Handle errors in commands.

examples/end-to-end/script/src/StreamTests.elm

@@ -37,6 +37,10 @@ run =
                 (\() ->
                     Expect.pass
                 )
+        , Stream.command "does-not-exist" []
+            |> Stream.run
+            |> expectError "command with error"
+                "Error: spawn does-not-exist ENOENT"
         , BackendTask.Custom.run "hello"
             Encode.null
             Decode.string
@@ -181,7 +185,10 @@ expectError name message task =
                     \() ->
                         case result of
                             Ok data ->
-                                Expect.fail "Expected a failure, but got success!"
+                                --Expect.fail "Expected a failure, but got success!"
+                                result
+                                    |> Debug.toString
+                                    |> Expect.equal "Expected a failure, but got success!"
 
                             Err error ->
                                 let

generator/src/render.js

@@ -768,7 +768,6 @@ async function pipePartToStream(
       retry: part.retries,
       timeout: part.timeoutInMs,
     });
-    // TODO what if there is an error?
     let metadata = {
       headers: Object.fromEntries(response.headers.entries()),
       statusCode: response.status,
@@ -799,6 +798,11 @@ async function pipePartToStream(
       env: env,
     });
 
+    newProcess.on("error", (error) => {
+      console.error("ERROR!");
+      resolve({ error: error.toString() });
+    });
+
     lastStream && lastStream.pipe(newProcess.stdin);
     let newStream;
     if (output === "MergeWithStdout") {

src/BackendTask/Stream.elm

@@ -272,8 +272,28 @@ run stream =
     BackendTask.Internal.Request.request
         { name = "stream"
         , body = BackendTask.Http.jsonBody (pipelineEncoder stream "none")
-        , expect = BackendTask.Http.expectJson (Decode.succeed ())
+        , expect =
+            BackendTask.Http.expectJson
+                (Decode.oneOf
+                    [ Decode.field "error" Decode.string
+                        |> Decode.andThen
+                            (\error ->
+                                Decode.succeed
+                                    (Err
+                                        (FatalError.recoverable
+                                            { title = "Stream Error"
+                                            , body = error
+                                            }
+                                            (StreamError error)
+                                        )
+                                    )
+                            )
+                    , Decode.succeed (Ok ())
+                    ]
+                )
         }
+        |> BackendTask.andThen BackendTask.fromResult
+        |> BackendTask.allowFatal
 
 
 pipelineEncoder : Stream error metadata kind -> String -> Encode.Value