readline: improve unicode support and tab completion

1. This reduces the number of write operations used during tab
   completion.
2. The tab completion calculated the string width using the length
   of the string instead of using the actual width. That is fixed.
3. The key decoder is now capable of handling characters composed
   out of two code points. That reduces the number of "keypress"
   events that are emitted which again lowers the amount of writes
   triggered.

PR-URL: #31288
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Author: BridgeAR

lib/internal/readline/utils.js

@@ -163,7 +163,6 @@ function stripVTControlCharacters(str) {
   return str.replace(ansi, '');
 }
 
-
 /*
   Some patterns seen in terminal key escape codes, derived from combos seen
   at http://www.midnight-commander.org/browser/lib/tty/key.c
@@ -450,7 +449,7 @@ function* emitKeys(stream) {
     if (s.length !== 0 && (key.name !== undefined || escaped)) {
       /* Named character or sequence */
       stream.emit('keypress', escaped ? undefined : s, key);
-    } else if (s.length === 1) {
+    } else if (charLengthAt(s, 0) === s.length) {
       /* Single unnamed character, e.g. "." */
       stream.emit('keypress', s, key);
     }

lib/readline.js

@@ -494,81 +494,67 @@ Interface.prototype._insertString = function(c) {
 };
 
 Interface.prototype._tabComplete = function(lastKeypressWasTab) {
-  const self = this;
-
-  self.pause();
-  self.completer(self.line.slice(0, self.cursor), function onComplete(err, rv) {
-    self.resume();
+  this.pause();
+  this.completer(this.line.slice(0, this.cursor), (err, value) => {
+    this.resume();
 
     if (err) {
-      self._writeToOutput(`Tab completion error: ${inspect(err)}`);
+      this._writeToOutput(`Tab completion error: ${inspect(err)}`);
       return;
     }
 
     // Result and the text that was completed.
-    const [completions, completeOn] = rv;
+    const [completions, completeOn] = value;
 
     if (!completions || completions.length === 0) {
       return;
     }
 
-    // Apply/show completions.
-    if (lastKeypressWasTab) {
-      self._writeToOutput('\r\n');
-      const width = completions.reduce((a, b) => {
-        return a.length > b.length ? a : b;
-      }).length + 2;  // 2 space padding
-      let maxColumns = MathFloor(self.columns / width);
-      if (!maxColumns || maxColumns === Infinity) {
-        maxColumns = 1;
-      }
-      let group = [];
-      for (const c of completions) {
-        if (c === '') {
-          handleGroup(self, group, width, maxColumns);
-          group = [];
-        } else {
-          group.push(c);
-        }
-      }
-      handleGroup(self, group, width, maxColumns);
-    }
-
     // If there is a common prefix to all matches, then apply that portion.
-    const f = completions.filter((e) => e);
-    const prefix = commonPrefix(f);
+    const prefix = commonPrefix(completions.filter((e) => e !== ''));
     if (prefix.length > completeOn.length) {
-      self._insertString(prefix.slice(completeOn.length));
+      this._insertString(prefix.slice(completeOn.length));
+      return;
     }
 
-    self._refreshLine();
-  });
-};
+    if (!lastKeypressWasTab) {
+      return;
+    }
 
-// this = Interface instance
-function handleGroup(self, group, width, maxColumns) {
-  if (group.length === 0) {
-    return;
-  }
-  const minRows = MathCeil(group.length / maxColumns);
-  for (let row = 0; row < minRows; row++) {
-    for (let col = 0; col < maxColumns; col++) {
-      const idx = row * maxColumns + col;
-      if (idx >= group.length) {
-        break;
+    // Apply/show completions.
+    const completionsWidth = completions.map((e) => getStringWidth(e));
+    const width = MathMax(...completionsWidth) + 2; // 2 space padding
+    let maxColumns = MathFloor(this.columns / width) || 1;
+    if (maxColumns === Infinity) {
+      maxColumns = 1;
+    }
+    let output = '\r\n';
+    let lineIndex = 0;
+    let whitespace = 0;
+    for (let i = 0; i < completions.length; i++) {
+      const completion = completions[i];
+      if (completion === '' || lineIndex === maxColumns) {
+        output += '\r\n';
+        lineIndex = 0;
+        whitespace = 0;
+      } else {
+        output += ' '.repeat(whitespace);
       }
-      const item = group[idx];
-      self._writeToOutput(item);
-      if (col < maxColumns - 1) {
-        for (let s = 0; s < width - item.length; s++) {
-          self._writeToOutput(' ');
-        }
+      if (completion !== '') {
+        output += completion;
+        whitespace = width - completionsWidth[i];
+        lineIndex++;
+      } else {
+        output += '\r\n';
       }
     }
-    self._writeToOutput('\r\n');
-  }
-  self._writeToOutput('\r\n');
-}
+    if (lineIndex !== 0) {
+      output += '\r\n\r\n';
+    }
+    this._writeToOutput(output);
+    this._refreshLine();
+  });
+};
 
 Interface.prototype._wordLeft = function() {
   if (this.cursor > 0) {
@@ -1125,7 +1111,7 @@ Interface.prototype[SymbolAsyncIterator] = function() {
  * accepts a readable Stream instance and makes it emit "keypress" events
  */
 
-function emitKeypressEvents(stream, iface) {
+function emitKeypressEvents(stream, iface = {}) {
   if (stream[KEYPRESS_DECODER]) return;
 
   stream[KEYPRESS_DECODER] = new StringDecoder('utf8');
@@ -1138,26 +1124,25 @@ function emitKeypressEvents(stream, iface) {
 
   function onData(b) {
     if (stream.listenerCount('keypress') > 0) {
-      const r = stream[KEYPRESS_DECODER].write(b);
-      if (r) {
+      const string = stream[KEYPRESS_DECODER].write(b);
+      if (string) {
         clearTimeout(timeoutId);
 
-        let escapeTimeout = ESCAPE_CODE_TIMEOUT;
-
-        if (iface) {
-          iface._sawKeyPress = r.length === 1;
-          escapeTimeout = iface.escapeCodeTimeout;
-        }
+        // This supports characters of length 2.
+        iface._sawKeyPress = charLengthAt(string, 0) === string.length;
+        const escapeTimeout = iface.escapeCodeTimeout || ESCAPE_CODE_TIMEOUT;
 
-        for (let i = 0; i < r.length; i++) {
-          if (r[i] === '\t' && typeof r[i + 1] === 'string' && iface) {
+        let length = 0;
+        for (const character of string) {
+          length += character.length;
+          if (character === '\t' && length !== string.length) {
             iface.isCompletionEnabled = false;
           }
 
           try {
-            stream[ESCAPE_DECODER].next(r[i]);
+            stream[ESCAPE_DECODER].next(character);
             // Escape letter at the tail position
-            if (r[i] === kEscape && i + 1 === r.length) {
+            if (character === kEscape && length === string.length) {
               timeoutId = setTimeout(escapeCodeTimeout, escapeTimeout);
             }
           } catch (err) {

test/parallel/test-readline-tab-complete.js

@@ -0,0 +1,68 @@
+'use strict';
+
+// Flags: --expose_internals
+
+const common = require('../common');
+const readline = require('readline');
+const assert = require('assert');
+const EventEmitter = require('events').EventEmitter;
+const { getStringWidth } = require('internal/readline/utils');
+
+// This test verifies that the tab completion supports unicode and the writes
+// are limited to the minimum.
+[
+  'あ',
+  '𐐷',
+  '🐕'
+].forEach((char) => {
+  [true, false].forEach((lineBreak) => {
+    const completer = (line) => [
+      [
+        'First group',
+        '',
+        `${char}${'a'.repeat(10)}`, `${char}${'b'.repeat(10)}`, char.repeat(11),
+      ],
+      line
+    ];
+
+    let output = '';
+    const width = getStringWidth(char) - 1;
+
+    class FakeInput extends EventEmitter {
+    columns = ((width + 1) * 10 + (lineBreak ? 0 : 10)) * 3
+
+    write = common.mustCall((data) => {
+      output += data;
+    }, 6)
+
+    resume() {}
+    pause() {}
+    end() {}
+    }
+
+    const fi = new FakeInput();
+    const rli = new readline.Interface({
+      input: fi,
+      output: fi,
+      terminal: true,
+      completer: completer
+    });
+
+    const last = '\r\nFirst group\r\n\r\n' +
+    `${char}${'a'.repeat(10)}${' '.repeat(2 + width * 10)}` +
+      `${char}${'b'.repeat(10)}` +
+      (lineBreak ? '\r\n' : ' '.repeat(2 + width * 10)) +
+      `${char.repeat(11)}\r\n` +
+    `\r\n\u001b[1G\u001b[0J> ${char}\u001b[${4 + width}G`;
+
+    const expectations = [char, '', last];
+
+    rli.on('line', common.mustNotCall());
+    for (const character of `${char}\t\t`) {
+      fi.emit('data', character);
+      assert.strictEqual(output, expectations.shift());
+      output = '';
+    }
+    rli.close();
+  });
+});