asdf elixir and erlang version detection

README.md

@@ -3,6 +3,7 @@
 ## Features
 
 * **Easy configuration** with `elixir_buildpack.config` file
+* Automatic elixir and erlang version detection if you are using asdf
 * Use **prebuilt Elixir binaries**
 * Allows configuring Erlang
 * If your app doesn't have a Procfile, default web task `mix run --no-halt` will be run.
@@ -14,7 +15,7 @@
 #### Version support
 
 * Erlang - Prebuilt packages (17.5, 17.4, etc)
-  * The full list of prebuilt packages can be found here: 
+  * The full list of prebuilt packages can be found here:
     * gigalixir-20 or heroku-20 stacks: https://builds.hex.pm/builds/otp/ubuntu-20.04/builds.txt
     * heroku-22 stacks: https://builds.hex.pm/builds/otp/ubuntu-22.04/builds.txt
     * All other stacks: https://github.com/HashNuke/heroku-buildpack-elixir-otp-builds/blob/master/otp-versions
@@ -28,7 +29,7 @@ Note: you should choose an Elixir and Erlang version that are [compatible with o
 
 * Cloud Native users should use [this buildpack](https://github.com/elixir-buildpack/cloud-native-buildpack)
 
-**This buildpack is not guaranteed to be Cloud Native compatible.** 
+**This buildpack is not guaranteed to be Cloud Native compatible.**
 The [elixir-buildpack/cloud-native-buildpack](https://github.com/elixir-buildpack/cloud-native-buildpack) is a buildpack that is actively under development
 and is designed specifically to follow the Cloud Native Buildpack conventions.
 
@@ -70,7 +71,7 @@ https://github.com/HashNuke/heroku-buildpack-elixir.git#883f33e10879b4b8b030753c
 
 #### Using Heroku CI
 
-This buildpack supports Heroku CI. 
+This buildpack supports Heroku CI.
 
 * To enable viewing test runs on Heroku, add [tapex](https://github.com/joshwlewis/tapex) to your project.
 * To detect compilation warnings use the `hook_compile` configuration option set to `mix compile --force --warnings-as-errors`.
@@ -130,8 +131,9 @@ test_args="--cover"
 
 
 #### Migrating from previous build pack
-the following has been deprecated and should be removed from `elixir_buildpack.config`:
-```
+The following has been deprecated and should be removed from `elixir_buildpack.config`:
+
+```shell
 # Export heroku config vars
 config_vars_to_export=(DATABASE_URL)
 ```
@@ -140,21 +142,21 @@ config_vars_to_export=(DATABASE_URL)
 
 * Use prebuilt Elixir release
 
-```
+```shell
 elixir_version=1.2.0
 ```
 
 * Use prebuilt Elixir branch, the *branch* specifier ensures that it will be downloaded every time
 
-```
+```shell
 elixir_version=(branch master)
 ```
 
 #### Specifying Erlang version
 
 * You can specify an Erlang release version like below
 
-```
+```shell
 erlang_version=18.2.1
 ```
 
@@ -196,12 +198,14 @@ heroku config:set MY_VAR=the_value
 ## Testing
 
 To run tests
-```
+
+```shell
 git clone https://github.com/HashNuke/heroku-buildpack-elixir
 export BUILDPACK="$(pwd)/heroku-buildpack-elixir"
 git clone https://github.com/jesseshieh/heroku-buildpack-testrunner
 git clone https://github.com/jesseshieh/shunit2
 export SHUNIT_HOME="$(pwd)/shunit2"
+
 cd heroku-buildpack-testrunner
 bin/run $BUILDPACK
 ```

bin/compile

@@ -25,6 +25,7 @@ source ${build_pack_path}/lib/elixir_funcs.sh
 source ${build_pack_path}/lib/app_funcs.sh
 source ${build_pack_path}/lib/canonical_version.sh
 
+rm -rf $(build_platform_tools_path)
 mkdir $(build_platform_tools_path)
 
 export_env_vars

lib/misc_funcs.sh

@@ -53,23 +53,44 @@ function assert_elixir_version_set() {
   fi
 }
 
+function asdf_extract_versions() {
+    local file=$1
+    local line
+
+    # Initialize as empty
+    local elixir_version_raw=""
+
+    while IFS= read -r line; do
+        if [[ $line == erlang* ]]; then
+            erlang_version="${line#erlang }"
+        elif [[ $line == elixir* ]]; then
+            elixir_version_raw="${line#elixir }"
+            elixir_version="${elixir_version_raw%-otp*}"
+        fi
+    done < "$file"
+}
+
 function load_config() {
   output_section "Checking Erlang and Elixir versions"
 
   local custom_config_file="${build_path}/elixir_buildpack.config"
+  local custom_asdf_file="${build_path}/.tool-versions"
 
   # Source for default versions file from buildpack first
   source "${build_pack_path}/elixir_buildpack.config"
 
   if [ -f $custom_config_file ];
   then
     source $custom_config_file
+    assert_elixir_version_set $custom_config_file
+  elif [ -f $custom_asdf_file ]; then
+    echo "asdf file found, extracting versions from source"
+    asdf_extract_versions $custom_asdf_file
   else
     output_line "Sorry, an elixir_buildpack.config is required. Please see https://github.com/HashNuke/heroku-buildpack-elixir#configuration"
     exit 1
   fi
 
-  assert_elixir_version_set $custom_config_file
   fix_erlang_version
   fix_elixir_version