Add jsAttributesHandler

This adds `jsAttributesHandler` to run arbitrary Handler code before
building the attributes map for the script tag generated by `widgetFile`.
This is useful if you need to add a randomised nonce value to that tag.

Closes https://github.com/yesodweb/yesod/issues/1621

yesod-core/ChangeLog.md

@@ -1,5 +1,10 @@
 # ChangeLog for yesod-core
 
+## 1.6.16
+
+* Add `jsAttributesHandler` to run arbitrary Handler code before building the
+  attributes map for the script tag generated by `widgetFile` [#1622](https://github.com/yesodweb/yesod/pull/1622)
+
 ## 1.6.15
 
 * Move `redirectToPost` JavaScript form submission from HTML element to

yesod-core/src/Yesod/Core/Class/Yesod.hs

@@ -249,6 +249,17 @@ class RenderRoute site => Yesod site where
     jsAttributes :: site -> [(Text, Text)]
     jsAttributes _ = []
 
+    -- | Same as @jsAttributes@ but allows you to run arbitrary Handler code
+    --
+    -- This is useful if you need to add a randomised nonce value to the script
+    -- tag generated by @widgetFile@. If you use both this function and
+    -- @jsAttributes@, the two attribute maps will be merged, favouring the
+    -- keys from @jsAttributes@ in case of a collision.
+    --
+    -- @since 1.6.16
+    jsAttributesHandler :: HandlerFor site [(Text, Text)]
+    jsAttributesHandler = pure []
+
     -- | Create a session backend. Returning 'Nothing' disables
     -- sessions. If you'd like to change the way that the session
     -- cookies are created, take a look at
@@ -520,7 +531,9 @@ defaultCsrfMiddleware = defaultCsrfSetCookieMiddleware . defaultCsrfCheckMiddlew
 widgetToPageContent :: Yesod site
                     => WidgetFor site ()
                     -> HandlerFor site (PageContent (Route site))
-widgetToPageContent w = HandlerFor $ \hd -> do
+widgetToPageContent w = do
+  jsAttrsFromHandler <- jsAttributesHandler
+  HandlerFor $ \hd -> do
   master <- unHandlerFor getYesod hd
   ref <- newIORef mempty
   unWidgetFor w WidgetData
@@ -531,6 +544,10 @@ widgetToPageContent w = HandlerFor $ \hd -> do
   let title = maybe mempty unTitle mTitle
       scripts = runUniqueList scripts'
       stylesheets = runUniqueList stylesheets'
+      jsAttrs =
+        let jsAttrsStatic = Map.fromList (jsAttributes master)
+            jsAttrsDynamic = Map.fromList jsAttrsFromHandler
+         in Map.toList $ Map.union jsAttrsStatic jsAttrsDynamic
 
   flip unHandlerFor hd $ do
     render <- getUrlRenderParams
@@ -564,7 +581,7 @@ widgetToPageContent w = HandlerFor $ \hd -> do
                 ^{mkScriptTag s}
             $maybe j <- jscript
                 $maybe s <- jsLoc
-                    <script src="#{s}" *{jsAttributes master}>
+                    <script src="#{s}" *{jsAttrs}>
                 $nothing
                     <script>^{jelper j}
         |]

yesod-core/yesod-core.cabal

@@ -1,5 +1,5 @@
 name:            yesod-core
-version:         1.6.15
+version:         1.6.16
 license:         MIT
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>