Merge #67

67: Salsa r=matklad a=matklad

The aim of this PR is to transition from rather ad-hock FileData and ModuleMap caching strategy to something resembling a general-purpose red-green engine. 

Ideally, we shouldn't recompute ModuleMap at all, unless the set of mod decls or files changes.



Co-authored-by: Aleksey Kladov <aleksey.kladov@gmail.com>

crates/libsyntax2/src/lib.rs

@@ -61,7 +61,7 @@ use {
     yellow::{GreenNode, SyntaxRoot},
 };
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Hash)]
 pub struct File {
     root: SyntaxNode
 }