fix(cli/prompt_secret): fix backspace handling

cli/prompt_secret.ts

@@ -4,8 +4,11 @@ const input = Deno.stdin;
 const output = Deno.stdout;
 const encoder = new TextEncoder();
 const decoder = new TextDecoder();
-const LF = "\n".charCodeAt(0);
-const CR = "\r".charCodeAt(0);
+const LF = "\n".charCodeAt(0); // ^J - Enter on Linux
+const CR = "\r".charCodeAt(0); // ^M - Enter on macOS and Windows (CRLF)
+const BS = "\b".charCodeAt(0); // ^H - Backspace on Linux and Windows
+const DEL = 0x7f; // ^? - Backspace on macOS
+const CLR = encoder.encode("\r\u001b[K"); // Clear the current line
 
 /**
  * Shows the given message and waits for the user's input. Returns the user's input as string.
@@ -20,16 +23,18 @@ export function promptSecret(
     return null;
   }
 
-  const maskChar = encoder.encode(mask);
-  const callback = mask === "" ? undefined : () => {
-    output.writeSync(maskChar);
+  const callback = mask === "" ? undefined : (n: number) => {
+    // Clear the current line
+    output.writeSync(CLR);
+    output.writeSync(encoder.encode(`${message}${mask.repeat(n)}`));
   };
   output.writeSync(encoder.encode(message));
 
   Deno.stdin.setRaw(true, { cbreak: true });
   try {
     return readLineFromStdinSync(callback);
   } finally {
+    output.writeSync(CLR);
     Deno.stdin.setRaw(false);
   }
 }
@@ -38,7 +43,7 @@ export function promptSecret(
 // This implementation immediately break on CR or LF and accept callback.
 // The original version waits LF when CR is received.
 // https://github.com/denoland/deno/blob/e4593873a9c791238685dfbb45e64b4485884174/runtime/js/41_prompt.js#L52-L77
-function readLineFromStdinSync(callback?: () => void): string {
+function readLineFromStdinSync(callback?: (n: number) => void): string {
   const c = new Uint8Array(1);
   const buf = [];
 
@@ -50,8 +55,12 @@ function readLineFromStdinSync(callback?: () => void): string {
     if (c[0] === CR || c[0] === LF) {
       break;
     }
-    buf.push(c[0]);
-    if (callback) callback();
+    if (c[0] === BS || c[0] === DEL) {
+      buf.pop();
+    } else {
+      buf.push(c[0]);
+    }
+    if (callback) callback(buf.length);
   }
   return decoder.decode(new Uint8Array(buf));
 }