InvalidPackageDeclaration doesn't enforce that the rootPackage is present

[mateot1]

The rootPackage config for InvalidPackageDeclaration allows us to account for a file path that doesn't include the root part of the package, but it doesn't check that the package declaration contains this rootPackage. This can lead to inconsistency, for example:

with config rootPackage: 'my.root.package'
file/path containing a file with package my.root.package.file.path passes as expected
file/path containing a file with package file.path also passes

Expected Behavior of the rule

The rule should ensure that all classes in a given file path have the same package declaration. This means that if a rootPackage is defined, it should also enforce that it is present in the package declaration.

Context

For bettor or worse I work in a codebase that has a file structure that does not contain the root directories for kotlin src files which allows these inconsistencies to arise...

[cortinico]

I think this is a nice improvement. However, I would like to point out how this is a behavior change. Specifically, before the rootPackage was used just to ignore part of the package declaration.

Please also note how this is explained in the documentation:

detekt/detekt-rules-naming/src/main/kotlin/io/gitlab/arturbosch/detekt/rules/naming/InvalidPackageDeclaration.kt

Lines 28 to 29 in 56e7fa9

	@Configuration("if specified this part of the package structure is ignored")
	private val rootPackage: String by config("")

If we end up merging #4484, we should also update that documentation to clarify this behavioral change.

[mateot1]

updated!

[cortinico]

Fixed by #4484