Add support for per per-query types

The documentation states that you can pass custom type processors to
query objects. See:

https://node-postgres.com/features/queries#types

This didn't actually work. This commit adds an initial implementation
of per-query type-parsing. Caveats:

* It does not work with pg-native. That would require a separate pull
  request to pg-native, and a rather significant change to how that
  library handles query results.

* Per-query types do not "inherit" from types assigned to the Client,
  ala TypeOverrides.

lib/client.js

@@ -455,8 +455,9 @@ Client.prototype.query = function (config, values, callback) {
   if (this.binary && !query.binary) {
     query.binary = true
   }
-  if (query._result) {
-    query._result._getTypeParser = this._types.getTypeParser.bind(this._types)
+
+  if (query._result && !query._result._types) {
+    query._result._types = this._types
   }
 
   if (!this._queryable) {

lib/result.js

@@ -12,13 +12,14 @@ var types = require('pg-types')
 // result object returned from query
 // in the 'end' event and also
 // passed as second argument to provided callback
-var Result = function (rowMode) {
+var Result = function (rowMode, types) {
   this.command = null
   this.rowCount = null
   this.oid = null
   this.rows = []
   this.fields = []
   this._parsers = []
+  this._types = types
   this.RowCtor = null
   this.rowAsArray = rowMode === 'array'
   if (this.rowAsArray) {
@@ -94,11 +95,9 @@ Result.prototype.addFields = function (fieldDescriptions) {
   for (var i = 0; i < fieldDescriptions.length; i++) {
     var desc = fieldDescriptions[i]
     this.fields.push(desc)
-    var parser = this._getTypeParser(desc.dataTypeID, desc.format || 'text')
+    var parser = (this._types || types).getTypeParser(desc.dataTypeID, desc.format || 'text')
     this._parsers.push(parser)
   }
 }
 
-Result.prototype._getTypeParser = types.getTypeParser
-
 module.exports = Result

test/integration/client/custom-types-tests.js

@@ -3,13 +3,13 @@ const helper = require('./test-helper')
 const Client = helper.pg.Client
 const suite = new helper.Suite()
 
-const client = new Client({
-  types: {
-    getTypeParser: () => () => 'okay!'
-  }
-})
+const customTypes = {
+  getTypeParser: () => () => 'okay!'
+}
 
 suite.test('custom type parser in client config', (done) => {
+  const client = new Client({ types: customTypes })
+
   client.connect()
     .then(() => {
       client.query('SELECT NOW() as val', assert.success(function (res) {
@@ -18,3 +18,21 @@ suite.test('custom type parser in client config', (done) => {
       }))
     })
 })
+
+// Custom type-parsers per query are not supported in native
+if (!helper.args.native) {
+  suite.test('custom type parser in query', (done) => {
+    const client = new Client()
+
+    client.connect()
+      .then(() => {
+        client.query({
+          text: 'SELECT NOW() as val',
+          types: customTypes
+        }, assert.success(function (res) {
+          assert.equal(res.rows[0].val, 'okay!')
+          client.end().then(done)
+        }))
+      })
+  })
+}