LLDB command for identifying views in a broken constraint.

commands.py

'''
LLDB commands for debugging iOS projecs in XCode
References:
    * [LLDB Python reference](https://lldb.llvm.org/python-reference.html)
    * [LLDB Python API[(https://lldb.llvm.org/python_reference/index.html)

To install, put this in your ~/.iidbinit:

    command script import [path to this file]
'''

import inspect
import sys
from string import Template

# add LLDB library location to the path so it can be imported
sys.path += ':/Applications/Xcode.app/Contents/SharedFrameworks/LLDB.framework/Resources/Python/'

import lldb


def border_misconstrained_view(debugger, command, exe_ctx, result, internal_dict):
    '''
    Install this as a breakpoint for UIViewAlertForUnsatisfiableConstraints
    Examines the constraint defined by $arg1, which is being broken due to unsatisfiable constraints.
    Draws a thick red border around the first view of the constraint, and a thick blue border around
    the second view.
    '''
    frame = exe_ctx.GetFrame()

    if not frame.IsValid():
        print "Unable to get frame"
        result.SetError('invalid frame')
        return

    arg1 = frame.FindRegister('x0').GetValue()

    if arg1 is None:
        # possibly simulator - try rcx
        arg1 = frame.FindRegister('rcx').GetValue()

    template = '''
        import UIKit
        let constraint = unsafeBitCast($addr, to: NSLayoutConstraint.self)
        if let firstView = constraint.firstItem as? UIView {
            firstView.layer.borderColor = UIColor.red.cgColor
            firstView.layer.borderWidth = 4
        }
        
        if let secondView = constraint.secondItem as? UIView {
            secondView.layer.borderColor = UIColor.blue.cgColor
            secondView.layer.borderWidth = 4
        }
    '''

    swift_code = Template(template).substitute(addr=arg1)
    debugger.HandleCommand('e -l swift -- {}'.format(swift_code))
    result.AppendMessage('A red border has been applied to the mis-constrained view')
    result.Succeeded()

def __lldb_init_module(debugger, internal_dict):
    '''
    Runs when this script is imported into LLDB. Installs all functions into LLDB
    '''
    for (name, func) in inspect.getmembers(sys.modules[__name__], inspect.isfunction):
        args = inspect.getargspec(func)[0]
        print(args)
        if args == ['debugger', 'command', 'exe_ctx', 'result', 'internal_dict']:
            debugger.HandleCommand('command script add -f {}.{} {}'.format(__name__, name, name))
            print('{} has been installed'.format(name))

Also check out Chisel