This is fine for a text diff, but I want my code review tool to show me something different. Separate problem, and the flaw here isn’t the diff, or the tool that produced the diff, rather the tool displaying it to me. Let me do whatever I want to my code and show me BOTH the visual (unimportant) and semantic differences.

Good point. Are there any code-semantics-aware diff tool out there though?

If you're looking for a VS Code extension or a GitHub app, check out https://semanticdiff.com/. I'm a co-founder of this project.

If you prefer a CLI tool, check out https://github.com/Wilfred/difftastic. It supports more languages, but doesn't recognize when code has been replaced by an equivalent version ("invariances"). So it will show some changes (e.g. replacing a character in a string with an escape sequence) even though they are technically equivalent.

Is that down to the formatter - which you've configured to enforce a certain line length (https://prettier.io/docs/en/options.html#print-width) - or the diff visualiser that doesn't show a difference between whitespace and other changes?

It's impossible to turn off line length rules. You can only change the width, which means if you set it to a big number it will aggressively unwrap code you want to keep wrapped sensibly. Awful and unacceptable.