False negative on "import java.util.*", expected no-wildcard-imports

[greg-patterson]

Expected Behavior

When java.util.* is included as a wildcard import, it should trigger the warning for no-wildcard-imports. When none of the classes in that package are used (both no-wildcard-imports and no-unused-imports rules apply), then at least one of no-wildcard-imports or no-unused-imports should be triggered.

Observed Behavior

When java.util.* is included as a wildcard import, it triggers no warnings for no-wildcard-imports. When no classes from the package are used, it also does not trigger a no-unused-imports warning.

Changing to a specific class like java.util.UUID produces the expected no-unused-imports, and a different wildcard like javax.net.* or java.time.* produces the expected no-wildcard-imports. Also, moving the java.util.* to above a different import produces the expected import-ordering.

Screenshots

Showing error case (false negative with incorrect build success):

Similar but different cases without error (correctly failing):

Steps to Reproduce

Add java.util.* as an import in the correct ordering, run ktlint.

Your Environment

• Version of ktlint used: 0.48.2
• Relevant parts of the .editorconfig settings: no file, defaults only
• Name and version (or code for custom task) of integration used (Gradle plugin, Maven plugin, command line, custom Gradle task): Reproduced via both gradle task and command line
• Version of Gradle used (if applicable): 7.6
• Operating System and version: Reproduced on MacOS 12.6, Windows 10, and Alpine Linux

[paul-dingemans]

Can you check whether property ij_kotlin_packages_to_use_import_on_demand has been set? Imports set in this property are allowed to be used with a wildcard.

[greg-patterson]

This was with no .editorconfig at all, so just using defaults.

Although, that got me looking a little deeper, and I see now that this is a feature, not a bug:

ktlint/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/NoWildcardImportsRule.kt

Lines 96 to 101 in 481ad64

	* Default IntelliJ IDEA style: Use wildcard imports for packages in "java.util", "kotlin.android.synthetic" and
	* it's subpackages.
	*
	* https://github.com/JetBrains/kotlin/blob/ffdab473e28d0d872136b910eb2e0f4beea2e19c/idea/formatter/src/org/jetbrains/kotlin/idea/core/formatter/KotlinCodeStyleSettings.java#L81-L82
	*/
	defaultValue = parseAllowedWildcardImports("java.util.*,kotlinx.android.synthetic.**"),

Based on the comment, it's also part of the IntelliJ default config, and there appears to be some confusion on the JetBrains side with regard to why the exception was made in the first place, with a decision to leave it in place regardless, just for consistency.
https://youtrack.jetbrains.com/issue/KTIJ-12967

However, at some point in the past I must have disabled that particular setting in my IntelliJ config. The defaults are set in Preferences->Editor->Code Style->Kotlin, which are currently blank for me (that gets stored in .idea/codeStyles/Project.xml, in a field called PACKAGES_TO_USE_STAR_IMPORTS).

The ktlint documentation also suggests overwriting the Project.xml with a blank value for PACKAGES_TO_USE_STAR_IMPORTS:
https://pinterest.github.io/ktlint/rules/configuration-intellij-idea/

Given that, I think it makes sense that ktlint should stop including those two paths as default wildcard exceptions.

As a temporary workaround, adding an .editorconfig file to the project with just this removes those defaults:

[*.{kt,kts}]
ij_kotlin_packages_to_use_import_on_demand = nothing

Also, the second issue does appear genuine: an allowed wildcard import (due to this default, or from ij_kotlin_packages_to_use_import_on_demand) that is not used in the code, should still trigger the no-unused-imports rule.

[paul-dingemans]

Tnx for your elaborative analysis. The feature to respect setting ij_kotlin_packages_to_use_import_on_demand was implemented not too long ago in ktlint 0.45.x via #1272. The reason for adding the default values is that they seems to be hard-coded in IntelliJ IDEA as well (https://github.com/JetBrains/kotlin/blob/ffdab473e28d0d872136b910eb2e0f4beea2e19c/idea/formatter/src/org/jetbrains/kotlin/idea/core/formatter/KotlinCodeStyleSettings.java#L81-L82).

If the property is not set explicitly, IntelliJ IDEA allows imports java.util.* and kotlinx.android.synthetic.*. If ktlint would not do the same, this would result in a conclict between ktlint and IntelliJ IDEA. Lots of users of ktlint dislike that.

Your approach by setting the property in .editorconfig is not a workaround but a good solution as it makes explicit that it is never allowed. It should be added to the documentation.

[*.{kt,kts}]
ij_kotlin_packages_to_use_import_on_demand = nothing

Currently, I am working on a new codestyle ktlint_official which will not have the limitation that it should be in sync with IntelliJ IDEA. In that codestyle, it would make sense to remove the default value. I will create a new issue for that.

Also, the second issue does appear genuine: an allowed wildcard import (due to this default, or from ij_kotlin_packages_to_use_import_on_demand) that is not used in the code, should still trigger the no-unused-imports rule.
Please see #1754 why this can/will not be fixed.

[paul-dingemans]

Closed as follow-up issues are created.