Handle empty arguments in ArgvToCommandLine (#563)

* Handle empty arguments in ArgvToCommandLine

* Format

Author: dunhor

include/wil/win32_helpers.h

@@ -1076,6 +1076,7 @@ inline std::basic_string<CharT> ArgvToCommandLine(RangeT&& range, ArgvToCommandL
     // Somewhat of a hack to avoid the fact that we can't conditionalize a string literal on a template
     static constexpr const CharT empty_string[] = {'\0'};
     static constexpr const CharT single_quote_string[] = {'"', '\0'};
+    static constexpr const CharT double_quote_string[] = {'"', '"', '\0'};
     static constexpr const CharT space_string[] = {' ', '\0'};
     static constexpr const CharT quoted_space_string[] = {'"', ' ', '"', '\0'};
 
@@ -1093,6 +1094,7 @@ inline std::basic_string<CharT> ArgvToCommandLine(RangeT&& range, ArgvToCommandL
     {
         auto currentIndex = index++;
         result += prefix;
+        prefix = nextPrefix;
 
         const CharT* searchString = initialSearchString;
 
@@ -1102,6 +1104,14 @@ inline std::basic_string<CharT> ArgvToCommandLine(RangeT&& range, ArgvToCommandL
 
         // We need to escape any quotes and CONDITIONALLY any backslashes
         string_view_type str(strRaw);
+        if (str.empty() && !forceQuotes)
+        {
+            // The argument is empty. If we want to preserve it in the command line string, we need to manually insert
+            // a pair of quotes since normal parsing won't handle this case
+            result.append(double_quote_string);
+            continue;
+        }
+
         size_t pos = 0;
         while (pos < str.size())
         {
@@ -1201,8 +1211,6 @@ inline std::basic_string<CharT> ArgvToCommandLine(RangeT&& range, ArgvToCommandL
         {
             result.push_back('"');
         }
-
-        prefix = nextPrefix;
     }
 
     // NOTE: We optimize the force quotes case by including them in the prefix string. We're not appending a prefix

tests/wiTest.cpp

@@ -4207,6 +4207,10 @@ TEST_CASE("WindowsInternalTests::ArgvToCommandLine", "[win32_helpers]")
         R"(test.exe " front" "mid dle" "end " " every where ")",
         R"("test.exe" " front" "mid dle" "end " " every where ")");
 
+    // Empty arguments should always force quotes
+    DoArgvToCommandLineTest(
+        {"", "test", "", "foo", "", "", "bar", ""}, R"("" test "" foo "" "" bar "")", R"("" "test" "" "foo" "" "" "bar" "")");
+
     // CommandLineToArgvW treats tab characters the same as spaces; test that here
     DoArgvToCommandLineTest(
         {"test.exe", "\tfront", "mid\tdle", "end\t", "\tevery\twhere\t"},