Detect filename is not compliant with PascalCase convention

[bedla]

Hi,
I found that FilenameRule does not check PascalCase convention mentioned in https://kotlinlang.org/docs/coding-conventions.html#source-file-names
What do you think?
Thx
Ivos

[shashachu]

hi @bedla thanks for the PR. Reading the Kotlin docs, my take is that filenames should always conform to Pascal case, regardless of the contents. Is that not also your understanding?

[bedla]

Yep, from my understanding PascalCase is only viable name of the file.

I have rebased to current master.

[bedla]

I have update PR to current master

[paul-dingemans]

The code seems unnecessary complex to me. Basically, I would expect it do the following:

1. Determine the number of top level declarations
2. Determine the name of the first class
3. If one top level declaration was found and the first class name is not null than the name of file should be identical to the name of the class followed by ".kt". Otherwise check if the filename adheres to the the PascalCase convention.

[paul-dingemans]

@bedla Do you plan to follow up on my remarks on this PR?

[bedla]

Yes, I will. Sorry for being late, I had some rush in work.

[bedla]

Just pushed requested changes. I have rewritten original logic to make it more explicit from my point of view. Pls, take a look. Thx

[paul-dingemans]

Please see commits for changes. The logic changes that I wanted was too difficult to describe in words, so I choose to implement it to check whether it worked.

Code and tests did not comply with KtLints code formatting rules. So please ensure to also run the gradle "ktlint".

Linting did pint out that also four KtLint files do not comply with the naming standard of this rule. I changed one of them, for which I had not objections to change it. But remaining three files, made me doubt about the rule (https://github.com/pinterest/ktlint/runs/5397719779?check_suite_focus=true):

ktlint/ktlint/src/main/kotlin/com/pinterest/ktlint/internal/CommandLineExt.kt:1:1: Extension function printHelpOrVersionUsage should be declared in a file named printHelpOrVersionUsage.kt (cannot be auto-corrected) (filename)
ktlint/ktlint/src/main/kotlin/com/pinterest/ktlint/internal/ByteArrayExt.kt:1:1: Extension property hex should be declared in a file named hex.kt (cannot be auto-corrected) (filename)
ktlint/buildSrc/src/main/kotlin/ToolchainForTests.kt:1:1: All elements with receiver Project should be declared in a file named Project.kt (cannot be auto-corrected) (filename)

https://kotlinlang.org/docs/coding-conventions.html#source-file-names is not very clear about files contain 1 toplevel function which is not a class. The current implementation enforces PascalName with the name of that toplevel function while the coding convention says that you should choose a name describing what the file contains and use uppercase PascalNotation. Based on that, and the example given above, I think this should be changed. Please let me know what you think of it.

[bedla]

I see. Let me check it and add more tests. I will be at vacations next week, so result of my changes will be available after.

[bedla]

Hmm, interesting "edge cases".

• CommandLineExt & ByteArrayExt - actually I like more this convention with DescriptiveName+Ext.kt ... could we extends original Kotlin's convention with exception to Ext suffix in this case? It seems reasonable to me.
• ToolchainForTests - I agree with rule that filename should be Project.kt, but on the other hand there should be possible to add exceptions from the rule.

What do you thing?

[paul-dingemans]

• CommandLineExt & ByteArrayExt - actually I like more this convention with DescriptiveName+Ext.kt ... could we extends original Kotlin's convention with exception to Ext suffix in this case? It seems reasonable to me.

• ToolchainForTests - I agree with rule that filename should be Project.kt, but on the other hand there should be possible to add exceptions from the rule.

I think we should handle both cases similar. If a file does not contain any class and has filename ending with "Ext" or "Extension" and is following the PascalCase convention then there should be no violation about the file name. Would that be feasible?

[bedla]

Ok, I will take a look at it. I have also created https://youtrack.jetbrains.com/issue/KT-51919 to know Kotlin creator's opinion on this edge case (I do not know if they will join discussion, but why not try :) ).

[bedla]

Mr. Elizarov responded in Youtrack issue. I think that he is right.

But it means that should remove checks around allOfSameReceiver. And also his response invalidate what was mentioned in original code https://github.com/pinterest/ktlint/blob/0.45.2/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/FilenameRule.kt#L67 ... If I get it correctly, it is because of situation when we want to name file with same name like Receiver name, when we have only extensions in the file. But this one is not explicitly noted in lang-docs.

What do you think?
Do you know why exactly is that note at line 67?

[paul-dingemans]

It looks like that https://github.com/pinterest/ktlint/blob/0.45.2/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/FilenameRule.kt#L67 is just the example of a file in which extension functions have the same receiver. There can be a good reason to group such functions together in one file, but I agree that we should not force that the file is named after the receiver. It would be enough to enforce the upper PascalCase convention here.

When applying above, a project can still use a filename like SomeReceiverExt.kt as it adheres to the upper PascalCase convention. But the other way around, a file which only contain extension functions on the Foo receiver does not necessarily to be named as Foo.kt but could be named as RedundantBar.kt.

[paul-dingemans]

@bedla Do you have some time to finish up the issue? I expect a new release to be build in a couple of weeks.

[bedla]

ahh, sorry I missed your previous comment. let me re-check it.

[bedla]

I have removed that all-top-level receivers exception, but it still fails on:

C:\Users\ivo.smid\IdeaProjects\ktlint\ktlint\src\main\kotlin\com\pinterest\ktlint\internal\ByteArrayExt.kt:1:1: Extension property hex should be declared in a file named hex.kt (cannot be auto-corrected) (filename)
C:\Users\ivo.smid\IdeaProjects\ktlint\ktlint\src\main\kotlin\com\pinterest\ktlint\internal\CommandLineExt.kt:1:1: Extension function printHelpOrVersionUsage should be declared in a file named printHelpOrVersionUsage.kt (cannot be auto-corrected) (filename)

So if I get it correctly, I should remove also this sub-rule for Extension functions & Extension property? What do you think?

[paul-dingemans]

I have removed that all-top-level receivers exception, but it still fails on:

C:\Users\ivo.smid\IdeaProjects\ktlint\ktlint\src\main\kotlin\com\pinterest\ktlint\internal\ByteArrayExt.kt:1:1: Extension property hex should be declared in a file named hex.kt (cannot be auto-corrected) (filename)
C:\Users\ivo.smid\IdeaProjects\ktlint\ktlint\src\main\kotlin\com\pinterest\ktlint\internal\CommandLineExt.kt:1:1: Extension function printHelpOrVersionUsage should be declared in a file named printHelpOrVersionUsage.kt (cannot be auto-corrected) (filename)

So if I get it correctly, I should remove also this sub-rule for Extension functions & Extension property? What do you think?

Yes they should be removed as well for two reasons:

• The rule forces the name the file to start with a lowercase character as that is the convention for function and property names
• Only when the file contains exactly one class, then the file should be named identical to that class name. In all other cases a descriptive name has to be chosen.

[paul-dingemans]

There is one more file ("RuleExtension") which needs a better name. I will rename that file in the future as it is heavily refactored in another open PR.

[vanniktech]

Is it desired that with this change, the following file:

package com.vanniktech.feature.boardmoney.data

import app.cash.sqldelight.adapter.primitive.IntColumnAdapter
import app.cash.sqldelight.db.SqlDriver
import com.vanniktech.boardmoney.QueryWrapper

internal fun createQueryWrapper(driver: SqlDriver) = QueryWrapper(
  driver = driver,
  boardMoneyPlayerAdapter = BoardMoneyPlayer.Adapter(
    colorAdapter = IntColumnAdapter,
  ),
)

gets linted with the following:

/Users/niklas/dev/GitHub/vanniktech/feature-board-money/src/commonMain/kotlin/com/vanniktech/feature/boardmoney/data/Db.kt:1:1: File 'Db.kt' contains a single top level declaration and should be named 'CreateQueryWrapper.kt' (cannot be auto-corrected) (filename)

That does not seem right to me.

[paul-dingemans]

It is debatable. According to the Kotlin styleguide a meaningfull name should be chosen. Depending on the context, Db.kt and CreateQueryWrapper.kt can be meaningfull names. On top of the style guide, ktlint enforces the file to be named after the top level declaration if the file only contains one top level declaration. In general, I see no added value for having a different filename in such cases.

[vanniktech]

If a Kotlin file contains a single class or interface (potentially with related top-level declarations), its name should be the same as the name of the class, with the .kt extension appended. It applies to all types of classes and interfaces. If a file contains multiple classes, or only top-level declarations, choose a name describing what the file contains, and name the file accordingly. Use upper camel case with an uppercase first letter (also known as Pascal case), for example, ProcessDeclarations.kt.

I'd agree for a Class / Interface, but not for a given function (as in my case).