allow an optional USING btree for EXCLUDE constraints

pg_dump uses that for the default EXCLUDE constraints. This allows
migrations to work again for projects that use EXCLUDE
constraints. A more sophisticated fix would allow the different index
types here.

IHP/IDE/SchemaDesigner/Parser.hs

@@ -189,6 +189,7 @@ parseCheckConstraint name = do
 
 parseExcludeConstraint name = do
     lexeme "EXCLUDE"
+    optional $ lexeme "USING btree"
     excludeElements <- between (char '(' >> space) (char ')' >> space) $ excludeElement `sepBy` (char ',' >> space)
     predicate <- optional do
         lexeme "WHERE"

Test/IDE/SchemaDesigner/ParserSpec.hs

@@ -348,6 +348,21 @@ tests = do
                     , deferrableType = Nothing
                     }
 
+        it "should parse ALTER TABLE .. ADD CONSTRAINT .. EXCLUDE USING btree .." do
+            parseSql "ALTER TABLE posts ADD CONSTRAINT unique_title_by_author EXCLUDE USING btree (title WITH =, author WITH =);" `shouldBe` AddConstraint
+                    { tableName = "posts"
+                    , constraint = ExcludeConstraint
+                        { name = "unique_title_by_author"
+                        , excludeElements =
+                            [ ExcludeConstraintElement { element = "title", operator = "=" }
+                            , ExcludeConstraintElement { element = "author", operator = "=" }
+                            ]
+                        , predicate = Nothing
+                        }
+                    , deferrable = Nothing
+                    , deferrableType = Nothing
+                    }
+
         it "should parse ALTER TABLE .. ADD CONSTRAINT .. EXCLUDE .. WHERE .." do
             parseSql "ALTER TABLE posts ADD CONSTRAINT unique_title_by_author EXCLUDE (title WITH =, author WITH =) WHERE (title = 'why');" `shouldBe` AddConstraint
                     { tableName = "posts"