repl: handle dot commands in multiline input

lib/repl.js

@@ -76,6 +76,7 @@ const {
   StringPrototypeCharAt,
   StringPrototypeEndsWith,
   StringPrototypeIncludes,
+  StringPrototypeLastIndexOf,
   StringPrototypeRepeat,
   StringPrototypeSlice,
   StringPrototypeStartsWith,
@@ -802,7 +803,31 @@ class REPLServer extends Interface {
       }
 
       // Check REPL keywords and empty lines against a trimmed line input.
-      const trimmedCmd = StringPrototypeTrim(cmd);
+      let trimmedCmd = StringPrototypeTrim(cmd);
+
+      // TTY multiline input is stored as one editable line by readline. Check
+      // the newest physical line so dot-commands work from a continuation
+      // prompt, while keeping the previous lines buffered.
+      if (self.terminal &&
+          !self[kBufferedCommandSymbol] &&
+          StringPrototypeIncludes(cmd, '\n')) {
+        const lastNewlineIndex = StringPrototypeLastIndexOf(cmd, '\n');
+        const commandLine = StringPrototypeSlice(cmd, lastNewlineIndex + 1);
+        const trimmedCommandLine = StringPrototypeTrim(commandLine);
+
+        if (StringPrototypeCharAt(trimmedCommandLine, 0) === '.' &&
+            StringPrototypeCharAt(trimmedCommandLine, 1) !== '.' &&
+            NumberIsNaN(NumberParseFloat(trimmedCommandLine))) {
+          const matches = RegExpPrototypeExec(/^\.([^\s]+)\s*(.*)$/, trimmedCommandLine);
+          const keyword = matches?.[1];
+
+          if (self.commands[keyword]) {
+            self[kBufferedCommandSymbol] =
+              StringPrototypeSlice(cmd, 0, lastNewlineIndex + 1);
+            trimmedCmd = trimmedCommandLine;
+          }
+        }
+      }
 
       // Check to see if a REPL keyword was used. If it returns true,
       // display next prompt and return.

test/parallel/test-repl-multiline.js

@@ -4,6 +4,8 @@ const assert = require('assert');
 const { startNewREPLServer } = require('../common/repl');
 
 const input = ['const foo = {', '};', 'foo'];
+const dotCommandSyntaxError =
+  /Uncaught SyntaxError: Unexpected token '\.'/;
 
 function run({ useColors }) {
   const { replServer, output } = startNewREPLServer({ useColors });
@@ -27,3 +29,47 @@ function run({ useColors }) {
 
 run({ useColors: true });
 run({ useColors: false });
+
+function runDotCommandAfterRecoverable(command, validate) {
+  const { replServer, output } = startNewREPLServer();
+
+  replServer.on('exit', common.mustCall());
+  replServer.write('function a() {\n');
+  replServer.write(`${command}\n`);
+
+  assert.doesNotMatch(output.accumulator, dotCommandSyntaxError);
+  validate(replServer, output);
+
+  replServer.close();
+}
+
+runDotCommandAfterRecoverable('.break', (replServer, output) => {
+  replServer.write('1 + 1\n');
+  assert.doesNotMatch(output.accumulator, dotCommandSyntaxError);
+  assert.match(output.accumulator, /2\n/);
+});
+
+runDotCommandAfterRecoverable('.help', (replServer, output) => {
+  assert.match(output.accumulator, /\.break\s+Sometimes you get stuck/);
+  assert.match(output.accumulator, /\.help\s+Print this help message/);
+
+  replServer.write('.break\n');
+  replServer.write('1 + 1\n');
+
+  assert.doesNotMatch(output.accumulator, dotCommandSyntaxError);
+  assert.match(output.accumulator, /2\n/);
+});
+
+{
+  const { replServer, output } = startNewREPLServer();
+  let exited = false;
+
+  replServer.on('exit', common.mustCall(() => {
+    exited = true;
+  }));
+  replServer.write('function a() {\n');
+  replServer.write('.exit\n');
+
+  assert.strictEqual(exited, true);
+  assert.doesNotMatch(output.accumulator, dotCommandSyntaxError);
+}