20 files changed, 363 insertions, 175 deletions

diff --git a/crates/ra_ide/src/completion.rs b/crates/ra_ide/src/completion.rs
index 191300704..d890b69d2 100644
--- a/crates/ra_ide/src/completion.rs
+++ b/crates/ra_ide/src/completion.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
-
 mod completion_config;
 mod completion_item;
 mod completion_context;
@@ -35,6 +33,51 @@ pub use crate::completion::{
     completion_item::{CompletionItem, CompletionItemKind, CompletionScore, InsertTextFormat},
 };
 
+//FIXME: split the following feature into fine-grained features.
+
+// Feature: Magic Completions
+//
+// In addition to usual reference completion, rust-analyzer provides some ✨magic✨
+// completions as well:
+//
+// Keywords like `if`, `else` `while`, `loop` are completed with braces, and cursor
+// is placed at the appropriate position. Even though `if` is easy to type, you
+// still want to complete it, to get ` { }` for free! `return` is inserted with a
+// space or `;` depending on the return type of the function.
+//
+// When completing a function call, `()` are automatically inserted. If a function
+// takes arguments, the cursor is positioned inside the parenthesis.
+//
+// There are postfix completions, which can be triggered by typing something like
+// `foo().if`. The word after `.` determines postfix completion. Possible variants are:
+//
+// - `expr.if` -> `if expr {}` or `if let ... {}` for `Option` or `Result`
+// - `expr.match` -> `match expr {}`
+// - `expr.while` -> `while expr {}` or `while let ... {}` for `Option` or `Result`
+// - `expr.ref` -> `&expr`
+// - `expr.refm` -> `&mut expr`
+// - `expr.not` -> `!expr`
+// - `expr.dbg` -> `dbg!(expr)`
+//
+// There also snippet completions:
+//
+// .Expressions
+// - `pd` -> `println!("{:?}")`
+// - `ppd` -> `println!("{:#?}")`
+//
+// .Items
+// - `tfn` -> `#[test] fn f(){}`
+// - `tmod` ->
+// ```rust
+// #[cfg(test)]
+// mod tests {
+//     use super::*;
+//
+//     #[test]
+//     fn test_fn() {}
+// }
+// ```
+
 /// Main entry point for completion. We run completion as a two-phase process.
 ///
 /// First, we look at the position and collect a so-called `CompletionContext.
diff --git a/crates/ra_ide/src/completion/complete_postfix.rs b/crates/ra_ide/src/completion/complete_postfix.rs
index 02e660ca8..59b58bf98 100644
--- a/crates/ra_ide/src/completion/complete_postfix.rs
+++ b/crates/ra_ide/src/completion/complete_postfix.rs
@@ -1,12 +1,11 @@
 //! FIXME: write short doc here
-
+use ra_assists::utils::TryEnum;
 use ra_syntax::{
     ast::{self, AstNode},
     TextRange, TextSize,
 };
 use ra_text_edit::TextEdit;
 
-use super::completion_config::SnippetCap;
 use crate::{
     completion::{
         completion_context::CompletionContext,
@@ -14,7 +13,8 @@ use crate::{
     },
     CompletionItem,
 };
-use ra_assists::utils::TryEnum;
+
+use super::completion_config::SnippetCap;
 
 pub(super) fn complete_postfix(acc: &mut Completions, ctx: &CompletionContext) {
     if !ctx.config.enable_postfix_completions {
diff --git a/crates/ra_ide/src/display/structure.rs b/crates/ra_ide/src/display/structure.rs
index 967eee5d2..aad5a8e4d 100644
--- a/crates/ra_ide/src/display/structure.rs
+++ b/crates/ra_ide/src/display/structure.rs
@@ -1,10 +1,6 @@
-//! FIXME: write short doc here
-
-use crate::TextRange;
-
 use ra_syntax::{
     ast::{self, AttrsOwner, NameOwner, TypeAscriptionOwner, TypeParamsOwner},
-    match_ast, AstNode, SourceFile, SyntaxKind, SyntaxNode, WalkEvent,
+    match_ast, AstNode, SourceFile, SyntaxKind, SyntaxNode, TextRange, WalkEvent,
 };
 
 #[derive(Debug, Clone)]
@@ -18,6 +14,19 @@ pub struct StructureNode {
     pub deprecated: bool,
 }
 
+// Feature: File Structure
+//
+// Provides a tree of the symbols defined in the file. Can be used to
+//
+// * fuzzy search symbol in a file (super useful)
+// * draw breadcrumbs to describe the context around the cursor
+// * draw outline of the file
+//
+// |===
+// | Editor  | Shortcut
+//
+// | VS Code | kbd:[Ctrl+Shift+O]
+// |===
 pub fn file_structure(file: &SourceFile) -> Vec<StructureNode> {
     let mut res = Vec::new();
     let mut stack = Vec::new();
diff --git a/crates/ra_ide/src/expand_macro.rs b/crates/ra_ide/src/expand_macro.rs
index f536ba3e7..54a47aac0 100644
--- a/crates/ra_ide/src/expand_macro.rs
+++ b/crates/ra_ide/src/expand_macro.rs
@@ -1,5 +1,3 @@
-//! This modules implements "expand macro" functionality in the IDE
-
 use hir::Semantics;
 use ra_ide_db::RootDatabase;
 use ra_syntax::{
@@ -14,6 +12,15 @@ pub struct ExpandedMacro {
     pub expansion: String,
 }
 
+// Feature: Expand Macro Recursively
+//
+// Shows the full macro expansion of the macro at current cursor.
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Rust Analyzer: Expand macro recursively**
+// |===
 pub(crate) fn expand_macro(db: &RootDatabase, position: FilePosition) -> Option<ExpandedMacro> {
     let sema = Semantics::new(db);
     let file = sema.parse(position.file_id);
diff --git a/crates/ra_ide/src/extend_selection.rs b/crates/ra_ide/src/extend_selection.rs
index 554594a43..a4bc93cdb 100644
--- a/crates/ra_ide/src/extend_selection.rs
+++ b/crates/ra_ide/src/extend_selection.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
-
 use std::iter::successors;
 
 use hir::Semantics;
@@ -14,6 +12,16 @@ use ra_syntax::{
 
 use crate::FileRange;
 
+// Feature: Extend Selection
+//
+// Extends the current selection to the encompassing syntactic construct
+// (expression, statement, item, module, etc). It works with multiple cursors.
+//
+// |===
+// | Editor  | Shortcut
+//
+// | VS Code | kbd:[Ctrl+Shift+→]
+// |===
 pub(crate) fn extend_selection(db: &RootDatabase, frange: FileRange) -> TextRange {
     let sema = Semantics::new(db);
     let src = sema.parse(frange.file_id);
diff --git a/crates/ra_ide/src/goto_definition.rs b/crates/ra_ide/src/goto_definition.rs
index 90e85d419..a6c86e99c 100644
--- a/crates/ra_ide/src/goto_definition.rs
+++ b/crates/ra_ide/src/goto_definition.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
-
 use hir::Semantics;
 use ra_ide_db::{
     defs::{classify_name, classify_name_ref},
@@ -17,6 +15,15 @@ use crate::{
     FilePosition, NavigationTarget, RangeInfo,
 };
 
+// Feature: Go to Definition
+//
+// Navigates to the definition of an identifier.
+//
+// |===
+// | Editor  | Shortcut
+//
+// | VS Code | kbd:[F12]
+// |===
 pub(crate) fn goto_definition(
     db: &RootDatabase,
     position: FilePosition,
diff --git a/crates/ra_ide/src/impls.rs b/crates/ra_ide/src/goto_implementation.rs
index ea2225f70..0cec0657e 100644
--- a/crates/ra_ide/src/impls.rs
+++ b/crates/ra_ide/src/goto_implementation.rs
@@ -1,11 +1,18 @@
-//! FIXME: write short doc here
-
 use hir::{Crate, ImplDef, Semantics};
 use ra_ide_db::RootDatabase;
 use ra_syntax::{algo::find_node_at_offset, ast, AstNode};
 
 use crate::{display::ToNav, FilePosition, NavigationTarget, RangeInfo};
 
+// Feature: Go to Implementation
+//
+// Navigates to the impl block of structs, enums or traits. Also implemented as a code lens.
+//
+// |===
+// | Editor  | Shortcut
+//
+// | VS Code | kbd:[Ctrl+F12]
+// |===
 pub(crate) fn goto_implementation(
     db: &RootDatabase,
     position: FilePosition,
diff --git a/crates/ra_ide/src/goto_type_definition.rs b/crates/ra_ide/src/goto_type_definition.rs
index a84637489..91a3097fb 100644
--- a/crates/ra_ide/src/goto_type_definition.rs
+++ b/crates/ra_ide/src/goto_type_definition.rs
@@ -1,10 +1,17 @@
-//! FIXME: write short doc here
-
 use ra_ide_db::RootDatabase;
 use ra_syntax::{ast, match_ast, AstNode, SyntaxKind::*, SyntaxToken, TokenAtOffset};
 
 use crate::{display::ToNav, FilePosition, NavigationTarget, RangeInfo};
 
+// Feature: Go to Type Definition
+//
+// Navigates to the type of an identifier.
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Go to Type Definition*
+// |===
 pub(crate) fn goto_type_definition(
     db: &RootDatabase,
     position: FilePosition,
diff --git a/crates/ra_ide/src/hover.rs b/crates/ra_ide/src/hover.rs
index 3e721dcca..d96cb5596 100644
--- a/crates/ra_ide/src/hover.rs
+++ b/crates/ra_ide/src/hover.rs
@@ -1,10 +1,10 @@
-//! Logic for computing info that is displayed when the user hovers over any
-//! source code items (e.g. function call, struct field, variable symbol...)
+use std::iter::once;
 
 use hir::{
     Adt, AsAssocItem, AssocItemContainer, FieldSource, HasSource, HirDisplay, ModuleDef,
     ModuleSource, Semantics,
 };
+use itertools::Itertools;
 use ra_db::SourceDatabase;
 use ra_ide_db::{
     defs::{classify_name, classify_name_ref, Definition},
@@ -21,8 +21,6 @@ use crate::{
     display::{macro_label, rust_code_markup, rust_code_markup_with_doc, ShortLabel},
     FilePosition, RangeInfo,
 };
-use itertools::Itertools;
-use std::iter::once;
 
 /// Contains the results when hovering over an item
 #[derive(Debug, Default)]
@@ -62,6 +60,63 @@ impl HoverResult {
     }
 }
 
+// Feature: Hover
+//
+// Shows additional information, like type of an expression or documentation for definition when "focusing" code.
+// Focusing is usually hovering with a mouse, but can also be triggered with a shortcut.
+pub(crate) fn hover(db: &RootDatabase, position: FilePosition) -> Option<RangeInfo<HoverResult>> {
+    let sema = Semantics::new(db);
+    let file = sema.parse(position.file_id).syntax().clone();
+    let token = pick_best(file.token_at_offset(position.offset))?;
+    let token = sema.descend_into_macros(token);
+
+    let mut res = HoverResult::new();
+
+    if let Some((node, name_kind)) = match_ast! {
+        match (token.parent()) {
+            ast::NameRef(name_ref) => {
+                classify_name_ref(&sema, &name_ref).map(|d| (name_ref.syntax().clone(), d.definition()))
+            },
+            ast::Name(name) => {
+                classify_name(&sema, &name).map(|d| (name.syntax().clone(), d.definition()))
+            },
+            _ => None,
+        }
+    } {
+        let range = sema.original_range(&node).range;
+        res.extend(hover_text_from_name_kind(db, name_kind));
+
+        if !res.is_empty() {
+            return Some(RangeInfo::new(range, res));
+        }
+    }
+
+    let node = token
+        .ancestors()
+        .find(|n| ast::Expr::cast(n.clone()).is_some() || ast::Pat::cast(n.clone()).is_some())?;
+
+    let ty = match_ast! {
+        match node {
+            ast::MacroCall(_it) => {
+                // If this node is a MACRO_CALL, it means that `descend_into_macros` failed to resolve.
+                // (e.g expanding a builtin macro). So we give up here.
+                return None;
+            },
+            ast::Expr(it) => {
+                sema.type_of_expr(&it)
+            },
+            ast::Pat(it) => {
+                sema.type_of_pat(&it)
+            },
+            _ => None,
+        }
+    }?;
+
+    res.extend(Some(rust_code_markup(&ty.display(db))));
+    let range = sema.original_range(&node).range;
+    Some(RangeInfo::new(range, res))
+}
+
 fn hover_text(
     docs: Option<String>,
     desc: Option<String>,
@@ -160,59 +215,6 @@ fn hover_text_from_name_kind(db: &RootDatabase, def: Definition) -> Option<Strin
     }
 }
 
-pub(crate) fn hover(db: &RootDatabase, position: FilePosition) -> Option<RangeInfo<HoverResult>> {
-    let sema = Semantics::new(db);
-    let file = sema.parse(position.file_id).syntax().clone();
-    let token = pick_best(file.token_at_offset(position.offset))?;
-    let token = sema.descend_into_macros(token);
-
-    let mut res = HoverResult::new();
-
-    if let Some((node, name_kind)) = match_ast! {
-        match (token.parent()) {
-            ast::NameRef(name_ref) => {
-                classify_name_ref(&sema, &name_ref).map(|d| (name_ref.syntax().clone(), d.definition()))
-            },
-            ast::Name(name) => {
-                classify_name(&sema, &name).map(|d| (name.syntax().clone(), d.definition()))
-            },
-            _ => None,
-        }
-    } {
-        let range = sema.original_range(&node).range;
-        res.extend(hover_text_from_name_kind(db, name_kind));
-
-        if !res.is_empty() {
-            return Some(RangeInfo::new(range, res));
-        }
-    }
-
-    let node = token
-        .ancestors()
-        .find(|n| ast::Expr::cast(n.clone()).is_some() || ast::Pat::cast(n.clone()).is_some())?;
-
-    let ty = match_ast! {
-        match node {
-            ast::MacroCall(_it) => {
-                // If this node is a MACRO_CALL, it means that `descend_into_macros` failed to resolve.
-                // (e.g expanding a builtin macro). So we give up here.
-                return None;
-            },
-            ast::Expr(it) => {
-                sema.type_of_expr(&it)
-            },
-            ast::Pat(it) => {
-                sema.type_of_pat(&it)
-            },
-            _ => None,
-        }
-    }?;
-
-    res.extend(Some(rust_code_markup(&ty.display(db))));
-    let range = sema.original_range(&node).range;
-    Some(RangeInfo::new(range, res))
-}
-
 fn pick_best(tokens: TokenAtOffset<SyntaxToken>) -> Option<SyntaxToken> {
     return tokens.max_by_key(priority);
     fn priority(n: &SyntaxToken) -> usize {
diff --git a/crates/ra_ide/src/inlay_hints.rs b/crates/ra_ide/src/inlay_hints.rs
index b391f903a..75bd3c96b 100644
--- a/crates/ra_ide/src/inlay_hints.rs
+++ b/crates/ra_ide/src/inlay_hints.rs
@@ -1,5 +1,3 @@
-//! This module defines multiple types of inlay hints and their visibility
-
 use hir::{Adt, HirDisplay, Semantics, Type};
 use ra_ide_db::RootDatabase;
 use ra_prof::profile;
@@ -39,6 +37,26 @@ pub struct InlayHint {
     pub label: SmolStr,
 }
 
+// Feature: Inlay Hints
+//
+// rust-analyzer shows additional information inline with the source code.
+// Editors usually render this using read-only virtual text snippets interspersed with code.
+//
+// rust-analyzer shows hits for
+//
+// * types of local variables
+// * names of function arguments
+// * types of chained expressions
+//
+// **Note:** VS Code does not have native support for inlay hints https://github.com/microsoft/vscode/issues/16221[yet] and the hints are implemented using decorations.
+// This approach has limitations, the caret movement and bracket highlighting near the edges of the hint may be weird:
+// https://github.com/rust-analyzer/rust-analyzer/issues/1623[1], https://github.com/rust-analyzer/rust-analyzer/issues/3453[2].
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Rust Analyzer: Toggle inlay hints*
+// |===
 pub(crate) fn inlay_hints(
     db: &RootDatabase,
     file_id: FileId,
diff --git a/crates/ra_ide/src/join_lines.rs b/crates/ra_ide/src/join_lines.rs
index af1ade8a1..5036c1fb0 100644
--- a/crates/ra_ide/src/join_lines.rs
+++ b/crates/ra_ide/src/join_lines.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
-
 use itertools::Itertools;
 use ra_fmt::{compute_ws, extract_trivial_expression};
 use ra_syntax::{
@@ -11,6 +9,15 @@ use ra_syntax::{
 };
 use ra_text_edit::{TextEdit, TextEditBuilder};
 
+// Feature: Join Lines
+//
+// Join selected lines into one, smartly fixing up whitespace, trailing commas, and braces.
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Rust Analyzer: Join lines**
+// |===
 pub fn join_lines(file: &SourceFile, range: TextRange) -> TextEdit {
     let range = if range.is_empty() {
         let syntax = file.syntax();
diff --git a/crates/ra_ide/src/lib.rs b/crates/ra_ide/src/lib.rs
index d983cd910..12d5716e8 100644
--- a/crates/ra_ide/src/lib.rs
+++ b/crates/ra_ide/src/lib.rs
@@ -23,6 +23,7 @@ mod completion;
 mod runnables;
 mod goto_definition;
 mod goto_type_definition;
+mod goto_implementation;
 mod extend_selection;
 mod hover;
 mod call_hierarchy;
@@ -30,7 +31,6 @@ mod call_info;
 mod syntax_highlighting;
 mod parent_module;
 mod references;
-mod impls;
 mod diagnostics;
 mod syntax_tree;
 mod folding_ranges;
@@ -373,7 +373,7 @@ impl Analysis {
         &self,
         position: FilePosition,
     ) -> Cancelable<Option<RangeInfo<Vec<NavigationTarget>>>> {
-        self.with_db(|db| impls::goto_implementation(db, position))
+        self.with_db(|db| goto_implementation::goto_implementation(db, position))
     }
 
     /// Returns the type definitions for the symbol at `position`.
diff --git a/crates/ra_ide/src/matching_brace.rs b/crates/ra_ide/src/matching_brace.rs
index b85348706..407a9636d 100644
--- a/crates/ra_ide/src/matching_brace.rs
+++ b/crates/ra_ide/src/matching_brace.rs
@@ -1,7 +1,16 @@
-//! FIXME: write short doc here
-
 use ra_syntax::{ast::AstNode, SourceFile, SyntaxKind, TextSize, T};
 
+// Feature: Matching Brace
+//
+// If the cursor is on any brace (`<>(){}[]`) which is a part of a brace-pair,
+// moves cursor to the matching brace. It uses the actual parser to determine
+// braces, so it won't confuse generics with comparisons.
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Rust Analyzer: Find matching brace**
+// |===
 pub fn matching_brace(file: &SourceFile, offset: TextSize) -> Option<TextSize> {
     const BRACES: &[SyntaxKind] =
         &[T!['{'], T!['}'], T!['['], T![']'], T!['('], T![')'], T![<], T![>]];
diff --git a/crates/ra_ide/src/parent_module.rs b/crates/ra_ide/src/parent_module.rs
index a083fb1eb..fa1535da5 100644
--- a/crates/ra_ide/src/parent_module.rs
+++ b/crates/ra_ide/src/parent_module.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
-
 use hir::Semantics;
 use ra_db::{CrateId, FileId, FilePosition};
 use ra_ide_db::RootDatabase;
@@ -11,6 +9,16 @@ use test_utils::mark;
 
 use crate::NavigationTarget;
 
+// Feature: Parent Module
+//
+// Navigates to the parent module of the current module.
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Rust Analyzer: Locate parent module**
+// |===
+
 /// This returns `Vec` because a module may be included from several places. We
 /// don't handle this case yet though, so the Vec has length at most one.
 pub(crate) fn parent_module(db: &RootDatabase, position: FilePosition) -> Vec<NavigationTarget> {
diff --git a/crates/ra_ide/src/runnables.rs b/crates/ra_ide/src/runnables.rs
index 6e7e47199..286d45eee 100644
--- a/crates/ra_ide/src/runnables.rs
+++ b/crates/ra_ide/src/runnables.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
-
 use hir::{AsAssocItem, Attrs, HirFileId, InFile, Semantics};
 use itertools::Itertools;
 use ra_ide_db::RootDatabase;
@@ -44,6 +42,17 @@ pub enum RunnableKind {
     Bin,
 }
 
+// Feature: Run
+//
+// Shows a popup suggesting to run a test/benchmark/binary **at the current cursor
+// location**. Super useful for repeatedly running just a single test. Do bind this
+// to a shortcut!
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Rust Analyzer: Run**
+// |===
 pub(crate) fn runnables(db: &RootDatabase, file_id: FileId) -> Vec<Runnable> {
     let sema = Semantics::new(db);
     let source_file = sema.parse(file_id);
diff --git a/crates/ra_ide/src/ssr.rs b/crates/ra_ide/src/ssr.rs
index 130d3b4c3..93e9aee1d 100644
--- a/crates/ra_ide/src/ssr.rs
+++ b/crates/ra_ide/src/ssr.rs
@@ -1,5 +1,3 @@
-//!  structural search replace
-
 use std::{collections::HashMap, iter::once, str::FromStr};
 
 use ra_db::{SourceDatabase, SourceDatabaseExt};
@@ -25,6 +23,28 @@ impl std::fmt::Display for SsrError {
 
 impl std::error::Error for SsrError {}
 
+// Feature: Structural Seach and Replace
+//
+// Search and replace with named wildcards that will match any expression.
+// The syntax for a structural search replace command is `<search_pattern> ==>> <replace_pattern>`.
+// A `$<name>:expr` placeholder in the search pattern will match any expression and `$<name>` will reference it in the replacement.
+// Available via the command `rust-analyzer.ssr`.
+//
+// ```rust
+// // Using structural search replace command [foo($a:expr, $b:expr) ==>> ($a).foo($b)]
+//
+// // BEFORE
+// String::from(foo(y + 5, z))
+//
+// // AFTER
+// String::from((y + 5).foo(z))
+// ```
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Rust Analyzer: Structural Search Replace**
+// |===
 pub fn parse_search_replace(
     query: &str,
     parse_only: bool,
diff --git a/crates/ra_ide/src/status.rs b/crates/ra_ide/src/status.rs
index 30eb5c995..5b7992920 100644
--- a/crates/ra_ide/src/status.rs
+++ b/crates/ra_ide/src/status.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
-
 use std::{fmt, iter::FromIterator, sync::Arc};
 
 use hir::MacroFile;
@@ -26,6 +24,15 @@ fn macro_syntax_tree_stats(db: &RootDatabase) -> SyntaxTreeStats {
     db.query(hir::db::ParseMacroQuery).entries::<SyntaxTreeStats>()
 }
 
+// Feature: Status
+//
+// Shows internal statistic about memory usage of rust-analyzer.
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Rust Analyzer: Status**
+// |===
 pub(crate) fn status(db: &RootDatabase) -> String {
     let files_stats = db.query(FileTextQuery).entries::<FilesStats>();
     let syntax_tree_stats = syntax_tree_stats(db);
diff --git a/crates/ra_ide/src/syntax_highlighting.rs b/crates/ra_ide/src/syntax_highlighting.rs
index cd6464b40..0b53ebe69 100644
--- a/crates/ra_ide/src/syntax_highlighting.rs
+++ b/crates/ra_ide/src/syntax_highlighting.rs
@@ -1,5 +1,3 @@
-//! Implements syntax highlighting.
-
 mod tags;
 mod html;
 #[cfg(test)]
@@ -32,81 +30,15 @@ pub struct HighlightedRange {
     pub binding_hash: Option<u64>,
 }
 
-#[derive(Debug)]
-struct HighlightedRangeStack {
-    stack: Vec<Vec<HighlightedRange>>,
-}
-
-/// We use a stack to implement the flattening logic for the highlighted
-/// syntax ranges.
-impl HighlightedRangeStack {
-    fn new() -> Self {
-        Self { stack: vec![Vec::new()] }
-    }
-
-    fn push(&mut self) {
-        self.stack.push(Vec::new());
-    }
-
-    /// Flattens the highlighted ranges.
-    ///
-    /// For example `#[cfg(feature = "foo")]` contains the nested ranges:
-    /// 1) parent-range: Attribute [0, 23)
-    /// 2) child-range: String [16, 21)
-    ///
-    /// The following code implements the flattening, for our example this results to:
-    /// `[Attribute [0, 16), String [16, 21), Attribute [21, 23)]`
-    fn pop(&mut self) {
-        let children = self.stack.pop().unwrap();
-        let prev = self.stack.last_mut().unwrap();
-        let needs_flattening = !children.is_empty()
-            && !prev.is_empty()
-            && prev.last().unwrap().range.contains_range(children.first().unwrap().range);
-        if !needs_flattening {
-            prev.extend(children);
-        } else {
-            let mut parent = prev.pop().unwrap();
-            for ele in children {
-                assert!(parent.range.contains_range(ele.range));
-                let mut cloned = parent.clone();
-                parent.range = TextRange::new(parent.range.start(), ele.range.start());
-                cloned.range = TextRange::new(ele.range.end(), cloned.range.end());
-                if !parent.range.is_empty() {
-                    prev.push(parent);
-                }
-                prev.push(ele);
-                parent = cloned;
-            }
-            if !parent.range.is_empty() {
-                prev.push(parent);
-            }
-        }
-    }
-
-    fn add(&mut self, range: HighlightedRange) {
-        self.stack
-            .last_mut()
-            .expect("during DFS traversal, the stack must not be empty")
-            .push(range)
-    }
-
-    fn flattened(mut self) -> Vec<HighlightedRange> {
-        assert_eq!(
-            self.stack.len(),
-            1,
-            "after DFS traversal, the stack should only contain a single element"
-        );
-        let mut res = self.stack.pop().unwrap();
-        res.sort_by_key(|range| range.range.start());
-        // Check that ranges are sorted and disjoint
-        assert!(res
-            .iter()
-            .zip(res.iter().skip(1))
-            .all(|(left, right)| left.range.end() <= right.range.start()));
-        res
-    }
-}
-
+// Feature: Semantic Syntax Highlighting
+//
+// rust-analyzer highlights the code semantically.
+// For example, `bar` in `foo::Bar` might be colored differently depending on whether `Bar` is an enum or a trait.
+// rust-analyzer does not specify colors directly, instead it assigns tag (like `struct`) and a set of modifiers (like `declaration`) to each token.
+// It's up to the client to map those to specific colors.
+//
+// The general rule is that a reference to an entity gets colored the same way as the entity itself.
+// We also give special modifier for `mut` and `&mut` local variables.
 pub(crate) fn highlight(
     db: &RootDatabase,
     file_id: FileId,
@@ -291,6 +223,81 @@ pub(crate) fn highlight(
     stack.flattened()
 }
 
+#[derive(Debug)]
+struct HighlightedRangeStack {
+    stack: Vec<Vec<HighlightedRange>>,
+}
+
+/// We use a stack to implement the flattening logic for the highlighted
+/// syntax ranges.
+impl HighlightedRangeStack {
+    fn new() -> Self {
+        Self { stack: vec![Vec::new()] }
+    }
+
+    fn push(&mut self) {
+        self.stack.push(Vec::new());
+    }
+
+    /// Flattens the highlighted ranges.
+    ///
+    /// For example `#[cfg(feature = "foo")]` contains the nested ranges:
+    /// 1) parent-range: Attribute [0, 23)
+    /// 2) child-range: String [16, 21)
+    ///
+    /// The following code implements the flattening, for our example this results to:
+    /// `[Attribute [0, 16), String [16, 21), Attribute [21, 23)]`
+    fn pop(&mut self) {
+        let children = self.stack.pop().unwrap();
+        let prev = self.stack.last_mut().unwrap();
+        let needs_flattening = !children.is_empty()
+            && !prev.is_empty()
+            && prev.last().unwrap().range.contains_range(children.first().unwrap().range);
+        if !needs_flattening {
+            prev.extend(children);
+        } else {
+            let mut parent = prev.pop().unwrap();
+            for ele in children {
+                assert!(parent.range.contains_range(ele.range));
+                let mut cloned = parent.clone();
+                parent.range = TextRange::new(parent.range.start(), ele.range.start());
+                cloned.range = TextRange::new(ele.range.end(), cloned.range.end());
+                if !parent.range.is_empty() {
+                    prev.push(parent);
+                }
+                prev.push(ele);
+                parent = cloned;
+            }
+            if !parent.range.is_empty() {
+                prev.push(parent);
+            }
+        }
+    }
+
+    fn add(&mut self, range: HighlightedRange) {
+        self.stack
+            .last_mut()
+            .expect("during DFS traversal, the stack must not be empty")
+            .push(range)
+    }
+
+    fn flattened(mut self) -> Vec<HighlightedRange> {
+        assert_eq!(
+            self.stack.len(),
+            1,
+            "after DFS traversal, the stack should only contain a single element"
+        );
+        let mut res = self.stack.pop().unwrap();
+        res.sort_by_key(|range| range.range.start());
+        // Check that ranges are sorted and disjoint
+        assert!(res
+            .iter()
+            .zip(res.iter().skip(1))
+            .all(|(left, right)| left.range.end() <= right.range.start()));
+        res
+    }
+}
+
 fn highlight_format_specifier(kind: FormatSpecifier) -> Option<HighlightTag> {
     Some(match kind {
         FormatSpecifier::Open
diff --git a/crates/ra_ide/src/syntax_tree.rs b/crates/ra_ide/src/syntax_tree.rs
index 86c70ff83..a341684fd 100644
--- a/crates/ra_ide/src/syntax_tree.rs
+++ b/crates/ra_ide/src/syntax_tree.rs
@@ -1,6 +1,4 @@
-//! FIXME: write short doc here
-
-use ra_db::SourceDatabase;
+use ra_db::{FileId, SourceDatabase};
 use ra_ide_db::RootDatabase;
 use ra_syntax::{
     algo, AstNode, NodeOrToken, SourceFile,
@@ -8,8 +6,16 @@ use ra_syntax::{
     SyntaxToken, TextRange, TextSize,
 };
 
-pub use ra_db::FileId;
-
+// Feature: Show Syntax Tree
+//
+// Shows the parse tree of the current file. It exists mostly for debugging
+// rust-analyzer itself.
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Rust Analyzer: Show Syntax Tree**
+// |===
 pub(crate) fn syntax_tree(
     db: &RootDatabase,
     file_id: FileId,
diff --git a/crates/ra_ide/src/typing.rs b/crates/ra_ide/src/typing.rs
index 39bb3b357..67e2c33a0 100644
--- a/crates/ra_ide/src/typing.rs
+++ b/crates/ra_ide/src/typing.rs
@@ -32,6 +32,13 @@ pub(crate) use on_enter::on_enter;
 
 pub(crate) const TRIGGER_CHARS: &str = ".=>";
 
+// Feature: On Typing Assists
+//
+// Some features trigger on typing certain characters:
+//
+// - typing `let =` tries to smartly add `;` if `=` is followed by an existing expression
+// - Enter inside comments automatically inserts `///`
+// - typing `.` in a chain method call auto-indents
 pub(crate) fn on_char_typed(
     db: &RootDatabase,
     position: FilePosition,