pexpect test for commandline --current-process

It was not clear to me hwo this behaves when there are comments.

Include a friendly helper to compute control characters.
No functional change.

build_tools/pexpect_helper.py

@@ -341,3 +341,25 @@ class SpawnedProc(object):
             "LIGHTCYAN": ansic(96),
             "WHITE": ansic(97),
         }
+
+
+def control(char: str) -> str:
+    """ Returns the char sent when control is pressed along the given key. """
+    assert len(char) == 1
+    char = char.lower()
+    if ord("a") <= ord(char) <= ord("z"):
+        return chr(ord(char) - ord("a") + 1)
+    return chr({
+        "@": 0,
+        "`": 0,
+        "[": 27,
+        "{": 27,
+        "\\": 28,
+        "|": 28,
+        "]": 29,
+        "}": 29,
+        "^": 30,
+        "~": 30,
+        "_": 31,
+        "?": 127,
+    }[char])

tests/pexpects/commandline.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-from pexpect_helper import SpawnedProc
+from pexpect_helper import SpawnedProc, control
 
 sp = SpawnedProc()
 send, sendline, sleep, expect_prompt, expect_re, expect_str = (
@@ -59,3 +59,28 @@ send("\b" * 64)
 # Commandline works when run on its own (#8807).
 sendline("commandline whatever")
 expect_re("prompt [0-9]+>whatever")
+
+# Test --current-process output
+send(control("u"))
+sendline(r"bind \cb 'set tmp (commandline --current-process)'")
+expect_prompt()
+send("echo process1; echo process2")
+send(control("a"))
+send(control("b"))
+send(control("k"))
+sendline("echo first process is <$tmp>")
+expect_str("first process is <echo process1>")
+
+send("echo process # comment")
+send(control("a"))
+send(control("b"))
+send(control("k"))
+sendline('echo "process extent is <$tmp>"')
+expect_str("process extent is <echo process # comment>")
+
+sendline(r"bind \cb 'set tmp (commandline --current-process | count)'")
+sendline(r'commandline "echo line1 \\" "# comment" "line2"')
+send(control("b"))
+send(control("u") * 6)
+sendline('echo "process spans $tmp lines"')
+expect_str("process spans 3 lines")