Added test for check doc strings in crates.

#1856

crates/ra_mbe/src/lib.rs

@@ -1,7 +1,7 @@
-/// `mbe` (short for Macro By Example) crate contains code for handling
-/// `macro_rules` macros. It uses `TokenTree` (from `ra_tt` package) as the
-/// interface, although it contains some code to bridge `SyntaxNode`s and
-/// `TokenTree`s as well!
+//! `mbe` (short for Macro By Example) crate contains code for handling
+//! `macro_rules` macros. It uses `TokenTree` (from `ra_tt` package) as the
+//! interface, although it contains some code to bridge `SyntaxNode`s and
+//! `TokenTree`s as well!
 
 mod parser;
 mod mbe_expander;

crates/ra_mbe/src/mbe_expander/matcher.rs

@@ -1,3 +1,5 @@
+//! FIXME: write short doc here
+
 use crate::{
     mbe_expander::{Binding, Bindings, Fragment},
     parser::{parse_pattern, Op, RepeatKind, Separator},

crates/ra_mbe/src/subtree_source.rs

@@ -1,3 +1,5 @@
+//! FIXME: write short doc here
+
 use ra_parser::{Token, TokenSource};
 use ra_syntax::{classify_literal, SmolStr, SyntaxKind, SyntaxKind::*, T};
 use std::cell::{Cell, Ref, RefCell};

crates/ra_mbe/src/syntax_bridge.rs

@@ -1,3 +1,5 @@
+//! FIXME: write short doc here
+
 use ra_parser::{
     FragmentKind::{self, *},
     ParseError, TreeSink,

crates/ra_mbe/src/tt_iter.rs

@@ -1,3 +1,5 @@
+//! FIXME: write short doc here
+
 #[derive(Debug, Clone)]
 pub(crate) struct TtIter<'a> {
     pub(crate) inner: std::slice::Iter<'a, tt::TokenTree>,