Does GitHub Copilot Improve Code Quality?

Microsoft-owned GitHub published a blog post asking "Does GitHub Copilot improve code quality? Here's what the data says."

Its first paragraph includes statistics from past studies — that GitHub Copilot has helped developers code up to 55% faster, leaving 88% of developers feeling more "in the flow" and 85% feeling more confident in their code.

But does it improve code quality? [W]e recruited 202 [Python] developers with at least five years of experience. Half were randomly assigned GitHub Copilot access and the other half were instructed not to use any AI tools... We then evaluated the code with unit tests and with an expert review conducted by developers.

Our findings overall show that code authored with GitHub Copilot has increased functionality and improved readability, is of better quality, and receives higher approval rates... Developers with GitHub Copilot access had a 56% greater likelihood of passing all 10 unit tests in the study, indicating that GitHub Copilot helps developers write more functional code by a wide margin. In blind reviews, code written with GitHub Copilot had significantly fewer code readability errors, allowing developers to write 13.6% more lines of code, on average, without encountering readability problems. Readability improved by 3.62%, reliability by 2.94%, maintainability by 2.47%, and conciseness by 4.16%. All numbers were statistically significant... Developers were 5% more likely to approve code written with GitHub Copilot, meaning that such code is ready to be merged sooner, speeding up the time to fix bugs or deploy new features.
"While GitHub's reports have been positive, a few others haven't," reports Visual Studio magazine: For example, a recent study from Uplevel Data Labs said, "Developers with Copilot access saw a significantly higher bug rate while their issue throughput remained consistent."

And earlier this year a "Coding on Copilot" whitepaper from GitClear said, "We find disconcerting trends for maintainability. Code churn — the percentage of lines that are reverted or updated less than two weeks after being authored — is projected to double in 2024 compared to its 2021, pre-AI baseline. We further find that the percentage of 'added code' and 'copy/pasted code' is increasing in proportion to 'updated,' 'deleted,' and 'moved 'code. In this regard, AI-generated code resembles an itinerant contributor, prone to violate the DRY-ness [don't repeat yourself] of the repos visited."

No.

[Local ID10T]

/betteridge

It's also...

[Kelxin]

100% more likely to be stolen and used by other people for monetary gain.

Anecdotal evidence

[Misagon]

Every account of using it I've read online has been negative about code quality.

Re:

[martin-boundary]

And let's not forget code security. Real production code is about 10x more lines than the copypasta you get from a blog or git hub AI.

My rule of thumb is: if it's readable and clear to a random stranger, then it's not security hardened. Is Microsoft claiming that VS copilot is making your code 10% more vulnerable? You decide!

Re: Anecdotal evidence

[dwater]

Is that different to "security through obscurity"?

Re:

[SeaFox]

My rule of thumb is: if it's readable and clear to a random stranger, then it's not security hardened.

Wouldn't this defeat the entire premise of security when it comes to open-source code? If the code is available for anyone to read and no one can understand it it's not possible for others to scrutinize it, and if they can read it then by your rule it must not be very secure.

Re:

[phantomfive]

The primary positive accounts I've heard about Copilot is that it works as a substitute for Stackoverflow. It helps you figure out what to do when documentation is crappy or nonexistent (but you still need to test it because Stackoverflow can really lead you astray).

Phillip Morris says cigarettes don't cause cancer

[stuff-n-things]

No conflict of interest at Github/Micro$oft either. ;-)

Re:

[Morromist]

I'm sure Microsoft is being 1000% ethical and if there was any evidence that AI actually makes code worse they would definitely let Github publish stuff about that despite Microsoft investing $100 billion or more in AI and AI related stuff.

AI is trained on peoples mistakes

[rapjr]

so the common mistakes of people will become pasted into your code by AI. Since training an AI is a statistical process it seems likely that the most average code examples will be what it generates. This might be ok for some things, but it may lower overall code quality. Imagine working with someone who is ok but average in your project and they keep inserting average code into your codebase, perhaps reverting it to less desirable states. Security in particular is not well represented in public code bas

Yes and no

[Drethon]

Based on absolutely no studies or anything but my own opinion... I suspect AI will make good coders better and bad coders worse. Good coders will consider the suggestions, take the good ones and reject the bad ones. Bad coders will take everything.

I investigated: three answers so far

[davecb]

The best idea is Advait Sarkar's. He noticed how bad LLMs are at anything creative, and instead suggested we use them for things they're good at, predicting what humans would say. Especially if they were asked what a critic would say. See https://leaflessca.wordpress.c... [wordpress.com]

Trying Pull Requests with CodeRabbit. One of the things I think LLMs can do well is compare my text with a whole body of other people's work. In that vein, CodeRabbit now offers to review git pull requests. https://leaflessca.wordpress.c [wordpress.com]

Re:

[phantomfive]

Yeah, but they are pretty cool. And someone else paid for it.

Confidence

[phantomfive]

"85% feeling more confident in their code."

Imagine having such low confidence in the quality of your own code that you feel an LLM is doing you better.

Re:

[Morromist]

Oooo. Burn.

CoPilot in Python is excellent

[Pegasuce]

The success you'll have with copilot will depend on the language used. Python is the language that CoPilot generates more useful code between java, Angular et C#.

Re: CoPilot in Python is excellent

[dwater]

Interesting. Some languages have more "gotcha"s, so there are surely more examples our there of code that falls into those traps, and so the AI surely uses those in its answers too. Languages with fewer "gotchas" result in better AI code...

No?