1 files changed, 45 insertions, 2 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.