Extract version from go.mod files (#32)

* Extract version from go.mod files

* make it work on linux too

* whitespace

* ignore asdf testing checkout

* fix test

.gitignore

@@ -0,0 +1 @@
+/asdf/

.travis.yml

@@ -1,5 +1,5 @@
 language: c
-script: asdf plugin test golang . --asdf-plugin-gitref $TRAVIS_COMMIT go version
+script: asdf plugin test golang $TRAVIS_BUILD_DIR --asdf-plugin-gitref $TRAVIS_COMMIT go version
 before_script:
   - if [ $TRAVIS_OS_NAME = linux ]; then sudo apt-get install -y bsdmainutils; fi
   - git clone https://github.com/asdf-vm/asdf.git

bin/list-legacy-filenames

@@ -1,3 +1,3 @@
 #!/usr/bin/env bash
 
-echo ".go-version"
+echo ".go-version go.mod"

bin/parse-legacy-file

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+get_legacy_version() {
+  current_file="$1"
+  basename=$(basename -- "$current_file")
+
+  if [ "$basename" == "go.mod" ]; then
+    GOLANG_VERSION=$(grep 'go\s*[0-9]' "$current_file" |
+                       sed -e 's/.*heroku goVersion //' \
+                           -e 's/[[:space:]]//' \
+                           -e 's/go\(.*\)/\1/' |
+                       head -1
+      )
+  else
+    GOLANG_VERSION=$(cat "$current_file")
+  fi
+
+  echo "$GOLANG_VERSION"
+}
+
+get_legacy_version "$1"