From b71af05d628025b8df2b5b6a737c2a9611211c8d Mon Sep 17 00:00:00 2001
From: Guo Xiang Tan <tgx_world@hotmail.com>
Date: Mon, 17 Sep 2018 14:44:29 +0800
Subject: [PATCH] Backward compatibility for dropping functions in
 `ColumnDropper`.

https://meta.discourse.org/t/launcher-rebuild-error-pg-error-schema-discourse-functions-does-not-exist/96209
---
 lib/migration/base_dropper.rb   | 17 ++++++++++++++++-
 lib/migration/column_dropper.rb |  3 +++
 lib/migration/table_dropper.rb  |  3 +++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/lib/migration/base_dropper.rb b/lib/migration/base_dropper.rb
index eff5fcdb1b5..9215c559df2 100644
--- a/lib/migration/base_dropper.rb
+++ b/lib/migration/base_dropper.rb
@@ -82,7 +82,22 @@ module Migration
         "readonly()"
       ].compact.join("_")
 
-      "#{FUNCTION_SCHEMA_NAME}.#{function_name}"
+      if DB.exec(<<~SQL).to_s == '1'
+         SELECT schema_name
+         FROM information_schema.schemata
+         WHERE schema_name = '#{FUNCTION_SCHEMA_NAME}'
+         SQL
+
+        "#{FUNCTION_SCHEMA_NAME}.#{function_name}"
+      else
+        function_name
+      end
+    end
+
+    def self.old_readonly_function_name(table_name, column_name = nil)
+      readonly_function_name(table_name, column_name).sub(
+        "#{FUNCTION_SCHEMA_NAME}.", ''
+      )
     end
 
     def self.readonly_trigger_name(table_name, column_name = nil)
diff --git a/lib/migration/column_dropper.rb b/lib/migration/column_dropper.rb
index 10e7b37b1c4..77f3d118813 100644
--- a/lib/migration/column_dropper.rb
+++ b/lib/migration/column_dropper.rb
@@ -57,6 +57,9 @@ module Migration
         DB.exec <<~SQL
           DROP TRIGGER IF EXISTS #{BaseDropper.readonly_trigger_name(@table, column)} ON #{@table};
           DROP FUNCTION IF EXISTS #{BaseDropper.readonly_function_name(@table, column)} CASCADE;
+          -- Backward compatibility for old functions created in the public
+          -- schema
+          DROP FUNCTION IF EXISTS #{BaseDropper.old_readonly_function_name(@table, column)} CASCADE;
         SQL
 
         # safe cause it is protected on method entry, can not be passed in params
diff --git a/lib/migration/table_dropper.rb b/lib/migration/table_dropper.rb
index 0e1a938983a..5718ac0ecb7 100644
--- a/lib/migration/table_dropper.rb
+++ b/lib/migration/table_dropper.rb
@@ -75,6 +75,9 @@ module Migration
 
       DB.exec <<~SQL
         DROP FUNCTION IF EXISTS #{BaseDropper.readonly_function_name(@old_name)} CASCADE;
+        -- Backward compatibility for old functions created in the public
+        -- schema
+        DROP FUNCTION IF EXISTS #{BaseDropper.old_readonly_function_name(@old_name)} CASCADE;
       SQL
     end
   end