java.project.exclusion is not working as expected

[jdneo]

Steps to repro:

1. Use the project: https://github.com/eclipse/eclipse.jdt.ls/tree/master/org.eclipse.jdt.ls.tests/projects/maven/multimodule,
2. Before open it in VS Code, set the java.import.exlusions in settings.json:

"java.import.exclusions": [
    "**",
    "!**/module1/**"
]

3. Open it in VS Code

Expected result

modules under **/module1/** gets imported

Actual result

no projects imported into workspace

Investigation of the root cause

In the code here, we will skip subtree scan if a folder is excluded.

In the above case, since we have **/* in the setting, all the sub folder are ignored even we have the negative (!) pattern in the exclusion setting.

It seems that having the early return logic here makes the negative pattern never takes effect.

Can we just exclude the unwanted folders?

What if we set the java.import.exclusions to:

"java.import.exclusions": [
    "**/module2/**",
    "**/module3/**",
]

The result is that all the modules are still get imported into the workspace. This is because the MavenImporter will collect all the related projects from the scanning result, as long as the parent pom is included, all the child poms will be included as well.

[jdneo]

One solution I can think of is to scan twice when java.import.exclusions contains negative patterns.

1. The first scan includes those folders which match the negative patterns
2. Then remove those negative patterns and leave all the positive exclusion and do a second scan