readline: fix position computation

The implementation of _getDisplayPos, used to compute the cursor
position and to find out how many lines to clear up when re-rendering
the readline output, was counting each line (except the last one) from
the input as one row, even if they were wraping.  This caused some
rendering issues when the 'prompt' have at least one wide line ending
with a newline char, duplicating the lines at the top of the prompt when
calling _refreshLine (ex: when the user hits backspace).

This patch fixes the issue by computing the real rows count for each new
line in the input string.

PR-URL: #28272
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/readline.js

@@ -732,8 +732,9 @@ Interface.prototype._getDisplayPos = function(str) {
       i++;
     }
     if (code === 0x0a) { // new line \n
+      // row must be incremented by 1 even if offset = 0 or col = +Infinity
+      row += Math.ceil(offset / col) || 1;
       offset = 0;
-      row += 1;
       continue;
     }
     const width = getStringWidth(code);

test/parallel/test-readline-interface.js

@@ -1042,7 +1042,7 @@ function isWarned(emitter) {
       rli.close();
     }
 
-    // multi-line cursor position
+    // Multi-line input cursor position
     {
       const fi = new FakeInput();
       const rli = new readline.Interface({
@@ -1059,6 +1059,23 @@ function isWarned(emitter) {
       rli.close();
     }
 
+    // Multi-line prompt cursor position
+    {
+      const fi = new FakeInput();
+      const rli = new readline.Interface({
+        input: fi,
+        output: fi,
+        prompt: '\nfilledline\nwraping text\n> ',
+        terminal: terminal
+      });
+      fi.columns = 10;
+      fi.emit('data', 't');
+      const cursorPos = rli._getCursorPos();
+      assert.strictEqual(cursorPos.rows, 4);
+      assert.strictEqual(cursorPos.cols, 3);
+      rli.close();
+    }
+
     // Clear the whole screen
     {
       const fi = new FakeInput();