Properly handling inaccessible process path on Linux

README.md

@@ -127,7 +127,7 @@ A block continues until the next block (respectively the end of the file). The b
 ...
 ```
 
-:warning: The device filter is currently only available on Linux and the process path may not be available on Wayland and for applications running as administrator on Windows.
+:warning: The `device` filter is currently only available on Linux and the process `path` may not be available on Wayland and for processes with higher privileges.
 
 Class and device filters match contexts with the _exact_ same string, others match contexts _containing_ the string.
 For finer control [regular expressions](https://en.wikipedia.org/wiki/Regular_expression) can be used. These have to be delimited with slashes. Optionally `i` can be appended to make the comparison case insensitive:

src/client/linux/FocusedWindowImpl.cpp

@@ -80,6 +80,8 @@ std::string get_process_path_by_pid(int pid) {
   char path[32];
   std::sprintf(path, "/proc/%d/exe", pid);
   const auto resolved = ::realpath(path, nullptr);
+  if (!resolved)
+    return { };
   auto result = std::string(resolved);
   ::free(resolved);
   return result;

src/client/linux/FocusedWindowX11.cpp

@@ -55,14 +55,13 @@ class FocusedWindowX11 : public FocusedWindowSystem {
 
     // window handles can become invalid any time
     auto window_class = get_window_class(window);
-    auto window_path = get_window_path(window);
-    if (window_class.empty() || window_title.empty() || window_path.empty())
+    if (window_class.empty() || window_title.empty())
       return false;
 
     m_focused_window = window;
     m_data.window_class = std::move(window_class);
     m_data.window_title = std::move(window_title);
-    m_data.window_path = std::move(window_path);
+    m_data.window_path = get_window_path(window);
     return true;
   }