dev/lldb-smoker: LLDB smoke test using NIO (apple#1840)

Motivation:

We often hit a bunch of problems with LLDB, especially on Linux. So
maybe it would be cool if we could smoke test LLDB using SwiftNIO.

Modifications:

Add script `dev/lldb-smoker` which does the following things:

- takes 2000 random picks amongst all the files in the package
- for each of those files, pick a random line number
- write an LLDB script which sets break points for each of the file/line
  pairs (one-shot breakpoints)
- runs the program
- for each breakpoint hit, run `frame variable` to list all the
  variables

Result:

LLDB smoke test

Author: weissi

dev/lldb-smoker

@@ -0,0 +1,72 @@
+#!/bin/bash
+
+set -eu
+
+here="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+
+number_of_breaks=2000
+package_dir=$(cd "${1-"$here/.."}" && pwd -P)
+files=( "$package_dir"/Sources/*/*.swift "$package_dir"/Tests/*/*.swift )
+
+function random_array_element() {
+    arr=("${!1}")
+    echo ${arr["$[RANDOM % ${#arr[@]}]"]}
+}
+
+function number_of_lines() {
+    wc -l < "$1"
+}
+
+function random_line_number() {
+    echo $(( 1 + ( RANDOM % $(number_of_lines "$1") ) ))
+}
+
+echo "Package dir: $package_dir"
+( set -eux && cd "$package_dir" && swift build --build-tests )
+xctest_bundle=( "$package_dir/.build/debug"/*PackageTests.xctest )
+echo "xctest bundle: $xctest_bundle"
+
+if [[ ! -e "$xctest_bundle" ]]; then
+    echo >&2 "ERROR: Couldn't find xctest bundle at $xctest_bundle"
+    exit 1
+fi
+run_command=()
+if [[ "$(uname -s)" == Darwin ]]; then
+    xctest=$(xcrun -f xctest)
+    run_command+=( "$xctest" "$xctest_bundle" )
+else
+    run_command+=( "$xctest_bundle" )
+fi
+
+lldb_file=()
+for f in $(seq "$number_of_breaks"); do
+    file=$(random_array_element "files[@]")
+    line=$(random_line_number "$file")
+
+    lldb_file+=( "break set -o true -f '$file' -l '$line'" )
+done
+lldb_file+=( run )
+for f in $(seq "$number_of_breaks"); do
+    lldb_file+=( 'frame variable --show-all-children' )
+
+    lldb_file+=( cont )
+done
+
+lldb_response_file=$(mktemp /tmp/lldb-smoker_XXXXXX)
+for command in "${lldb_file[@]}"; do
+    echo "$command" >> "$lldb_response_file"
+done
+
+echo "LLDB response file: $lldb_response_file"
+sleep 0.5
+lldb_command=( lldb --batch --source "$lldb_response_file" -- \
+    "${run_command[@]}" )
+
+set +e
+set -x
+"${lldb_command[@]}"
+set +x
+set -e
+
+echo "LLDB response file: $lldb_response_file"
+echo "LLDB command: ${lldb_command[*]}"