Edit tool messes with indentation (but this is not shown in the diff)

[joeldrapper]

Description

It looks like whenever the agent uses the edit tool, it replaces all tab indentation with two tabs. I was able to reproduce this with a simple one-line edit. The diff showed the correct edit but all tabs in the file had been replaced with two tabs.

Plugins

no

OpenCode version

1.2.10

Steps to reproduce

1. Have a file that uses single-tab indentation
2. Ask agent to edit the file — any edit will do
3. The diff will show the correct edit but the file will actually have had all \t replaced with \t\t.

I was editing a Ruby file with ruby-lap enabled.

Screenshot and/or share link

No response

Operating System

macOS

Terminal

Zed

[ariane-emory]

This is likely due to a formatter, as those take effect after tools like the edit tool.

Personally, I prefer to turn off all formatters by adding this line to my configuration file:

  "formatter": false,

I believe that there is also a way to turn off specific formatters for specific languages as well, I'm sure that you can find it in the documentation if you take a look.

[joeldrapper]

I don't think it could be the formatter. The only formatter OpenCode could reasonably by using for Ruby is Rubocop and that's what I use to correct the mess.

Will try to figure out if it's only Ruby today.

[tellnes]

This also affects space-indented files, not just tab-indented ones.

Reproduction: a bash script using 4-space indentation. Asking for a single-word change on one line causes the edit tool to reformat the entire file (case patterns, continuation lines, etc.).

Adding an .editorconfig with the correct indent_style and indent_size reduces the damage (prevents changing indent size) but the tool still reformats unrelated lines throughout the file.

Environment: opencode 1.2.20, macOS, shell script files

[MartinEmrich]

Confirmed... I blamed poor Qwen3.5 27B multiple times, until it by itself found out that the "edit" tool messed up the formatting, and switched to sed toolcalls. Thanks for the hint to disable the formatters!

I am sure devs meant well with calling language specific formatters after edit, but this seems to conflict with code style instructions in AGENTS.md. A session with any code-style hints in AGENTS.md should prefer these over default values of whatever formatter found and used.

[joeldrapper]

I think what is happening is OpenCode is generating code with space based indentation and that triggers a bug in Rubocop when it tries to convert it to tabs.

[MartinEmrich]

For me it was a shell script, and shfmt by default converted my 2-space-indentation to tabs. After disabling formatting, the model-generated code matched the surrounding style.

[joeldrapper]

I am not able to reproduce this now, edits seem to work fine with tabs and formatting. Not sure if it’s a new version of OpenCode or Ruocop or something else.

[Nowaker]

OpenCode has been consistently messing up my shell script indentation from 2 spaces to 3 spaces. Citing OpenCode itself:

The Write tool is converting my spaces to tabs.

So it ends up using sed to apply the changes without messing the indentation.

I don't use any formatters, have no .editorconfig file, or whatnot. It's just pure OpenCode wanting my scripts formatted that way. Not even the AI. Write tool messes it up.

[MartinEmrich]

Yup, today it (Sonnet 4.6, so no slouch) randomly decided to reformat a few lines of a Python script from 4 to 5 spaces, and, confronted, claims the edit tool has done this (but was able to correct it). So just disabling the formatter via configuration is not ideal either.