Ensure escaped trailing spaces are not trimmed

src/reader.cpp

@@ -3226,8 +3226,29 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
                 }
 
                 // Historical behavior is to trim trailing spaces.
+                // However, escaped spaces ('\ ') should not be trimmed (#7661)
                 while (!text.empty() && text.back() == L' ') {
-                    text.pop_back();
+                    // This can be done by counting pre-trailing '\'
+                    // If there's an odd number, this must be an excaped space
+                  
+                    // first check if the trailing space can be escaped at all
+                    //   (making the common case fast)
+                    if(text.length() == 1 || text[text.length()-2] != L'\\') {
+                        text.pop_back();
+                    } else {
+                        // We've found one backslash so far, count the rest
+                        size_t num_pretrailing_backslashes = 1;
+                        for(size_t i_offset=text.length()-2;
+                            i_offset > 0 && text[i_offset-1] == L'\\'; --i_offset)
+                            num_pretrailing_backslashes++;
+                        if(num_pretrailing_backslashes%2 == 0) {
+                            // even; this space is not escaped and should be removed
+                            text.pop_back();
+                        }
+                        // Because the above accounts for the final character,
+                        // we're done here. Break so there's not an infinite loop
+                        break;
+                    }
                 }
 
                 if (history && !conf.in_silent_mode) {