Repository: ggml-org/llama.cpp
Pull request: console: allow using arrow left/right, home/end keys and history mode

Fix https://github.com/ggml-org/llama.cpp/issues/17828

Fix https://github.com/ggml-org/llama.cpp/issues/17829

To test it, run `llama-cli`, write some text (without sending it) and use left/right arrows to edit them

Edit: Home/end keys and history support is allso added thanks to @ServeurpersoCom 

https://github.com/user-attachments/assets/afaa2399-21cb-4f45-adc1-97279c8c7302

Disclosure AI usage: `next_utf8_char_pos` is written by AI because I have no experience working with windows API. The rest is mostly written by me (minus some small auto-completion)


Changed files:
filename: common/console.cpp
patch: @@ -1,6 +1,11 @@
 #include "console.h"
 #include <vector>
 #include <iostream>
+#include <cassert>
+#include <cstddef>
+#include <cctype>
+#include <cwctype>
+#include <cstdint>
 
 #if defined(_WIN32)
 #define WIN32_LEAN_AND_MEAN
@@ -35,9 +40,26 @@
 
 namespace console {
 
+#if defined (_WIN32)
+    namespace {
+        // Use private-use unicode values to represent special keys that are not reported
+        // as characters (e.g. arrows on Windows). These values should never clash with
+        // real input and let the rest of the code handle navigation uniformly.
+        static constexpr char32_t KEY_ARROW_LEFT       = 0xE000;
+        static constexpr char32_t KEY_ARROW_RIGHT      = 0xE001;
+        static constexpr char32_t KEY_ARROW_UP         = 0xE002;
+        static constexpr char32_t KEY_ARROW_DOWN       = 0xE003;
+        static constexpr char32_t KEY_HOME             = 0xE004;
+        static constexpr char32_t KEY_END              = 0xE005;
+        static constexpr char32_t KEY_CTRL_ARROW_LEFT  = 0xE006;
+        static constexpr char32_t KEY_CTRL_ARROW_RIGHT = 0xE007;
+        static constexpr char32_t KEY_DELETE           = 0xE008;
+    }
+
     //
     // Console state
     //
+#endif
 
     static bool      advanced_display = false;
     static bool      simple_io        = true;
@@ -176,7 +198,18 @@ namespace console {
             if (record.EventType == KEY_EVENT && record.Event.KeyEvent.bKeyDown) {
                 wchar_t wc = record.Event.KeyEvent.uChar.UnicodeChar;
                 if (wc == 0) {
-                    continue;
+                    const DWORD ctrl_mask = LEFT_CTRL_PRESSED | RIGHT_CTRL_PRESSED;
+                    const bool ctrl_pressed = (record.Event.KeyEvent.dwControlKeyState & ctrl_mask) != 0;
+                    switch (record.Event.KeyEvent.wVirtualKeyCode) {
+                        case VK_LEFT:   return ctrl_pressed ? KEY_CTRL_ARROW_LEFT  : KEY_ARROW_LEFT;
+                        case VK_RIGHT:  return ctrl_pressed ? KEY_CTRL_ARROW_RIGHT : KEY_ARROW_RIGHT;
+                        case VK_UP:     return KEY_ARROW_UP;
+                        case VK_DOWN:   return KEY_ARROW_DOWN;
+                        case VK_HOME:   return KEY_HOME;
+                        case VK_END:    return KEY_END;
+                        case VK_DELETE: return KEY_DELETE;
+                        default:        continue;
+                    }
                 }
 
                 if ((wc >= 0xD800) && (wc <= 0xDBFF)) { // Check if wc is a high surrogate
@@ -315,6 +348,52 @@ namespace console {
 #endif
     }
 
+    static char32_t decode_utf8(const std::string & input, size_t pos, size_t & advance) {
+        unsigned char c = static_cast<unsigned char>(input[pos]);
+        if ((c & 0x80u) == 0u) {
+            advance = 1;
+            return c;
+        }
+        if ((c & 0xE0u) == 0xC0u && pos + 1 < input.size()) {
+            unsigned char c1 = static_cast<unsigned char>(input[pos + 1]);
+            if ((c1 & 0xC0u) != 0x80u) {
+                advance = 1;
+                return 0xFFFD;
+            }
+            advance = 2;
+            return ((c & 0x1Fu) << 6) | (static_cast<unsigned char>(input[pos + 1]) & 0x3Fu);
+        }
+        if ((c & 0xF0u) == 0xE0u && pos + 2 < input.size()) {
+            unsigned char c1 = static_cast<unsigned char>(input[pos + 1]);
+            unsigned char c2 = static_cast<unsigned char>(input[pos + 2]);
+            if ((c1 & 0xC0u) != 0x80u || (c2 & 0xC0u) != 0x80u) {
+                advance = 1;
+                return 0xFFFD;
+            }
+            advance = 3;
+            return ((c & 0x0Fu) << 12) |
+                   ((static_cast<unsigned char>(input[pos + 1]) & 0x3Fu) << 6) |
+                   (static_cast<unsigned char>(input[pos + 2]) & 0x3Fu);
+        }
+        if ((c & 0xF8u) == 0xF0u && pos + 3 < input.size()) {
+            unsigned char c1 = static_cast<unsigned char>(input[pos + 1]);
+            unsigned char c2 = static_cast<unsigned char>(input[pos + 2]);
+            unsigned char c3 = static_cast<unsigned char>(input[pos + 3]);
+            if ((c1 & 0xC0u) != 0x80u || (c2 & 0xC0u) != 0x80u || (c3 & 0xC0u) != 0x80u) {
+                advance = 1;
+                return 0xFFFD;
+            }
+            advance = 4;
+            return ((c & 0x07u) << 18) |
+                   ((static_cast<unsigned char>(input[pos + 1]) & 0x3Fu) << 12) |
+                   ((static_cast<unsigned char>(input[pos + 2]) & 0x3Fu) << 6) |
+                   (static_cast<unsigned char>(input[pos + 3]) & 0x3Fu);
+        }
+
+        advance = 1;
+        return 0xFFFD; // replacement character for invalid input
+    }
+
     static void append_utf8(char32_t ch, std::string & out) {
         if (ch <= 0x7F) {
             out.push_back(static_cast<unsigned char>(ch));
@@ -336,22 +415,319 @@ namespace console {
     }
 
     // Helper function to remove the last UTF-8 character from a string
-    static void pop_back_utf8_char(std::string & line) {
-        if (line.empty()) {
+    static size_t prev_utf8_char_pos(const std::string & line, size_t pos) {
+        if (pos == 0) return 0;
+        pos--;
+        while (pos > 0 && (line[pos] & 0xC0) == 0x80) {
+            pos--;
+        }
+        return pos;
+    }
+
+    static size_t next_utf8_char_pos(const std::string & line, size_t pos) {
+        if (pos >= line.length()) return line.length();
+        pos++;
+        while (pos < line.length() && (line[pos] & 0xC0) == 0x80) {
+            pos++;
+        }
+        return pos;
+    }
+
+    static void move_cursor(int delta);
+    static void move_word_left(size_t & char_pos, size_t & byte_pos, const std::vector<int> & widths, const std::string & line);
+    static void move_word_right(size_t & char_pos, size_t & byte_pos, const std::vector<int> & widths, const std::string & line);
+    static void move_to_line_start(size_t & char_pos, size_t & byte_pos, const std::vector<int> & widths);
+    static void move_to_line_end(size_t & char_pos, size_t & byte_pos, const std::vector<int> & widths, const std::string & line);
+
+    static void delete_at_cursor(std::string & line, std::vector<int> & widths, size_t & char_pos, size_t & byte_pos) {
+        if (char_pos >= widths.size()) {
             return;
         }
 
-        size_t pos = line.length() - 1;
+        size_t next_pos = next_utf8_char_pos(line, byte_pos);
+        int w = widths[char_pos];
+        size_t char_len = next_pos - byte_pos;
+
+        line.erase(byte_pos, char_len);
+        widths.erase(widths.begin() + char_pos);
+
+        size_t p = byte_pos;
+        int tail_width = 0;
+        for (size_t i = char_pos; i < widths.size(); ++i) {
+            size_t following = next_utf8_char_pos(line, p);
+            put_codepoint(line.c_str() + p, following - p, widths[i]);
+            tail_width += widths[i];
+            p = following;
+        }
+
+        for (int i = 0; i < w; ++i) {
+            fputc(' ', out);
+        }
+
+        move_cursor(-(tail_width + w));
+    }
+
+    static void clear_current_line(const std::vector<int> & widths) {
+        int total_width = 0;
+        for (int w : widths) {
+            total_width += (w > 0 ? w : 1);
+        }
+
+        if (total_width > 0) {
+            std::string spaces(total_width, ' ');
+            fwrite(spaces.c_str(), 1, total_width, out);
+            move_cursor(-total_width);
+        }
+    }
+
+    static void set_line_contents(std::string new_line, std::string & line, std::vector<int> & widths, size_t & char_pos,
+                                  size_t & byte_pos) {
+        move_to_line_start(char_pos, byte_pos, widths);
+        clear_current_line(widths);
 
-        // Find the start of the last UTF-8 character (checking up to 4 bytes back)
-        for (size_t i = 0; i < 3 && pos > 0; ++i, --pos) {
-            if ((line[pos] & 0xC0) != 0x80) {
-                break; // Found the start of the character
+        line = std::move(new_line);
+        widths.clear();
+        byte_pos = 0;
+        char_pos = 0;
+
+        size_t idx = 0;
+        while (idx < line.size()) {
+            size_t advance = 0;
+            char32_t cp = decode_utf8(line, idx, advance);
+            int expected_width = estimateWidth(cp);
+            int real_width = put_codepoint(line.c_str() + idx, advance, expected_width);
+            if (real_width < 0) real_width = 0;
+            widths.push_back(real_width);
+            idx += advance;
+            ++char_pos;
+            byte_pos = idx;
+        }
+    }
+
+    static void move_to_line_start(size_t & char_pos, size_t & byte_pos, const std::vector<int> & widths) {
+        int back_width = 0;
+        for (size_t i = 0; i < char_pos; ++i) {
+            back_width += widths[i];
+        }
+        move_cursor(-back_width);
+        char_pos = 0;
+        byte_pos = 0;
+    }
+
+    static void move_to_line_end(size_t & char_pos, size_t & byte_pos, const std::vector<int> & widths, const std::string & line) {
+        int forward_width = 0;
+        for (size_t i = char_pos; i < widths.size(); ++i) {
+            forward_width += widths[i];
+        }
+        move_cursor(forward_width);
+        char_pos = widths.size();
+        byte_pos = line.length();
+    }
+
+    static bool has_ctrl_modifier(const std::string & params) {
+        size_t start = 0;
+        while (start < params.size()) {
+            size_t end = params.find(';', start);
+            size_t len = (end == std::string::npos) ? params.size() - start : end - start;
+            if (len > 0) {
+                int value = 0;
+                for (size_t i = 0; i < len; ++i) {
+                    char ch = params[start + i];
+                    if (!std::isdigit(static_cast<unsigned char>(ch))) {
+                        value = -1;
+                        break;
+                    }
+                    value = value * 10 + (ch - '0');
+                }
+                if (value == 5) {
+                    return true;
+                }
+            }
+
+            if (end == std::string::npos) {
+                break;
+            }
+            start = end + 1;
+        }
+        return false;
+    }
+
+    static bool is_space_codepoint(char32_t cp) {
+        return std::iswspace(static_cast<wint_t>(cp)) != 0;
+    }
+
+    static void move_word_left(size_t & char_pos, size_t & byte_pos, const std::vector<int> & widths, const std::string & line) {
+        if (char_pos == 0) {
+            return;
+        }
+
+        size_t new_char_pos = char_pos;
+        size_t new_byte_pos = byte_pos;
+        int move_width = 0;
+
+        while (new_char_pos > 0) {
+            size_t prev_byte = prev_utf8_char_pos(line, new_byte_pos);
+            size_t advance = 0;
+            char32_t cp = decode_utf8(line, prev_byte, advance);
+            if (!is_space_codepoint(cp)) {
+                break;
+            }
+            move_width += widths[new_char_pos - 1];
+            new_char_pos--;
+            new_byte_pos = prev_byte;
+        }
+
+        while (new_char_pos > 0) {
+            size_t prev_byte = prev_utf8_char_pos(line, new_byte_pos);
+            size_t advance = 0;
+            char32_t cp = decode_utf8(line, prev_byte, advance);
+            if (is_space_codepoint(cp)) {
+                break;
             }
+            move_width += widths[new_char_pos - 1];
+            new_char_pos--;
+            new_byte_pos = prev_byte;
         }
-        line.erase(pos);
+
+        move_cursor(-move_width);
+        char_pos = new_char_pos;
+        byte_pos = new_byte_pos;
     }
 
+    static void move_word_right(size_t & char_pos, size_t & byte_pos, const std::vector<int> & widths, const std::string & line) {
+        if (char_pos >= widths.size()) {
+            return;
+        }
+
+        size_t new_char_pos = char_pos;
+        size_t new_byte_pos = byte_pos;
+        int move_width = 0;
+
+        while (new_char_pos < widths.size()) {
+            size_t advance = 0;
+            char32_t cp = decode_utf8(line, new_byte_pos, advance);
+            if (!is_space_codepoint(cp)) {
+                break;
+            }
+            move_width += widths[new_char_pos];
+            new_char_pos++;
+            new_byte_pos += advance;
+        }
+
+        while (new_char_pos < widths.size()) {
+            size_t advance = 0;
+            char32_t cp = decode_utf8(line, new_byte_pos, advance);
+            if (is_space_codepoint(cp)) {
+                break;
+            }
+            move_width += widths[new_char_pos];
+            new_char_pos++;
+            new_byte_pos += advance;
+        }
+
+        while (new_char_pos < widths.size()) {
+            size_t advance = 0;
+            char32_t cp = decode_utf8(line, new_byte_pos, advance);
+            if (!is_space_codepoint(cp)) {
+                break;
+            }
+            move_width += widths[new_char_pos];
+            new_char_pos++;
+            new_byte_pos += advance;
+        }
+
+        move_cursor(move_width);
+        char_pos = new_char_pos;
+        byte_pos = new_byte_pos;
+    }
+
+    static void move_cursor(int delta) {
+        if (delta == 0) return;
+#if defined(_WIN32)
+        if (hConsole != NULL) {
+            CONSOLE_SCREEN_BUFFER_INFO bufferInfo;
+            GetConsoleScreenBufferInfo(hConsole, &bufferInfo);
+            COORD newCursorPosition = bufferInfo.dwCursorPosition;
+            int width = bufferInfo.dwSize.X;
+            int newX = newCursorPosition.X + delta;
+            int newY = newCursorPosition.Y;
+
+            while (newX >= width) {
+                newX -= width;
+                newY++;
+            }
+            while (newX < 0) {
+                newX += width;
+                newY--;
+            }
+
+            newCursorPosition.X = newX;
+            newCursorPosition.Y = newY;
+            SetConsoleCursorPosition(hConsole, newCursorPosition);
+        }
+#else
+        if (delta < 0) {
+            for (int i = 0; i < -delta; i++) fprintf(out, "\b");
+        } else {
+            for (int i = 0; i < delta; i++) fprintf(out, "\033[C");
+        }
+#endif
+    }
+
+    struct history_t {
+        std::vector<std::string> entries;
+        size_t viewing_idx = SIZE_MAX;
+        std::string backup_line; // current line before viewing history
+        void add(const std::string & line) {
+            if (line.empty()) {
+                return;
+            }
+            // avoid duplicates with the last entry
+            if (entries.empty() || entries.back() != line) {
+                entries.push_back(line);
+            }
+            // also clear viewing state
+            end_viewing();
+        }
+        bool prev(std::string & cur_line) {
+            if (entries.empty()) {
+                return false;
+            }
+            if (viewing_idx == SIZE_MAX) {
+                return false;
+            }
+            if (viewing_idx > 0) {
+                viewing_idx--;
+            }
+            cur_line = entries[viewing_idx];
+            return true;
+        }
+        bool next(std::string & cur_line) {
+            if (entries.empty() || viewing_idx == SIZE_MAX) {
+                return false;
+            }
+            viewing_idx++;
+            if (viewing_idx >= entries.size()) {
+                cur_line = backup_line;
+                end_viewing();
+            } else {
+                cur_line = entries[viewing_idx];
+            }
+            return true;
+        }
+        void begin_viewing(const std::string & line) {
+            backup_line = line;
+            viewing_idx = entries.size();
+        }
+        void end_viewing() {
+            viewing_idx = SIZE_MAX;
+            backup_line.clear();
+        }
+        bool is_viewing() const {
+            return viewing_idx != SIZE_MAX;
+        }
+    } history;
+
     static bool readline_advanced(std::string & line, bool multiline_input) {
         if (out != stdout) {
             fflush(stdout);
@@ -362,16 +738,41 @@ namespace console {
         bool is_special_char = false;
         bool end_of_stream = false;
 
+        size_t byte_pos = 0; // current byte index
+        size_t char_pos = 0; // current character index (one char can be multiple bytes)
+
         char32_t input_char;
         while (true) {
+            assert(char_pos <= byte_pos);
+            assert(char_pos <= widths.size());
+            auto history_prev = [&]() {
+                if (!history.is_viewing()) {
+                    history.begin_viewing(line);
+                }
+                std::string new_line;
+                if (!history.prev(new_line)) {
+                    return;
+                }
+                set_line_contents(new_line, line, widths, char_pos, byte_pos);
+            };
+            auto history_next = [&]() {
+                if (history.is_viewing()) {
+                    std::string new_line;
+                    if (!history.next(new_line)) {
+                        return;
+                    }
+                    set_line_contents(new_line, line, widths, char_pos, byte_pos);
+                }
+            };
+
             fflush(out); // Ensure all output is displayed before waiting for input
             input_char = getchar32();
 
             if (input_char == '\r' || input_char == '\n') {
                 break;
             }
 
-            if (input_char == (char32_t) WEOF || input_char == 0x04 /* Ctrl+D*/) {
+            if (input_char == (char32_t) WEOF || input_char == 0x04 /* Ctrl+D */) {
                 end_of_stream = true;
                 break;
             }
@@ -384,36 +785,179 @@ namespace console {
 
             if (input_char == '\033') { // Escape sequence
                 char32_t code = getchar32();
-                if (code == '[' || code == 0x1B) {
+                if (code == '[') {
+                    std::string params;
+                    while (true) {
+                        code = getchar32();
+                        if ((code >= 'A' && code <= 'Z') || (code >= 'a' && code <= 'z') || code == '~' || code == (char32_t) WEOF) {
+                            break;
+                        }
+                        params.push_back(static_cast<char>(code));
+                    }
+
+                    const bool ctrl_modifier = has_ctrl_modifier(params);
+
+                    if (code == 'D') { // left
+                        if (ctrl_modifier) {
+                            move_word_left(char_pos, byte_pos, widths, line);
+                        } else if (char_pos > 0) {
+                            int w = widths[char_pos - 1];
+                            move_cursor(-w);
+                            char_pos--;
+                            byte_pos = prev_utf8_char_pos(line, byte_pos);
+                        }
+                    } else if (code == 'C') { // right
+                        if (ctrl_modifier) {
+                            move_word_right(char_pos, byte_pos, widths, line);
+                        } else if (char_pos < widths.size()) {
+                            int w = widths[char_pos];
+                            move_cursor(w);
+                            char_pos++;
+                            byte_pos = next_utf8_char_pos(line, byte_pos);
+                        }
+                    } else if (code == 'H') { // home
+                        move_to_line_start(char_pos, byte_pos, widths);
+                    } else if (code == 'F') { // end
+                        move_to_line_end(char_pos, byte_pos, widths, line);
+                    } else if (code == 'A' || code == 'B') {
+                        // up/down
+                        if (code == 'A') {
+                            history_prev();
+                            is_special_char = false;
+                        } else if (code == 'B') {
+                            history_next();
+                            is_special_char = false;
+                        }
+                    } else if ((code == '~' || (code >= 'A' && code <= 'Z') || (code >= 'a' && code <= 'z')) && !params.empty()) {
+                        std::string digits;
+                        for (char ch : params) {
+                            if (ch == ';') {
+                                break;
+                            }
+                            if (std::isdigit(static_cast<unsigned char>(ch))) {
+                                digits.push_back(ch);
+                            }
+                        }
+
+                        if (code == '~') {
+                            if (digits == "1" || digits == "7") { // home
+                                move_to_line_start(char_pos, byte_pos, widths);
+                            } else if (digits == "4" || digits == "8") { // end
+                                move_to_line_end(char_pos, byte_pos, widths, line);
+                            } else if (digits == "3") { // delete
+                                delete_at_cursor(line, widths, char_pos, byte_pos);
+                            }
+                        }
+                    }
+                } else if (code == 0x1B) {
                     // Discard the rest of the escape sequence
                     while ((code = getchar32()) != (char32_t) WEOF) {
                         if ((code >= 'A' && code <= 'Z') || (code >= 'a' && code <= 'z') || code == '~') {
                             break;
                         }
                     }
                 }
+#if defined(_WIN32)
+            } else if (input_char == KEY_ARROW_LEFT) {
+                if (char_pos > 0) {
+                    int w = widths[char_pos - 1];
+                    move_cursor(-w);
+                    char_pos--;
+                    byte_pos = prev_utf8_char_pos(line, byte_pos);
+                }
+            } else if (input_char == KEY_ARROW_RIGHT) {
+                if (char_pos < widths.size()) {
+                    int w = widths[char_pos];
+                    move_cursor(w);
+                    char_pos++;
+                    byte_pos = next_utf8_char_pos(line, byte_pos);
+                }
+            } else if (input_char == KEY_CTRL_ARROW_LEFT) {
+                move_word_left(char_pos, byte_pos, widths, line);
+            } else if (input_char == KEY_CTRL_ARROW_RIGHT) {
+                move_word_right(char_pos, byte_pos, widths, line);
+            } else if (input_char == KEY_HOME) {
+                move_to_line_start(char_pos, byte_pos, widths);
+            } else if (input_char == KEY_END) {
+                move_to_line_end(char_pos, byte_pos, widths, line);
+            } else if (input_char == KEY_DELETE) {
+                delete_at_cursor(line, widths, char_pos, byte_pos);
+            } else if (input_char == KEY_ARROW_UP || input_char == KEY_ARROW_DOWN) {
+                if (input_char == KEY_ARROW_UP) {
+                    history_prev();
+                    is_special_char = false;
+                } else if (input_char == KEY_ARROW_DOWN) {
+                    history_next();
+                    is_special_char = false;
+                }
+#endif
             } else if (input_char == 0x08 || input_char == 0x7F) { // Backspace
-                if (!widths.empty()) {
-                    int count;
-                    do {
-                        count = widths.back();
-                        widths.pop_back();
-                        // Move cursor back, print space, and move cursor back again
-                        for (int i = 0; i < count; i++) {
-                            replace_last(' ');
-                            pop_cursor();
-                        }
-                        pop_back_utf8_char(line);
-                    } while (count == 0 && !widths.empty());
+                if (char_pos > 0) {
+                    int w = widths[char_pos - 1];
+                    move_cursor(-w);
+                    char_pos--;
+                    size_t prev_pos = prev_utf8_char_pos(line, byte_pos);
+                    size_t char_len = byte_pos - prev_pos;
+                    byte_pos = prev_pos;
+
+                    // remove the character
+                    line.erase(byte_pos, char_len);
+                    widths.erase(widths.begin() + char_pos);
+
+                    // redraw tail
+                    size_t p = byte_pos;
+                    int tail_width = 0;
+                    for (size_t i = char_pos; i < widths.size(); ++i) {
+                        size_t next_p = next_utf8_char_pos(line, p);
+                        put_codepoint(line.c_str() + p, next_p - p, widths[i]);
+                        tail_width += widths[i];
+                        p = next_p;
+                    }
+
+                    // clear display
+                    for (int i = 0; i < w; ++i) {
+                        fputc(' ', out);
+                    }
+                    move_cursor(-(tail_width + w));
                 }
             } else {
-                int offset = line.length();
-                append_utf8(input_char, line);
-                int width = put_codepoint(line.c_str() + offset, line.length() - offset, estimateWidth(input_char));
-                if (width < 0) {
-                    width = 0;
+                // insert character
+                std::string new_char_str;
+                append_utf8(input_char, new_char_str);
+                int w = estimateWidth(input_char);
+
+                if (char_pos == widths.size()) {
+                    // insert at the end
+                    line += new_char_str;
+                    int real_w = put_codepoint(new_char_str.c_str(), new_char_str.length(), w);
+                    if (real_w < 0) real_w = 0;
+                    widths.push_back(real_w);
+                    byte_pos += new_char_str.length();
+                    char_pos++;
+                } else {
+                    // insert in middle
+                    line.insert(byte_pos, new_char_str);
+
+                    int real_w = put_codepoint(new_char_str.c_str(), new_char_str.length(), w);
+                    if (real_w < 0) real_w = 0;
+
+                    widths.insert(widths.begin() + char_pos, real_w);
+
+                    // print the tail
+                    size_t p = byte_pos + new_char_str.length();
+                    int tail_width = 0;
+                    for (size_t i = char_pos + 1; i < widths.size(); ++i) {
+                        size_t next_p = next_utf8_char_pos(line, p);
+                        put_codepoint(line.c_str() + p, next_p - p, widths[i]);
+                        tail_width += widths[i];
+                        p = next_p;
+                    }
+
+                    move_cursor(-tail_width);
+
+                    byte_pos += new_char_str.length();
+                    char_pos++;
                 }
-                widths.push_back(width);
             }
 
             if (!line.empty() && (line.back() == '\\' || line.back() == '/')) {
@@ -451,6 +995,15 @@ namespace console {
             }
         }
 
+        if (!end_of_stream && !line.empty()) {
+            // remove the trailing newline for history storage
+            if (!line.empty() && line.back() == '\n') {
+                line.pop_back();
+            }
+            // TODO: maybe support multiline history entries?
+            history.add(line);
+        }
+
         fflush(out);
         return has_more;
     }