Merge #429

429: Reorganize hir public API in terms of code model r=matklad a=matklad

Recently, I've been thinking about introducing "object orient code model" API for rust: a set of APIs with types like `Function`, `Module`, etc, with methods like `get_containing_declaration()`, `get_type()`, etc. 

Here's how a similar API might look like in .Net land:

https://docs.microsoft.com/en-us/dotnet/api/microsoft.codeanalysis.semanticmodel?view=roslyn-dotnet

https://docs.microsoft.com/en-us/dotnet/api/microsoft.codeanalysis.imethodsymbol?view=roslyn-dotnet

The main feature of such API is that it can be powered by different backends. For example, one can imagine a backend based on salsa, and a backend which reads all the data from a specially prepared JSON file. The "OO" bit is interesting mostly in this "can swap implementations via dynamic dispatch" aspect, the actual API could have a more database/ECS flavored feeling.

It's not clear at this moment how exactly should we implement such a dynamically (or if we even need dynamism in the first pace) swapable API in Rust, but I'd love to experiment with this a bit. 

For starters, I propose creating a `code_model_api` which contains various definition types and their public methods (mandatory implemented as one-liners, so that the API has a header-file feel). Specifically, I propose that each type is a wrapper around some integer ID, and that all methods of it accept a `&db` argument.  The actual impl goes elsewhere: into the db queries or, absent a better place, into the `code_model_api_impl`. In the first commit, I've moved the simplest type, `Crate`, over to this pattern.

I *think* that we, at least initially, will be used types from `code_model_api` *inside* `hir` as well, but this is not required: we might pick a different implementation down the line, while preserving the API. 

Long term I'd love to replace the `db: &impl HirDatabase` argument by a `mp: &dyn ModelProvider`, implement `ModelProvider` for `T: HirDatabase`, and move `code_model_api` into the separate crate, which does not depend on `hir`. 

@flodiebold you've recently done some `Def`s work, would do you think of this plan? Could it become a good API in the future, or is it just a useless boilerplate duplicating method signatures between `code_model_api` and `code_model_impl`?


Co-authored-by: Aleksey Kladov <[email protected]>

1 files changed, 45 insertions, 0 deletions

diff --git a/crates/ra_hir/src/code_model_impl/krate.rs b/crates/ra_hir/src/code_model_impl/krate.rs
new file mode 100644
index 000000000..591a81597
--- /dev/null
+++ b/crates/ra_hir/src/code_model_impl/krate.rs
@@ -0,0 +1,45 @@
+use ra_db::{CrateId, Cancelable};
+
+use crate::{
+    HirFileId, Crate, CrateDependency, AsName, DefLoc, DefKind, Module,
+    db::HirDatabase,
+};
+
+impl Crate {
+    pub(crate) fn new(crate_id: CrateId) -> Crate {
+        Crate { crate_id }
+    }
+    pub(crate) fn dependencies_impl(&self, db: &impl HirDatabase) -> Vec<CrateDependency> {
+        let crate_graph = db.crate_graph();
+        crate_graph
+            .dependencies(self.crate_id)
+            .map(|dep| {
+                let krate = Crate::new(dep.crate_id());
+                let name = dep.as_name();
+                CrateDependency { krate, name }
+            })
+            .collect()
+    }
+    pub(crate) fn root_module_impl(&self, db: &impl HirDatabase) -> Cancelable<Option<Module>> {
+        let crate_graph = db.crate_graph();
+        let file_id = crate_graph.crate_root(self.crate_id);
+        let source_root_id = db.file_source_root(file_id);
+        let file_id = HirFileId::from(file_id);
+        let module_tree = db.module_tree(source_root_id)?;
+        // FIXME: teach module tree about crate roots instead of guessing
+        let (module_id, _) = ctry!(module_tree
+            .modules_with_sources()
+            .find(|(_, src)| src.file_id() == file_id));
+
+        let def_loc = DefLoc {
+            kind: DefKind::Module,
+            source_root_id,
+            module_id,
+            source_item_id: module_id.source(&module_tree).0,
+        };
+        let def_id = def_loc.id(db);
+
+        let module = Module::new(def_id);
+        Ok(Some(module))
+    }
+}