Change to returning nullptr rather than triggering a fatal error.

Instead of triggering a fatal error on failure, return `nullptr` and
let the caller decide what to do about it.  The CommandLine code should
trigger a fatal error, of course.

rdar://103397975

Author: al45tair

include/swift/Runtime/Win32.h

@@ -33,7 +33,7 @@ namespace win32 {
 /// @returns The string, converted to UTF-8.  The caller is responsible
 ///          for freeing this string with @c free() when done with it.
 ///
-/// If @a str cannot be converted to UTF-8, a fatal error occurs.
+/// If @a str cannot be converted to UTF-8, @c nullptr is returned.
 SWIFT_RUNTIME_STDLIB_INTERNAL
 char *copyUTF8FromWide(const wchar_t *str);
 
@@ -44,7 +44,7 @@ char *copyUTF8FromWide(const wchar_t *str);
 /// @returns The string, converted to UTF-16.  The caller is responsible
 ///          for freeing this string with @c free() when done with it.
 ///
-/// If @a str cannot be converted to UTF-16, a fatal error occurs.
+/// If @a str cannot be converted to UTF-16, @c nullptr is returned.
 SWIFT_RUNTIME_STDLIB_INTERNAL
 wchar_t *copyWideFromUTF8(const char *str);
 

stdlib/public/CommandLineSupport/CommandLine.cpp

@@ -204,6 +204,15 @@ static void swift::enumerateUnsafeArgv(const F& body) {
   if (LPWSTR *wargv = CommandLineToArgvW(GetCommandLineW(), &argc)) {
     std::for_each(wargv, wargv + argc, [=] (wchar_t *warg) {
       auto arg = swift::win32::copyUTF8FromWide(warg);
+      if (!arg) {
+        // Note that GetLastError() and errno may not be so useful here,
+        // as in the error case we may have called free(), which might reset
+        // either or both of them.
+        swift::fatalError(0,
+                          "Fatal error: Unable to convert argument '%ls' to "
+                          "UTF-8: %lx, %d.\n",
+                          warg, ::GetLastError(), errno);
+      }
       body(argc, arg);
       free(arg);
     });

stdlib/public/runtime/Win32.cpp

@@ -28,30 +28,23 @@ swift::win32::copyUTF8FromWide(const wchar_t *str) {
                                   str, -1,
                                   nullptr, 0,
                                   nullptr, nullptr);
-  if (len <= 0) {
-    swift::fatalError(0, "failed to convert string '%ls' "
-                      "from wide to UTF-8: %lx\n",
-                      str, ::GetLastError());
-  }
+  if (len <= 0)
+    return nullptr;
 
   result = reinterpret_cast<char *>(std::malloc(len));
-  if (!result) {
-    swift::fatalError(0, "unable to allocate space to convert '%ls': %d\n",
-                      str, errno);
-  }
+  if (!result)
+    return nullptr;
 
   len = ::WideCharToMultiByte(CP_UTF8, WC_ERR_INVALID_CHARS,
                               str, -1,
                               result, len,
                               nullptr, nullptr);
 
-  if (len <= 0) {
-    swift::fatalError(0, "failed to convert string '%ls' "
-                      "from wide to UTF-8: %lx\n",
-                      str, ::GetLastError());
-  }
+  if (len)
+    return result;
 
-  return result;
+  free(result);
+  return nullptr;
 }
 
 wchar_t *
@@ -60,28 +53,22 @@ swift::win32::copyWideFromUTF8(const char *str) {
   int len = ::MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS,
                                   str, -1,
                                   nullptr, 0);
-  if (len <= 0) {
-    swift::fatalError(0, "failed to convert string '%s' "
-                      "from UTF-8 to wide: %lx\n",
-                      str, ::GetLastError());
-  }
+  if (len <= 0)
+    return nullptr;
 
   result = reinterpret_cast<wchar_t *>(std::malloc(len * sizeof(wchar_t)));
-  if (!result) {
-    swift::fatalError(0, "unable to allocate space to convert '%s': %d\n",
-                      str, errno);
-  }
+  if (!result)
+    return nullptr;
 
   len = ::MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS,
                               str, -1,
                               result, len);
-  if (len <= 0) {
-    swift::fatalError(0, "failed to convert string '%s' "
-                      "from UTF-8 to wide: %lx\n",
-                      str, ::GetLastError());
-  }
 
-  return result;
+  if (len)
+    return result;
+
+  free(result);
+  return nullptr;
 }
 
 #endif // defined(_WIN32)