Fix error messages in `check-release.sh`

- `check_tag`: Report file name correctly. Use named variables.
- Introduce `read_version` helper function. Simplify the implementation.
- Show meaningful error message if `GITHUB_REF` is not set or its format
  is incorrect.

.github/scripts/check-release.sh

@@ -1,24 +1,41 @@
-#!/bin/bash
+#!/usr/bin/env bash
+set -eu -o pipefail
 
-# check_tag $current_tag $file_tag $file_name
-function check_tag {
-  if [[ "$1" != "$2" ]]; then
-      echo "Error: the current tag does not match the version in Cargo.toml: found $2 - expected $1"
-      ret=1
-  fi
+check_tag() {
+    local expected=$1
+    local actual=$2
+    local filename=$3
+
+    if [[ $actual != $expected ]]; then
+        echo >&2 "Error: the current tag does not match the version in $filename: found $actual, expected $expected"
+        return 1
+    fi
 }
 
+read_version() {
+    grep '^version = ' | cut -d \" -f 2
+}
+
+if [[ -z "${GITHUB_REF:-}" ]]; then
+    echo >&2 "Error: GITHUB_REF is not set"
+    exit 1
+fi
+
+if [[ ! "$GITHUB_REF" =~ ^refs/tags/v[0-9]+\.[0-9]+\.[0-9]+(-[a-z0-9]+)?$ ]]; then
+    echo >&2 "Error: GITHUB_REF is not a valid tag: $GITHUB_REF"
+    exit 1
+fi
+
+current_tag=${GITHUB_REF#refs/tags/v}
 ret=0
-current_tag=${GITHUB_REF#'refs/tags/v'}
 
-file_tag="$(grep '^version = ' Cargo.toml | cut -d '=' -f 2 | tr -d '"' | tr -d ' ')"
-check_tag $current_tag $file_tag
+toml_tag="$(cat Cargo.toml | read_version)"
+check_tag "$current_tag" "$toml_tag" Cargo.toml || ret=1
 
-lock_file='Cargo.lock'
-lock_tag=$(grep -A 1 'name = "meilisearch-auth"' $lock_file | grep version | cut -d '=' -f 2 | tr -d '"' | tr -d ' ')
-check_tag $current_tag $lock_tag $lock_file
+lock_tag=$(grep -A 1 '^name = "meilisearch-auth"' Cargo.lock | read_version)
+check_tag "$current_tag" "$lock_tag" Cargo.lock || ret=1
 
-if [[ "$ret" -eq 0 ]] ; then
-  echo 'OK'
+if (( ret == 0 )); then
+    echo 'OK'
 fi
 exit $ret