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> Are they? I feel like intellisense is largely a subset of what a compiler already has to do. They are distinct! Well, not just intellisense, but pretty much everything. I'll paraphrase this blog post, but the best way to think about think about the difference between a traditional compiler and an IDE is that compilers are top-down (e.g, you start compiling a program from a compilation unit's entrypoint, a `lib.rs` or `main.rs` in Rust), but IDEs are cursor-centric—they're trying to compile/analyze the minimal amount of code necessary to understand the program. After all, the best way to go fast is to avoid unnecessary work! > If you wanted to argue that intellisense is a subset of compiling and it can be done faster and more efficiently I could buy that argument. But if you’re going to declare the tasks are at odds with one another I’d love to hear specific details! Beyond the philosophical/architectural difference I mentioned above, compilers typically have a one-way mapping between syntax and mapping, but to support things like refactors or assists, you often need to do the opposite: go from semantics to syntax. For instance, if you want to refactor from struct to an enum, you often need to find all instances of said struct, make the semantic change, then construct the new syntax tree from the semantics. For simple transformations like a struct to an enum, a purely syntax-based based approach might work (albeit, at the cost of accuracy if you have two structs with same name), but you start to run into issues when you consider traits, interfaces (for example: think about how a type implements an interface in Go!), or generics. It doesn't really make sense for a compiler to support above use cases, but they're are _foundational_ to an IDE. However, if a compiler is query-centric (as rustc is), then it's pretty feasible for rustc and rust-analyzer to share, for instance, the trait solver or the borrow checker (we're planning/scoping work on the former right now). |