postgres(normalize types to eliminate noop migrations) (#1518)

* postgres(normalize types to eliminate noop migrations)

* add test and update changelog

persistent-postgresql/Database/Persist/Postgresql.hs

@@ -1103,7 +1103,15 @@ getColumn _ _ columnName _ =
 -- | Intelligent comparison of SQL types, to account for SqlInt32 vs SqlOther integer
 sqlTypeEq :: SqlType -> SqlType -> Bool
 sqlTypeEq x y =
-    T.toCaseFold (showSqlType x) == T.toCaseFold (showSqlType y)
+    let
+        -- Non exhaustive helper to map postgres aliases to the same name. Based on
+        -- https://www.postgresql.org/docs/9.5/datatype.html.
+        -- This prevents needless `ALTER TYPE`s when the type is the same.
+        normalize "int8"    = "bigint"
+        normalize "serial8" = "bigserial"
+        normalize v         = v
+    in
+        normalize (T.toCaseFold (showSqlType x)) == normalize (T.toCaseFold (showSqlType y))
 
 findAlters
     :: [EntityDef]

persistent-postgresql/test/EquivalentTypeTestPostgres.hs

@@ -21,15 +21,15 @@ import PgInit
 
 share [mkPersist sqlSettings, mkMigrate "migrateAll1"] [persistLowerCase|
 EquivalentType sql=equivalent_types
-    field1 Int
+    field1 Int    sqltype=bigint
     field2 T.Text sqltype=text
     field3 T.Text sqltype=us_postal_code
     deriving Eq Show
 |]
 
 share [mkPersist sqlSettings, mkMigrate "migrateAll2"] [persistLowerCase|
 EquivalentType2 sql=equivalent_types
-    field1 Int
+    field1 Int    sqltype=int8
     field2 T.Text
     field3 T.Text sqltype=us_postal_code
     deriving Eq Show

persistent/ChangeLog.md

@@ -1,4 +1,9 @@
-# Changelog for persistent
+# Changelog for persistentChan
+
+## 2.14.6.1 (unreleased)
+
+* [#1518](https://github.com/yesodweb/persistent/pull/1518)
+    * Normalize postgres type aliases to prevent noop migrations
 
 ## 2.14.6.0