Fix fixes the compile warning,

../../../../github/wayfire/wayfire.git/src/debug.cpp: In function ‘std::string read_output(std::string)’: ../../../../github/wayfire/wayfire.git/src/debug.cpp:95:10: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
95 | fgets(buffer, MAX_FUNCTION_NAME, file);
| ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In this case there is a potential problem: if gets returns NULL,
then nothing was read and the buffer is uninitialized. Not only
would this function be returning uninitialized data, an arbitrary
amount of memory could be allocated into line (and be returned)
when std::string line = buffer; is searching for a terminating
zero in the uninitialized buffer.

src/debug.cpp

@@ -92,9 +92,14 @@ std::string read_output(std::string command)
         return "";
     }
 
-    fgets(buffer, MAX_FUNCTION_NAME, file);
+    char *line_as_c_str = fgets(buffer, MAX_FUNCTION_NAME, file);
     pclose(file);
 
+    if (!line_as_c_str)
+    {
+        return {};
+    }
+
     std::string line = buffer;
     if (line.size() && (line.back() == '\n'))
     {