main : Fix Ctrl+D/newline handling (#12951)

This restores the behavior from #491. This does not affect Ctrl+D's ability to
terminate --multiline-input lines (#1040).

This also actually implements #587: "If the user wants the text to end in a
newline, this should be accomplished by explicitly adding a newline by using
\ followed by return, then returning control by pressing return again."

Fixes #12949

examples/main/main.cpp

@@ -865,9 +865,22 @@ int main(int argc, char ** argv) {
                 console::set_display(console::reset);
                 display = true;
 
-                // Add tokens to embd only if the input buffer is non-empty
-                // Entering a empty line lets the user pass control back
-                if (buffer.length() > 1) {
+                if (buffer.empty()) { // Ctrl+D on empty line exits
+                    LOG("EOF by user\n");
+                    break;
+                }
+
+                if (buffer.back() == '\n') {
+                    // Implement #587:
+                    // If the user wants the text to end in a newline,
+                    // this should be accomplished by explicitly adding a newline by using \ followed by return,
+                    // then returning control by pressing return again.
+                    buffer.pop_back();
+                }
+
+                if (buffer.empty()) { // Enter key on empty line lets the user pass control back
+                    LOG_DBG("empty line, passing control back\n");
+                } else { // Add tokens to embd only if the input buffer is non-empty
                     // append input suffix if any
                     if (!params.input_suffix.empty() && !params.conversation_mode) {
                         LOG_DBG("appending input suffix: '%s'\n", params.input_suffix.c_str());
@@ -915,8 +928,6 @@ int main(int argc, char ** argv) {
 
                     n_remain -= line_inp.size();
                     LOG_DBG("n_remain: %d\n", n_remain);
-                } else {
-                    LOG_DBG("empty line, passing control back\n");
                 }
 
                 input_echo = false; // do not echo this again