repl: support previews by eager evaluating input

This adds input previews by using the inspectors eager evaluation
functionality.
It is implemented as additional line that is not counted towards
the actual input. In case no colors are supported, it will be visible
as comment. Otherwise it's grey.
It will be triggered on any line change. It is heavily tested against
edge cases and adheres to "dumb" terminals (previews are deactived
in that case).

PR-URL: https://github.com/nodejs/node/pull/30811
Fixes: https://github.com/nodejs/node/issues/20977
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

1 files changed, 17 insertions, 1 deletions

diff --git a/lib/repl.js b/lib/repl.js
index b6876bb8c6..98b0d2415d 100644
--- a/lib/repl.js
+++ b/lib/repl.js
@@ -98,7 +98,8 @@ const experimentalREPLAwait = require('internal/options').getOptionValue(
 );
 const {
   isRecoverableError,
-  kStandaloneREPL
+  kStandaloneREPL,
+  setupPreview,
 } = require('internal/repl/utils');
 const {
   getOwnNonIndexProperties,
@@ -204,6 +205,9 @@ function REPLServer(prompt,
     }
   }
 
+  const preview = options.terminal &&
+    (options.preview !== undefined ? !!options.preview : true);
+
   this.inputStream = options.input;
   this.outputStream = options.output;
   this.useColors = !!options.useColors;
@@ -804,9 +808,20 @@ function REPLServer(prompt,
     }
   });
 
+  const {
+    clearPreview,
+    showInputPreview
+  } = setupPreview(
+    this,
+    kContextId,
+    kBufferedCommandSymbol,
+    preview
+  );
+
   // Wrap readline tty to enable editor mode and pausing.
   const ttyWrite = self._ttyWrite.bind(self);
   self._ttyWrite = (d, key) => {
+    clearPreview();
     key = key || {};
     if (paused && !(self.breakEvalOnSigint && key.ctrl && key.name === 'c')) {
       pausedBuffer.push(['key', [d, key]]);
@@ -819,6 +834,7 @@ function REPLServer(prompt,
         self.clearLine();
       }
       ttyWrite(d, key);
+      showInputPreview();
       return;
     }