From e983501bfd1fd17ac73869a1047ce8b988e0b945 Mon Sep 17 00:00:00 2001
From: Trent Nadeau <tanadeau@gmail.com>
Date: Tue, 26 Jan 2016 04:45:03 +0000
Subject: [PATCH] Don't error when lexing UTF-8 BOM

---
 lib/Parse/Lexer.cpp                       | 10 +++++++++-
 test/Parse/{BOM.swift => utf16_bom.swift} |  0
 test/Parse/utf8_bom.swift                 |  2 ++
 3 files changed, 11 insertions(+), 1 deletion(-)
 rename test/Parse/{BOM.swift => utf16_bom.swift} (100%)
 create mode 100644 test/Parse/utf8_bom.swift

diff --git a/lib/Parse/Lexer.cpp b/lib/Parse/Lexer.cpp
index 1c338af587d12..94f883290b042 100644
--- a/lib/Parse/Lexer.cpp
+++ b/lib/Parse/Lexer.cpp
@@ -177,7 +177,15 @@ Lexer::Lexer(const LangOptions &Options,
   StringRef contents = SM.extractText(SM.getRangeForBuffer(BufferID));
   BufferStart = contents.data();
   BufferEnd = contents.data() + contents.size();
-  CurPtr = BufferStart;
+
+  // Check for Unicode BOM at start of file (Only UTF-8 BOM supported now).
+  size_t BOMLength = llvm::StringSwitch<size_t>(contents)
+    .StartsWith("\xEF\xBB\xBF", 3)
+    .Default(0);
+
+  // Since the UTF-8 BOM doesn't carry information (UTF-8 has no dependency
+  // on byte order), throw it away.
+  CurPtr = BufferStart + BOMLength;
 
   // Initialize code completion.
   if (BufferID == SM.getCodeCompletionBufferID()) {
diff --git a/test/Parse/BOM.swift b/test/Parse/utf16_bom.swift
similarity index 100%
rename from test/Parse/BOM.swift
rename to test/Parse/utf16_bom.swift
diff --git a/test/Parse/utf8_bom.swift b/test/Parse/utf8_bom.swift
new file mode 100644
index 0000000000000..27f997a590f7a
--- /dev/null
+++ b/test/Parse/utf8_bom.swift
@@ -0,0 +1,2 @@
+// RUN: %target-parse-verify-swift
+struct UTF8Test {}