ktfmt unused imports removal incorrectly removes import with backticks

[bhamiltoncx]

Kotlin allows arbitrarily escaping reserved words and symbols in import statements using backticks, e.g.

import foo.bar.baz

and

import `foo.bar.baz`

are both supported and work. However, using the latter form causes ktfmt's unused imports removal feature to incorrectly remove the import statement entirely:

% cat /tmp/Test.kt
import `blech.quux`
import `corge.grault` as xyzzy
import foo.bar.baz

fun doStuff() = baz + quux + xyzzy
% ktfmt - < /tmp/Test.kt 2>/dev/null
import `corge.grault` as xyzzy
import foo.bar.baz

fun doStuff() = baz + quux + xyzzy
% ktfmt --do-not-remove-unused-imports - < /tmp/Test.kt 2>/dev/null
import `blech.quux`
import `corge.grault` as xyzzy
import foo.bar.baz

fun doStuff() = baz + quux + xyzzy

Interestingly, this happens only if there is no alias at the end of the import statement.

I made a repro in 9e53104 . Here's the output of the test when it fails:

    KtImportDirective import `com.used.Foo.Bar.baz`
      LeafPsiElement import
      PsiWhiteSpaceImpl  
      KtNameReferenceExpression `com.used.Foo.Bar.baz`
        LeafPsiElement `com.used.Foo.Bar.baz`
    PsiWhiteSpaceImpl \n
    KtImportDirective import `com.used.Foo.Baz.blech` as quux
      LeafPsiElement import
      PsiWhiteSpaceImpl  
      KtNameReferenceExpression `com.used.Foo.Baz.blech`
        LeafPsiElement `com.used.Foo.Baz.blech`
      PsiWhiteSpaceImpl  
      KtImportAlias as quux
        LeafPsiElement as
        PsiWhiteSpaceImpl  
        LeafPsiElement quux
    PsiWhiteSpaceImpl \n

# Input: 
####################
import com.unused.Sample
import `com.used.Foo.Bar.baz`
import `com.used.Foo.Baz.blech` as quux
import com.used.FooBarBaz as Baz
import com.used.bar // test
import com.used.`class`
import com.used.a.*
import com.used.b as `if`
import com.used.b as we
import com.unused.a as `when`
import com.unused.a as wow

fun test(input: we) {
  Baz(`class`)
  `if` { bar }
  `else` { baz + quux }
  val x = unused()
}


# Output: 
####################
import `com.used.Foo.Baz.blech` as quux
import com.used.FooBarBaz as Baz
import com.used.a.*
import com.used.b as `if`
import com.used.b as we
import com.used.bar // test
import com.used.`class`

fun test(input: we) {
  Baz(`class`)
  `if` { bar }
  `else` { baz + quux }
  val x = unused()
}

# Expected: 
####################
import `com.used.Foo.Bar.baz`
import `com.used.Foo.Bar.blech` as quux
import com.used.FooBarBaz as Baz
import com.used.a.*
import com.used.b as `if`
import com.used.b as we
import com.used.bar // test
import com.used.`class`

fun test(input: we) {
  Baz(`class`)
  `if` { bar }
  `else` { baz + quux }
  val x = unused()
}

####################

[bhamiltoncx]

This could be a Kotlin compiler bug, a bug in RedundantImportDetector, or both.

I see for statements like import `com.used.Foo.Bar.baz` that this helper function to calculate the identifier is returning "com.used.Foo.Bar.baz" instead of just "baz":

https://github.com/facebook/ktfmt/blame/bcec853c9bd86c529cb285b0376aa35ca37ec3b0/core/src/main/java/com/facebook/ktfmt/format/RedundantImportDetector.kt#L180-L182

which means it always thinks isUsed is false, since nothing is using an identifier named com.used.Foo.Bar.baz, just baz.

If I fix that, then this logic isFromThisPackage fails:

https://github.com/facebook/ktfmt/blame/bcec853c9bd86c529cb285b0376aa35ca37ec3b0/core/src/main/java/com/facebook/ktfmt/format/RedundantImportDetector.kt#L171

since the parent of com.used.Foo.Bar.baz is the root package.

[hick209]

Great findings! Thanks for reporting it

[hick209]

Looks like a compiler issue from looking at the PSI tree.

'import `blech.quux`' is broken down like this:

    KtImportDirective import `blech.quux`
      LeafPsiElement import
      PsiWhiteSpaceImpl
      KtNameReferenceExpression `blech.quux`
        LeafPsiElement `blech.quux`

While it without backticks turns into

    KtImportDirective import blech.quux
      LeafPsiElement import
      PsiWhiteSpaceImpl
      KtDotQualifiedExpression blech.quux
        KtNameReferenceExpression blech
          LeafPsiElement blech
        LeafPsiElement .
        KtNameReferenceExpression quux
          LeafPsiElement quux

What is your current use case for this?
This seems like a super edge case that might be worth just waiting for a fix upstream

[bhamiltoncx]

I’m using this for module names which contain reserved words and special symbols. They’re automatically generated via cimport in our case (bazel build system generates the module names from its target names). Ben

…

On Wed, May 21, 2025 at 00:49 Nivaldo Bondança ***@***.***> wrote: *hick209* left a comment (facebook/ktfmt#532) <#532 (comment)> Looks like a compiler issue from looking at the PSI tree. 'import `blech.quux`' is broken down like this: KtImportDirective import `blech.quux` LeafPsiElement import PsiWhiteSpaceImpl KtNameReferenceExpression `blech.quux` LeafPsiElement `blech.quux` While it without backticks turns into KtImportDirective import blech.quux LeafPsiElement import PsiWhiteSpaceImpl KtDotQualifiedExpression blech.quux KtNameReferenceExpression blech LeafPsiElement blech LeafPsiElement . KtNameReferenceExpression quux LeafPsiElement quux What is your current use case for this? This seems like a super edge case that might be worth just waiting for a fix upstream — Reply to this email directly, view it on GitHub <#532 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAFEAUY7C7FZSN45IFYBFOT27QOW5AVCNFSM6AAAAAB3NUEB36VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDQOJWG44TKMRQGE> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[hick209]

@bhamiltoncx I think it would work if you updated to

import `blech`.`quux`