[BUG]: Edit tool applies formatter to entire file, causing unintended changes outside the edited range

[DRBragg]

Bug Description

The Edit tool's post-edit formatting step reformats the entire file, not just the edited range. This causes cosmetic changes (removed blank lines, indentation adjustments) on lines the user never intended to modify, producing noisy diffs that require manual cleanup.

Steps to Reproduce

1. Open a project with a formatter configured (e.g., Prettier detected automatically, or ruby-lsp in LSP config)
2. Use the Edit tool to make a single-line change in an ERB, HTML, or JS file
3. Run git diff on the file

Expected: Only the targeted line changes.
Actual: Additional blank lines are removed, indentation is adjusted, and other cosmetic changes appear on unrelated lines.

Concrete Example

Editing a single turbo_stream_from line in an ERB file:

oldString: '  <%= turbo_stream_from "chat_list_#{Current.user.id}" %>'
newString: '  <%= turbo_stream_from "chat_list_#{Current.user.model_name.param_key}_#{Current.user.id}" %>'

Resulting diff shows 5 unrelated changes in addition to the intended one:

 <%# locals(conversations:, pagy:) %>
-
 <%= content_for(:title_tag, ": Chat") %>
-
 <%= render(Podia::UI::CardComponent.new(
...
   <% end %>
-
-  <%= turbo_stream_from "chat_list_#{Current.user.id}" %>
+  <%= turbo_stream_from "chat_list_#{Current.user.model_name.param_key}_#{Current.user.id}" %>
...
-            <%= render CMS::Chat::ItemComponent.with_collection(conversations) %>
+          <%= render CMS::Chat::ItemComponent.with_collection(conversations) %>

Three blank lines were removed and one line's indentation was changed — none of which were part of the oldString or newString.

The same edit performed with sed produces a clean single-line diff.

Impact

This is a significant workflow disruption in codebases with style conventions. Every Edit tool change to a template or JS file requires:

1. Running git diff to check for damage
2. git checkout to restore the file
3. Re-doing the edit with sed or manual editing

This happens consistently — not occasionally — on every Edit tool invocation on files where a formatter is detected.

Workaround

Using sed for surgical replacements instead of the Edit tool, or setting "formatter": false in opencode.json (which disables all formatting, including on genuinely new code).

Relation to #4603

Issue #4603 proposed range-based formatting as a feature. This bug report is the flip side: the current whole-file formatting behavior is a bug that produces incorrect diffs. PR #4604 would resolve this by restricting formatting to the edited range only.

Environment

• OpenCode version: 1.2.6
• File types affected: .erb, .html, .js (likely any file with a detected formatter)
• OS: macOS Tahoe 26.3

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• On file edit it is also formatted #8387: "On file edit it is also formatted" — same root issue (whole-file formatting applied on every Edit tool invocation)
• Automatic stylistic changes due to linting errors are not ideal #6876: "Automatic stylistic changes due to linting errors are not ideal" — same symptom of unintended formatting changes polluting diffs
• [FEATURE]: Restrict formatting only to the edited range for clang-format (and Prettier) #4603: "[FEATURE]: Restrict formatting only to the edited range" — the feature request you already reference, which addresses the same underlying behavior

You may want to consolidate with one of those or add a comment there instead.

[DRBragg]

Closing as duplicate. This is the same issue reported in #8387, #6876, and #4603. I searched before filing but missed them with all the open issues (while contributing to the problem 🙇). Sorry for the noise!

For anyone landing here: #8387 is the closest match (whole-file formatting on edit), and #4603 has a PR (#4604) with a range-based formatting fix.