If U+FEFF (BOM) is present, running formatter deletes all code in a file

[FylmTM]

Expected Behavior

Code should be put back into a file, but formatted.

Observed Behavior

All code in a file that has violation is deleted.

Steps to Reproduce

Create test.kt file with content:

val b = "text" +
                "another text"

Run formatter:

ktlint -F test.kt

Before:

$ cat test.kt
<U+FEFF>val b = "text" +
    "another text"

After:

$ cat test.kt
<U+FEFF>

Your Environment

• Version of ktlint used: 0.40.0
• Name and version (or code for custom task) of integration used (Gradle plugin, Maven plugin, command line, custom Gradle task): ktlint (installed via brew), kotlinter-gradle plugin)
• Version of Gradle used (if applicable): 6.5.1
• Operating System and version: macOS Big Sur

[FylmTM]

I have encountered this bug when configuring ktlint for our project. We had some files that had (for unknown reasons) BOM set.

As a fix for myself - I am going to remove BOM from those files.