Lint for misleading indentation

Issue by glaebhoerl
Thursday Nov 14, 2013 at 13:41 GMT

For earlier discussion, see https://github.com/rust-lang/rust/issues/10483

This issue was labelled with: A-lint, I-wishlist in the Rust repository

While working in C++, I was recently bitten by having accidentally omitted the closing brace of one if-else statement among many others. The compiler only complained of a syntax error many lines lower down at the beginning of the next function, and it took me a while to find where the problem was, because visually, I normally interpret code by looking at indentation, which matched my intent. On the other hand, the compiler ignores indentation and looks only at braces, which did not match my intent. In this case I got a compile error, but in other cases bad indentation can cause a human to derive a different meaning when reading (syntactically well-formed) code than the compiler does, leading to bugs.

This is the drawback of whitespace-irrelevant syntax: the programmer has to encode the same information in two separate ways, introducing more opportunities to make mistakes. We could have a lint which complains if the "logical" and visual indentations of code don't align to help catch these kind of problems.

Start by reading the earlier discussion in rust-lang/rust issue 10483 and the Rust RFC process context. Clarify the intended definition of misleading indentation, the cases the lint should cover, and how completion would be evaluated before proposing the RFC.