Fix(transformer/elm): handle elm error properly without errors property

packages/core/integration-tests/test/elm.js

@@ -133,4 +133,47 @@ describe('elm', function () {
       },
     );
   });
+
+  it('should produce correct formatting and indentation when elm fails without errors property', async function () {
+    await assert.rejects(
+      () =>
+        bundle(path.join(__dirname, 'integration/elm-error/index.js'), {
+          mode: 'production',
+        }),
+
+      {
+        name: 'BuildError',
+        diagnostics: [
+          {
+            message:
+              '\n' +
+              '-- DEBUG REMNANTS ------------------------------------------------------------- \n' +
+              '\n' +
+              'There are uses of the `Debug` module in the following modules:\n' +
+              '\n' +
+              '    **Main**\n' +
+              '\n' +
+              'But the --optimize flag only works if all `Debug` functions are removed!\n' +
+              '\n' +
+              '__Note__: The issue is that --optimize strips out info needed by `Debug` functions.\n' +
+              'Here are two examples:\n' +
+              '\n' +
+              '    (1) It shortens record field names. This makes the generated JavaScript is\n' +
+              '    smaller, but `Debug.toString` cannot know the real field names anymore.\n' +
+              '\n' +
+              '    (2) Values like `type Height = Height Float` are unboxed. This reduces\n' +
+              '    allocation, but it also means that `Debug.toString` cannot tell if it is\n' +
+              '    looking at a `Height` or `Float` value.\n' +
+              '\n' +
+              'There are a few other cases like that, and it will be much worse once we start\n' +
+              'inlining code. That optimization could move `Debug.log` and `Debug.todo` calls,\n' +
+              'resulting in unpredictable behavior. I hope that clarifies why this restriction\n' +
+              'exists!',
+            origin: '@parcel/elm-transformer',
+            stack: '',
+          },
+        ],
+      },
+    );
+  });
 });

packages/core/integration-tests/test/integration/elm-error/elm.json

@@ -0,0 +1,24 @@
+{
+    "type": "application",
+    "source-directories": [
+        "src"
+    ],
+    "elm-version": "0.19.1",
+    "dependencies": {
+        "direct": {
+            "elm/browser": "1.0.2",
+            "elm/core": "1.0.5",
+            "elm/html": "1.0.0"
+        },
+        "indirect": {
+            "elm/json": "1.1.3",
+            "elm/time": "1.0.0",
+            "elm/url": "1.0.0",
+            "elm/virtual-dom": "1.0.2"
+        }
+    },
+    "test-dependencies": {
+        "direct": {},
+        "indirect": {}
+    }
+}

packages/core/integration-tests/test/integration/elm-error/index.js

@@ -0,0 +1,5 @@
+var local = require('./src/Main.elm');
+
+module.exports = function () {
+    return local;
+};

packages/core/integration-tests/test/integration/elm-error/package.json

@@ -0,0 +1 @@
+{}

packages/core/integration-tests/test/integration/elm-error/src/Main.elm

@@ -0,0 +1,49 @@
+module Main exposing (main)
+
+import Browser
+import Html exposing (Html, button, div, text)
+import Html.Events exposing (onClick)
+
+
+type alias Model =
+    { count : Int }
+
+
+initialModel : Model
+initialModel =
+    { count = 0 }
+
+
+type Msg
+    = Increment
+    | Decrement
+
+
+update : Msg -> Model -> Model
+update msg model =
+    case msg of
+        Increment ->
+            Debug.log "incremented!!"
+            { model | count = model.count + 1 }
+
+        Decrement ->
+            Debug.log "decremented!!"
+            { model | count = model.count - 1 }
+
+
+view : Model -> Html Msg
+view model =
+    div []
+        [ button [ onClick Increment ] [ text "+1" ]
+        , div [] [ text <| String.fromInt model.count ]
+        , button [ onClick Decrement ] [ text "-1" ]
+        ]
+
+
+main : Program () Model Msg
+main =
+    Browser.sandbox
+        { init = initialModel
+        , view = view
+        , update = update
+        }

packages/transformers/elm/src/ElmTransformer.js

@@ -64,6 +64,20 @@ export default (new Transformer({
       let compilerJson = e.message.split('\n')[1];
       let compilerDiagnostics = JSON.parse(compilerJson);
 
+      // sometimes, `errors` property does not exist on the error object thrown by `compileToString` module.
+      // In such case, a content equal to `error.errors[num].problems[num]` is expanded.
+      // so this line handle such a case.
+      if (!compilerDiagnostics.errors) {
+        throw new ThrowableDiagnostic({
+          diagnostic: elmProblemToParcelDiagnostic(
+            compilerDiagnostics,
+            compilerDiagnostics.path
+              ? path.relative(process.cwd(), compilerDiagnostics.path)
+              : '',
+          ),
+        });
+      }
+
       throw new ThrowableDiagnostic({
         diagnostic: compilerDiagnostics.errors.flatMap(
           elmErrorToParcelDiagnostics,
@@ -173,22 +187,26 @@ function formatMessagePiece(piece) {
   return md`${piece}`;
 }
 
+function elmProblemToParcelDiagnostic(problem, relativePath) {
+  const padLength = 80 - 5 - problem.title.length - relativePath.length;
+  const dashes = '-'.repeat(padLength);
+  const message = [
+    '',
+    `-- ${problem.title} ${dashes} ${relativePath}`,
+    '',
+    problem.message.map(formatMessagePiece).join(''),
+  ].join('\n');
+
+  return {
+    message,
+    origin: '@parcel/elm-transformer',
+    stack: '', // set stack to empty since it is not useful
+  };
+}
+
 function elmErrorToParcelDiagnostics(error) {
   const relativePath = path.relative(process.cwd(), error.path);
   return error.problems.map(problem => {
-    const padLength = 80 - 5 - problem.title.length - relativePath.length;
-    const dashes = '-'.repeat(padLength);
-    const message = [
-      '',
-      `-- ${problem.title} ${dashes} ${relativePath}`,
-      '',
-      problem.message.map(formatMessagePiece).join(''),
-    ].join('\n');
-
-    return {
-      message,
-      origin: '@parcel/elm-transformer',
-      stack: '', // set stack to empty since it is not useful
-    };
+    return elmProblemToParcelDiagnostic(problem, relativePath);
   });
 }