Enforce Syntax Trees Invariantrs - Githubissues

rust-lang / rust-analyzer

A Rust compiler front-end for IDEs

https://rust-analyzer.github.io/

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Enforce Syntax Trees Invariantrs #5006

Open matklad opened 4 years ago

matklad commented 4 years ago

We have couple of weak invariants about our syntax trees, which are not really enforced and sometimes are broken in practice. We should

document invariants
assert them
make sure that they are obeyed in practice

Here's the tentative list of invariants:

The only node that is allowed to be empty is SourceFile
The only token kind that is allowed to be empty are fake dollar parens from macro expansion
Braces should play well with incremental reparsing (see https://github.com/rust-analyzer/rust-analyzer/pull/4680#issuecomment-641346748)

Notably, the following is not an invariant, but we rely on it in some ast extensions:

Parent nodes are not guaranteed to exist.

For example, ast::EnumVariant should return Option

matklad commented 3 years ago

https://github.com/rust-analyzer/rust-analyzer/pull/4680 is something we neeed to look at as well.