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Debugging the Swift Toolchain

Use these steps to debug components of the Swift toolchain. This allows you to see Swift's source code from the debugger – instead of disassembly. The debugger can also provide some variable names and values. This has been initially tested with libswiftCore.dylib.

These instructions were updated as of Swift 5.2.1.

Prerequisites

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addbranch() {
    local branch=$1
    git config --add remote.origin.fetch "+refs/heads/${branch}:refs/remotes/origin/${branch}"
    git fetch
    git checkout "$branch"
}

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extension UIView {
    /// Example: call someView.nudge(0, 30)
    func nudge(_ dx: CGFloat, _ dy: CGFloat) {
        self.frame = self.frame.offsetBy(dx: dx, dy: dy)
        CATransaction.flush()
    }
}

extension UIView {
    /// Example: po UIView.root

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void addMainThreadCheck(Class cls, SEL selector) {
#if DEBUG
    void *symbol = dlsym(RTLD_DEFAULT, "__main_thread_add_check_for_selector");
    if (!symbol) {
        return;
    }
    void (*addCheck)(Class, SEL) = (__typeof__(addCheck))symbol;
    addCheck(cls, selector);
#endif
}

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wut() {
  readonly error_code=$1
  local domain
  for domain in posix mach; do
    tput bold; echo $domain; tput sgr0
    launchctl error $domain $error_code
  done

  tput bold; echo security; tput sgr0
  security error $error_code

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// Given an imported C function, that uses a context pointer and a C callback function:
//
//     func for_each(_ x: X, context: UnsafeMutableRawPointer!, callback: @convention(c) (UnsafeMutableRawPointer?, Element) -> Void)
//
// When is it safe to use this pattern?

// Example with two captured variables.
typealias Context = (Type1, Type2)
var context = (capture1, capture2)
for_each(x, context: &context) { context, element in

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#!/usr/bin/env python3

import argparse
import ast
import astor
import os
import re
import sys

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#!/bin/bash

set -euo pipefail

hfs-compress() {
  local files=("$@")

  local filepath perms temppath
  for filepath in "${files[@]}"; do
    perms=$(stat -f %p "$filepath")

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Recently, we wanted call swift-demangle from code, but calling out to the process frequently was a bit too slow, and meant parsing the output of -tree-only, since we wanted to access module and class names, for example.

Fortunately there's libswiftDemangle.dylib for this, but it's a C++ API. Compiling against it requires #includeing headers from both Swift and LLVM.

Using CMake, both Swift and LLVM can easily be added as dependencies, but we build this project with SwiftPM. To build with SwiftPM, we imported the necessary headers. Roughly, here are the steps to determine which specific Swift

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#!/bin/bash

set -e

_xcrun() {
  DEVELOPER_DIR=/Applications/Xcode-beta.app/Contents/Developer \
    xcrun -sdk iphonesimulator \
    "$@"
}