      Regex UmbrellaRegex(EscapedString);
+      if (!MarkandMoveUmbrellaInHeaders(UmbrellaRegex, Type)) {
+        Diags->Report(diag::err_no_such_umbrella_header_file)
+            << HeaderPath << (unsigned)Type - 1;
----------------
ributzka wrote:

Could the `HeaderType` enum be reshuffled so this arithmetic is not required?

https://github.com/llvm/llvm-project/pull/86587