From ef22b131f156943f36cf757e56c9f7f648352324 Mon Sep 17 00:00:00 2001
From: James Parker <dev@jamesparker.me>
Date: Tue, 31 Jan 2017 15:25:44 -0500
Subject: [PATCH 1/2] Fix for bug in identifyForm with empty forms. #1072

---
 yesod-form/Yesod/Form/Functions.hs | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/yesod-form/Yesod/Form/Functions.hs b/yesod-form/Yesod/Form/Functions.hs
index fc1e9903a..73e260600 100644
--- a/yesod-form/Yesod/Form/Functions.hs
+++ b/yesod-form/Yesod/Form/Functions.hs
@@ -62,7 +62,7 @@ import Yesod.Core
 import Yesod.Core.Handler (defaultCsrfParamName)
 import Network.Wai (requestMethod)
 import Text.Hamlet (shamlet)
-import Data.Monoid (mempty)
+import Data.Monoid (mempty, (<>))
 import Data.Maybe (listToMaybe, fromMaybe)
 import qualified Data.Map as Map
 import qualified Data.Text.Encoding as TE
@@ -336,13 +336,13 @@ identifyForm identVal form = \fragment -> do
     -- Create hidden <input>.
     let fragment' =
           [shamlet|
-            <input type=hidden name=#{identifyFormKey} value=#{identVal}>
+            <input type=hidden name=#{identifyFormKey} value=identify-#{identVal}>
             #{fragment}
           |]
 
     -- Check if we got its value back.
     mp <- askParams
-    let missing = (mp >>= Map.lookup identifyFormKey) /= Just [identVal]
+    let missing = (mp >>= Map.lookup identifyFormKey) /= Just ["identify-" <> identVal]
 
     -- Run the form proper (with our hidden <input>).  If the
     -- data is missing, then do not provide any params to the
@@ -350,7 +350,10 @@ identifyForm identVal form = \fragment -> do
     -- doing this avoids having lots of fields with red errors.
     let eraseParams | missing   = local (\(_, h, l) -> (Nothing, h, l))
                     | otherwise = id
-    eraseParams (form fragment')
+    ( res', w) <- eraseParams (form fragment')
+
+    let res = if missing then FormMissing else res'
+    return ( res, w)
 
 identifyFormKey :: Text
 identifyFormKey = "_formid"

From d59344b78b9a5be1d45d72911a53820173e7a571 Mon Sep 17 00:00:00 2001
From: James Parker <dev@jamesparker.me>
Date: Thu, 2 Feb 2017 01:55:00 -0500
Subject: [PATCH 2/2] housekeeping

---
 yesod-form/ChangeLog.md            | 4 ++++
 yesod-form/Yesod/Form/Functions.hs | 1 +
 yesod-form/yesod-form.cabal        | 2 +-
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/yesod-form/ChangeLog.md b/yesod-form/ChangeLog.md
index fdd3f56c5..58731e1c0 100644
--- a/yesod-form/ChangeLog.md
+++ b/yesod-form/ChangeLog.md
@@ -1,3 +1,7 @@
+## 1.4.10
+
+* Fixed `identifyForm` to properly return `FormMissing` for empty forms. [#1072](https://github.com/yesodweb/yesod/issues/1072)
+
 ## 1.4.9
 
 * Added a `ToValue` instance for `Enctype` [#1296](https://github.com/yesodweb/yesod/pull/1296)
diff --git a/yesod-form/Yesod/Form/Functions.hs b/yesod-form/Yesod/Form/Functions.hs
index 73e260600..ed83624f0 100644
--- a/yesod-form/Yesod/Form/Functions.hs
+++ b/yesod-form/Yesod/Form/Functions.hs
@@ -352,6 +352,7 @@ identifyForm identVal form = \fragment -> do
                     | otherwise = id
     ( res', w) <- eraseParams (form fragment')
 
+    -- Empty forms now properly return FormMissing. [#1072](https://github.com/yesodweb/yesod/issues/1072)
     let res = if missing then FormMissing else res'
     return ( res, w)
 
diff --git a/yesod-form/yesod-form.cabal b/yesod-form/yesod-form.cabal
index bd5296e6f..9f8a31de7 100644
--- a/yesod-form/yesod-form.cabal
+++ b/yesod-form/yesod-form.cabal
@@ -1,5 +1,5 @@
 name:            yesod-form
-version:         1.4.9
+version:         1.4.10
 license:         MIT
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>