I implemented this for a large monorepo last year, it runs as an analysis during code review and it shows what are possible similar snippets wrt the code under review. It was a very nice project. It also allows to see across the repo what are the most common constructs for the different languages. This could also be helpful to see if some code has been copied e.g. from open source projects.
I built Slopo to solve one specific problem: finding similar code that is hardest to detect by other tools, coding AI agents, and humans.
It finds similar-looking code with embeddings. This detects more than just copy-paste clones or even clones with minor changes. Similar code is often not a clone to refactor, and this is a trade-off. Initial results need to be verified, but coding agents can do this quickly. Example prompts are available on https://slopo.dev
Additionally, similar code distant in the codebase is ranked higher to focus on less obvious duplication.
The results differ a lot depending on the codebase. I noticed that sometimes most of the detected duplicates are false positives, but the remaining ones are strong candidates to refactor or even bugs. Sometimes it reveals much more real duplication.
Correct me if I'm wrong, but looking at [1] it seems to be specifically using function definitions (I'm guessing this works with functions, methods, and lambdas (the "<unknown>" part)?) as units of repetition. If yes, that's fine, but I would seriously consider adding some settings to allow the user to control that granularity. Sometimes, the repeated code is a conditional branch within larger functions (i.e., "every else:" or "every except Ex:" looks the same). If the functions are large enough, the dissimilarity of the rest of the body would (probably?) cause such things to be missed.
I would also consider - perhaps as a separate pass, with scoring set differently - to analyze comments (especially docstrings in Python). If I read the code correctly, you're currently just stripping them, which is the right thing to do when looking for code duplication, but duplicated docstrings are also often a signal that something is wrong in the codebase. The "different scoring" is because we expect docstring to be structured similarly (at least more than normal code), so some tweaking would be needed.
No. It depends the most on general code quality and architecture. Some implementations require more code similarity by design. Some languages, like Java, may tend to have more duplication, but it's only a theoretical guess. It also depends on what kind of software is developed with what language.
This is a great use case for embeddings. Code deduplication across distant modules is notoriously hard for traditional AST-based tools.
How do you handle chunking and parsing for different languages to make sure the embeddings capture semantic meaning effectively? For instance, do you chunk by functions/classes, or use a fixed token window? If a function is too long or too short, it can drastically skew the embedding similarity.
Recently there was a popular article on HN saying that sometimes code duplication is better than abstraction, so I assume that this question is not a joke.
While testing this tool, one detected duplication was interesting for a use case. Permission check logic was duplicated and placed in different distant places in the codebase. The code was similar, but not identical, the logic was not the same. One version had stricter checks. I analyzed this with the coding agent, and we found out that both versions are used for the same thing, which means that in some cases validation is insufficient. Having only a single validation place, this bug could be prevented or easily detected.
I implemented this for a large monorepo last year, it runs as an analysis during code review and it shows what are possible similar snippets wrt the code under review. It was a very nice project. It also allows to see across the repo what are the most common constructs for the different languages. This could also be helpful to see if some code has been copied e.g. from open source projects.
I built Slopo to solve one specific problem: finding similar code that is hardest to detect by other tools, coding AI agents, and humans.
It finds similar-looking code with embeddings. This detects more than just copy-paste clones or even clones with minor changes. Similar code is often not a clone to refactor, and this is a trade-off. Initial results need to be verified, but coding agents can do this quickly. Example prompts are available on https://slopo.dev
Additionally, similar code distant in the codebase is ranked higher to focus on less obvious duplication.
The results differ a lot depending on the codebase. I noticed that sometimes most of the detected duplicates are false positives, but the remaining ones are strong candidates to refactor or even bugs. Sometimes it reveals much more real duplication.
Correct me if I'm wrong, but looking at [1] it seems to be specifically using function definitions (I'm guessing this works with functions, methods, and lambdas (the "<unknown>" part)?) as units of repetition. If yes, that's fine, but I would seriously consider adding some settings to allow the user to control that granularity. Sometimes, the repeated code is a conditional branch within larger functions (i.e., "every else:" or "every except Ex:" looks the same). If the functions are large enough, the dissimilarity of the rest of the body would (probably?) cause such things to be missed.
I would also consider - perhaps as a separate pass, with scoring set differently - to analyze comments (especially docstrings in Python). If I read the code correctly, you're currently just stripping them, which is the right thing to do when looking for code duplication, but duplicated docstrings are also often a signal that something is wrong in the codebase. The "different scoring" is because we expect docstring to be structured similarly (at least more than normal code), so some tweaking would be needed.
Finally: very nice project, congrats! :)
[1] https://github.com/rafal-qa/slopo/blob/main/src/slopo/indexi...
If it did PHP I would love to run it over WordPress. What would it take to add that?
have you considered a deterministic tier before the embedding pass? I feel that approach can be more efficient.
Nice idea. I can see this being useful before refactors, especially when the duplication is semantic rather than copy paste.
What a simple and smart idea. Wonderful
This is neat. Have you noticed any difference in duplicate detection between strongly typed and loosely typed languages / code bases?
No. It depends the most on general code quality and architecture. Some implementations require more code similarity by design. Some languages, like Java, may tend to have more duplication, but it's only a theoretical guess. It also depends on what kind of software is developed with what language.
If you are interested in data, you can check my article. Analysis was done with this tool, but a previous version where exact-copy duplicates were excluded from analysis. https://rkochanowski.com/article/analysis-code-duplication/
self plug (for similar tool): https://github.com/forhadahmed/refactor
Very nice. I can imagine putting this into a pre push hook to keep things clean after an initial sweep.
This is a great use case for embeddings. Code deduplication across distant modules is notoriously hard for traditional AST-based tools.
How do you handle chunking and parsing for different languages to make sure the embeddings capture semantic meaning effectively? For instance, do you chunk by functions/classes, or use a fixed token window? If a function is too long or too short, it can drastically skew the embedding similarity.
I think that this is pretty cool, but is there any reason why we would want to remove similar/possible duplicate code?
Recently there was a popular article on HN saying that sometimes code duplication is better than abstraction, so I assume that this question is not a joke.
While testing this tool, one detected duplication was interesting for a use case. Permission check logic was duplicated and placed in different distant places in the codebase. The code was similar, but not identical, the logic was not the same. One version had stricter checks. I analyzed this with the coding agent, and we found out that both versions are used for the same thing, which means that in some cases validation is insufficient. Having only a single validation place, this bug could be prevented or easily detected.
(without sarcasm) Is this a serious question?
If so - maintainability, testability. This is old software engineering best practice at this point.
You shouldn’t hyper optimize for deduplication, but it’s usually worth considering. Fewer places to fix issues or improve as well.
Have you written software before?