4 files changed, 36 insertions, 2 deletions

diff --git a/Cargo.lock b/Cargo.lock
index f93f11a82..7f329c4db 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -485,6 +485,16 @@ dependencies = [
 ]
 
 [[package]]
+name = "im"
+version = "13.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sized-chunks 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "typenum 1.11.2 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "indexmap"
 version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1006,6 +1016,7 @@ dependencies = [
  "chalk-rust-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git)",
  "chalk-solve 0.1.0 (git+https://github.com/rust-lang/chalk.git)",
  "ena 0.13.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "im 13.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "insta 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "lalrpop-intern 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1551,6 +1562,14 @@ dependencies = [
 ]
 
 [[package]]
+name = "sized-chunks"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "typenum 1.11.2 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "slab"
 version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1685,6 +1704,11 @@ dependencies = [
 ]
 
 [[package]]
+name = "typenum"
+version = "1.11.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
 name = "unicase"
 version = "2.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1893,6 +1917,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum globset 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)" = "925aa2cac82d8834e2b2a4415b6f6879757fb5c0928fc445ae76461a12eed8f2"
 "checksum heck 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)" = "20564e78d53d2bb135c343b3f47714a56af2061f1c928fdb541dc7b9fdd94205"
 "checksum idna 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "02e2673c30ee86b5b96a9cb52ad15718aa1f966f5ab9ad54a8b95d5ca33120a9"
+"checksum im 13.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "8db49f8bc08d5cc4e2bb0f7d25a6d1db2c79bc6f7d7c86c96c657eb3d214125f"
 "checksum indexmap 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "a4d6d89e0948bf10c08b9ecc8ac5b83f07f857ebe2c0cbe38de15b4e4f510356"
 "checksum indicatif 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "2c60da1c9abea75996b70a931bba6c750730399005b61ccd853cee50ef3d0d0c"
 "checksum inotify 0.6.1 (registry+https://github.com/rust-lang/crates.io-index)" = "40b54539f3910d6f84fbf9a643efd6e3aa6e4f001426c0329576128255994718"
@@ -1987,6 +2012,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum serde_json 1.0.40 (registry+https://github.com/rust-lang/crates.io-index)" = "051c49229f282f7c6f3813f8286cc1e3323e8051823fce42c7ea80fe13521704"
 "checksum serde_repr 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "cd02c7587ec314570041b2754829f84d873ced14a96d1fd1823531e11db40573"
 "checksum serde_yaml 0.8.9 (registry+https://github.com/rust-lang/crates.io-index)" = "38b08a9a90e5260fe01c6480ec7c811606df6d3a660415808c3c3fa8ed95b582"
+"checksum sized-chunks 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)" = "f01db57d7ee89c8e053245deb77040a6cc8508311f381c88749c33d4b9b78785"
 "checksum slab 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)" = "c111b5bd5695e56cffe5129854aa230b39c93a305372fdbb2668ca2394eea9f8"
 "checksum smallvec 0.6.10 (registry+https://github.com/rust-lang/crates.io-index)" = "ab606a9c5e214920bb66c458cd7be8ef094f813f20fe77a54cc7dbfff220d4b7"
 "checksum smol_str 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)" = "590700be3630457c56f8c73c0ea39881476ad7076cd84057d44f4f38f79914fb"
@@ -2002,6 +2028,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum thread_local 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)" = "c6b53e329000edc2b34dbe8545fd20e55a333362d0a321909685a19bd28c3f1b"
 "checksum threadpool 1.7.1 (registry+https://github.com/rust-lang/crates.io-index)" = "e2f0c90a5f3459330ac8bc0d2f879c693bb7a2f59689c1083fc4ef83834da865"
 "checksum time 0.1.42 (registry+https://github.com/rust-lang/crates.io-index)" = "db8dcfca086c1143c9270ac42a2bbd8a7ee477b78ac8e45b19abfb0cbede4b6f"
+"checksum typenum 1.11.2 (registry+https://github.com/rust-lang/crates.io-index)" = "6d2783fe2d6b8c1101136184eb41be8b1ad379e4657050b8aaff0c79ee7575f9"
 "checksum unicase 2.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "2e2e6bd1e59e56598518beb94fd6db628ded570326f0a98c679a304bd9f00150"
 "checksum unicode-bidi 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)" = "49f2bd0c6468a8230e1db229cff8029217cf623c767ea5d60bfbd42729ea54d5"
 "checksum unicode-normalization 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)" = "141339a08b982d942be2ca06ff8b076563cbe223d1befd5450716790d44e2426"
diff --git a/crates/ra_hir/Cargo.toml b/crates/ra_hir/Cargo.toml
index d9bed4dda..f955dc3e6 100644
--- a/crates/ra_hir/Cargo.toml
+++ b/crates/ra_hir/Cargo.toml
@@ -6,6 +6,7 @@ authors = ["rust-analyzer developers"]
 
 [dependencies]
 arrayvec = "0.4.10"
+im = "13.0.0"
 log = "0.4.5"
 relative-path = "0.4.0"
 rustc-hash = "1.0"
diff --git a/crates/ra_hir/src/nameres.rs b/crates/ra_hir/src/nameres.rs
index befbb2a9b..7e5138d05 100644
--- a/crates/ra_hir/src/nameres.rs
+++ b/crates/ra_hir/src/nameres.rs
@@ -54,6 +54,7 @@ mod mod_resolution;
 #[cfg(test)]
 mod tests;
 
+use std::hash::BuildHasherDefault;
 use std::sync::Arc;
 
 use once_cell::sync::Lazy;
@@ -61,7 +62,7 @@ use ra_arena::{impl_arena_id, Arena, RawId};
 use ra_db::{Edition, FileId};
 use ra_prof::profile;
 use ra_syntax::ast;
-use rustc_hash::{FxHashMap, FxHashSet};
+use rustc_hash::{FxHashMap, FxHashSet, FxHasher};
 use test_utils::tested_by;
 
 use crate::{
@@ -73,6 +74,8 @@ use crate::{
     AstId, BuiltinType, Crate, HirFileId, MacroDef, Module, ModuleDef, Name, Path, PathKind, Trait,
 };
 
+pub(crate) type ImmFxHashMap<K, V> = im::HashMap<K, V, BuildHasherDefault<FxHasher>>;
+
 pub(crate) use self::raw::{ImportSourceMap, RawItems};
 
 pub use self::{
@@ -139,7 +142,7 @@ pub(crate) struct ModuleData {
 pub struct ModuleScope {
     items: FxHashMap<Name, Resolution>,
     macros: FxHashMap<Name, MacroDef>,
-    textual_macros: FxHashMap<Name, MacroDef>,
+    textual_macros: ImmFxHashMap<Name, MacroDef>,
 }
 
 static BUILTIN_SCOPE: Lazy<FxHashMap<Name, Resolution>> = Lazy::new(|| {
diff --git a/crates/ra_hir/src/nameres/collector.rs b/crates/ra_hir/src/nameres/collector.rs
index 10c32ffa1..3803c7185 100644
--- a/crates/ra_hir/src/nameres/collector.rs
+++ b/crates/ra_hir/src/nameres/collector.rs
@@ -631,6 +631,7 @@ where
         modules[res].parent = Some(self.module_id);
         modules[res].declaration = Some(declaration);
         modules[res].definition = definition;
+        // Cloning immutable map is lazy and fast
         modules[res].scope.textual_macros = modules[self.module_id].scope.textual_macros.clone();
         modules[self.module_id].children.insert(name.clone(), res);
         let resolution = Resolution {
@@ -707,6 +708,8 @@ where
     }
 
     fn import_all_textual_macros(&mut self, module_id: CrateModuleId) {
+        // `clone()` is needed here to avoid mutable borrow `self.def_collector` when first borrow is alive
+        // Cloning immutable map is lazy and fast
         let macros = self.def_collector.def_map[module_id].scope.textual_macros.clone();
         for (name, macro_) in macros {
             self.def_collector.define_textual_macro(self.module_id, name.clone(), macro_.id);