Preparing the frontend (?) create a target directory; files should exist in build

[christoph-frick]

Desktop (please complete the following information):

• OS: Linux
• JDK version: Zulu 8
• Gradle version: 6.0.1
• Vaadin Plugin version: 0.5

Describe the bug

Probably vaadinPrepareFrontend creates a target directory in the
root.

To Reproduce

Given a simple project like
https://github.com/christoph-frick/try-vaadin14-gradle/blob/master/build.gradle
building or running the project (assumption: the task
vaadinPrepareFrontend is the culprit), the project contains a target
directory afterwards, which usually is associated with a maven build:

$ find target
target
target/frontend
target/frontend/generated-flow-imports.js
target/frontend/package.json
target/frontend/generated-flow-imports-fallback.js

Expected behavior

All build artifacts should reside somewhere inside the build
directory.

Screenshots

n/a

Additional context

n/a

[mvysny]

I completely agree. Unfortunately there's a catch as hinted at https://github.com/vaadin/vaadin-gradle-plugin/blob/master/src/main/kotlin/com/vaadin/gradle/VaadinFlowPluginExtension.kt#L71 :

In order to have stuff in build/ instead of target/ we need Flow 2.2 or higher.

Flow 2.2 means Vaadin 14.2+; that would mean that the plugin would not support apps using Vaadin 14.1.x (since the VaadinServlet in development mode expects stuff to reside in target/).

However, I propose to leave this bug report open, since at some point it should be good to follow Gradle convention and generate files in build/ .

[lightoze]

Perhaps this can be now fixed in 17 branch?

[mvysny]

Definitely! Let me try.

[mvysny]

Hmm, I'm not sure it's possible yet. The target/ path is hard-coded in the FrontendUtils.TARGET constant, which is also used for example by DEFAULT_GENERATED_DIR. The value is then read by DevModeInitializer class and NodeTasks class, and both use the same approach: the value may only be overridden via a Java System property FrontendUtils.PARAM_GENERATED_DIR (vaadin.frontend.generated.folder).

Therefore, it's not enough to only configure the value in the Gradle plugin - the value must probably be also configured in runtime in the Vaadin app itself. Please let me verify this finding; if it is indeed so, I will open a feature request for Flow to move this property to e.g. flow-build-info.json.

[mvysny]

Even if you try to change the value of generatedFolder to e.g. generatedFolder = File(project.projectDir, "build/frontend"), Vaadin will still generate a bunch of files into target/ folder:

├── flow-frontend
│   ├── form
│   │   └── package.json
│   └── package.json
├── index.html
└── index.ts

[mvysny]

Let me open a bug report at https://github.com/vaadin/flow/issues to start a discussion in order to possibly fix this.

[mvysny]

Blocked by vaadin/flow#8953

[mvysny]

Blocked by vaadin/flow#10335