Format only modified lines

[kylegmaxwell]

Issue Type

Feature Request

Description

It would be helpful if there were a way to format only the modified lines. What is modified would be determined by source control. Currently formatOnType only works with semi colon (see microsoft/vscode-cpptools#1419), and formatOnSave formats the entire file. This is undesirable when working on large codebases with legacy code. In that case I want to make a small change, and have it automatically formatted on save, but not modify the rest of the file, which would create a huge diff.
It would also be great to have similar behavior for trimming trailing white space.

VS Code Info

VS Code version: Code 1.20.1 (f88bbf9, 2018-02-13T15:31:21.019Z)
OS version: Linux x64 4.14.16-200.fc26.x86_64

Steps to Reproduce:

1. Set preferences:
   "editor.formatOnSave": true,
   "C_Cpp.clang_format_path": "/usr/bin/clang-format",
2. Open a C++ file with multiple formatting errors
3. Modify the file on one line.
4. Note that multiple modifications have been made to the file.

Does this issue occur when all extensions are disabled?:

No, formatting does not work at all in that case.

[Gruntfuggly]

Been hoping for this for a while. In the meantime, I've knocked up an extension...

https://marketplace.visualstudio.com/items?itemName=Gruntfuggly.format-modified

[kylegmaxwell]

Awesome! Just tried it out and it seems to work so far.

[alekseyt]

Great job, but this shouldn't be an extension IMO, this is a legit issue with editor and i don't personally think "feature-request" label is applicable here. I'm in the same boat and i have to use external merge tool (e.g.meld) to rollback unwanted changes.

[guillochon]

That extension appears to be C++ only, anyone know of a Python equivalent?

[devinrhode2]

Extension appears to support many languages now, but only because clang-format supports multiple languages

format-modified.languages

Use this to control which files are formatted. It is set to ["cpp"] by default, so .cpp and .h files are formatted. Use F1 -> Change Language Mode to show a list of language identifiers. Java, Javascript, Objective-C, Proto are supported by clang-format, but I have not tested them.