Fix issue with inifinite loop, now give proper error message for frontmatter decoding errors.

src/BackendTask/File.elm

@@ -65,7 +65,7 @@ frontmatter frontmatterDecoder =
 
     import BackendTask exposing (BackendTask)
     import BackendTask.File as File
-    import Decode as Decode exposing (Decoder)
+    import Decode exposing (Decoder)
 
     blogPost : BackendTask BlogPostMetadata
     blogPost =
@@ -101,7 +101,7 @@ It's common to parse the body with a markdown parser or other format.
 
     import BackendTask exposing (BackendTask)
     import BackendTask.File as File
-    import Decode as Decode exposing (Decoder)
+    import Decode exposing (Decoder)
     import Html exposing (Html)
 
     example :
@@ -174,7 +174,7 @@ just the metadata.
 
     import BackendTask exposing (BackendTask)
     import BackendTask.File as File
-    import Decode as Decode exposing (Decoder)
+    import Decode exposing (Decoder)
 
     blogPost : BackendTask BlogPostMetadata
     blogPost =
@@ -198,7 +198,7 @@ the [`BackendTask`](BackendTask) API along with [`BackendTask.Glob`](BackendTask
 
     import BackendTask exposing (BackendTask)
     import BackendTask.File as File
-    import Decode as Decode exposing (Decoder)
+    import Decode exposing (Decoder)
 
     blogPostFiles : BackendTask (List String)
     blogPostFiles =
@@ -231,8 +231,23 @@ onlyFrontmatter :
             }
             frontmatter
 onlyFrontmatter frontmatterDecoder filePath =
-    read filePath
+    BackendTask.Internal.Request.request2
-        (frontmatter frontmatterDecoder)
+        { name = "read-file"
+        , body = BackendTask.Http.stringBody "" filePath
+        , expect = frontmatter frontmatterDecoder
+        , errorDecoder = Decode.field "errorCode" (errorDecoder filePath)
+        , onError =
+            \frontmatterDecodeError ->
+                { fatal =
+                    { title = "BackendTask.File Decoder Error"
+                    , body =
+                        "I encountered a Json Decoder error from a call to BackendTask.File.onlyFrontmatter.\n\n"
+                            ++ Decode.errorToString frontmatterDecodeError
+                    }
+                        |> FatalError.build
+                , recoverable = DecodingError frontmatterDecodeError
+                }
+        }
 
 
 {-| Same as `bodyWithFrontmatter` except it doesn't include the frontmatter.

src/BackendTask/Internal/Request.elm

@@ -1,7 +1,9 @@
-module BackendTask.Internal.Request exposing (request)
+module BackendTask.Internal.Request exposing (request, request2)
 
 import BackendTask exposing (BackendTask)
-import BackendTask.Http exposing (Body, Expect)
+import BackendTask.Http exposing (Body, Error(..), Expect)
+import Json.Decode exposing (Decoder)
+import Json.Encode as Encode
 
 
 request :
@@ -22,7 +24,50 @@ request ({ name, body, expect } as params) =
         }
         expect
         |> BackendTask.onError
-            (\_ ->
+            (\error ->
+                let
+                    _ =
+                        Debug.log "BackendTask.Internal.Request" error
+                in
                 -- TODO avoid crash here, this should be handled as an internal error
                 request params
             )
+
+
+request2 :
+    { name : String
+    , body : Body
+    , expect : Decoder a
+    , errorDecoder : Decoder error
+    , onError : Json.Decode.Error -> error
+    }
+    -> BackendTask error a
+request2 ({ name, body, expect, onError, errorDecoder } as params) =
+    -- elm-review: known-unoptimized-recursion
+    BackendTask.Http.request
+        { url = "elm-pages-internal://" ++ name
+        , method = "GET"
+        , headers = []
+        , body = body
+        , timeoutInMs = Nothing
+        , retries = Nothing
+        }
+        (BackendTask.Http.expectJson Json.Decode.value)
+        |> BackendTask.onError
+            (\error ->
+                BackendTask.succeed Encode.null
+            )
+        |> BackendTask.andThen
+            (\decodeValue ->
+                case Json.Decode.decodeValue errorDecoder decodeValue of
+                    Ok a ->
+                        BackendTask.fail a
+
+                    Err _ ->
+                        case Json.Decode.decodeValue expect decodeValue of
+                            Ok a ->
+                                BackendTask.succeed a
+
+                            Err e ->
+                                BackendTask.fail (onError e)
+            )

src/FatalError.elm

@@ -1,4 +1,7 @@
-module FatalError exposing (FatalError, fromString, recoverable)
+module FatalError exposing
+    ( FatalError, fromString, recoverable
+    , build
+    )
 
 {-| The Elm language doesn't have the concept of exceptions or special control flow for errors. It just has
 Custom Types, and by convention types like `Result` and the `Err` variant are used to represent possible failure states