Index: clang-tools-extra/trunk/include-fixer/YamlXrefsDB.h
===================================================================
--- clang-tools-extra/trunk/include-fixer/YamlXrefsDB.h
+++ clang-tools-extra/trunk/include-fixer/YamlXrefsDB.h
@@ -12,6 +12,7 @@
 
 #include "XrefsDB.h"
 #include "find-all-symbols/SymbolInfo.h"
+#include "llvm/Support/ErrorOr.h"
 #include <map>
 #include <vector>
 
@@ -21,12 +22,20 @@
 /// Yaml format database.
 class YamlXrefsDB : public XrefsDB {
 public:
-  YamlXrefsDB(llvm::StringRef FilePath);
+  /// Create a new Yaml db from a file.
+  static llvm::ErrorOr<std::unique_ptr<YamlXrefsDB>>
+  createFromFile(llvm::StringRef FilePath);
+  /// Look for a file called \c Name in \c Directory and all parent directories.
+  static llvm::ErrorOr<std::unique_ptr<YamlXrefsDB>>
+  createFromDirectory(llvm::StringRef Directory, llvm::StringRef Name);
 
   std::vector<clang::find_all_symbols::SymbolInfo>
   search(llvm::StringRef Identifier) override;
 
 private:
+  explicit YamlXrefsDB(std::vector<clang::find_all_symbols::SymbolInfo> Symbols)
+      : Symbols(std::move(Symbols)) {}
+
   std::vector<clang::find_all_symbols::SymbolInfo> Symbols;
 };
 
Index: clang-tools-extra/trunk/include-fixer/YamlXrefsDB.cpp
===================================================================
--- clang-tools-extra/trunk/include-fixer/YamlXrefsDB.cpp
+++ clang-tools-extra/trunk/include-fixer/YamlXrefsDB.cpp
@@ -8,10 +8,11 @@
 //===----------------------------------------------------------------------===//
 
 #include "YamlXrefsDB.h"
-
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/Support/Errc.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Path.h"
 #include <string>
 #include <vector>
 
@@ -20,15 +21,30 @@
 namespace clang {
 namespace include_fixer {
 
-YamlXrefsDB::YamlXrefsDB(llvm::StringRef FilePath) {
-  int ReadFD = 0;
-  if (llvm::sys::fs::openFileForRead(FilePath, ReadFD))
-    return;
-  auto Buffer = llvm::MemoryBuffer::getOpenFile(ReadFD, FilePath, -1);
+llvm::ErrorOr<std::unique_ptr<YamlXrefsDB>>
+YamlXrefsDB::createFromFile(llvm::StringRef FilePath) {
+  auto Buffer = llvm::MemoryBuffer::getFile(FilePath);
   if (!Buffer)
-    return;
-  Symbols = clang::find_all_symbols::ReadSymbolInfosFromYAML(
-      Buffer.get()->getBuffer());
+    return Buffer.getError();
+
+  return std::unique_ptr<YamlXrefsDB>(
+      new YamlXrefsDB(clang::find_all_symbols::ReadSymbolInfosFromYAML(
+          Buffer.get()->getBuffer())));
+}
+
+llvm::ErrorOr<std::unique_ptr<YamlXrefsDB>>
+YamlXrefsDB::createFromDirectory(llvm::StringRef Directory,
+                                 llvm::StringRef Name) {
+  // Walk upwards from Directory, looking for files.
+  for (llvm::SmallString<128> PathStorage = Directory; !Directory.empty();
+       Directory = llvm::sys::path::parent_path(Directory)) {
+    assert(Directory.size() <= PathStorage.size());
+    PathStorage.resize(Directory.size()); // Shrink to parent.
+    llvm::sys::path::append(PathStorage, Name);
+    if (auto DB = createFromFile(PathStorage))
+      return DB;
+  }
+  return llvm::make_error_code(llvm::errc::no_such_file_or_directory);
 }
 
 std::vector<SymbolInfo> YamlXrefsDB::search(llvm::StringRef Identifier) {
Index: clang-tools-extra/trunk/include-fixer/tool/ClangIncludeFixer.cpp
===================================================================
--- clang-tools-extra/trunk/include-fixer/tool/ClangIncludeFixer.cpp
+++ clang-tools-extra/trunk/include-fixer/tool/ClangIncludeFixer.cpp
@@ -73,8 +73,26 @@
     break;
   }
   case yaml: {
-    XrefsDBMgr->addXrefsDB(
-        llvm::make_unique<include_fixer::YamlXrefsDB>(Input));
+    llvm::ErrorOr<std::unique_ptr<include_fixer::YamlXrefsDB>> DB(nullptr);
+    if (!Input.empty()) {
+      DB = include_fixer::YamlXrefsDB::createFromFile(Input);
+    } else {
+      // If we don't have any input file, look in the directory of the first
+      // file and its parents.
+      SmallString<128> AbsolutePath(
+          tooling::getAbsolutePath(options.getSourcePathList().front()));
+      StringRef Directory = llvm::sys::path::parent_path(AbsolutePath);
+      DB = include_fixer::YamlXrefsDB::createFromDirectory(
+          Directory, "find_all_symbols_db.yaml");
+    }
+
+    if (!DB) {
+      llvm::errs() << "Couldn't find YAML db: " << DB.getError().message()
+                   << '\n';
+      return 1;
+    }
+
+    XrefsDBMgr->addXrefsDB(std::move(*DB));
     break;
   }
   }
Index: clang-tools-extra/trunk/test/include-fixer/yamldb_autodetect.cpp
===================================================================
--- clang-tools-extra/trunk/test/include-fixer/yamldb_autodetect.cpp
+++ clang-tools-extra/trunk/test/include-fixer/yamldb_autodetect.cpp
@@ -0,0 +1,12 @@
+// REQUIRES: shell
+// RUN: mkdir -p %T/foo/bar
+// RUN: cp %p/Inputs/fake_yaml_db.yaml %T/find_all_symbols_db.yaml
+// RUN: cd %T/foo
+// RUN: sed -e 's#//.*$##' %s > bar/test.cpp
+// RUN: clang-include-fixer -db=yaml bar/test.cpp --
+// RUN: FileCheck %s -input-file=bar/test.cpp
+
+// CHECK: #include "foo.h"
+// CHECK: b::a::foo f;
+
+b::a::foo f;