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Difftastic: A diff that understands syntax

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Re: Difftastic: A diff that understands syntax

#121

Post by Wilfred »

loxias wrote: post #22

This looks really cool and I can't wait to try it, tho... a bit of a PITA to get running. ;) Took a while to figure out how to build, and had to install 400MB of dependencies first.... Edit: And after installing cargo, watching it fail to build, then determining I must need a newer version of cargo, so I built that from source... it fails. Apparently I need to install `rustc-mozilla` and not `rustc`. "obviously". Thi…

The getting started section of the manual should help: https://difftastic.wilfred.me.uk/getting_started.html

I've documented the minimum rust version required today, although I'm looking at lowering the minimum version.

Re: Difftastic: A diff that understands syntax

#122

Post by zukzuk »

teeray wrote: post #107
scythmic_waves wrote: post #68

Earlier quoted context omitted.

Not OP, but the docs call out some "Tricky Cases" [1]. [1] https://difftastic.wilfred.me.uk/tricky_cases.html

I’d imagine there’s some challenging judgement calls that such a tool would have to make. Like, in Go, you can reorder the members of a struct definition. In many cases this is just diff noise to reviewers. HOWEVER, it does impact the layout of the struct in memory, so it can be semantically meaningful in performance work.

I wrote a masters thesis about the more general problem here (https://tspace.library.utoronto.ca/bitstream/1807/65616/11/Z...).

The tl;dr is that there's an almost infinite number of ways to atomize/conceptualize code into meaningful "units" (to "register" it, in my supervisor's words), and the most appropriate way to do that is largely perspectival — it depends on what you care about after the fact, and there is no single maximal way to do it up front.

Re: Difftastic: A diff that understands syntax

#123

Post by Wilfred »

rom1v wrote: post #77

It might be useful for reviewing merge/pull requests. But is there a way to display the diff "interleaved" instead of 2-columns side-by-side? (when executing `GIT_EXTERNAL_DIFF=difft git log -p --ext-diff` for example)

There's a basic single-column 'inline' display available if you do `INLINE=y`, but it's not as mature as the side-by-side display yet.

Re: Difftastic: A diff that understands syntax

#125

Post by jhgb »

danbruc wrote: post #117
jhgb wrote: post #110

Earlier quoted context omitted.

My point was that test suites should give you a heuristic on what corrections are good and which are bad. A source code change that turns a test fail into a test pass should be considered an improvement.

I am still lost. Test suite for what? We have a parser - binary, source code and maybe a test suite if the parser developers decided to write tests - and a random text file that we throw at the parser and for which the parser hopefully generates a useful syntax tree if the content is a well-formed or not too badly malformed program in a language the parser understands.

What "test suite for the parser"? Of course a test suite for the faulty program you're trying to correct into a working one.

Re: Difftastic: A diff that understands syntax

#126

Post by autarch »

lstamour wrote: post #105
chockchocschoir wrote: post #81

Earlier quoted context omitted.

Indeed. One could just do `diff $(jq . $fileOne) $(jq . $fileTwo)` and you'll end up with a "nice enough" diff even if $fileOne and $fileTwo were very differently formatted.

The problem is when a file also needs to be normalized - e.g. object keys in a different order, YAML syntax expansion. It can be very useful to indicate when a JSON file is identical to another JSON file but some of the properties or array items are out of order and that requires more in-depth knowledge of the data format. Let's not mention that you could UTF-8 encode characters or write out the same character using…

I wrote a tool that tidies JSON and can do things like re-orders keys in a fixed order - https://github.com/ActiveState/json-ordered-tidy

Re: Difftastic: A diff that understands syntax

#127

Post by CodeIsTheEnd »

arxanas wrote: post #99
CodeIsTheEnd wrote: post #89

Earlier quoted context omitted.

EDIT: Wilfred IS the original author [3]; my apologies. Not to discredit Wilfred (it looks like he's taken over the project as the maintainer), but, based on the historical contributions [1], it looks like it was originally developed by Max Brunsfeld, who also created Tree-sitter. [2] [1]: https://github.com/Wilfred/difftastic/graphs/contributors [2]: https://github.com/tree-sitter/tree-sitter [3]: https://github.com…

I think the contributor graph is misleading, and that he's using git-subtree to vendor tree-sitter, which makes it look like others have contributed more to the project.

Oops, I think you're right! Thank you for pointing that out.

My apologies to Wilfred.

Re: Difftastic: A diff that understands syntax

#128

Post by Wilfred »

pluc wrote: post #91
mkdirp wrote: post #66

Earlier quoted context omitted.

Why?

because it's an automated piece of software making decisions about what is an "equal diff" and what is a "difference diff" because a diff no longer means just a change, it now has to be a meaningful enough change .. If you removed something like `if (true)` or whatever, that's still a diff that could have some importance and/or unknown consequences. I appreciate the value, but the fact that it allows refactoring to b…

Difftastic is only ignoring whitespace that isn't significant. If you remove `if (true)`, it will get highlighted.

With a textual diff today, your only choices are 'highlight all whitespace changes' (e.g the git default) or 'ignore all whitespace' (e.g. diff --word-diff).

If difftastic says there are no changes, then both files have the same parse tree and the same comments.

Re: Difftastic: A diff that understands syntax

#129

Post by Wilfred »

emacsen wrote: post #5

This looks absolutely amazing. One thing I do find interesting (and a wish were different) is that only programming languages are supported, rather than data formats as well. For example, two JSON documents may be valid but formatted slightly differently, or a common task for me is comparing two YAML files. Comparing config files that have a well defined syntax and or can be abstracted into a tree (JSON, YAML, TOML,…

JSON and CSS are supported today, and I'm interested in adding more structured text formats.

If a format has a tree-sitter parser, it can be added to difftastic. The TOML tree-sitter parser looks good, but there isn't a mature markdown parser for tree-sitter. There are other markdown parsers available, so in principle difftastic could support markdown that way.

The display logic might need a little tuning for prose-heavy formats like markdown though. I'm not happy with how difftastic handles block comments yet either.

I'm not sure about formats that contain more prose, such as markdown or HTML.

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