From bb2bafb606cb38f0a9ec8bb44693c149ba4288cd Mon Sep 17 00:00:00 2001
From: Aleksey Kladov <aleksey.kladov@gmail.com>
Date: Thu, 20 Dec 2018 13:47:32 +0300
Subject: docs for input queries

---
 crates/ra_db/src/input.rs | 56 +++++++++++++++++++++++++++++++++++++----------
 1 file changed, 45 insertions(+), 11 deletions(-)

(limited to 'crates/ra_db/src')

diff --git a/crates/ra_db/src/input.rs b/crates/ra_db/src/input.rs
index cccf37cc2..095730521 100644
--- a/crates/ra_db/src/input.rs
+++ b/crates/ra_db/src/input.rs
@@ -1,3 +1,6 @@
+/// This modules specifies the input to rust-analyzer. In some sense, this is
+/// **the** most important module, because all other fancy stuff is strickly
+/// derived from this input.
 use std::sync::Arc;
 
 use rustc_hash::{FxHashMap};
@@ -5,20 +8,48 @@ use relative_path::RelativePathBuf;
 use ra_syntax::SmolStr;
 use salsa;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
-pub struct SourceRootId(pub u32);
-
+/// `FileId` is an integer which uniquely identifies a file. File paths are
+/// messy and system-dependent, so most of the code should work directly with
+/// `FileId`, without inspecting the path. The mapping between `FileId` and path
+/// and `SourceRoot` is constant. File rename is represented as a pair of
+/// deletion/creation.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct FileId(pub u32);
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct CrateId(pub u32);
+/// Files are grouped into source roots. A source root is a directory on the
+/// file systems which is watched for changes. Typically it corresponds to a
+/// Cargo package. Source roots *might* be nested: in this case, file belongs to
+/// the nearest enclosing source root. Path to files are always relative to a
+/// source root, and analyzer does not know the root path of the source root at
+/// all. So, a file from one source root can't refere a file in another source
+/// root by path.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct SourceRootId(pub u32);
+
+#[derive(Default, Clone, Debug, PartialEq, Eq)]
+pub struct SourceRoot {
+    pub files: FxHashMap<RelativePathBuf, FileId>,
+}
 
+/// `CrateGraph` is a bit of information which turns a set of text files into a
+/// number of Rust crates. Each Crate is the `FileId` of it's root module, the
+/// set of cfg flags (not yet implemented) and the set of dependencies. Note
+/// that, due to cfg's, there might be several crates for a single `FileId`! As
+/// in the rust-lang proper, a crate does not have a name. Instead, names are
+/// specified on dependency edges. That is, a crate might be known under
+/// different names in different dependant crates.
+///
+/// Note that `CrateGraph` is build-system agnostic: it's a concept of the Rust
+/// langauge proper, not a concept of the build system. In practice, we get
+/// `CrateGraph` by lowering `cargo metadata` output.
 #[derive(Debug, Clone, Default, PartialEq, Eq)]
 pub struct CrateGraph {
     arena: FxHashMap<CrateId, CrateData>,
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct CrateId(pub u32);
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 struct CrateData {
     file_id: FileId,
@@ -57,7 +88,7 @@ impl CrateGraph {
         assert!(prev.is_none());
         crate_id
     }
-    //FIXME: check that we don't have cycles here.
+    // FIXME: check that we don't have cycles here.
     // Just a simple depth first search from `to` should work,
     // the graph is small.
     pub fn add_dep(&mut self, from: CrateId, name: SmolStr, to: CrateId) {
@@ -83,6 +114,7 @@ impl CrateGraph {
 
 salsa::query_group! {
     pub trait FilesDatabase: salsa::Database {
+        /// Text of the file.
         fn file_text(file_id: FileId) -> Arc<String> {
             type FileTextQuery;
             storage input;
@@ -92,30 +124,32 @@ salsa::query_group! {
             type FileRelativePathQuery;
             storage input;
         }
+        /// Source root of the file.
         fn file_source_root(file_id: FileId) -> SourceRootId {
             type FileSourceRootQuery;
             storage input;
         }
+        /// Contents of the source root.
         fn source_root(id: SourceRootId) -> Arc<SourceRoot> {
             type SourceRootQuery;
             storage input;
         }
+        /// The set of "local" (that is, from the current workspace) roots.
+        /// Files in local roots are assumed to change frequently.
         fn local_roots() -> Arc<Vec<SourceRootId>> {
             type LocalRootsQuery;
             storage input;
         }
+        /// The set of roots for crates.io libraries.
+        /// Files in libraries are assumed to never change.
         fn library_roots() -> Arc<Vec<SourceRootId>> {
             type LibraryRootsQuery;
             storage input;
         }
+        /// The crate graph.
         fn crate_graph() -> Arc<CrateGraph> {
             type CrateGraphQuery;
             storage input;
         }
     }
 }
-
-#[derive(Default, Clone, Debug, PartialEq, Eq)]
-pub struct SourceRoot {
-    pub files: FxHashMap<RelativePathBuf, FileId>,
-}
-- 
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