Add Regenerate Lock File With Newer Bundler as a Ruby TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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-_1710 TILs and counting..._
+_1711 TILs and counting..._
 
 See some of the other learning resources I work on:
 
@@ -1445,6 +1445,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Read The First Line From A File](ruby/read-the-first-line-from-a-file.md)
 - [Refer To Implicit Block Argument With It](ruby/refer-to-implicit-block-argument-with-it.md)
 - [Reference Hash Key With Safe Navigation](ruby/reference-hash-key-with-safe-navigation.md)
+- [Regenerate Lock File With Newer Bundler](ruby/regenerate-lock-file-with-newer-bundler.md)
 - [Rendering ERB](ruby/rendering-erb.md)
 - [Replace The Current Process With An External Command](ruby/replace-the-current-process-with-an-external-command.md)
 - [Require Entire Gemfile In Pry Session](ruby/require-entire-gemfile-in-pry-session.md)

ruby/regenerate-lock-file-with-newer-bundler.md

@@ -0,0 +1,34 @@
+# Regenerate Lock File With Newer Bundler
+
+While upgrading to the latest Ruby version (4.0.0), I also wanted to upgrade the
+version of `bundler` that my project uses. This shows up at the bottom of the
+`Gemfile.lock` file as the `BUNDLED WITH` line. Despite installing the latest
+version of `bundler`, I get the following message when I try to install
+dependencies.
+
+```bash
+$ bundle install
+
+Bundler 4.0.3 is running, but your lockfile was generated with 2.6.2.
+Installing Bundler 2.6.2 and restarting using that version.
+...
+```
+
+Instead, what we need to tell `bundle` to update the locked version of `bundler`
+in the `Gemfile.lock`.
+
+```bash
+$ bundle update --bundler
+
+Fetching gem metadata from https://rubygems.org/.........
+Resolving dependencies...
+Bundle updated!
+```
+
+The `--bundler` flag for `bundle-update` says the following:
+
+> Update the locked version of bundler to the invoked bundler version.
+
+So we could pass a specific `bundler` version to that flag, but in this case I
+want to use the version I'm invoking it with which is the latest that I just
+installed.