From d737e2ef6f98dbb0ebefa88839975d69bee8de06 Mon Sep 17 00:00:00 2001
From: Gareth Jones <jones258@gmail.com>
Date: Sun, 13 Aug 2023 10:47:23 +1200
Subject: [PATCH] feat: check `PACKAGE_JSON_FALLBACK_MANAGER` for default
 fallback manager

---
 README.md            | 7 +++++--
 lib/package_json.rb  | 8 ++++++--
 sig/package_json.rbs | 2 ++
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index 4263621..214eb0c 100644
--- a/README.md
+++ b/README.md
@@ -90,8 +90,11 @@ does not exist or does not have the `packageManager` property:
 PackageJson.new(fallback_manager: :yarn_classic)
 ```
 
-The default fallback is `:npm`; supported package managers are `:npm`,
-`:yarn_classic`, and `:pnpm`.
+If a fallback manager is not defined, then the value of the env variable
+`PACKAGE_JSON_FALLBACK_MANAGER` will be used if set, or otherwise falling back
+to `npm`.
+
+Supported package managers are `:npm`, `:yarn_classic`, and `:pnpm`.
 
 If the `package.json` does not exist, then the `packageManager` property will be
 included based on this value, but it will _not_ be updated if the file already
diff --git a/lib/package_json.rb b/lib/package_json.rb
index 9699167..b41a6c8 100644
--- a/lib/package_json.rb
+++ b/lib/package_json.rb
@@ -14,7 +14,11 @@ class NotImplementedError < Error; end
 
   attr_reader :manager, :path
 
-  def self.read(path_to_directory = Dir.pwd, fallback_manager: :npm)
+  def self.fetch_default_fallback_manager
+    ENV.fetch("PACKAGE_JSON_FALLBACK_MANAGER", "npm").to_sym
+  end
+
+  def self.read(path_to_directory = Dir.pwd, fallback_manager: PackageJson.fetch_default_fallback_manager)
     unless File.exist?("#{path_to_directory}/package.json")
       raise Error, "#{path_to_directory} does not contain a package.json"
     end
@@ -22,7 +26,7 @@ def self.read(path_to_directory = Dir.pwd, fallback_manager: :npm)
     new(path_to_directory, fallback_manager: fallback_manager)
   end
 
-  def initialize(path_to_directory = Dir.pwd, fallback_manager: :npm)
+  def initialize(path_to_directory = Dir.pwd, fallback_manager: PackageJson.fetch_default_fallback_manager)
     @path = path_to_directory
 
     ensure_package_json_exists(fallback_manager)
diff --git a/sig/package_json.rbs b/sig/package_json.rbs
index 610479e..a6307db 100644
--- a/sig/package_json.rbs
+++ b/sig/package_json.rbs
@@ -10,6 +10,8 @@ class PackageJson
   attr_reader manager: Managers::Base
   attr_reader path: String
 
+  def self.fetch_default_fallback_manager: () -> Symbol
+
   def self.read: (?String path_to_directory, ?package_manager: (:npm | :yarn_classic | :pnpm)) -> PackageJson
 
   def initialize: (?String path_to_directory, ?package_manager: (:npm | :yarn_classic | :pnpm)) -> PackageJson