Respect the TMPDIR environment variable on Unix

On Mac, this is important as TMPDIR points to a user-specific temp dir
which avoids a potential problem where an app bundle created in the temp dir
running as User A cannot later be replaced by a copy of the updater running
as User B.

MD-19088 #time 30m
Reviewed-by: Nicolas Esteves

src/FileUtils.cpp

@@ -450,7 +450,12 @@ std::string FileUtils::toUnixPathSeparators(const std::string& str)
 std::string FileUtils::tempPath()
 {
 #ifdef PLATFORM_UNIX
-	return "/tmp";
+	std::string tmpDir(notNullString(getenv("TMPDIR")));
+	if (tmpDir.empty())
+	{
+		tmpDir = "/tmp";
+	}
+	return tmpDir;
 #else
 	char buffer[MAX_PATH+1];
 	GetTempPath(MAX_PATH+1,buffer);

src/tests/TestFileUtils.cpp

@@ -33,11 +33,18 @@ void TestFileUtils::testSymlinkFileExists()
 #endif
 }
 
+void TestFileUtils::testStandardDirs()
+{
+	std::string tmpDir = FileUtils::tempPath();
+	TEST_COMPARE(FileUtils::fileExists(tmpDir.data()), true);
+}
+
 int main(int,char**)
 {
 	TestList<TestFileUtils> tests;
 	tests.addTest(&TestFileUtils::testDirName);
 	tests.addTest(&TestFileUtils::testIsRelative);
 	tests.addTest(&TestFileUtils::testSymlinkFileExists);
+	tests.addTest(&TestFileUtils::testStandardDirs);
 	return TestUtils::runTest(tests);
 }

src/tests/TestFileUtils.h

@@ -6,4 +6,5 @@ class TestFileUtils
 		void testDirName();
 		void testIsRelative();
 		void testSymlinkFileExists();
+		void testStandardDirs();
 };