Add formula for Sqitch

Based on the sqitchers/sqitch tap, it supports PostgreSQL, MySQL, and
SQLite out of the box, and Snowflake, Exasol, and Vertica with ODBC via
the installation of additional client libraries. Snowflake support could
use the `snowflake-snowsql` formula, but it's Cask only. The caveat
output points to a URL that describes how to install these additional
dependencies, which will be updated appropriately by
sqitchers/sqitch.org#13.

The install method installs all Perl modules in the Cellar directory,
which is useful for keeping everything together and avoiding conflicts
with other Perl applications, but means that they must all be
re-installed when upgrading to a new version.

Not supported: Oracle and Firebase, since there are no formulas for
Instant Client or the Firebase server (or clients). The URL emitted by
the Caveat points users who need to manage Oracle or Firebase databases
to the Sqitch tap.

Author: theory

Formula/sqitch.rb

@@ -0,0 +1,82 @@
+class Sqitch < Formula
+  desc       "Sensible database change management"
+  homepage   "https://sqitch.org/"
+  url        "https://www.cpan.org/authors/id/D/DW/DWHEELER/App-Sqitch-v1.3.1.tar.gz"
+  sha256     "f5e768d298cd4047ee2ae42319782e8c2cda312737bcbdbfaf580bd47efe8b94"
+  license    "MIT"
+  head       "https://github.com/sqitchers/sqitch.git", branch: "develop"
+
+  depends_on "cpm" => :build
+  depends_on "libiodbc"
+  depends_on "libpq"
+  depends_on "mysql-client"
+  depends_on "perl"
+  uses_from_macos "sqlite"
+
+  if build.head?
+    depends_on "gettext" => :build
+    depends_on "openssl@3" => :build
+  end
+
+  def install
+    # Download Module::Build and Menlo::CLI::Compat.
+    cpm_args = %w[install --local-lib-contained instutil --no-test]
+    cpm_args.push("--verbose") if verbose?
+    system "cpm", *cpm_args, "Menlo::CLI::Compat", "Module::Build"
+
+    ENV["PERL5LIB"] = "#{buildpath}/instutil/lib/perl5"
+    ENV["PERL_MM_OPT"] = "INSTALLDIRS=vendor"
+    ENV["PERL_MB_OPT"] = "--installdirs vendor"
+
+    if build.head?
+      # Need to tell the compiler where to find Gettext.
+      ENV.prepend_path "PATH", Formula["gettext"].opt_bin
+
+      # Download Dist::Zilla and plugins, then make and cd into a build dir.
+      system "cpm", *cpm_args, "Dist::Zilla"
+      system "./instutil/bin/dzil authordeps --missing | xargs cpm " + cpm_args.join(" ")
+      system "./instutil/bin/dzil", "build", "--in", ".brew"
+      Dir.chdir ".brew"
+    end
+
+    # Assemble the Build.PL args, including supported native and ODBC engines.
+    # Oracle and Firebird not currently supported.
+    args = %W[
+      Build.PL --install_base #{prefix} --etcdir #{etc}/sqitch
+      --with postgres --with sqlite --with mysql
+      --with vertica --with exasol --with snowflake
+    ]
+    args.push("--verbose") if verbose?
+    args.push("--quiet") if quiet?
+
+    # Build and bundle (install).
+    system "perl", *args
+    system "./Build", "bundle"
+
+    # Wrap the binary in client paths.
+    mkdir_p libexec
+    mv bin/"sqitch", libexec/"sqitch"
+    paths = [
+      Formula["libpq"].opt_bin,
+      Formula["mysql-client"],
+    ]
+    (bin/"sqitch").write_env_script libexec/"sqitch", PATH: "#{paths.join(":")}:$PATH"
+
+    # Move the man pages from #{prefix}/man to man.
+    mkdir share
+    mv "#{prefix}/man", man
+  end
+
+  def caveats
+    <<~EOS
+      This Sqitch install includes clients to manage Postgres, MySQL, and SQLite.
+      See https://sqitch.org/download/macos/ to install the client libraries
+      required to manage Snowflake, Exasol, and Vertica. Use the sqitchers/sqitch
+      tap to manage Oracle or Firebird.
+    EOS
+  end
+
+  test do
+    system bin/"sqitch", "--version"
+  end
+end