2 files changed, 44 insertions, 2 deletions
diff --git a/clang/lib/Lex/HeaderMap.cpp b/clang/lib/Lex/HeaderMap.cpp
index d44ef29c..4b60cfa 100644
--- a/clang/lib/Lex/HeaderMap.cpp
+++ b/clang/lib/Lex/HeaderMap.cpp
@@ -240,3 +240,32 @@ StringRef HeaderMapImpl::lookupFilename(StringRef Filename,
     return StringRef(DestPath.begin(), DestPath.size());
   }
 }
+
+StringRef HeaderMapImpl::reverseLookupFilename(StringRef DestPath) const {
+  if (!ReverseMap.empty())
+    return ReverseMap.lookup(DestPath);
+
+  const HMapHeader &Hdr = getHeader();
+  unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
+  StringRef RetKey;
+  for (unsigned i = 0; i != NumBuckets; ++i) {
+    HMapBucket B = getBucket(i);
+    if (B.Key == HMAP_EmptyBucketKey)
+      continue;
+
+    Optional<StringRef> Key = getString(B.Key);
+    Optional<StringRef> Prefix = getString(B.Prefix);
+    Optional<StringRef> Suffix = getString(B.Suffix);
+    if (LLVM_LIKELY(Key && Prefix && Suffix)) {
+      SmallVector<char, 1024> Buf;
+      Buf.append(Prefix->begin(), Prefix->end());
+      Buf.append(Suffix->begin(), Suffix->end());
+      StringRef Value(Buf.begin(), Buf.size());
+      ReverseMap[Value] = *Key;
+
+      if (DestPath == Value)
+        RetKey = *Key;
+    }
+  }
+  return RetKey;
+}
diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index 99c92e9..9970c3c 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -1834,7 +1834,7 @@ std::string HeaderSearch::suggestPathToFileForDiagnostics(
   };
 
   for (unsigned I = 0; I != SearchDirs.size(); ++I) {
-    // FIXME: Support this search within frameworks and header maps.
+    // FIXME: Support this search within frameworks.
     if (!SearchDirs[I].isNormalDir())
       continue;
 
@@ -1848,6 +1848,19 @@ std::string HeaderSearch::suggestPathToFileForDiagnostics(
   if (!BestPrefixLength && CheckDir(path::parent_path(MainFile)) && IsSystem)
     *IsSystem = false;
 
+  // Try resolving resulting filename via reverse search in header maps,
+  // key from header name is user prefered name for the include file.
+  StringRef Filename = File.drop_front(BestPrefixLength);
+  for (unsigned I = 0; I != SearchDirs.size(); ++I) {
+    if (!SearchDirs[I].isHeaderMap())
+      continue;
 
-  return path::convert_to_slash(File.drop_front(BestPrefixLength));
+    StringRef SpelledFilename =
+        SearchDirs[I].getHeaderMap()->reverseLookupFilename(Filename);
+    if (!SpelledFilename.empty()) {
+      Filename = SpelledFilename;
+      break;
+    }
+  }
+  return path::convert_to_slash(Filename);
 }