Update Ruby to 4.0.0

.ruby-version

@@ -1 +1 @@
-3.4.7
+4.0.0

Gemfile.lock

@@ -2296,7 +2296,7 @@ CHECKSUMS
   zeitwerk (2.7.4) sha256=2bef90f356bdafe9a6c2bd32bcd804f83a4f9b8bc27f3600fff051eb3edcec8b
 
 RUBY VERSION
-  ruby 3.4.7p58
+  ruby 4.0.0
 
 BUNDLED WITH
-  4.0.1
+  4.0.3

docker/dev/backend/Dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:3.4.7-trixie AS develop
+FROM ruby:4.0.0-trixie AS develop
 LABEL org.opencontainers.image.authors="operations@openproject.com"
 
 ARG DEV_UID=1000

docker/prod/Dockerfile

@@ -1,4 +1,4 @@
-ARG RUBY_VERSION="3.4.7"
+ARG RUBY_VERSION="4.0.0"
 ARG DEBIAN_BASE="trixie"
 # Add SBOM scan context for intermediate steps
 ARG BUILDKIT_SBOM_SCAN_CONTEXT=true

docs/development/development-environment/linux/README.md

@@ -40,10 +40,10 @@ sudo apt-get install git curl build-essential zlib1g-dev libyaml-dev libssl-dev
 Use [rbenv](https://github.com/rbenv/rbenv) and [ruby-build](https://github.com/rbenv/ruby-build#readme) to install
 Ruby.
 You can check available ruby versions with `rbenv install --list`.
-At the time of this writing, the latest stable version is `3.4.7`, which we also require.
+At the time of this writing, the latest stable version is `4.0.0`, which we also require.
 
 We suggest you install the version we require in [.ruby-version](https://github.com/opf/openproject/blob/dev/.ruby-version).
-Read the first line e.g. `3.4.7` and install that version.
+Read the first line e.g. `4.0.0` and install that version.
 
 #### Install rbenv and ruby-build
 
@@ -80,18 +80,18 @@ With both installed, we can now install ruby.
 You can check available ruby versions with `rbenv install --list`.
 
 We suggest you install the version we require in [.ruby-version](https://github.com/opf/openproject/blob/dev/.ruby-version).
-Read the first line e.g. `3.4.7` and install that version.
+Read the first line e.g. `4.0.0` and install that version.
 
 ```shell
 # Install the required version as read from the .ruby-version file
-rbenv install 3.4.7
+rbenv install 4.0.0
 ```
 
 This might take a while depending on whether ruby is built from source. After it is complete, you need to tell rbenv to
 globally activate this version
 
 ```shell
-rbenv global 3.4.7
+rbenv global 4.0.0
 rbenv rehash
 ```
 
@@ -181,7 +181,7 @@ You should now have an active ruby and node installation. Verify that it works w
 
 ```shell
 ruby --version
-ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [arm64-darwin25]
+ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [arm64-darwin25]
 
 bundler --version
 Bundler version 4.0.1

docs/development/development-environment/macos/README.md

@@ -28,7 +28,7 @@ their homepage.
 Use [rbenv](https://github.com/rbenv/rbenv) and [ruby-build](https://github.com/rbenv/ruby-build#readme) to install
 Ruby. We always require the latest ruby versions, and you can check which version is required
 by [checking the Gemfile](https://github.com/opf/openproject/blob/dev/Gemfile#L31) for the `ruby "~> X.Y"` statement. At
-the time of writing, this version is "3.4.7"
+the time of writing, this version is "4.0.0"
 
 #### Install rbenv and ruby-build
 
@@ -48,18 +48,18 @@ With both installed, we can now install the actual ruby version.
 You can check available ruby versions with `rbenv install --list`.
 
 We suggest you install the version we require in [.ruby-version](https://github.com/opf/openproject/blob/dev/.ruby-version).
-Read the first line e.g. `3.4.7` and install that version.
+Read the first line e.g. `4.0.0` and install that version.
 
 ```shell
 # Install the required version as read from the .ruby-version file
-rbenv install 3.4.7
+rbenv install 4.0.0
 ```
 
 This might take a while depending on whether ruby is built from source. After it is complete, you need to tell rbenv to
 globally activate this version
 
 ```shell
-rbenv global 3.4.7
+rbenv global 4.0.0
 ```
 
 You also need to install [bundler](https://github.com/bundler/bundler/), the ruby gem bundler.
@@ -134,7 +134,7 @@ You should now have an active ruby and node installation. Verify that it works w
 
 ```shell
 $ ruby --version
-ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [arm64-darwin25]4]
+ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [arm64-darwin25]
 
 $ bundler --version
 Bundler version 4.0.1

docs/installation-and-operations/installation/manual/README.md

@@ -106,19 +106,19 @@ Please be aware that the actual installation of a specific Ruby version takes so
 ```
 
 We suggest you install the version we require in [.ruby-version](https://github.com/opf/openproject/blob/dev/.ruby-version).
-Read the first line e.g. `3.4.7` and install that version.
+Read the first line e.g. `4.0.0` and install that version.
 
 ```shell
-[openproject@host] rbenv install 3.4.7
+[openproject@host] rbenv install 4.0.0
 [openproject@host] rbenv rehash
-[openproject@host] rbenv global 3.4.7
+[openproject@host] rbenv global 4.0.0
 ```
 
 To check our Ruby installation we run `ruby --version`. It should output
 something very similar to:
 
 ```text
-ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [arm64-darwin25]
+ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [arm64-darwin25]
 ```
 
 ## Installation of Node