rewrite error-handling for nml import to satisfy flow

Author: philippotto

app/assets/javascripts/libs/utils.js

@@ -503,6 +503,28 @@ const Utils = {
     // Big endian
     return [a, b, g, r];
   },
+
+  promiseAllWithErrors: async function<T>(
+    promises: Array<Promise<T>>,
+  ): Promise<{ successes: Array<T>, errors: Array<Error> }> {
+    const successOrErrorObjects = await Promise.all(promises.map(p => p.catch(error => error)));
+    return successOrErrorObjects.reduce(
+      ({ successes, errors }, successOrError) => {
+        if (successOrError instanceof Error) {
+          return {
+            successes,
+            errors: errors.concat([successOrError]),
+          };
+        } else {
+          return {
+            successes: successes.concat([successOrError]),
+            errors,
+          };
+        }
+      },
+      { successes: [], errors: [] },
+    );
+  },
 };
 
 export default Utils;

app/assets/javascripts/oxalis/view/nml_upload_zone_container.js

@@ -13,6 +13,7 @@ import Store from "oxalis/store";
 import type { OxalisState } from "oxalis/store";
 import { connect } from "react-redux";
 import FormattedDate from "components/formatted_date";
+import Utils from "libs/utils";
 
 type State = {
   files: Array<*>,
@@ -134,8 +135,9 @@ class NmlUploadZoneContainer extends React.PureComponent<Props, State> {
     this.setState({
       isImporting: true,
     });
+
     try {
-      const importActions = await Promise.all(
+      const { successes: importActions, errors } = await Utils.promiseAllWithErrors(
         this.state.files.map(async file => {
           const nmlString = await readFileAsText(file);
           try {
@@ -145,20 +147,19 @@ class NmlUploadZoneContainer extends React.PureComponent<Props, State> {
             );
             return addTreesAndGroupsAction(trees, treeGroups);
           } catch (e) {
-            return new Error(`"${file.name}" could not be parsed. ${e.message}`);
+            throw new Error(`"${file.name}" could not be parsed. ${e.message}`);
           }
         }),
       );
 
-      const errors = importActions.filter(action => action instanceof Error);
       if (errors.length > 0) {
         throw errors;
       }
 
       // Dispatch the actual actions as the very last step, so that
       // not a single store mutation happens if something above throws
       // an error
-      importActions.forEach(action => Store.dispatch(action));
+      importActions.forEach(actionOrError => Store.dispatch(actionOrError));
     } catch (e) {
       (Array.isArray(e) ? e : [e]).forEach(e => Toast.error(e.message));
     } finally {