Support plain SQL migrations

lib/rom/sql/errors.rb

@@ -19,6 +19,8 @@ module SQL
     MissingPrimaryKeyError    = Class.new(StandardError)
     MigrationError            = Class.new(StandardError)
     UnsupportedConversion     = Class.new(MigrationError)
+    SQLParseError             = Class.new(MigrationError)
+    SQLEnvError               = Class.new(MigrationError)
 
     ERROR_MAP = {
       Sequel::DatabaseError => DatabaseError,

lib/rom/sql/migration/migrator.rb

@@ -9,6 +9,8 @@
 require 'rom/sql/migration/inline_runner'
 require 'rom/sql/migration/writer'
 
+Sequel.extension :sql_migrations
+
 module ROM
   module SQL
     module Migration

lib/rom/sql/migration/sql_migration.rb

@@ -0,0 +1,110 @@
+# frozen_string_literal: true
+
+require "dry/struct"
+
+require "rom/sql/types"
+
+module ROM
+  module SQL
+    module Migration
+      # A single executable statement extracted from a `.sql` migration
+      # section, paired with the source line where it begins. The line is
+      # used to annotate backtraces when execution fails.
+      #
+      # @api private
+      Statement = Data.define(:sql, :line)
+
+      # A migration translated from a `.sql` file by `SQLParser`.
+      #
+      # @api private
+      class SQLMigration < Dry::Struct
+        Filename   = Types::Coercible::String
+        Settings   = Types::Strict::Hash.default { {} }
+        Direction  = Types::Strict::Symbol.enum(:up, :down)
+        Statements = Types::Array.of(Types.Instance(Statement))
+
+        # Matches `${NAME}` substitution references in statement bodies when the
+        # `env=true` pragma is set. Only the braced form is recognized, leaving
+        # `$$`-quoted bodies and `$1` positional params untouched.
+        SUBSTITUTION = /\$\{(?<name>[A-Za-z_]\w*)\}/
+
+        attribute :filename, Filename
+        attribute :settings, Settings
+
+        attribute :up, Statements
+        attribute? :down, Statements
+
+        # Return a copy with additional settings merged in.
+        #
+        # @api private
+        def with(**settings)
+          new(settings: self.settings.merge(settings))
+        end
+
+        # Whether to run inside a transaction.
+        #
+        # @return [true, false, nil] nil leaves the choice to the database default
+        #
+        # @api private
+        def use_transactions
+          settings[:transaction]
+        end
+
+        # Execute the statements for the given direction against the database.
+        #
+        # @param db [Sequel::Database]
+        # @param direction [:up, :down]
+        #
+        # @api private
+        def apply(db, direction)
+          unless Direction.valid?(direction)
+            raise ArgumentError, "Invalid migration direction specified (#{direction.inspect})"
+          end
+
+          statements = public_send(direction) or return
+
+          # Resolve every statement before running any, so a missing environment
+          # variable aborts before producing side effects.
+          finalized = statements.map { |statement| sub(statement) }
+
+          finalized.each do |statement|
+            db.run(statement.sql)
+          rescue Sequel::DatabaseError => e
+            raise annotate(e, statement, direction)
+          end
+        end
+
+        private
+
+        # Return the statement with `${NAME}` environment-variable substitution
+        # applied to its SQL when the `env` pragma is set. Raises `SQLEnvError`
+        # for a referenced variable that is not present in `ENV`.
+        #
+        # @api private
+        def sub(statement)
+          return statement unless settings[:env]
+
+          sql = statement.sql.gsub(SUBSTITUTION) do
+            name = Regexp.last_match[:name]
+            ENV.fetch(name) do
+              raise SQLEnvError,
+                    "Undefined environment variable ${#{name}} in #{filename}:#{statement.line}"
+            end
+          end
+
+          statement.with(sql:)
+        end
+
+        # Prepend a synthetic frame pointing at the failing statement's source
+        # location, so the migration file appears at the top of the backtrace.
+        #
+        # @api private
+        def annotate(error, statement, direction)
+          frame = "#{filename}:#{statement.line}:in '#{direction}'"
+          error.set_backtrace([frame, *(error.backtrace || [])])
+          error
+        end
+      end
+    end
+  end
+end