Do not delete generated package.json on mvn clean

For various reasons, you run mvn clean package on your project instead of mvn package. This might be to update dependencies and remove old ones, to make sure code is re-generated or whatever other reason.

When doing mvn clean package, npm install is triggered even though the generated package.json has not been updated. Because the generated file is stored in target, it is removed by mvn clean and comparing the newly generated one to the existing one does not work.

This should be solved so mvn clean package does not need to run npm install.

Potential solutions:

1. Move the generated package.json out of target so it is not removed. E.g. use the same webpack.config.js+webpack.generated.js pattern and name it /package.generated.json
2. Store a hash of the generated package.json contents somewhere else for comparison purposes, e.g. main package.json

[caalador]

As the contents for the folder ./target/frontend will be copied to ./node_modules/@vaadin/flow-deps we could do a compare on build. if we haven’t run npm install we won’t have the file available in node_modules as it is copied at that time, and if we have run it we can compare the created package.json against the node_modules version and only if they differ we execute npm install.

[Artur-]

If you have two package.json files in the same folder then you might have some problems if both happen to install something into the same node_modules folder