Truncater counts OSC sequence contents (hyperlinks) as printable width

[katestud]

Description

The CLI::UI::Truncater correctly skips CSI sequences (\x1b[...) when calculating printable width, but it doesn't handle OSC sequences (\x1b]...). This causes strings containing hyperlinks to be truncated much more aggressively than expected, since the URL inside the hyperlink escape codes is counted as printable characters.

Reproduction

require 'cli/ui'

# Create a hyperlink
url = "https://github.com/Shopify/shopify/pull/12345"
link = CLI::UI.link(url, "#12345")  # displays as "#12345" but links to full URL

puts "Link string: #{link.inspect}"
puts "Printing width (ANSI.printing_width): #{CLI::UI::ANSI.printing_width(link)}"

# Try to truncate to 20 chars - should be plenty for "#12345"
truncated = CLI::UI::Truncater.call(link, 20)
puts "Truncated to 20: #{truncated.inspect}"

Expected behavior

• ANSI.printing_width correctly returns 6 (the length of #12345)
• Truncater.call(link, 20) should return the original string unchanged since #12345 is only 6 characters

Actual behavior

• ANSI.printing_width correctly returns 6 ✓
• Truncater.call(link, 20) truncates the string because it counts 8;;https://github.com/Shopify/shopify/pull/12345 (the URL inside the OSC sequence) as printable characters

Root cause

In lib/cli/ui/truncater.rb, the escape sequence parser only handles CSI sequences:

when PARSE_ESC
  mode = case cp
  when LEFT_SQUARE_BRACKET  # 0x5b = '['
    PARSE_ANSI
  else
    PARSE_ROOT  # <-- OSC sequences start with ']' (0x5d), so they fall through here
  end

OSC sequences have the format \x1b]...ST where ST is either \x07 (BEL) or \x1b\ (ESC + backslash). Since the Truncater doesn't recognize ] after ESC, it returns to PARSE_ROOT and counts the OSC content as visible characters.

Impact

This affects any use of CLI::UI::SpinGroup (spinners) with hyperlinks in titles. The spinner uses Truncater to fit titles to terminal width, causing hyperlink titles to be truncated far more than necessary.

Example output with a hyperlink in a spinner title:

┃ ⚠ https://github.com/Shop…

Even though there's plenty of terminal width remaining, the title is truncated because the hidden URL is counted.

Suggested fix

Add OSC sequence handling to the Truncater, similar to how ANSI.strip_codes already handles it:

RIGHT_SQUARE_BRACKET = 0x5d  # ]
BACKSLASH = 0x5c  # \
BEL = 0x07

# In the parser:
when PARSE_ESC
  mode = case cp
  when LEFT_SQUARE_BRACKET
    PARSE_ANSI
  when RIGHT_SQUARE_BRACKET
    PARSE_OSC  # New state for OSC sequences
  else
    PARSE_ROOT
  end

when PARSE_OSC
  # OSC sequences end with BEL or ESC+backslash
  case cp
  when BEL
    mode = PARSE_ROOT
  when ESC
    mode = PARSE_OSC_END
  end

when PARSE_OSC_END
  # Expecting backslash to complete ST
  mode = PARSE_ROOT