chore(script): generate changelog from structure

doc/changes/scripts/build_changelog.sh

@@ -0,0 +1,84 @@
+#!/usr/bin/env bash
+
+# Script name: build_changelog.sh
+# Description: this script updates the CHANGES.md file from the the files in
+# the changes directory, removing the files as it goes.
+# Author(s): The Dune team
+# Date: 2025-09-29
+#
+# Usage: $ ./build_changelog.sh <X.Y.Z> 
+# where X.Y.Z is the version of Dune
+
+set -euo pipefail
+
+# Variables
+version="$1"
+output=".changelog.new"
+doc_dir="./doc/changes"
+
+## Functions
+add_newline() {
+  echo "" >> "$output"
+}
+
+generate_version_header() {
+  today=$(date "+%Y-%m-%d")
+
+  header="$version ($today)"
+  header_size=$(echo "$header" | wc -m)
+  echo "$header" >> "$output"
+
+  for i in $(seq $header_size); do
+    echo -n "-" >> "$output"
+  done
+
+  add_newline
+  add_newline
+}
+
+append_files_in_dir_if_not_empty() {
+  subheader="$1"
+  category="$2"
+  dir="$doc_dir/$category"
+
+  if [ ! -d "$dir" ]; then
+    echo "Error: directory $dir doesn't exist."
+    exit 1
+  fi
+
+  list_of_files=$(find "$dir" -maxdepth 1 -type f -not -name '.*' -name '*.md')
+
+  if [ -z "$list_of_files" ] ; then
+    return 0
+  fi
+
+  echo "## $subheader" >> "$output"
+  add_newline
+  for file in $list_of_files; do
+      cat "$file" >> "$output"
+      add_newline
+      rm "$file"
+  done
+}
+
+# Move to the Dune root directory
+cd $(dirname $0)
+cd ../../../
+
+# Create the output file
+touch "$output"
+
+# Add the header to the changelog
+generate_version_header
+
+# Extract the information from the changes/**/*.md files
+append_files_in_dir_if_not_empty "Fixed" "fixed"
+append_files_in_dir_if_not_empty "Added" "added"
+append_files_in_dir_if_not_empty "Changed" "changed"
+
+# We remove the unreleased header and add the previous changelog to the new
+# changelog
+tail -n +8 CHANGES.md >> "$output"
+
+# Replace the old changelog with the new one. It ereases the new one.
+mv "$output" CHANGES.md