Add bin/report script to capture buildpack metadata (heroku#110)

* Add `bin/report` script to capture buildpack metadata

[W-15039947](https://gus.lightning.force.com/lightning/r/a07EE00001k7v4BYAQ/view)

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Add `bin/report` script to capture buildpack metadata
 
 ## 2021-03-10
 

bin/report

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+# bin/report <build-dir> <cache-dir> <env-dir>
+
+### Configure environment
+
+set -o errexit    # always exit on error
+set -o pipefail   # don't ignore exit codes when piping output
+
+BUILD_DIR=${1:-}
+
+packages=()
+custom_packages=()
+custom_repositories=()
+
+while IFS= read -r line; do
+  if grep --silent -e "^:repo:" <<< "${line}"; then
+    custom_repositories+=("${line//:repo:/}")
+  elif [[ $line == *deb ]]; then
+    custom_packages+=("${line}")
+  else
+    packages+=("${line}")
+  fi
+done < <(grep --invert-match -e "^#" -e "^\s*$" "${BUILD_DIR}/Aptfile")
+
+output_key_value() {
+  local key value
+  key="$1"
+  shift
+  # sort & join the array values with a ',' then escape both '\' and '"' characters
+  value=$(printf '%s\n' "$@" | sort | tr '\n' ',' | sed 's/,$/\n/' | sed 's/\\/\\\\/g' | sed 's/"/\\"/g')
+  if [[ -n "${value}" ]]; then
+    echo "$key: \"$value\""
+  fi
+}
+
+output_key_value "packages" "${packages[@]}"
+output_key_value "custom_packages" "${custom_packages[@]}"
+output_key_value "custom_repositories" "${custom_repositories[@]}"