From ac6a5aab45ef721e92a28e1b0515aa2a514d740b Mon Sep 17 00:00:00 2001
From: Ben Dunbobbin <bd1976llvm@gmail.com>
Date: Fri, 18 Aug 2017 16:55:44 +0000
Subject: [PATCH] [Support] env vars with empty values on windows

An environment variable can be in one of three states:

1. undefined.
2. defined with a non-empty value.
3. defined but with an empty value.

The windows implementation did not support case 3
(it was not handling errors). The Linux implementation
is already correct.

Differential Revision: https://reviews.llvm.org/D36394

llvm-svn: 311174
---
 llvm/lib/Support/Windows/Process.inc   |  5 +++--
 llvm/unittests/Support/ProcessTest.cpp | 10 +++++++++-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Support/Windows/Process.inc b/llvm/lib/Support/Windows/Process.inc
index 18aef610d54a..3fe9f89f1ef5 100644
--- a/llvm/lib/Support/Windows/Process.inc
+++ b/llvm/lib/Support/Windows/Process.inc
@@ -129,9 +129,10 @@ Optional<std::string> Process::GetEnv(StringRef Name) {
   size_t Size = MAX_PATH;
   do {
     Buf.reserve(Size);
+    SetLastError(NO_ERROR);
     Size =
-        GetEnvironmentVariableW(NameUTF16.data(), Buf.data(), Buf.capacity());
-    if (Size == 0)
+      GetEnvironmentVariableW(NameUTF16.data(), Buf.data(), Buf.capacity());
+    if (Size == 0 && GetLastError() == ERROR_ENVVAR_NOT_FOUND)
       return None;
 
     // Try again with larger buffer.
diff --git a/llvm/unittests/Support/ProcessTest.cpp b/llvm/unittests/Support/ProcessTest.cpp
index 298a0a373234..37587bf47996 100644
--- a/llvm/unittests/Support/ProcessTest.cpp
+++ b/llvm/unittests/Support/ProcessTest.cpp
@@ -42,10 +42,18 @@ TEST(ProcessTest, None) {
   Optional<std::string> val(
       Process::GetEnv("__LLVM_TEST_ENVIRON_NO_SUCH_VAR__"));
   EXPECT_FALSE(val.hasValue());
-}
+} 
 #endif
 
 #ifdef LLVM_ON_WIN32
+
+TEST(ProcessTest, EmptyVal) {
+  SetEnvironmentVariableA("__LLVM_TEST_ENVIRON_VAR__", "");
+  Optional<std::string> val(Process::GetEnv("__LLVM_TEST_ENVIRON_VAR__"));
+  EXPECT_TRUE(val.hasValue());
+  EXPECT_STREQ("", val->c_str());
+}
+
 TEST(ProcessTest, Wchar) {
   SetEnvironmentVariableW(L"__LLVM_TEST_ENVIRON_VAR__", L"abcdefghijklmnopqrs");
   Optional<std::string> val(Process::GetEnv("__LLVM_TEST_ENVIRON_VAR__"));