readline: fix issue with newline-less last line

lib/internal/readline/interface.js

@@ -1324,21 +1324,19 @@ class Interface extends InterfaceConstructor {
           if (typeof s === 'string' && s) {
             // Erase state of previous searches.
             lineEnding.lastIndex = 0;
-            let nextMatch = RegExpPrototypeExec(lineEnding, s);
-            // If no line endings are found, just insert the string as is.
-            if (nextMatch === null) {
-              this[kInsertString](s);
-            } else {
-              // Keep track of the end of the last match.
-              let lastIndex = 0;
-              do {
-                this[kInsertString](StringPrototypeSlice(s, lastIndex, nextMatch.index));
-                ({ lastIndex } = lineEnding);
-                this[kLine]();
-                // Restore lastIndex as the call to kLine could have mutated it.
-                lineEnding.lastIndex = lastIndex;
-              } while ((nextMatch = RegExpPrototypeExec(lineEnding, s)) !== null);
+            let nextMatch;
+            // Keep track of the end of the last match.
+            let lastIndex = 0;
+            while ((nextMatch = RegExpPrototypeExec(lineEnding, s)) !== null) {
+              this[kInsertString](StringPrototypeSlice(s, lastIndex, nextMatch.index));
+              ({ lastIndex } = lineEnding);
+              this[kLine]();
+              // Restore lastIndex as the call to kLine could have mutated it.
+              lineEnding.lastIndex = lastIndex;
             }
+            // This ensures that the last line is written if it doesn't end in a newline.
+            // Note that the last line may be the first line, in which case this still works.
+            this[kInsertString](StringPrototypeSlice(s, lastIndex));
           }
       }
     }

test/fixtures/repl-load-multiline-no-trailing-newline.js

@@ -0,0 +1,6 @@
+const getLunch = () =>
+  placeOrder('tacos')
+    .then(eat);
+
+const placeOrder = (order) => Promise.resolve(order);
+const eat = (food) => '<nom nom nom>';

test/parallel/test-readline-interface-no-trailing-newline.js

@@ -0,0 +1,24 @@
+'use strict';
+const common = require('../common');
+const ArrayStream = require('../common/arraystream');
+const assert = require('assert');
+
+common.skipIfDumbTerminal();
+
+const readline = require('readline');
+const rli = new readline.Interface({
+  terminal: true,
+  input: new ArrayStream(),
+  output: new ArrayStream(),
+});
+
+// Minimal reproduction for #47305
+const testInput = '{\n}';
+
+let accum = '';
+
+rli.output.write = data => accum += data.replace('\r', '');
+
+rli.write(testInput);
+
+assert.strictEqual(accum, testInput);

test/parallel/test-repl-load-multiline-no-trailing-newline.js

@@ -0,0 +1,41 @@
+'use strict';
+const common = require('../common');
+const ArrayStream = require('../common/arraystream');
+const fixtures = require('../common/fixtures');
+const assert = require('assert');
+const repl = require('repl');
+
+common.skipIfDumbTerminal();
+
+const command = `.load ${fixtures.path('repl-load-multiline-no-trailing-newline.js')}`;
+const terminalCode = '\u001b[1G\u001b[0J \u001b[1G';
+const terminalCodeRegex = new RegExp(terminalCode.replace(/\[/g, '\\['), 'g');
+
+const expected = `${command}
+const getLunch = () =>
+  placeOrder('tacos')
+    .then(eat);
+
+const placeOrder = (order) => Promise.resolve(order);
+const eat = (food) => '<nom nom nom>';
+undefined
+`;
+
+let accum = '';
+
+const inputStream = new ArrayStream();
+const outputStream = new ArrayStream();
+
+outputStream.write = (data) => accum += data.replace('\r', '');
+
+const r = repl.start({
+  prompt: '',
+  input: inputStream,
+  output: outputStream,
+  terminal: true,
+  useColors: false
+});
+
+r.write(`${command}\n`);
+assert.strictEqual(accum.replace(terminalCodeRegex, ''), expected);
+r.close();