WinMerge - ignore all whitespace including newlines and formatting changes

Question

How can I ignore "code style" changes while using WinMerge as a difftool? Specifically across two commits.

So that

thing
{
  a,
  b
}

and

thing { a, b }

would be treated as identical.

Essentially this question, but for winmerge rather than diff.

.gitconfig:

[diff]
    tool = winmerge
[difftool]
    prompt = false
[difftool "winmerge"]
    cmd = "$HOME/scripts/winmerge.sh" "$LOCAL" "$REMOTE"
[mergetool]
    prompt = false
    keepBackup = false
    keepTemporaries = false
[merge]
    tool = winmerge
[mergetool "winmerge"]
    cmd = "'C:/Program Files (x86)/WinMerge/WinMergeU.exe'" -e -u -fm -dl \"Local\" -dr \"Remote\" "$LOCAL" "$MERGED" "$REMOTE"

(winmerge.sh just calls WinMergeU.exe -e -u -wr "$1" "$2")

None of the command line options seem to fit, and I think line filters won't work because they are per-line.

Swellfish

Diff tools are traditionally line-based as programs are written as text in lines. You're basically asking for a diff at the tokenized & normalized level, not at the textual level. See here, but it's not directly usable answer, just an explanation of the conceptual and practical problem. – Osana

@Osana yes, and JD Frias's answer gets closest to that idea. My "solution" since I asked this question has been to enforce clang-format rules in my team :). I could envision a theoretical tool which runs a formatter but keeps track of the original source locations, and then does a diff on the formatted text but shows the user the source-mapped originals for editing. Similar to how you can debug transpiled javascript by stepping through the typescript. I'm not sure that tool exists currently, as you said. – Swellfish

Coming back to this two years later: There is no option in WinMerge to do this. I have found difftastic to do what I was actually asking here, which is syntax-tree-based diffs. It does so at the cost of speed and memory, so I end up having both winmerge and difftastic in my gitconfig and switch between them depending on my needs. For my given example (with .cpp extensions), difftastic prints "No syntactic changes". – Swellfish

Answer 1

To answer my own question with the benefit of more time:

• This is not possible with WinMerge
• difftastic does this for read-only diffs at the cost of speed and memory
• No tool that I'm aware of does writable diffs (e.g. conflict resolution) while showing semantic-based diffs

Not-quite-there solutions:

Ignore blank lines; Ignore carriage return differences (Windows/Unix/Mac)

This ignores line feed differences, and full blank line differences, but does not compare files semantically. It does help in certain simple cases.

Line filter ^\s*$

Same as "Ignore blank lines"

.gitattributes formatter with textconv for specific file types

This is the closest option for read-only diffs, with the downsides of:

• needing to define a separate attribute (and formatter) for each file type
• displaying the formatted versions of the files rather than the original

My current solution

• For conflict resolution, use WinMerge as-is with as much of the "ignore" options turned on as possible. Resolving conflicts with formatting changes is a massive pain no matter what you do, so try to isolate formatting changes to their own merges.
• For diff viewing, use difftastic which uses tree-sitter to compare code on an AST level rather than a textual level
• When difftastic is slow or hogging memory, fall back to diff/WinMerge/VSCode

Swellfish

Answer 2

This option works for me:

WinMerge -> Edit -> Options -> Compare -> General: Ignore blank lines; Ignore carriage return differences (Windows/Unix/Mac)

etc.

The answer was taken from https://superuser.com/questions/174275/can-i-compare-only-file-contents

Crossed

This doesn't do it if you have one file with some blank lines inserted and the other one doesn't AND there are character-level differences between the non-blank lines. In that case, "Align similar lines" is needed. And these other options seem redundant to that one (except the line conversion probably). – Diphthong

The question is how to do get the identitcal diff result when comparing the same text where in one file it is in a long line and in the other with separated line (to fit a column length for example). – Obsess

Answer 3

You could add a .gitattributes for your file. This would run a tool to normalize/beautify/prettify both files before comparison.

This will run .json files through json_pp before compare:

echo "*.json diff=json" >> .gitattributes
git config diff.json.textconv json_pp

Check out git documentation for details: https://git-scm.com/docs/gitattributes

Source: https://t-a-w.blogspot.com/2016/05/sensible-git-diff-for-json-files.html

Modality

This definitely does work to show semantic diffs, but I would still rather a winmerge-specific option that still shows the original files, but doesn't highlight the code style differences. Running a formatter can get a little slow for larger cpp files, and I'm also worried about the issues it could cause when editing diffs and saving them. I don't want to accidentally commit formatting changes if I don't need to. – Swellfish

I use Beyond Compare has custom rules for comparison, and tons of other features. It is paid though, well wroth it in my opinion #notsponsored – Modality

Answer 4

In addition of ignoring white spaces/blank lines/...etc. Do the following

• Go to Tools->Filter
• Select "Linefilters" tab
• Check Enable Line Filters
• Add the following expr, and make sure it is checked ^\s*$

-Refresh the comparison

Acerbate

Thanks for your answer, but this will just filter out blank lines, which is not what I'm asking. I wanted the behavior of difftastic, which does AST-based semantic diffs. I use that tool now if I need that, and winmerge when I don't. – Swellfish