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.

[ronakg]

Any update on this issue? I don't want to use the extension mentioned above because all my formatting is set up via their respective language servers. This is a very valid use-case that needs addressing.

[jrieken]

This will land with the August release. This is what I planning to merge later this afternoon

• new setting editor.formatOnSaveMode with options file and modifications
• new command "Format Modified Lines"

Note that knowing "what is modified" requires active source control, like git. Without source control there are no modifications and nothing will be formatted.

[jrieken]

[kylegmaxwell]

Looks awesome, thank you!

[ronakg]

This will land with the August release. This is what I planning to merge later this afternoon

• new setting editor.formatOnSaveMode with options file and modifications
• new command "Format Modified Lines"

Note that knowing "what is modified" requires active source control, like git. Without source control there are no modifications and nothing will be formatted.

@jrieken This looks great, thanks! When you say that without source control there are no modifications, are you saying that the setting editor.formatOnType won't have any effect also? Right now I'm relying on this setting to auto-format the newly added lines.

[jrieken]

Yes - if a project is not under source control and format on save is limited to modifications then no formatting happens. Tho, when a project is under source control than all modified and added lines/files are formatted.

[ronakg]

Yes - if a project is not under source control and format on save is limited to modifications then no formatting happens. Tho, when a project is under source control than all modified and added lines/files are formatted.

I'm asking about a different setting editor.formatOnType, which is separate from editor.formatOnSave. Can you clarify how these 2 will work together now? I'm guessing editor.formatOnType will work as usual irrespective of editor.formatOnSave.

[jrieken]

Oh, misread that. Yeah, format on type has nothing to do with format on save and nothing has changed for that

[icharge]

This feature is great. I like it.
Please provide not only just on save.

[Nabav]

The command Format Modified Lines is not showing up in the commands list.

[jrieken]

It will only show up when you have a formatter that supports formatting modified ranges, e.g one that support range formatting. The rule of thumb is that if you have "Format Selection" then you also have "Format Modified Lines"

[MikeYuanMY]

which popular formatters currently support this? I have prettier but cannot seem working with this feature

[jrieken]

https:/prettier/prettier-vscode/blob/main/README.md#format-selection

[icharge]

Oh I see, I'm using Prettier then I have to set new shortcut key. :)

[kylegmaxwell]

A lot of people are asking for format modified on type instead of save. I didn't ask for that since I thought it does not make sense. If you format on type then you always just format the lines as you modify them. I needed format modified since I wanted to make changes to several lines and then save and see just those lines formatted. Also I was using C++ with clang_format which does not work well with formatting single lines since it sometimes removes the line you are typing on, hence the desire to format modified lines on save.

[sheerun]

Unfortunately this often doesn't work often giving "Overlapping ranges are not allowed! error prettier/prettier-vscode#497

[valeryan]

My extension uses PHPCS/CBF to format PHP files and because many of the rules are dealing with whitespace formatting allowing format selection does not work well. PHPCBF has an option to only format modified lines. I would like to be able to implement this without also implementing format by selection and just format the document using PHPCBF's internal filter for git modified. However, it seems that as far as I can tell the Format only Modified Lines feature just piggybacks off of the already established API for format selection which I do not want to support.

Also, because I do not implement registerDocumentRangeFormattingEditProvider my extension is not activated on save when a user now sets Format on Save Mode to modified. This is causing confusion because no errors or information is shown to the user to help them understand why my extension is not functioning in this mode.

[trentbullard]

not sure if this is the right place for this, but thank you for this @kylegmaxwell it was a sad day when i had to disable formatOnSave