Add reproducible local development matrix

.docker/Dockerfile

@@ -0,0 +1,13 @@
+ARG PHP_VERSION=8.4
+
+FROM php:${PHP_VERSION}-cli
+
+COPY --from=composer:2 /usr/bin/composer /usr/local/bin/composer
+
+RUN apt-get update \
+	&& apt-get install --no-install-recommends --yes unzip \
+	&& rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+
+COPY . .

.dockerignore

@@ -0,0 +1,12 @@
+.git
+.direnv
+.idea
+vendor
+composer.lock
+result
+result-*
+tests/coverage.dat
+tests/**/*.actual
+tests/**/*.expected
+tests/tmp/*
+!tests/tmp/.gitignore

.envrc

@@ -0,0 +1,2 @@
+# shellcheck shell=bash
+use flake

.gitignore

@@ -3,3 +3,8 @@
 vendor
 
 composer.lock
+
+.direnv
+
+result
+result-*

README.md

@@ -30,6 +30,40 @@ composer require kdyby/forms-replicator
 
 **Note:** Version 3.0 requires `nette/component-model >= 3.1.0`.
 
+## Local compatibility testing
+
+Enter the reproducible development shell with [Nix](https://nixos.org/) and [direnv](https://direnv.net/):
+
+```sh
+direnv allow
+```
+
+The shell provides PHP 8.5, Composer, Just, the Docker CLI, ShellCheck, Actionlint, and the Nix formatter. Install highest dependencies locally for development and editor indexing with:
+
+```sh
+just install
+```
+
+Composer runs as your local user, so `vendor/` remains writable by your editor and development tools.
+
+Run the local CI suite against the installed dependencies with `just ci`.
+
+Docker is the compatibility source of truth. Run the complete PHP and dependency matrix with:
+
+```sh
+just matrix
+```
+
+The matrix copies source into ephemeral images instead of bind-mounting the checkout. Container-owned dependencies and lock files therefore never alter host permissions; only Composer's immutable download cache is shared through a Docker volume.
+
+The seven cells cover PHP 8.2, 8.3, and 8.4 with lowest and highest Composer dependencies, plus PHP 8.5 with highest dependencies. PHP 8.5 with lowest dependencies is excluded because component-model 3.1 itself emits PHP 8.5 deprecations.
+
+To run one focused cell, pass its PHP version and dependency set directly:
+
+```sh
+just cell 8.2 lowest
+```
+
 ## Overview
 
 - [Learn more in the documentation](https://github.com/Kdyby/FormsReplicator/blob/master/docs/en/index.md)

bin/test-matrix

@@ -0,0 +1,127 @@
+#!/bin/sh
+
+set -eu
+
+usage() {
+	printf 'Usage: %s [<php-version> <lowest|highest>]\n' "$0" >&2
+}
+
+case $# in
+	0)
+		php_versions='8.2 8.3 8.4 8.5'
+		dependency_sets='lowest highest'
+		;;
+	2)
+		case $1 in
+			8.2|8.3|8.4|8.5) ;;
+			*)
+				printf 'Unsupported PHP version: %s\n' "$1" >&2
+				usage
+				exit 2
+				;;
+		esac
+
+		case $2 in
+			lowest|highest) ;;
+			*)
+				printf 'Unsupported dependency set: %s\n' "$2" >&2
+				usage
+				exit 2
+				;;
+		esac
+
+		if [ "$1" = '8.5' ] && [ "$2" = 'lowest' ]; then
+			printf 'PHP 8.5 with lowest dependencies is not supported.\n' >&2
+			exit 2
+		fi
+
+		php_versions=$1
+		dependency_sets=$2
+		;;
+	*)
+		usage
+		exit 2
+		;;
+esac
+
+project_root=$(CDPATH='' cd "$(dirname "$0")/.." && pwd)
+cd "$project_root"
+
+cache_volume='forms-replicator-composer-download-cache'
+
+cleanup_exit() {
+	status=$?
+	trap - 0
+	[ -z "$iidfile" ] || rm -f "$iidfile" || :
+	exit "$status"
+}
+
+cleanup_signal() {
+	signal=$1
+	trap - 0 1 2 15
+	[ -z "$iidfile" ] || rm -f "$iidfile" || :
+	kill -s "$signal" "$$"
+}
+
+for php_version in $php_versions; do
+	image="forms-replicator-test-matrix:php-${php_version}"
+	iidfile=''
+	trap cleanup_exit 0
+	trap 'cleanup_signal HUP' 1
+	trap 'cleanup_signal INT' 2
+	trap 'cleanup_signal TERM' 15
+	iidfile=$(mktemp "${TMPDIR:-/tmp}/forms-replicator-test-matrix.XXXXXX")
+
+	printf '\nBuilding source image for PHP %s\n' "$php_version"
+	if docker build \
+		--build-arg "PHP_VERSION=$php_version" \
+		--file .docker/Dockerfile \
+		--iidfile "$iidfile" \
+		--tag "$image" \
+		.; then
+		:
+	else
+		status=$?
+		printf 'Matrix image build failed: PHP %s\n' "$php_version" >&2
+		exit "$status"
+	fi
+
+	IFS= read -r image_id < "$iidfile" || [ -n "$image_id" ]
+	rm -f "$iidfile"
+	trap - 0 1 2 15
+
+	for dependency_set in $dependency_sets; do
+		cell="PHP $php_version / $dependency_set"
+		if [ "$php_version" = '8.5' ] && [ "$dependency_set" = 'lowest' ]; then
+			printf '\nSkipping unsupported matrix cell: %s\n' "$cell"
+			continue
+		fi
+
+		printf '\nRunning matrix cell: %s\n' "$cell"
+
+		case $dependency_set in
+			lowest)
+				commands='composer update --prefer-dist --no-interaction --no-progress --prefer-lowest --prefer-stable && composer phpstan && composer test'
+				;;
+			highest)
+				commands='composer update --prefer-dist --no-interaction --no-progress && composer ci'
+				;;
+		esac
+
+		if docker run \
+			--rm \
+			--env COMPOSER_ALLOW_SUPERUSER=1 \
+			--env COMPOSER_CACHE_DIR=/tmp/composer-cache \
+			--volume "$cache_volume:/tmp/composer-cache/files" \
+			"$image_id" \
+			sh -c "$commands"; then
+			printf 'Matrix cell passed: %s\n' "$cell"
+		else
+			status=$?
+			printf 'Matrix cell failed: %s\n' "$cell" >&2
+			exit "$status"
+		fi
+	done
+done
+
+printf '\nAll selected matrix cells passed.\n'

flake.nix

@@ -0,0 +1,33 @@
+{
+  description = "Development tools for Kdyby FormsReplicator";
+
+  inputs.nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+
+  outputs = {nixpkgs, ...}: let
+    supportedSystems = [
+      "aarch64-darwin"
+      "aarch64-linux"
+      "x86_64-linux"
+    ];
+    forAllSystems = function:
+      nixpkgs.lib.genAttrs supportedSystems (
+        system: function nixpkgs.legacyPackages.${system}
+      );
+  in {
+    formatter = forAllSystems (pkgs: pkgs.alejandra);
+
+    devShells = forAllSystems (pkgs: {
+      default = pkgs.mkShellNoCC {
+        packages = with pkgs; [
+          actionlint
+          alejandra
+          docker-client
+          just
+          php85
+          php85Packages.composer
+          shellcheck
+        ];
+      };
+    });
+  };
+}

justfile

@@ -0,0 +1,27 @@
+# List available development commands.
+default:
+    @just --list
+
+# Install highest dependencies locally for development and editor indexing.
+install:
+    composer update --prefer-dist --no-interaction --no-progress
+
+# Run the complete CI suite against locally installed dependencies.
+ci:
+    composer ci
+
+# Run every supported PHP and dependency combination in Docker.
+matrix:
+    ./bin/test-matrix
+
+# Run lowest dependencies on every compatible PHP version.
+lowest:
+    @set -eu; for php in 8.2 8.3 8.4; do ./bin/test-matrix "$php" lowest; done
+
+# Run highest dependencies on every supported PHP version.
+highest:
+    @set -eu; for php in 8.2 8.3 8.4 8.5; do ./bin/test-matrix "$php" highest; done
+
+# Run one Docker matrix cell, e.g. `just cell 8.5 highest`.
+cell $php $dependencies:
+    ./bin/test-matrix "$php" "$dependencies"