Start with the same substring

Oct 13, 2025 by talynt.org 66 views

Autocompleting Specifically Named Files Causes Panic (UTF8-Related)

Introduction

Autocompletion is a feature that helps users quickly complete file names or commands by suggesting possible completions based on the input provided. However, in certain situations, autocompleting specifically named files can cause a panic, especially when dealing with files that have non-ASCII characters in their names. In this article, we will explore the issue of autocompleting specifically named files causing a panic and provide a detailed explanation of the problem.

Describe the Bug

When we have multiple files whose names meet the following conditions:

Have a space character (0x20): The file name contains a space character.
Have a non-ASCII character before that space: The file name has a non-ASCII character before the space character.
Start with the same substring: The file name starts with the same substring as another file.

It is possible to cause a panic when autocompleting the file name. A practical example of this issue is when having two files called Лекція 1.docx and Лекція 2.docx in the same directory. Trying any of the following autocompletes causes a panic:

ls Л<Tab>
ls Ле<Tab>
ls Лекція<Tab>

Using ls is purely demonstrative, as autocompleting in any context causes a panic.

Curious Behavior

Curiously enough, the panic happens only when the last character of the user's prefix is non-ASCII. For example, when having two files ТестTest 1 and ТестTest 2, autocompleting ls Те<Tab> panics, but ls ТестTes<Tab> does not.

Quoted Autocompletion

This issue does not happen if you autocomplete with quotes. For example, ls "Лекц<Tab>" does not cause a panic.

Panic Message

The text of the panic itself (after attempting ls При<Tab>) is:

  × Main thread panicked.
  ├─▶ at /usr/src/debug/rust/rustc-1.84.1-src/library/core/src/str/
  │   mod.rs:648:21
  ╰─▶ byte index 6 is not a char boundary; it is inside 'и' (bytes 5..7) of
      ``Пример 1``

How to Reproduce

Here is a script generating useful examples:

mkdir example
cd example
touch "Пример 1" "Пример 2"     # Example
touch "例 1" "例 2"             # Example
touch "gggффф 1" "gggффф 2"     # ASCII then Unicode
touch "фффggg 1" "фффggg 2"     # Unicode then ASCII
touch "один файл"               # This one works correctly

To reproduce the issue, follow these steps:

Run the script.
(Optionally) enter the directory (works either way, just prepend example/ in examples below).
Try performing the following autocompletes:

ls один<Tab> # this one works
ls При<Tab>
ls Пример<Tab>
ls あ<Tab>
ls g<Tab> # this one works
ls ggg<Tab> # this also works
ls gggф<Tab>
ls gggффф<Tab>
ls ф<Tab>
ls фффg<Tab> # this one works (curiously)

Expected Behavior

No panic.

Configuration

key	value
version	0.102.0
major	0
minor	102
patch	0
branch	makepkg
commit_hash	1aa2ed1947a0b891398558fcf4e4289849cc5a1d
build_os	linux-x86_64
build_target	x86_64-unknown-linux-gnu
rust_version	rustc 1.84.1 (e71f9a9a9 2025-01-27) (Arch Linux rust 1:1.84.1-1)
cargo_version	cargo 1.84.1 (66221abde 2024-11-19)
build_time	2025-02-05 21:56:07 +00:00
build_rust_channel	release
allocator	mimalloc
features	default, sqlite, trash
installed_plugins

In conclusion, autocompleting specifically named files can cause a panic, especially when dealing with files that have non-ASCII characters in their names. This issue is related to the way the file system handles UTF8 encoding and can be reproduced using the provided script.
Autocompleting Specifically Named Files Causes Panic (UTF8-Related) - Q&A

Q: What is the issue with autocompleting specifically named files?

A: The issue is that when you have multiple files whose names meet certain conditions (having a space character, having a non-ASCII character before that space, and starting with the same substring), autocompleting the file name can cause a panic.

Q: What are the conditions that need to be met for the issue to occur?

A: The conditions are:

The file name contains a space character (0x20).
The file name has a non-ASCII character before the space character.
The file name starts with the same substring as another file.

Q: Why does the panic only happen when the last character of the user's prefix is non-ASCII?

A: This is a curious behavior of the issue. The panic only happens when the last character of the user's prefix is non-ASCII. For example, when having two files ТестTest 1 and ТестTest 2, autocompleting ls Те<Tab> panics, but ls ТестTes<Tab> does not.

Q: What happens if you autocomplete with quotes?

A: If you autocomplete with quotes, the issue does not occur. For example, ls "Лекц<Tab>" does not cause a panic.

Q: What is the text of the panic message?

A: The text of the panic message is:

  × Main thread panicked.
  ├─▶ at /usr/src/debug/rust/rustc-1.84.1-src/library/core/src/str/
  │   mod.rs:648:21
  ╰─▶ byte index 6 is not a char boundary; it is inside 'и' (bytes 5..7) of
      ``Пример 1``

Q: How can I reproduce the issue?

A: You can reproduce the issue by running the provided script:

mkdir example
cd example
touch "Пример 1" "Пример 2"     # Example
touch "例 1" "例 2"             # Example
touch "gggффф 1" "gggффф 2"     # ASCII then Unicode
touch "фффggg 1" "фффggg 2"     # Unicode then ASCII
touch "один файл"               # This one works correctly

Then, try performing the following autocompletes:

ls один<Tab> # this one works
ls При<Tab>
ls Пример<Tab>
ls あ<Tab>
ls g<Tab> # this one works
ls ggg<Tab> # this also works
ls gggф<Tab>
ls gggффф<Tab>
ls ф<Tab>
ls фффg<Tab> # this one works (curiously)

Q: What is the expected behavior?

A: The expected behavior is that no panic occurs.

Q: What is the configuration of the system that is experiencing the issue?

A: The configuration of the system is:

key	value
version	0.102.0
major	0
minor	102
patch	0
branch	makepkg
commit_hash	1aa2ed1947a0b891398558fcf4e4289849cc5a1d
build_os	linux-x86_64
build_target	x86_64-unknown-linux-gnu
rust_version	rustc 1.84.1 (e71f9a9a9 2025-01-27) (Arch Linux rust 1:1.84.1-1)
cargo_version	cargo 1.84.1 (66221abde 2024-11-19)
build_time	2025-02-05 21:56:07 +00:00
build_rust_channel	release
allocator	mimalloc
features	default, sqlite, trash
installed_plugins

Q: What can I do to resolve the issue?

A: Unfortunately, the issue is a bug in the system, and there is no known workaround. The best course of action is to report the issue to the system developers and wait for a fix.