5 files changed, 92 insertions, 55 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 74e5a8273..49022502d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -82,9 +82,9 @@ checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
 
 [[package]]
 name = "backtrace"
-version = "0.3.50"
+version = "0.3.51"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "46254cf2fdcdf1badb5934448c1bcbe046a56537b3987d96c51a7afc5d03f293"
+checksum = "ec1931848a574faa8f7c71a12ea00453ff5effbb5f51afe7f77d7a48cace6ac1"
 dependencies = [
  "addr2line",
  "cfg-if",
@@ -214,9 +214,9 @@ dependencies = [
 
 [[package]]
 name = "chrono"
-version = "0.4.18"
+version = "0.4.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d021fddb7bd3e734370acfa4a83f34095571d8570c039f1420d77540f68d5772"
+checksum = "670ad68c9088c2a963aaa298cb369688cf3f9465ce5e2d4ca10e6e0098a1ce73"
 dependencies = [
  "libc",
  "num-integer",
@@ -365,9 +365,9 @@ checksum = "37ab347416e802de484e4d03c7316c48f1ecb56574dfd4a46a80f173ce1de04d"
 
 [[package]]
 name = "flate2"
-version = "1.0.17"
+version = "1.0.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "766d0e77a2c1502169d4a93ff3b8c15a71fd946cd0126309752104e5f3c46d94"
+checksum = "da80be589a72651dcda34d8b35bcdc9b7254ad06325611074d9cc0fbb19f60ee"
 dependencies = [
  "cfg-if",
  "crc32fast",
@@ -453,9 +453,9 @@ dependencies = [
 
 [[package]]
 name = "hashbrown"
-version = "0.9.0"
+version = "0.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "00d63df3d41950fb462ed38308eea019113ad1508da725bbedcd0fa5a85ef5f7"
+checksum = "d7afe4a420e3fe79967a00898cc1f4db7c8a49a9333a29f8a4bd76a253d5cd04"
 
 [[package]]
 name = "heck"
@@ -725,9 +725,9 @@ checksum = "830d08ce1d1d941e6b30645f1a0eb5643013d835ce3779a5fc208261dbe10f55"
 
 [[package]]
 name = "libc"
-version = "0.2.77"
+version = "0.2.78"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f2f96b10ec2560088a8e76961b00d47107b3a625fecb76dedb29ee7ccbf98235"
+checksum = "aa7087f49d294270db4e1928fc110c976cd4b9e5a16348e0a1df09afa99e6c98"
 
 [[package]]
 name = "libloading"
@@ -1070,6 +1070,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "28b9b4df73455c861d7cbf8be42f01d3b373ed7f02e378d55fa84eafc6f638b1"
 
 [[package]]
+name = "pin-project-lite"
+version = "0.1.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e555d9e657502182ac97b539fb3dae8b79cda19e3e4f8ffb5e8de4f18df93c95"
+
+[[package]]
 name = "plain"
 version = "0.2.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1077,9 +1083,9 @@ checksum = "b4596b6d070b27117e987119b4dac604f3c58cfb0b191112e24771b2faeac1a6"
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.23"
+version = "1.0.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "51ef7cd2518ead700af67bf9d1a658d90b6037d77110fd9c0445429d0ba1c6c9"
+checksum = "1e0704ee1a7e00d7bb417d0770ea303c1bccbabf0ef1667dae92b5967f5f8a71"
 dependencies = [
  "unicode-xid",
 ]
@@ -1180,9 +1186,9 @@ dependencies = [
 
 [[package]]
 name = "rayon"
-version = "1.4.0"
+version = "1.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cfd016f0c045ad38b5251be2c9c0ab806917f82da4d36b2a327e5166adad9270"
+checksum = "dcf6960dc9a5b4ee8d3e4c5787b4a112a8818e0290a42ff664ad60692fdf2032"
 dependencies = [
  "autocfg",
  "crossbeam-deque",
@@ -1294,9 +1300,9 @@ dependencies = [
 
 [[package]]
 name = "rustc-ap-rustc_lexer"
-version = "673.0.0"
+version = "681.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f6b71fa1285bdefe5fb61e59b63d6cc246abf337f4acafdd620d721bc488e671"
+checksum = "01e579a90506e9d9c9a098f380cad55b9ecf9e7be9fa96cb67b31f52045f41a8"
 dependencies = [
  "unicode-xid",
 ]
@@ -1427,9 +1433,9 @@ dependencies = [
 
 [[package]]
 name = "serde_json"
-version = "1.0.57"
+version = "1.0.58"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "164eacbdb13512ec2745fb09d51fd5b22b0d65ed294a1dcf7285a360c80a675c"
+checksum = "a230ea9107ca2220eea9d46de97eddcb04cd00e92d13dda78e478dd33fa82bd4"
 dependencies = [
  "itoa",
  "ryu",
@@ -1623,11 +1629,12 @@ dependencies = [
 
 [[package]]
 name = "tracing"
-version = "0.1.19"
+version = "0.1.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6d79ca061b032d6ce30c660fded31189ca0b9922bf483cd70759f13a2d86786c"
+checksum = "b0987850db3733619253fe60e17cb59b82d37c7e6c0236bb81e4d6b87c879f27"
 dependencies = [
  "cfg-if",
+ "pin-project-lite",
  "tracing-attributes",
  "tracing-core",
 ]
@@ -1645,9 +1652,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-core"
-version = "0.1.16"
+version = "0.1.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5bcf46c1f1f06aeea2d6b81f3c863d0930a596c86ad1920d4e5bad6dd1d7119a"
+checksum = "f50de3927f93d202783f4513cda820ab47ef17f624b03c096e86ef00c67e6b5f"
 dependencies = [
  "lazy_static",
 ]
@@ -1696,9 +1703,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-tree"
-version = "0.1.5"
+version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e1a3dc4774db3a6b2d66a4f8d8de670e874ec3ed55615860c994927419b32c5f"
+checksum = "43aac8afb493b08e1e1904956f7407c1e671b9c83b26a17e1bd83d6a3520e350"
 dependencies = [
  "ansi_term",
  "atty",
diff --git a/crates/assists/src/utils/insert_use.rs b/crates/assists/src/utils/insert_use.rs
index 5719b06af..8dd4fe607 100644
--- a/crates/assists/src/utils/insert_use.rs
+++ b/crates/assists/src/utils/insert_use.rs
@@ -174,7 +174,7 @@ pub(crate) fn try_merge_trees(
     let (lhs_prefix, rhs_prefix) = common_prefix(&lhs_path, &rhs_path)?;
     let lhs = lhs.split_prefix(&lhs_prefix);
     let rhs = rhs.split_prefix(&rhs_prefix);
-    recursive_merge(&lhs, &rhs, merge).map(|(merged, _)| merged)
+    recursive_merge(&lhs, &rhs, merge)
 }
 
 /// Recursively "zips" together lhs and rhs.
@@ -182,20 +182,22 @@ fn recursive_merge(
     lhs: &ast::UseTree,
     rhs: &ast::UseTree,
     merge: MergeBehaviour,
-) -> Option<(ast::UseTree, bool)> {
+) -> Option<ast::UseTree> {
     let mut use_trees = lhs
         .use_tree_list()
         .into_iter()
         .flat_map(|list| list.use_trees())
-        // check if any of the use trees are nested, if they are and the behaviour is `last` we are not allowed to merge this
-        // so early exit the iterator by using Option's Intoiterator impl
-        .map(|tree| match merge == MergeBehaviour::Last && tree.use_tree_list().is_some() {
-            true => None,
-            false => Some(tree),
+        // we use Option here to early return from this function(this is not the same as a `filter` op)
+        .map(|tree| match merge.is_tree_allowed(&tree) {
+            true => Some(tree),
+            false => None,
         })
         .collect::<Option<Vec<_>>>()?;
     use_trees.sort_unstable_by(|a, b| path_cmp_opt(a.path(), b.path()));
     for rhs_t in rhs.use_tree_list().into_iter().flat_map(|list| list.use_trees()) {
+        if !merge.is_tree_allowed(&rhs_t) {
+            return None;
+        }
         let rhs_path = rhs_t.path();
         match use_trees.binary_search_by(|p| path_cmp_opt(p.path(), rhs_path.clone())) {
             Ok(idx) => {
@@ -239,17 +241,9 @@ fn recursive_merge(
                 }
                 let lhs = lhs_t.split_prefix(&lhs_prefix);
                 let rhs = rhs_t.split_prefix(&rhs_prefix);
-                let this_has_children = use_trees.len() > 0;
                 match recursive_merge(&lhs, &rhs, merge) {
-                    Some((_, has_multiple_children))
-                        if merge == MergeBehaviour::Last
-                            && this_has_children
-                            && has_multiple_children =>
-                    {
-                        return None
-                    }
-                    Some((use_tree, _)) => use_trees[idx] = use_tree,
-                    None => use_trees.insert(idx, rhs_t),
+                    Some(use_tree) => use_trees[idx] = use_tree,
+                    None => return None,
                 }
             }
             Err(_)
@@ -264,8 +258,7 @@ fn recursive_merge(
             }
         }
     }
-    let has_multiple_children = use_trees.len() > 1;
-    Some((lhs.with_use_tree_list(make::use_tree_list(use_trees)), has_multiple_children))
+    Some(lhs.with_use_tree_list(make::use_tree_list(use_trees)))
 }
 
 /// Traverses both paths until they differ, returning the common prefix of both.
@@ -308,6 +301,10 @@ fn segment_iter(path: &ast::Path) -> impl Iterator<Item = ast::PathSegment> + Cl
     successors(first_segment(path), |p| p.parent_path().parent_path().and_then(|p| p.segment()))
 }
 
+fn path_len(path: ast::Path) -> usize {
+    segment_iter(&path).count()
+}
+
 /// Orders paths in the following way:
 /// the sole self token comes first, after that come uppercase identifiers, then lowercase identifiers
 // FIXME: rustfmt sort lowercase idents before uppercase, in general we want to have the same ordering rustfmt has
@@ -352,6 +349,19 @@ pub enum MergeBehaviour {
     Last,
 }
 
+impl MergeBehaviour {
+    #[inline]
+    fn is_tree_allowed(&self, tree: &ast::UseTree) -> bool {
+        match self {
+            MergeBehaviour::Full => true,
+            // only simple single segment paths are allowed
+            MergeBehaviour::Last => {
+                tree.use_tree_list().is_none() && tree.path().map(path_len) <= Some(1)
+            }
+        }
+    }
+}
+
 #[derive(Eq, PartialEq, PartialOrd, Ord)]
 enum ImportGroup {
     // the order here defines the order of new group inserts
@@ -676,6 +686,11 @@ use std::io;",
     }
 
     #[test]
+    fn merge_last_into_self() {
+        check_last("foo::bar::baz", r"use foo::bar;", r"use foo::bar::{self, baz};");
+    }
+
+    #[test]
     fn merge_groups_full() {
         check_full(
             "std::io",
@@ -819,8 +834,24 @@ use std::io;",
     }
 
     #[test]
-    fn merge_last_too_long() {
-        check_last("foo::bar", r"use foo::bar::baz::Qux;", r"use foo::bar::{self, baz::Qux};");
+    fn skip_merge_last_too_long() {
+        check_last(
+            "foo::bar",
+            r"use foo::bar::baz::Qux;",
+            r"use foo::bar;
+use foo::bar::baz::Qux;",
+        );
+    }
+
+    #[test]
+    #[ignore] // FIXME: Order changes when switching lhs and rhs
+    fn skip_merge_last_too_long2() {
+        check_last(
+            "foo::bar::baz::Qux",
+            r"use foo::bar;",
+            r"use foo::bar;
+use foo::bar::baz::Qux;",
+        );
     }
 
     #[test]
diff --git a/crates/syntax/Cargo.toml b/crates/syntax/Cargo.toml
index af61bb658..0b15f10e9 100644
--- a/crates/syntax/Cargo.toml
+++ b/crates/syntax/Cargo.toml
@@ -13,7 +13,7 @@ doctest = false
 [dependencies]
 itertools = "0.9.0"
 rowan = "0.10.0"
-rustc_lexer = { version = "673.0.0", package = "rustc-ap-rustc_lexer" }
+rustc_lexer = { version = "681.0.0", package = "rustc-ap-rustc_lexer" }
 rustc-hash = "1.1.0"
 arrayvec = "0.5.1"
 once_cell = "1.3.1"
diff --git a/crates/syntax/src/parsing/lexer.rs b/crates/syntax/src/parsing/lexer.rs
index fa3be1016..f1202113b 100644
--- a/crates/syntax/src/parsing/lexer.rs
+++ b/crates/syntax/src/parsing/lexer.rs
@@ -120,10 +120,10 @@ fn rustc_token_kind_to_syntax_kind(
 
     let syntax_kind = {
         match rustc_token_kind {
-            rustc_lexer::TokenKind::LineComment => COMMENT,
+            rustc_lexer::TokenKind::LineComment { doc_style: _ } => COMMENT,
 
-            rustc_lexer::TokenKind::BlockComment { terminated: true } => COMMENT,
-            rustc_lexer::TokenKind::BlockComment { terminated: false } => {
+            rustc_lexer::TokenKind::BlockComment { doc_style: _, terminated: true } => COMMENT,
+            rustc_lexer::TokenKind::BlockComment { doc_style: _, terminated: false } => {
                 return (
                     COMMENT,
                     Some("Missing trailing `*/` symbols to terminate the block comment"),
@@ -164,7 +164,7 @@ fn rustc_token_kind_to_syntax_kind(
             rustc_lexer::TokenKind::Colon => T![:],
             rustc_lexer::TokenKind::Dollar => T![$],
             rustc_lexer::TokenKind::Eq => T![=],
-            rustc_lexer::TokenKind::Not => T![!],
+            rustc_lexer::TokenKind::Bang => T![!],
             rustc_lexer::TokenKind::Lt => T![<],
             rustc_lexer::TokenKind::Gt => T![>],
             rustc_lexer::TokenKind::Minus => T![-],
diff --git a/docs/dev/style.md b/docs/dev/style.md
index bcd86fd3f..f0fdb5adc 100644
--- a/docs/dev/style.md
+++ b/docs/dev/style.md
@@ -197,7 +197,7 @@ fn frobnicate(walrus: Option<Walrus>) {
 }
 ```
 
-Avoid preconditions that spawn function boundaries:
+Avoid preconditions that span across function boundaries:
 
 
 ```rust
@@ -218,9 +218,8 @@ fn foo() {
 }
 
 // Not as good
-fn is_string_literal(s: &str) -> Option<&str> {
+fn is_string_literal(s: &str) -> bool {
     s.starts_with('"') && s.ends_with('"')
-    Some()
 }
 
 fn foo() {
@@ -231,8 +230,8 @@ fn foo() {
 }
 ```
 
-In the "Not as good" version, the precondition that `1` is a valid char boundary is checked in `is_string_literal` and utilized in `foo`.
-In the "Good" version, precondition check and usage are checked in the same block, and then encoded in the types.
+In the "Not as good" version, the precondition that `1` is a valid char boundary is checked in `is_string_literal` and used in `foo`.
+In the "Good" version, the precondition check and usage are checked in the same block, and then encoded in the types.
 
 # Early Returns