129 files changed, 4949 insertions, 2755 deletions
diff --git a/Cargo.lock b/Cargo.lock
index c902caeb4..fdacd82a7 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -108,8 +108,8 @@ version = "0.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_derive 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 "serde_json 1.0.41 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -124,11 +124,21 @@ version = "0.1.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
+name = "chalk-derive"
+version = "0.1.0"
+source = "git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809#8314f2fcec8582a58c24b638f1a259d4145a0809"
+dependencies = [
+ "proc-macro2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+[[package]]
 name = "chalk-engine"
 version = "0.9.0"
-source = "git+https://github.com/rust-lang/chalk.git#13303bb0067c6ed0572322080ae367ee38f9e7c9"
+source = "git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809#8314f2fcec8582a58c24b638f1a259d4145a0809"
 dependencies = [
- "chalk-macros 0.1.1 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-macros 0.1.1 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
 "rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "stacker 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -136,17 +146,18 @@ dependencies = [
 [[package]]
 name = "chalk-ir"
 version = "0.1.0"
-source = "git+https://github.com/rust-lang/chalk.git#13303bb0067c6ed0572322080ae367ee38f9e7c9"
+source = "git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809#8314f2fcec8582a58c24b638f1a259d4145a0809"
 dependencies = [
- "chalk-engine 0.9.0 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-derive 0.1.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
- "chalk-macros 0.1.1 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-engine 0.9.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
+ "chalk-macros 0.1.1 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
 "lalrpop-intern 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
 name = "chalk-macros"
 version = "0.1.1"
-source = "git+https://github.com/rust-lang/chalk.git#13303bb0067c6ed0572322080ae367ee38f9e7c9"
+source = "git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809#8314f2fcec8582a58c24b638f1a259d4145a0809"
 dependencies = [
 "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -154,24 +165,25 @@ dependencies = [
 [[package]]
 name = "chalk-rust-ir"
 version = "0.1.0"
-source = "git+https://github.com/rust-lang/chalk.git#13303bb0067c6ed0572322080ae367ee38f9e7c9"
+source = "git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809#8314f2fcec8582a58c24b638f1a259d4145a0809"
 dependencies = [
- "chalk-engine 0.9.0 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-derive 0.1.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
- "chalk-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-engine 0.9.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
- "chalk-macros 0.1.1 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
+ "chalk-macros 0.1.1 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
 ]
 [[package]]
 name = "chalk-solve"
 version = "0.1.0"
-source = "git+https://github.com/rust-lang/chalk.git#13303bb0067c6ed0572322080ae367ee38f9e7c9"
+source = "git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809#8314f2fcec8582a58c24b638f1a259d4145a0809"
 dependencies = [
- "chalk-engine 0.9.0 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-engine 0.9.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
- "chalk-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
- "chalk-macros 0.1.1 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-macros 0.1.1 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
- "chalk-rust-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-rust-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
 "ena 0.13.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itertools 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "petgraph 0.4.13 (registry+https://github.com/rust-lang/crates.io-index)",
 "rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -288,7 +300,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "proc-macro2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
 "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -413,7 +425,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
 name = "getrandom"
-version = "0.1.12"
+version = "0.1.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "cfg-if 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -443,7 +455,7 @@ name = "heck"
 version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "unicode-segmentation 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "unicode-segmentation 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -501,7 +513,7 @@ dependencies = [
 "console 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "difference 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 "serde_json 1.0.41 (registry+https://github.com/rust-lang/crates.io-index)",
 "serde_yaml 0.8.11 (registry+https://github.com/rust-lang/crates.io-index)",
 "uuid 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -517,7 +529,7 @@ dependencies = [
 [[package]]
 name = "itertools"
-version = "0.8.0"
+version = "0.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "either 1.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -624,7 +636,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "crossbeam-channel 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
 "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 "serde_json 1.0.41 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -634,7 +646,7 @@ version = "0.61.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "bitflags 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 "serde_json 1.0.41 (registry+https://github.com/rust-lang/crates.io-index)",
 "serde_repr 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
 "url 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -790,7 +802,7 @@ dependencies = [
 "libc 0.2.65 (registry+https://github.com/rust-lang/crates.io-index)",
 "redox_syscall 0.1.56 (registry+https://github.com/rust-lang/crates.io-index)",
 "rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "smallvec 0.6.10 (registry+https://github.com/rust-lang/crates.io-index)",
+ "smallvec 0.6.11 (registry+https://github.com/rust-lang/crates.io-index)",
 "winapi 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -811,7 +823,7 @@ dependencies = [
 "proc-macro-hack 0.5.11 (registry+https://github.com/rust-lang/crates.io-index)",
 "proc-macro2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
 "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -845,7 +857,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "proc-macro2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
 "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -903,7 +915,7 @@ name = "ra_assists"
 version = "0.1.0"
 dependencies = [
 "format-buf 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itertools 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "join_to_string 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
 "ra_db 0.1.0",
 "ra_fmt 0.1.0",
@@ -970,7 +982,7 @@ dependencies = [
 name = "ra_fmt"
 version = "0.1.0"
 dependencies = [
- "itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itertools 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "ra_syntax 0.1.0",
 ]
@@ -979,9 +991,9 @@ name = "ra_hir"
 version = "0.1.0"
 dependencies = [
 "arrayvec 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "chalk-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
- "chalk-rust-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-rust-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
- "chalk-solve 0.1.0 (git+https://github.com/rust-lang/chalk.git)",
+ "chalk-solve 0.1.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)",
 "ena 0.13.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "insta 0.12.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "lalrpop-intern 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -991,6 +1003,27 @@ dependencies = [
 "ra_arena 0.1.0",
 "ra_cfg 0.1.0",
 "ra_db 0.1.0",
+ "ra_hir_def 0.1.0",
+ "ra_hir_expand 0.1.0",
+ "ra_mbe 0.1.0",
+ "ra_prof 0.1.0",
+ "ra_syntax 0.1.0",
+ "ra_tt 0.1.0",
+ "relative-path 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "test_utils 0.1.0",
+]
+[[package]]
+name = "ra_hir_def"
+version = "0.1.0"
+dependencies = [
+ "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "once_cell 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ra_arena 0.1.0",
+ "ra_cfg 0.1.0",
+ "ra_db 0.1.0",
+ "ra_hir_expand 0.1.0",
 "ra_mbe 0.1.0",
 "ra_prof 0.1.0",
 "ra_syntax 0.1.0",
@@ -1001,13 +1034,26 @@ dependencies = [
 ]
 [[package]]
+name = "ra_hir_expand"
+version = "0.1.0"
+dependencies = [
+ "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ra_arena 0.1.0",
+ "ra_db 0.1.0",
+ "ra_mbe 0.1.0",
+ "ra_prof 0.1.0",
+ "ra_syntax 0.1.0",
+ "ra_tt 0.1.0",
+]
+[[package]]
 name = "ra_ide_api"
 version = "0.1.0"
 dependencies = [
 "format-buf 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "fst 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
 "insta 0.12.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itertools 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "join_to_string 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
 "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
 "once_cell 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1049,7 +1095,7 @@ dependencies = [
 "ra_vfs_glob 0.1.0",
 "relative-path 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 "serde_json 1.0.41 (registry+https://github.com/rust-lang/crates.io-index)",
 "tempfile 3.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "test_utils 0.1.0",
@@ -1065,7 +1111,7 @@ dependencies = [
 "ra_syntax 0.1.0",
 "ra_tt 0.1.0",
 "rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "smallvec 0.6.10 (registry+https://github.com/rust-lang/crates.io-index)",
+ "smallvec 0.6.11 (registry+https://github.com/rust-lang/crates.io-index)",
 "test_utils 0.1.0",
 ]
@@ -1081,7 +1127,7 @@ name = "ra_prof"
 version = "0.1.0"
 dependencies = [
 "backtrace 0.3.40 (registry+https://github.com/rust-lang/crates.io-index)",
- "itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itertools 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "jemalloc-ctl 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
 "jemallocator 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
 "once_cell 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1097,7 +1143,7 @@ dependencies = [
 "ra_cfg 0.1.0",
 "ra_db 0.1.0",
 "rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 "serde_json 1.0.41 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -1106,7 +1152,7 @@ name = "ra_syntax"
 version = "0.1.0"
 dependencies = [
 "arrayvec 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itertools 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "once_cell 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "ra_parser 0.1.0",
 "ra_text_edit 0.1.0",
@@ -1180,7 +1226,7 @@ name = "rand"
 version = "0.7.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "getrandom 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)",
+ "getrandom 0.1.13 (registry+https://github.com/rust-lang/crates.io-index)",
 "libc 0.2.65 (registry+https://github.com/rust-lang/crates.io-index)",
 "rand_chacha 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "rand_core 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1224,7 +1270,7 @@ name = "rand_core"
 version = "0.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "getrandom 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)",
+ "getrandom 0.1.13 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -1370,7 +1416,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "base64 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "bitflags 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -1430,7 +1476,7 @@ dependencies = [
 "rand 0.7.2 (registry+https://github.com/rust-lang/crates.io-index)",
 "rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "salsa-macros 0.13.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "smallvec 0.6.10 (registry+https://github.com/rust-lang/crates.io-index)",
+ "smallvec 0.6.11 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -1441,7 +1487,7 @@ dependencies = [
 "heck 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "proc-macro2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
 "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -1463,7 +1509,7 @@ version = "0.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -1473,20 +1519,20 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
 name = "serde"
-version = "1.0.101"
+version = "1.0.102"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "serde_derive 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
 name = "serde_derive"
-version = "1.0.101"
+version = "1.0.102"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "proc-macro2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
 "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -1496,7 +1542,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "itoa 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)",
 "ryu 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -1506,7 +1552,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "proc-macro2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
 "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -1516,7 +1562,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "dtoa 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)",
 "linked-hash-map 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 "yaml-rust 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -1527,7 +1573,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
 name = "smallvec"
-version = "0.6.10"
+version = "0.6.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
@@ -1535,7 +1581,7 @@ name = "smol_str"
 version = "0.1.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -1557,7 +1603,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
 name = "syn"
-version = "1.0.5"
+version = "1.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "proc-macro2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1647,12 +1693,12 @@ name = "unicode-normalization"
 version = "0.1.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "smallvec 0.6.10 (registry+https://github.com/rust-lang/crates.io-index)",
+ "smallvec 0.6.11 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
 name = "unicode-segmentation"
-version = "1.3.0"
+version = "1.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
@@ -1673,7 +1719,7 @@ dependencies = [
 "idna 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "matches 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)",
 "percent-encoding 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -1682,7 +1728,7 @@ version = "0.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "rand 0.7.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 [[package]]
@@ -1759,7 +1805,7 @@ dependencies = [
 "proc-macro2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
 "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
 "ron 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 "walkdir 2.2.9 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -1794,11 +1840,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum cargo_metadata 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "8d2d1617e838936c0d2323a65cc151e03ae19a7678dd24f72bccf27119b90a5d"
 "checksum cc 1.0.46 (registry+https://github.com/rust-lang/crates.io-index)" = "0213d356d3c4ea2c18c40b037c3be23cd639825c18f25ee670ac7813beeef99c"
 "checksum cfg-if 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)" = "4785bdd1c96b2a846b2bd7cc02e86b6b3dbf14e7e53446c4f54c92a361040822"
-"checksum chalk-engine 0.9.0 (git+https://github.com/rust-lang/chalk.git)" = "<none>"
+"checksum chalk-derive 0.1.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)" = "<none>"
-"checksum chalk-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git)" = "<none>"
+"checksum chalk-engine 0.9.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)" = "<none>"
-"checksum chalk-macros 0.1.1 (git+https://github.com/rust-lang/chalk.git)" = "<none>"
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-"checksum chalk-rust-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git)" = "<none>"
+"checksum chalk-macros 0.1.1 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)" = "<none>"
-"checksum chalk-solve 0.1.0 (git+https://github.com/rust-lang/chalk.git)" = "<none>"
+"checksum chalk-rust-ir 0.1.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)" = "<none>"
+"checksum chalk-solve 0.1.0 (git+https://github.com/rust-lang/chalk.git?rev=8314f2fcec8582a58c24b638f1a259d4145a0809)" = "<none>"
 "checksum chrono 0.4.9 (registry+https://github.com/rust-lang/crates.io-index)" = "e8493056968583b0193c1bb04d6f7684586f3726992d6c573261941a895dbd68"
 "checksum clicolors-control 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "90082ee5dcdd64dc4e9e0d37fbf3ee325419e39c0092191e0393df65518f741e"
 "checksum cloudabi 0.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "ddfc5b9aa5d4507acaf872de71051dfd0e309860e88966e1051e462a077aac4f"
@@ -1828,7 +1875,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum fuchsia-cprng 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "a06f77d526c1a601b7c4cdd98f54b5eaabffc14d5f2f0296febdc7f357c6d3ba"
 "checksum fuchsia-zircon 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "2e9763c69ebaae630ba35f74888db465e49e259ba1bc0eda7d06f4a067615d82"
 "checksum fuchsia-zircon-sys 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3dcaa9ae7725d12cdb85b3ad99a434db70b468c09ded17e012d86b5c1010f7a7"
-"checksum getrandom 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)" = "473a1265acc8ff1e808cd0a1af8cee3c2ee5200916058a2ca113c29f2d903571"
+"checksum getrandom 0.1.13 (registry+https://github.com/rust-lang/crates.io-index)" = "e7db7ca94ed4cd01190ceee0d8a8052f08a247aa1b469a7f68c6a3b71afcf407"
 "checksum glob 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "9b919933a397b79c37e33b77bb2aa3dc8eb6e165ad809e58ff75bc7db2e34574"
 "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"
@@ -1839,7 +1886,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum inotify-sys 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "e74a1aa87c59aeff6ef2cc2fa62d41bc43f54952f55652656b18a02fd5e356c0"
 "checksum insta 0.12.0 (registry+https://github.com/rust-lang/crates.io-index)" = "0d499dc062e841590a67230d853bce62d0abeb91304927871670b7c55c461349"
 "checksum iovec 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "b2b3ea6ff95e175473f8ffe6a7eb7c00d054240321b84c57051175fe3c1e075e"
-"checksum itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5b8467d9c1cebe26feb08c640139247fac215782d35371ade9a2136ed6085358"
+"checksum itertools 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)" = "87fa75c9dea7b07be3138c49abbb83fd4bea199b5cdc76f9804458edc5da0d6e"
 "checksum itoa 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)" = "501266b7edd0174f8530248f87f99c88fbe60ca4ef3dd486835b8d8d53136f7f"
 "checksum jemalloc-ctl 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "c502a5ff9dd2924f1ed32ba96e3b65735d837b4bfd978d3161b1702e66aca4b7"
 "checksum jemalloc-sys 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "0d3b9f3f5c9b31aa0f5ed3260385ac205db665baa41d49bb8338008ae94ede45"
@@ -1922,17 +1969,17 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum scopeguard 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "b42e15e59b18a828bbf5c58ea01debb36b9b096346de35d941dcb89009f24a0d"
 "checksum semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
 "checksum semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
-"checksum serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)" = "9796c9b7ba2ffe7a9ce53c2287dfc48080f4b2b362fcc245a259b3a7201119dd"
+"checksum serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)" = "0c4b39bd9b0b087684013a792c59e3e07a46a01d2322518d8a1104641a0b1be0"
-"checksum serde_derive 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)" = "4b133a43a1ecd55d4086bd5b4dc6c1751c68b1bfbeba7a5040442022c7e7c02e"
+"checksum serde_derive 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)" = "ca13fc1a832f793322228923fbb3aba9f3f44444898f835d31ad1b74fa0a2bf8"
 "checksum serde_json 1.0.41 (registry+https://github.com/rust-lang/crates.io-index)" = "2f72eb2a68a7dc3f9a691bfda9305a1c017a6215e5a4545c258500d2099a37c2"
 "checksum serde_repr 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "cd02c7587ec314570041b2754829f84d873ced14a96d1fd1823531e11db40573"
 "checksum serde_yaml 0.8.11 (registry+https://github.com/rust-lang/crates.io-index)" = "691b17f19fc1ec9d94ec0b5864859290dff279dbd7b03f017afda54eb36c3c35"
 "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 smallvec 0.6.11 (registry+https://github.com/rust-lang/crates.io-index)" = "cefaa50e76a6f10b86f36e640eb1739eafbd4084865067778463913e43a77ff3"
 "checksum smol_str 0.1.15 (registry+https://github.com/rust-lang/crates.io-index)" = "34836c9a295c62c2ce3514471117c5cb269891e8421b2aafdd910050576c4d8b"
 "checksum stacker 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "d96fc4f13a0ac088e9a3cd9af1cc8c5cc1ab5deb2145cef661267dfc9c542f8a"
 "checksum superslice 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ab16ced94dbd8a46c82fd81e3ed9a8727dac2977ea869d217bcc4ea1f122e81f"
-"checksum syn 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)" = "66850e97125af79138385e9b88339cbcd037e3f28ceab8c5ad98e64f0f1f80bf"
+"checksum syn 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)" = "0e7bedb3320d0f3035594b0b723c8a28d7d336a3eda3881db79e61d676fb644c"
 "checksum tempfile 3.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "7a6e24d9338a0a5be79593e2fa15a648add6138caa803e2d5bc782c371732ca9"
 "checksum termios 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)" = "72b620c5ea021d75a735c943269bb07d30c9b77d6ac6b236bc8b5c496ef05625"
 "checksum text_unit 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)" = "e08bbcb7a3adbda0eb23431206b653bdad3d8dea311e72d36bf2215e27a42579"
@@ -1942,7 +1989,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "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"
-"checksum unicode-segmentation 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1967f4cdfc355b37fd76d2a954fb2ed3871034eb4f26d60537d88795cfc332a9"
+"checksum unicode-segmentation 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "dc5415c074426c7c65db13bd647c23d78c0fb2e10dca0b8fb0f40058a59bccdf"
 "checksum unicode-width 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "7007dbd421b92cc6e28410fe7362e2e0a2503394908f417b68ec8d1c364c4e20"
 "checksum unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "826e7639553986605ec5979c7dd957c7895e93eabed50ab2ffa7f6128a75097c"
 "checksum url 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "75b414f6c464c879d7f9babf951f23bc3743fb7313c081b2e6ca719067ea9d61"
diff --git a/crates/ra_assists/src/assist_ctx.rs b/crates/ra_assists/src/assist_ctx.rs
index e270c5d60..1908bdec9 100644
--- a/crates/ra_assists/src/assist_ctx.rs
+++ b/crates/ra_assists/src/assist_ctx.rs
@@ -1,11 +1,11 @@
-//! FIXME: write short doc here
+//! This module defines `AssistCtx` -- the API surface that is exposed to assists.
 use hir::db::HirDatabase;
 use ra_db::FileRange;
 use ra_fmt::{leading_indent, reindent};
 use ra_syntax::{
    algo::{self, find_covering_element, find_node_at_offset},
-    AstNode, SourceFile, SyntaxElement, SyntaxNode, SyntaxToken, TextRange, TextUnit,
+    AstNode, SourceFile, SyntaxElement, SyntaxKind, SyntaxNode, SyntaxToken, TextRange, TextUnit,
    TokenAtOffset,
 };
 use ra_text_edit::TextEditBuilder;
@@ -14,8 +14,8 @@ use crate::{AssistAction, AssistId, AssistLabel};
 #[derive(Clone, Debug)]
 pub(crate) enum Assist {
-    Unresolved(Vec<AssistLabel>),
+    Unresolved { label: AssistLabel },
-    Resolved(Vec<(AssistLabel, AssistAction)>),
+    Resolved { label: AssistLabel, action: AssistAction },
 }
 /// `AssistCtx` allows to apply an assist or check if it could be applied.
@@ -54,7 +54,6 @@ pub(crate) struct AssistCtx<'a, DB> {
    pub(crate) frange: FileRange,
    source_file: SourceFile,
    should_compute_edit: bool,
-    assist: Assist,
 }
 impl<'a, DB> Clone for AssistCtx<'a, DB> {
@@ -64,7 +63,6 @@ impl<'a, DB> Clone for AssistCtx<'a, DB> {
            frange: self.frange,
            source_file: self.source_file.clone(),
            should_compute_edit: self.should_compute_edit,
-            assist: self.assist.clone(),
        }
    }
 }
@@ -75,43 +73,41 @@ impl<'a, DB: HirDatabase> AssistCtx<'a, DB> {
        F: FnOnce(AssistCtx<DB>) -> T,
    {
        let parse = db.parse(frange.file_id);
-        let assist =
-            if should_compute_edit { Assist::Resolved(vec![]) } else { Assist::Unresolved(vec![]) };
-        let ctx = AssistCtx { db, frange, source_file: parse.tree(), should_compute_edit, assist };
+        let ctx = AssistCtx { db, frange, source_file: parse.tree(), should_compute_edit };
        f(ctx)
    }
-    pub(crate) fn add_action(
+    pub(crate) fn add_assist(
-        &mut self,
+        self,
        id: AssistId,
        label: impl Into<String>,
        f: impl FnOnce(&mut AssistBuilder),
-    ) -> &mut Self {
+    ) -> Option<Assist> {
        let label = AssistLabel { label: label.into(), id };
-        match &mut self.assist {
+        let assist = if self.should_compute_edit {
-            Assist::Unresolved(labels) => labels.push(label),
+            let action = {
-            Assist::Resolved(labels_actions) => {
+                let mut edit = AssistBuilder::default();
-                let action = {
+                f(&mut edit);
-                    let mut edit = AssistBuilder::default();
+                edit.build()
-                    f(&mut edit);
+            };
-                    edit.build()
+            Assist::Resolved { label, action }
-                };
+        } else {
-                labels_actions.push((label, action));
+            Assist::Unresolved { label }
-            }
+        };
-        }
-        self
-    }
-    pub(crate) fn build(self) -> Option<Assist> {
+        Some(assist)
-        Some(self.assist)
    }
    pub(crate) fn token_at_offset(&self) -> TokenAtOffset<SyntaxToken> {
        self.source_file.syntax().token_at_offset(self.frange.range.start())
    }
-    pub(crate) fn node_at_offset<N: AstNode>(&self) -> Option<N> {
+    pub(crate) fn find_token_at_offset(&self, kind: SyntaxKind) -> Option<SyntaxToken> {
+        self.token_at_offset().find(|it| it.kind() == kind)
+    }
+    pub(crate) fn find_node_at_offset<N: AstNode>(&self) -> Option<N> {
        find_node_at_offset(self.source_file.syntax(), self.frange.range.start())
    }
    pub(crate) fn covering_element(&self) -> SyntaxElement {
diff --git a/crates/ra_assists/src/assists/add_derive.rs b/crates/ra_assists/src/assists/add_derive.rs
index 77ecc33c9..764b17bd8 100644
--- a/crates/ra_assists/src/assists/add_derive.rs
+++ b/crates/ra_assists/src/assists/add_derive.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
 use hir::db::HirDatabase;
 use ra_syntax::{
    ast::{self, AstNode, AttrsOwner},
@@ -9,10 +7,28 @@ use ra_syntax::{
 use crate::{Assist, AssistCtx, AssistId};
-pub(crate) fn add_derive(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: add_derive
-    let nominal = ctx.node_at_offset::<ast::NominalDef>()?;
+//
+// Adds a new `#[derive()]` clause to a struct or enum.
+//
+// ```
+// struct Point {
+//     x: u32,
+//     y: u32,<|>
+// }
+// ```
+// ->
+// ```
+// #[derive()]
+// struct Point {
+//     x: u32,
+//     y: u32,
+// }
+// ```
+pub(crate) fn add_derive(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let nominal = ctx.find_node_at_offset::<ast::NominalDef>()?;
    let node_start = derive_insertion_offset(&nominal)?;
-    ctx.add_action(AssistId("add_derive"), "add `#[derive]`", |edit| {
+    ctx.add_assist(AssistId("add_derive"), "add `#[derive]`", |edit| {
        let derive_attr = nominal
            .attrs()
            .filter_map(|x| x.as_simple_call())
@@ -28,9 +44,7 @@ pub(crate) fn add_derive(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist>
        };
        edit.target(nominal.syntax().text_range());
        edit.set_cursor(offset)
-    });
+    })
-    ctx.build()
 }
 // Insert `derive` after doc comments.
diff --git a/crates/ra_assists/src/assists/add_explicit_type.rs b/crates/ra_assists/src/assists/add_explicit_type.rs
index 8c83dc987..ddda1a0f2 100644
--- a/crates/ra_assists/src/assists/add_explicit_type.rs
+++ b/crates/ra_assists/src/assists/add_explicit_type.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
 use hir::{db::HirDatabase, HirDisplay, Ty};
 use ra_syntax::{
    ast::{self, AstNode, LetStmt, NameOwner},
@@ -8,9 +6,23 @@ use ra_syntax::{
 use crate::{Assist, AssistCtx, AssistId};
-/// Add explicit type assist.
+// Assist: add_explicit_type
-pub(crate) fn add_explicit_type(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+//
-    let stmt = ctx.node_at_offset::<LetStmt>()?;
+// Specify type for a let binding.
+//
+// ```
+// fn main() {
+//     let x<|> = 92;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     let x: i32 = 92;
+// }
+// ```
+pub(crate) fn add_explicit_type(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let stmt = ctx.find_node_at_offset::<LetStmt>()?;
    let expr = stmt.initializer()?;
    let pat = stmt.pat()?;
    // Must be a binding
@@ -35,11 +47,10 @@ pub(crate) fn add_explicit_type(mut ctx: AssistCtx<impl HirDatabase>) -> Option<
        return None;
    }
-    ctx.add_action(AssistId("add_explicit_type"), "add explicit type", |edit| {
+    ctx.add_assist(AssistId("add_explicit_type"), "add explicit type", |edit| {
        edit.target(pat_range);
        edit.insert(name_range.end(), format!(": {}", ty.display(db)));
-    });
+    })
-    ctx.build()
 }
 /// Returns true if any type parameter is unknown
diff --git a/crates/ra_assists/src/assists/add_impl.rs b/crates/ra_assists/src/assists/add_impl.rs
index 94801fbc9..7da0cfd0d 100644
--- a/crates/ra_assists/src/assists/add_impl.rs
+++ b/crates/ra_assists/src/assists/add_impl.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
 use format_buf::format;
 use hir::db::HirDatabase;
 use join_to_string::join;
@@ -10,10 +8,29 @@ use ra_syntax::{
 use crate::{Assist, AssistCtx, AssistId};
-pub(crate) fn add_impl(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: add_impl
-    let nominal = ctx.node_at_offset::<ast::NominalDef>()?;
+//
+// Adds a new inherent impl for a type.
+//
+// ```
+// struct Ctx<T: Clone> {
+//      data: T,<|>
+// }
+// ```
+// ->
+// ```
+// struct Ctx<T: Clone> {
+//      data: T,
+// }
+//
+// impl<T: Clone> Ctx<T> {
+//
+// }
+// ```
+pub(crate) fn add_impl(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let nominal = ctx.find_node_at_offset::<ast::NominalDef>()?;
    let name = nominal.name()?;
-    ctx.add_action(AssistId("add_impl"), "add impl", |edit| {
+    ctx.add_assist(AssistId("add_impl"), "add impl", |edit| {
        edit.target(nominal.syntax().text_range());
        let type_params = nominal.type_param_list();
        let start_offset = nominal.syntax().text_range().end();
@@ -37,9 +54,7 @@ pub(crate) fn add_impl(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
        edit.set_cursor(start_offset + TextUnit::of_str(&buf));
        buf.push_str("\n}");
        edit.insert(start_offset, buf);
-    });
+    })
-    ctx.build()
 }
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/auto_import.rs b/crates/ra_assists/src/assists/add_import.rs
index 02c58e7c6..363ade016 100644
--- a/crates/ra_assists/src/assists/auto_import.rs
+++ b/crates/ra_assists/src/assists/add_import.rs
@@ -1,18 +1,81 @@
-//! FIXME: write short doc here
 use hir::{self, db::HirDatabase};
-use ra_text_edit::TextEditBuilder;
-use crate::{
-    assist_ctx::{Assist, AssistCtx},
-    AssistId,
-};
 use ra_syntax::{
    ast::{self, NameOwner},
    AstNode, Direction, SmolStr,
    SyntaxKind::{PATH, PATH_SEGMENT},
    SyntaxNode, TextRange, T,
 };
+use ra_text_edit::TextEditBuilder;
+use crate::{
+    assist_ctx::{Assist, AssistCtx},
+    AssistId,
+};
+/// This function produces sequence of text edits into edit
+/// to import the target path in the most appropriate scope given
+/// the cursor position
+pub fn auto_import_text_edit(
+    // Ideally the position of the cursor, used to
+    position: &SyntaxNode,
+    // The statement to use as anchor (last resort)
+    anchor: &SyntaxNode,
+    // The path to import as a sequence of strings
+    target: &[SmolStr],
+    edit: &mut TextEditBuilder,
+) {
+    let container = position.ancestors().find_map(|n| {
+        if let Some(module) = ast::Module::cast(n.clone()) {
+            return module.item_list().map(|it| it.syntax().clone());
+        }
+        ast::SourceFile::cast(n).map(|it| it.syntax().clone())
+    });
+    if let Some(container) = container {
+        let action = best_action_for_target(container, anchor.clone(), target);
+        make_assist(&action, target, edit);
+    }
+}
+// Assist: add_import
+//
+// Adds a use statement for a given fully-qualified path.
+//
+// ```
+// fn process(map: std::collections::<|>HashMap<String, String>) {}
+// ```
+// ->
+// ```
+// use std::collections::HashMap;
+//
+// fn process(map: HashMap<String, String>) {}
+// ```
+pub(crate) fn add_import(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let path: ast::Path = ctx.find_node_at_offset()?;
+    // We don't want to mess with use statements
+    if path.syntax().ancestors().find_map(ast::UseItem::cast).is_some() {
+        return None;
+    }
+    let hir_path = hir::Path::from_ast(path.clone())?;
+    let segments = collect_hir_path_segments(&hir_path)?;
+    if segments.len() < 2 {
+        return None;
+    }
+    let module = path.syntax().ancestors().find_map(ast::Module::cast);
+    let position = match module.and_then(|it| it.item_list()) {
+        Some(item_list) => item_list.syntax().clone(),
+        None => {
+            let current_file = path.syntax().ancestors().find_map(ast::SourceFile::cast)?;
+            current_file.syntax().clone()
+        }
+    };
+    ctx.add_assist(AssistId("add_import"), format!("import {}", fmt_segments(&segments)), |edit| {
+        apply_auto_import(&position, &path, &segments, edit.text_edit_builder());
+    })
+}
 fn collect_path_segments_raw(
    segments: &mut Vec<ast::PathSegment>,
@@ -61,9 +124,9 @@ fn fmt_segments_raw(segments: &[SmolStr], buf: &mut String) {
    }
 }
-// Returns the numeber of common segments.
+/// Returns the number of common segments.
 fn compare_path_segments(left: &[SmolStr], right: &[ast::PathSegment]) -> usize {
-    left.iter().zip(right).filter(|(l, r)| compare_path_segment(l, r)).count()
+    left.iter().zip(right).take_while(|(l, r)| compare_path_segment(l, r)).count()
 }
 fn compare_path_segment(a: &SmolStr, b: &ast::PathSegment) -> bool {
@@ -84,7 +147,7 @@ fn compare_path_segment_with_name(a: &SmolStr, b: &ast::Name) -> bool {
    a == b.text()
 }
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 enum ImportAction {
    Nothing,
    // Add a brand new use statement.
@@ -154,9 +217,17 @@ impl ImportAction {
            (
                ImportAction::AddNestedImport { common_segments: n, .. },
                ImportAction::AddInTreeList { common_segments: m, .. },
-            ) => n > m,
+            )
-            (
+            | (
+                ImportAction::AddInTreeList { common_segments: n, .. },
+                ImportAction::AddNestedImport { common_segments: m, .. },
+            )
+            | (
                ImportAction::AddInTreeList { common_segments: n, .. },
+                ImportAction::AddInTreeList { common_segments: m, .. },
+            )
+            | (
+                ImportAction::AddNestedImport { common_segments: n, .. },
                ImportAction::AddNestedImport { common_segments: m, .. },
            ) => n > m,
            (ImportAction::AddInTreeList { .. }, _) => true,
@@ -226,7 +297,7 @@ fn walk_use_tree_for_best_action(
        common if common == left.len() && left.len() == right.len() => {
            // e.g: target is std::fmt and we can have
            // 1- use std::fmt;
-            // 2- use std::fmt:{ ... }
+            // 2- use std::fmt::{ ... }
            if let Some(list) = tree_list {
                // In case 2 we need to add self to the nested list
                // unless it's already there
@@ -474,7 +545,7 @@ fn make_assist_add_nested_import(
        if add_colon_colon {
            buf.push_str("::");
        }
-        buf.push_str("{ ");
+        buf.push_str("{");
        if add_self {
            buf.push_str("self, ");
        }
@@ -505,7 +576,7 @@ fn apply_auto_import(
    }
 }
-pub fn collect_hir_path_segments(path: &hir::Path) -> Option<Vec<SmolStr>> {
+fn collect_hir_path_segments(path: &hir::Path) -> Option<Vec<SmolStr>> {
    let mut ps = Vec::<SmolStr>::with_capacity(10);
    match path.kind {
        hir::PathKind::Abs => ps.push("".into()),
@@ -521,87 +592,16 @@ pub fn collect_hir_path_segments(path: &hir::Path) -> Option<Vec<SmolStr>> {
    Some(ps)
 }
-// This function produces sequence of text edits into edit
-// to import the target path in the most appropriate scope given
-// the cursor position
-pub fn auto_import_text_edit(
-    // Ideally the position of the cursor, used to
-    position: &SyntaxNode,
-    // The statement to use as anchor (last resort)
-    anchor: &SyntaxNode,
-    // The path to import as a sequence of strings
-    target: &[SmolStr],
-    edit: &mut TextEditBuilder,
-) {
-    let container = position.ancestors().find_map(|n| {
-        if let Some(module) = ast::Module::cast(n.clone()) {
-            return module.item_list().map(|it| it.syntax().clone());
-        }
-        ast::SourceFile::cast(n).map(|it| it.syntax().clone())
-    });
-    if let Some(container) = container {
-        let action = best_action_for_target(container, anchor.clone(), target);
-        make_assist(&action, target, edit);
-    }
-}
-pub(crate) fn auto_import(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
-    let path: ast::Path = ctx.node_at_offset()?;
-    // We don't want to mess with use statements
-    if path.syntax().ancestors().find_map(ast::UseItem::cast).is_some() {
-        return None;
-    }
-    let hir_path = hir::Path::from_ast(path.clone())?;
-    let segments = collect_hir_path_segments(&hir_path)?;
-    if segments.len() < 2 {
-        return None;
-    }
-    if let Some(module) = path.syntax().ancestors().find_map(ast::Module::cast) {
-        if let (Some(item_list), Some(name)) = (module.item_list(), module.name()) {
-            ctx.add_action(
-                AssistId("auto_import"),
-                format!("import {} in mod {}", fmt_segments(&segments), name.text()),
-                |edit| {
-                    apply_auto_import(
-                        item_list.syntax(),
-                        &path,
-                        &segments,
-                        edit.text_edit_builder(),
-                    );
-                },
-            );
-        }
-    } else {
-        let current_file = path.syntax().ancestors().find_map(ast::SourceFile::cast)?;
-        ctx.add_action(
-            AssistId("auto_import"),
-            format!("import {} in the current file", fmt_segments(&segments)),
-            |edit| {
-                apply_auto_import(
-                    current_file.syntax(),
-                    &path,
-                    &segments,
-                    edit.text_edit_builder(),
-                );
-            },
-        );
-    }
-    ctx.build()
-}
 #[cfg(test)]
 mod tests {
-    use super::*;
    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use super::*;
    #[test]
    fn test_auto_import_add_use_no_anchor() {
        check_assist(
-            auto_import,
+            add_import,
            "
 std::fmt::Debug<|>
    ",
@@ -615,7 +615,7 @@ Debug<|>
    #[test]
    fn test_auto_import_add_use_no_anchor_with_item_below() {
        check_assist(
-            auto_import,
+            add_import,
            "
 std::fmt::Debug<|>
@@ -636,7 +636,7 @@ fn main() {
    #[test]
    fn test_auto_import_add_use_no_anchor_with_item_above() {
        check_assist(
-            auto_import,
+            add_import,
            "
 fn main() {
 }
@@ -657,7 +657,7 @@ Debug<|>
    #[test]
    fn test_auto_import_add_use_no_anchor_2seg() {
        check_assist(
-            auto_import,
+            add_import,
            "
 std::fmt<|>::Debug
    ",
@@ -672,7 +672,7 @@ fmt<|>::Debug
    #[test]
    fn test_auto_import_add_use() {
        check_assist(
-            auto_import,
+            add_import,
            "
 use stdx;
@@ -692,7 +692,7 @@ impl Debug<|> for Foo {
    #[test]
    fn test_auto_import_file_use_other_anchor() {
        check_assist(
-            auto_import,
+            add_import,
            "
 impl std::fmt::Debug<|> for Foo {
 }
@@ -709,7 +709,7 @@ impl Debug<|> for Foo {
    #[test]
    fn test_auto_import_add_use_other_anchor_indent() {
        check_assist(
-            auto_import,
+            add_import,
            "
    impl std::fmt::Debug<|> for Foo {
    }
@@ -726,7 +726,7 @@ impl Debug<|> for Foo {
    #[test]
    fn test_auto_import_split_different() {
        check_assist(
-            auto_import,
+            add_import,
            "
 use std::fmt;
@@ -734,7 +734,7 @@ impl std::io<|> for Foo {
 }
    ",
            "
-use std::{ io, fmt};
+use std::{io, fmt};
 impl io<|> for Foo {
 }
@@ -745,7 +745,7 @@ impl io<|> for Foo {
    #[test]
    fn test_auto_import_split_self_for_use() {
        check_assist(
-            auto_import,
+            add_import,
            "
 use std::fmt;
@@ -753,7 +753,7 @@ impl std::fmt::Debug<|> for Foo {
 }
    ",
            "
-use std::fmt::{ self, Debug, };
+use std::fmt::{self, Debug, };
 impl Debug<|> for Foo {
 }
@@ -764,7 +764,7 @@ impl Debug<|> for Foo {
    #[test]
    fn test_auto_import_split_self_for_target() {
        check_assist(
-            auto_import,
+            add_import,
            "
 use std::fmt::Debug;
@@ -772,7 +772,7 @@ impl std::fmt<|> for Foo {
 }
    ",
            "
-use std::fmt::{ self, Debug};
+use std::fmt::{self, Debug};
 impl fmt<|> for Foo {
 }
@@ -783,7 +783,7 @@ impl fmt<|> for Foo {
    #[test]
    fn test_auto_import_add_to_nested_self_nested() {
        check_assist(
-            auto_import,
+            add_import,
            "
 use std::fmt::{Debug, nested::{Display}};
@@ -802,7 +802,7 @@ impl nested<|> for Foo {
    #[test]
    fn test_auto_import_add_to_nested_self_already_included() {
        check_assist(
-            auto_import,
+            add_import,
            "
 use std::fmt::{Debug, nested::{self, Display}};
@@ -821,7 +821,7 @@ impl nested<|> for Foo {
    #[test]
    fn test_auto_import_add_to_nested_nested() {
        check_assist(
-            auto_import,
+            add_import,
            "
 use std::fmt::{Debug, nested::{Display}};
@@ -840,7 +840,7 @@ impl Debug<|> for Foo {
    #[test]
    fn test_auto_import_split_common_target_longer() {
        check_assist(
-            auto_import,
+            add_import,
            "
 use std::fmt::Debug;
@@ -848,7 +848,7 @@ impl std::fmt::nested::Display<|> for Foo {
 }
 ",
            "
-use std::fmt::{ nested::Display, Debug};
+use std::fmt::{nested::Display, Debug};
 impl Display<|> for Foo {
 }
@@ -859,7 +859,7 @@ impl Display<|> for Foo {
    #[test]
    fn test_auto_import_split_common_use_longer() {
        check_assist(
-            auto_import,
+            add_import,
            "
 use std::fmt::nested::Debug;
@@ -867,7 +867,7 @@ impl std::fmt::Display<|> for Foo {
 }
 ",
            "
-use std::fmt::{ Display, nested::Debug};
+use std::fmt::{Display, nested::Debug};
 impl Display<|> for Foo {
 }
@@ -876,9 +876,32 @@ impl Display<|> for Foo {
    }
    #[test]
+    fn test_auto_import_use_nested_import() {
+        check_assist(
+            add_import,
+            "
+use crate::{
+    ty::{Substs, Ty},
+    AssocItem,
+};
+fn foo() { crate::ty::lower<|>::trait_env() }
+",
+            "
+use crate::{
+    ty::{Substs, Ty, lower},
+    AssocItem,
+};
+fn foo() { lower<|>::trait_env() }
+",
+        );
+    }
+    #[test]
    fn test_auto_import_alias() {
        check_assist(
-            auto_import,
+            add_import,
            "
 use std::fmt as foo;
@@ -897,7 +920,7 @@ impl Debug<|> for Foo {
    #[test]
    fn test_auto_import_not_applicable_one_segment() {
        check_assist_not_applicable(
-            auto_import,
+            add_import,
            "
 impl foo<|> for Foo {
 }
@@ -908,7 +931,7 @@ impl foo<|> for Foo {
    #[test]
    fn test_auto_import_not_applicable_in_use() {
        check_assist_not_applicable(
-            auto_import,
+            add_import,
            "
 use std::fmt<|>;
 ",
@@ -918,7 +941,7 @@ use std::fmt<|>;
    #[test]
    fn test_auto_import_add_use_no_anchor_in_mod_mod() {
        check_assist(
-            auto_import,
+            add_import,
            "
 mod foo {
    mod bar {
diff --git a/crates/ra_assists/src/assists/add_missing_impl_members.rs b/crates/ra_assists/src/assists/add_missing_impl_members.rs
index 565b96fb5..41de23921 100644
--- a/crates/ra_assists/src/assists/add_missing_impl_members.rs
+++ b/crates/ra_assists/src/assists/add_missing_impl_members.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
 use hir::{db::HirDatabase, HasSource};
 use ra_syntax::{
    ast::{self, edit, make, AstNode, NameOwner},
@@ -14,6 +12,34 @@ enum AddMissingImplMembersMode {
    NoDefaultMethods,
 }
+// Assist: add_impl_missing_members
+//
+// Adds scaffold for required impl members.
+//
+// ```
+// trait T {
+//     Type X;
+//     fn foo(&self);
+//     fn bar(&self) {}
+// }
+//
+// impl T for () {<|>
+//
+// }
+// ```
+// ->
+// ```
+// trait T {
+//     Type X;
+//     fn foo(&self);
+//     fn bar(&self) {}
+// }
+//
+// impl T for () {
+//     fn foo(&self) { unimplemented!() }
+//
+// }
+// ```
 pub(crate) fn add_missing_impl_members(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
    add_missing_impl_members_inner(
        ctx,
@@ -23,6 +49,38 @@ pub(crate) fn add_missing_impl_members(ctx: AssistCtx<impl HirDatabase>) -> Opti
    )
 }
+// Assist: add_impl_default_members
+//
+// Adds scaffold for overriding default impl members.
+//
+// ```
+// trait T {
+//     Type X;
+//     fn foo(&self);
+//     fn bar(&self) {}
+// }
+//
+// impl T for () {
+//     Type X = ();
+//     fn foo(&self) {}<|>
+//
+// }
+// ```
+// ->
+// ```
+// trait T {
+//     Type X;
+//     fn foo(&self);
+//     fn bar(&self) {}
+// }
+//
+// impl T for () {
+//     Type X = ();
+//     fn foo(&self) {}
+//     fn bar(&self) {}
+//
+// }
+// ```
 pub(crate) fn add_missing_default_members(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
    add_missing_impl_members_inner(
        ctx,
@@ -33,12 +91,12 @@ pub(crate) fn add_missing_default_members(ctx: AssistCtx<impl HirDatabase>) -> O
 }
 fn add_missing_impl_members_inner(
-    mut ctx: AssistCtx<impl HirDatabase>,
+    ctx: AssistCtx<impl HirDatabase>,
    mode: AddMissingImplMembersMode,
    assist_id: &'static str,
    label: &'static str,
 ) -> Option<Assist> {
-    let impl_node = ctx.node_at_offset::<ast::ImplBlock>()?;
+    let impl_node = ctx.find_node_at_offset::<ast::ImplBlock>()?;
    let impl_item_list = impl_node.item_list()?;
    let trait_def = {
@@ -75,7 +133,7 @@ fn add_missing_impl_members_inner(
        return None;
    }
-    ctx.add_action(AssistId(assist_id), label, |edit| {
+    ctx.add_assist(AssistId(assist_id), label, |edit| {
        let n_existing_items = impl_item_list.impl_items().count();
        let items = missing_items
            .into_iter()
@@ -92,9 +150,7 @@ fn add_missing_impl_members_inner(
        edit.replace_ast(impl_item_list, new_impl_item_list);
        edit.set_cursor(cursor_position);
-    });
+    })
-    ctx.build()
 }
 fn add_body(fn_def: ast::FnDef) -> ast::FnDef {
diff --git a/crates/ra_assists/src/assists/apply_demorgan.rs b/crates/ra_assists/src/assists/apply_demorgan.rs
index 5f2b0dd18..068da1774 100644
--- a/crates/ra_assists/src/assists/apply_demorgan.rs
+++ b/crates/ra_assists/src/assists/apply_demorgan.rs
@@ -1,20 +1,30 @@
-//! This contains the functions associated with the demorgan assist.
-//! This assist transforms boolean expressions of the form `!a || !b` into
-//! `!(a && b)`.
 use hir::db::HirDatabase;
 use ra_syntax::ast::{self, AstNode};
 use ra_syntax::SyntaxNode;
 use crate::{Assist, AssistCtx, AssistId};
-/// Assist for applying demorgan's law
+// Assist: apply_demorgan
-///
+//
-/// This transforms expressions of the form `!l || !r` into `!(l && r)`.
+// Apply [De Morgan's law](https://en.wikipedia.org/wiki/De_Morgan%27s_laws).
-/// This also works with `&&`. This assist can only be applied with the cursor
+// This transforms expressions of the form `!l || !r` into `!(l && r)`.
-/// on either `||` or `&&`, with both operands being a negation of some kind.
+// This also works with `&&`. This assist can only be applied with the cursor
-/// This means something of the form `!x` or `x != y`.
+// on either `||` or `&&`, with both operands being a negation of some kind.
-pub(crate) fn apply_demorgan(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// This means something of the form `!x` or `x != y`.
-    let expr = ctx.node_at_offset::<ast::BinExpr>()?;
+//
+// ```
+// fn main() {
+//     if x != 4 ||<|> !y {}
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     if !(x == 4 && y) {}
+// }
+// ```
+pub(crate) fn apply_demorgan(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let expr = ctx.find_node_at_offset::<ast::BinExpr>()?;
    let op = expr.op_kind()?;
    let op_range = expr.op_token()?.text_range();
    let opposite_op = opposite_logic_op(op)?;
@@ -29,13 +39,12 @@ pub(crate) fn apply_demorgan(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Ass
    let not_lhs = undo_negation(lhs)?;
    let not_rhs = undo_negation(rhs)?;
-    ctx.add_action(AssistId("apply_demorgan"), "apply demorgan's law", |edit| {
+    ctx.add_assist(AssistId("apply_demorgan"), "apply demorgan's law", |edit| {
        edit.target(op_range);
        edit.replace(op_range, opposite_op);
        edit.replace(lhs_range, format!("!({}", not_lhs));
        edit.replace(rhs_range, format!("{})", not_rhs));
-    });
+    })
-    ctx.build()
 }
 // Return the opposite text for a given logical operator, if it makes sense
diff --git a/crates/ra_assists/src/assists/change_visibility.rs b/crates/ra_assists/src/assists/change_visibility.rs
index df92c6b67..132c9dc1d 100644
--- a/crates/ra_assists/src/assists/change_visibility.rs
+++ b/crates/ra_assists/src/assists/change_visibility.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
 use hir::db::HirDatabase;
 use ra_syntax::{
    ast::{self, NameOwner, VisibilityOwner},
@@ -13,14 +11,25 @@ use ra_syntax::{
 use crate::{Assist, AssistCtx, AssistId};
+// Assist: change_visibility
+//
+// Adds or changes existing visibility specifier.
+//
+// ```
+// <|>fn frobnicate() {}
+// ```
+// ->
+// ```
+// pub(crate) fn frobnicate() {}
+// ```
 pub(crate) fn change_visibility(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
-    if let Some(vis) = ctx.node_at_offset::<ast::Visibility>() {
+    if let Some(vis) = ctx.find_node_at_offset::<ast::Visibility>() {
        return change_vis(ctx, vis);
    }
    add_vis(ctx)
 }
-fn add_vis(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+fn add_vis(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
    let item_keyword = ctx.token_at_offset().find(|leaf| match leaf.kind() {
        T![fn] | T![mod] | T![struct] | T![enum] | T![trait] => true,
        _ => false,
@@ -48,13 +57,11 @@ fn add_vis(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
        (vis_offset(field.syntax()), ident.text_range())
    };
-    ctx.add_action(AssistId("change_visibility"), "make pub(crate)", |edit| {
+    ctx.add_assist(AssistId("change_visibility"), "make pub(crate)", |edit| {
        edit.target(target);
        edit.insert(offset, "pub(crate) ");
        edit.set_cursor(offset);
-    });
+    })
-    ctx.build()
 }
 fn vis_offset(node: &SyntaxNode) -> TextUnit {
@@ -68,24 +75,20 @@ fn vis_offset(node: &SyntaxNode) -> TextUnit {
        .unwrap_or_else(|| node.text_range().start())
 }
-fn change_vis(mut ctx: AssistCtx<impl HirDatabase>, vis: ast::Visibility) -> Option<Assist> {
+fn change_vis(ctx: AssistCtx<impl HirDatabase>, vis: ast::Visibility) -> Option<Assist> {
    if vis.syntax().text() == "pub" {
-        ctx.add_action(AssistId("change_visibility"), "change to pub(crate)", |edit| {
+        return ctx.add_assist(AssistId("change_visibility"), "change to pub(crate)", |edit| {
            edit.target(vis.syntax().text_range());
            edit.replace(vis.syntax().text_range(), "pub(crate)");
            edit.set_cursor(vis.syntax().text_range().start())
        });
-        return ctx.build();
    }
    if vis.syntax().text() == "pub(crate)" {
-        ctx.add_action(AssistId("change_visibility"), "change to pub", |edit| {
+        return ctx.add_assist(AssistId("change_visibility"), "change to pub", |edit| {
            edit.target(vis.syntax().text_range());
            edit.replace(vis.syntax().text_range(), "pub");
            edit.set_cursor(vis.syntax().text_range().start());
        });
-        return ctx.build();
    }
    None
 }
diff --git a/crates/ra_assists/src/assists/early_return.rs b/crates/ra_assists/src/assists/early_return.rs
index f7d7e12e7..ad6c5695a 100644
--- a/crates/ra_assists/src/assists/early_return.rs
+++ b/crates/ra_assists/src/assists/early_return.rs
@@ -1,26 +1,3 @@
-//! Assist: `convert_to_guarded_return`
-//!
-//! Replace a large conditional with a guarded return.
-//!
-//! ```text
-//! fn <|>main() {
-//!     if cond {
-//!         foo();
-//!         bar();
-//!     }
-//! }
-//! ```
-//! ->
-//! ```text
-//! fn main() {
-//!     if !cond {
-//!         return;
-//!     }
-//!     foo();
-//!     bar();
-//! }
-//! ```
 use std::ops::RangeInclusive;
 use hir::db::HirDatabase;
@@ -36,8 +13,30 @@ use crate::{
    AssistId,
 };
-pub(crate) fn convert_to_guarded_return(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: convert_to_guarded_return
-    let if_expr: ast::IfExpr = ctx.node_at_offset()?;
+//
+// Replace a large conditional with a guarded return.
+//
+// ```
+// fn main() {
+//     <|>if cond {
+//         foo();
+//         bar();
+//     }
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     if !cond {
+//         return;
+//     }
+//     foo();
+//     bar();
+// }
+// ```
+pub(crate) fn convert_to_guarded_return(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let if_expr: ast::IfExpr = ctx.find_node_at_offset()?;
    let expr = if_expr.condition()?.expr()?;
    let then_block = if_expr.then_branch()?.block()?;
    if if_expr.else_branch().is_some() {
@@ -51,7 +50,7 @@ pub(crate) fn convert_to_guarded_return(mut ctx: AssistCtx<impl HirDatabase>) ->
    }
    // check for early return and continue
-    let first_in_then_block = then_block.syntax().first_child()?.clone();
+    let first_in_then_block = then_block.syntax().first_child()?;
    if ast::ReturnExpr::can_cast(first_in_then_block.kind())
        || ast::ContinueExpr::can_cast(first_in_then_block.kind())
        || first_in_then_block
@@ -76,7 +75,7 @@ pub(crate) fn convert_to_guarded_return(mut ctx: AssistCtx<impl HirDatabase>) ->
    then_block.syntax().last_child_or_token().filter(|t| t.kind() == R_CURLY)?;
    let cursor_position = ctx.frange.range.start();
-    ctx.add_action(AssistId("convert_to_guarded_return"), "convert to guarded return", |edit| {
+    ctx.add_assist(AssistId("convert_to_guarded_return"), "convert to guarded return", |edit| {
        let if_indent_level = IndentLevel::from_node(&if_expr.syntax());
        let new_if_expr =
            if_indent_level.increase_indent(make::if_expression(&expr, early_expression));
@@ -106,8 +105,7 @@ pub(crate) fn convert_to_guarded_return(mut ctx: AssistCtx<impl HirDatabase>) ->
        edit.target(if_expr.syntax().text_range());
        edit.replace_ast(parent_block, ast::Block::cast(new_block).unwrap());
        edit.set_cursor(cursor_position);
-    });
+    })
-    ctx.build()
 }
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/fill_match_arms.rs b/crates/ra_assists/src/assists/fill_match_arms.rs
index e3f30b5de..2b74f355c 100644
--- a/crates/ra_assists/src/assists/fill_match_arms.rs
+++ b/crates/ra_assists/src/assists/fill_match_arms.rs
@@ -7,8 +7,32 @@ use ra_syntax::ast::{self, edit::IndentLevel, make, AstNode, NameOwner};
 use crate::{Assist, AssistCtx, AssistId};
-pub(crate) fn fill_match_arms(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: fill_match_arms
-    let match_expr = ctx.node_at_offset::<ast::MatchExpr>()?;
+//
+// Adds missing clauses to a `match` expression.
+//
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         <|>
+//     }
+// }
+// ```
+// ->
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } => (),
+//         Action::Stop => (),
+//     }
+// }
+// ```
+pub(crate) fn fill_match_arms(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let match_expr = ctx.find_node_at_offset::<ast::MatchExpr>()?;
    let match_arm_list = match_expr.match_arm_list()?;
    // We already have some match arms, so we don't provide any assists.
@@ -29,7 +53,7 @@ pub(crate) fn fill_match_arms(mut ctx: AssistCtx<impl HirDatabase>) -> Option<As
    };
    let variant_list = enum_def.variant_list()?;
-    ctx.add_action(AssistId("fill_match_arms"), "fill match arms", |edit| {
+    ctx.add_assist(AssistId("fill_match_arms"), "fill match arms", |edit| {
        let indent_level = IndentLevel::from_node(match_arm_list.syntax());
        let new_arm_list = {
@@ -43,9 +67,7 @@ pub(crate) fn fill_match_arms(mut ctx: AssistCtx<impl HirDatabase>) -> Option<As
        edit.target(match_expr.syntax().text_range());
        edit.set_cursor(expr.syntax().text_range().start());
        edit.replace_ast(match_arm_list, new_arm_list);
-    });
+    })
-    ctx.build()
 }
 fn is_trivial(arm: &ast::MatchArm) -> bool {
@@ -130,7 +152,7 @@ mod tests {
                    A::Bs => (),
                    A::Cs(_) => (),
                    A::Ds(_, _) => (),
-                    A::Es{ x, y } => (),
+                    A::Es { x, y } => (),
                }
            }
            "#,
@@ -183,7 +205,7 @@ mod tests {
            fn foo(a: &mut A) {
                match <|>a {
-                    A::Es{ x, y } => (),
+                    A::Es { x, y } => (),
                }
            }
            "#,
diff --git a/crates/ra_assists/src/assists/flip_binexpr.rs b/crates/ra_assists/src/assists/flip_binexpr.rs
index c51035282..386045eb0 100644
--- a/crates/ra_assists/src/assists/flip_binexpr.rs
+++ b/crates/ra_assists/src/assists/flip_binexpr.rs
@@ -1,13 +1,25 @@
-//! FIXME: write short doc here
 use hir::db::HirDatabase;
 use ra_syntax::ast::{AstNode, BinExpr, BinOp};
 use crate::{Assist, AssistCtx, AssistId};
-/// Flip binary expression assist.
+// Assist: flip_binexpr
-pub(crate) fn flip_binexpr(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+//
-    let expr = ctx.node_at_offset::<BinExpr>()?;
+// Flips operands of a binary expression.
+//
+// ```
+// fn main() {
+//     let _ = 90 +<|> 2;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     let _ = 2 + 90;
+// }
+// ```
+pub(crate) fn flip_binexpr(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let expr = ctx.find_node_at_offset::<BinExpr>()?;
    let lhs = expr.lhs()?.syntax().clone();
    let rhs = expr.rhs()?.syntax().clone();
    let op_range = expr.op_token()?.text_range();
@@ -22,16 +34,14 @@ pub(crate) fn flip_binexpr(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assis
        return None;
    }
-    ctx.add_action(AssistId("flip_binexpr"), "flip binary expression", |edit| {
+    ctx.add_assist(AssistId("flip_binexpr"), "flip binary expression", |edit| {
        edit.target(op_range);
        if let FlipAction::FlipAndReplaceOp(new_op) = action {
            edit.replace(op_range, new_op);
        }
        edit.replace(lhs.text_range(), rhs.text());
        edit.replace(rhs.text_range(), lhs.text());
-    });
+    })
-    ctx.build()
 }
 enum FlipAction {
diff --git a/crates/ra_assists/src/assists/flip_comma.rs b/crates/ra_assists/src/assists/flip_comma.rs
index e31cc5e7d..9be1c1dc6 100644
--- a/crates/ra_assists/src/assists/flip_comma.rs
+++ b/crates/ra_assists/src/assists/flip_comma.rs
@@ -1,12 +1,25 @@
-//! FIXME: write short doc here
 use hir::db::HirDatabase;
 use ra_syntax::{algo::non_trivia_sibling, Direction, T};
 use crate::{Assist, AssistCtx, AssistId};
-pub(crate) fn flip_comma(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: flip_comma
-    let comma = ctx.token_at_offset().find(|leaf| leaf.kind() == T![,])?;
+//
+// Flips two comma-separated items.
+//
+// ```
+// fn main() {
+//     ((1, 2),<|> (3, 4));
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     ((3, 4), (1, 2));
+// }
+// ```
+pub(crate) fn flip_comma(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let comma = ctx.find_token_at_offset(T![,])?;
    let prev = non_trivia_sibling(comma.clone().into(), Direction::Prev)?;
    let next = non_trivia_sibling(comma.clone().into(), Direction::Next)?;
@@ -16,13 +29,11 @@ pub(crate) fn flip_comma(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist>
        return None;
    }
-    ctx.add_action(AssistId("flip_comma"), "flip comma", |edit| {
+    ctx.add_assist(AssistId("flip_comma"), "flip comma", |edit| {
        edit.target(comma.text_range());
        edit.replace(prev.text_range(), next.to_string());
        edit.replace(next.text_range(), prev.to_string());
-    });
+    })
-    ctx.build()
 }
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/flip_trait_bound.rs b/crates/ra_assists/src/assists/flip_trait_bound.rs
new file mode 100644
index 000000000..6017b39dd
--- /dev/null
+++ b/crates/ra_assists/src/assists/flip_trait_bound.rs
@@ -0,0 +1,117 @@
+use hir::db::HirDatabase;
+use ra_syntax::{
+    algo::non_trivia_sibling,
+    ast::{self, AstNode},
+    Direction, T,
+};
+use crate::{Assist, AssistCtx, AssistId};
+// Assist: flip_trait_bound
+//
+// Flips two trait bounds.
+//
+// ```
+// fn foo<T: Clone +<|> Copy>() { }
+// ```
+// ->
+// ```
+// fn foo<T: Copy + Clone>() { }
+// ```
+pub(crate) fn flip_trait_bound(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    // We want to replicate the behavior of `flip_binexpr` by only suggesting
+    // the assist when the cursor is on a `+`
+    let plus = ctx.find_token_at_offset(T![+])?;
+    // Make sure we're in a `TypeBoundList`
+    if ast::TypeBoundList::cast(plus.parent()).is_none() {
+        return None;
+    }
+    let (before, after) = (
+        non_trivia_sibling(plus.clone().into(), Direction::Prev)?,
+        non_trivia_sibling(plus.clone().into(), Direction::Next)?,
+    );
+    ctx.add_assist(AssistId("flip_trait_bound"), "flip trait bound", |edit| {
+        edit.target(plus.text_range());
+        edit.replace(before.text_range(), after.to_string());
+        edit.replace(after.text_range(), before.to_string());
+    })
+}
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    #[test]
+    fn flip_trait_bound_assist_available() {
+        check_assist_target(flip_trait_bound, "struct S<T> where T: A <|>+ B + C { }", "+")
+    }
+    #[test]
+    fn flip_trait_bound_not_applicable_for_single_trait_bound() {
+        check_assist_not_applicable(flip_trait_bound, "struct S<T> where T: <|>A { }")
+    }
+    #[test]
+    fn flip_trait_bound_works_for_struct() {
+        check_assist(
+            flip_trait_bound,
+            "struct S<T> where T: A <|>+ B { }",
+            "struct S<T> where T: B <|>+ A { }",
+        )
+    }
+    #[test]
+    fn flip_trait_bound_works_for_trait_impl() {
+        check_assist(
+            flip_trait_bound,
+            "impl X for S<T> where T: A +<|> B { }",
+            "impl X for S<T> where T: B +<|> A { }",
+        )
+    }
+    #[test]
+    fn flip_trait_bound_works_for_fn() {
+        check_assist(flip_trait_bound, "fn f<T: A <|>+ B>(t: T) { }", "fn f<T: B <|>+ A>(t: T) { }")
+    }
+    #[test]
+    fn flip_trait_bound_works_for_fn_where_clause() {
+        check_assist(
+            flip_trait_bound,
+            "fn f<T>(t: T) where T: A +<|> B { }",
+            "fn f<T>(t: T) where T: B +<|> A { }",
+        )
+    }
+    #[test]
+    fn flip_trait_bound_works_for_lifetime() {
+        check_assist(
+            flip_trait_bound,
+            "fn f<T>(t: T) where T: A <|>+ 'static { }",
+            "fn f<T>(t: T) where T: 'static <|>+ A { }",
+        )
+    }
+    #[test]
+    fn flip_trait_bound_works_for_complex_bounds() {
+        check_assist(
+            flip_trait_bound,
+            "struct S<T> where T: A<T> <|>+ b_mod::B<T> + C<T> { }",
+            "struct S<T> where T: b_mod::B<T> <|>+ A<T> + C<T> { }",
+        )
+    }
+    #[test]
+    fn flip_trait_bound_works_for_long_bounds() {
+        check_assist(
+            flip_trait_bound,
+            "struct S<T> where T: A + B + C + D + E + F +<|> G + H + I + J { }",
+            "struct S<T> where T: A + B + C + D + E + G +<|> F + H + I + J { }",
+        )
+    }
+}
diff --git a/crates/ra_assists/src/assists/inline_local_variable.rs b/crates/ra_assists/src/assists/inline_local_variable.rs
index 9bd64decc..a7fd9b6d2 100644
--- a/crates/ra_assists/src/assists/inline_local_variable.rs
+++ b/crates/ra_assists/src/assists/inline_local_variable.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
 use hir::db::HirDatabase;
 use ra_syntax::{
    ast::{self, AstNode, AstToken},
@@ -9,8 +7,24 @@ use ra_syntax::{
 use crate::assist_ctx::AssistBuilder;
 use crate::{Assist, AssistCtx, AssistId};
-pub(crate) fn inline_local_varialbe(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: inline_local_variable
-    let let_stmt = ctx.node_at_offset::<ast::LetStmt>()?;
+//
+// Inlines local variable.
+//
+// ```
+// fn main() {
+//     let x<|> = 1 + 2;
+//     x * 4;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     (1 + 2) * 4;
+// }
+// ```
+pub(crate) fn inline_local_varialbe(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let let_stmt = ctx.find_node_at_offset::<ast::LetStmt>()?;
    let bind_pat = match let_stmt.pat()? {
        ast::Pat::BindPat(pat) => pat,
        _ => return None,
@@ -37,10 +51,8 @@ pub(crate) fn inline_local_varialbe(mut ctx: AssistCtx<impl HirDatabase>) -> Opt
    let mut wrap_in_parens = vec![true; refs.len()];
    for (i, desc) in refs.iter().enumerate() {
-        let usage_node = ctx
+        let usage_node =
-            .covering_node_for_range(desc.range)
+            ctx.covering_node_for_range(desc.range).ancestors().find_map(ast::PathExpr::cast)?;
-            .ancestors()
-            .find_map(|node| ast::PathExpr::cast(node))?;
        let usage_parent_option = usage_node.syntax().parent().and_then(ast::Expr::cast);
        let usage_parent = match usage_parent_option {
            Some(u) => u,
@@ -79,7 +91,7 @@ pub(crate) fn inline_local_varialbe(mut ctx: AssistCtx<impl HirDatabase>) -> Opt
    let init_str = initializer_expr.syntax().text().to_string();
    let init_in_paren = format!("({})", &init_str);
-    ctx.add_action(
+    ctx.add_assist(
        AssistId("inline_local_variable"),
        "inline local variable",
        move |edit: &mut AssistBuilder| {
@@ -93,9 +105,7 @@ pub(crate) fn inline_local_varialbe(mut ctx: AssistCtx<impl HirDatabase>) -> Opt
            }
            edit.set_cursor(delete_range.start())
        },
-    );
+    )
-    ctx.build()
 }
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/introduce_variable.rs b/crates/ra_assists/src/assists/introduce_variable.rs
index 43378c4b0..0623d4475 100644
--- a/crates/ra_assists/src/assists/introduce_variable.rs
+++ b/crates/ra_assists/src/assists/introduce_variable.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
 use format_buf::format;
 use hir::db::HirDatabase;
 use ra_syntax::{
@@ -14,7 +12,23 @@ use test_utils::tested_by;
 use crate::{Assist, AssistCtx, AssistId};
-pub(crate) fn introduce_variable(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: introduce_variable
+//
+// Extracts subexpression into a variable.
+//
+// ```
+// fn main() {
+//     <|>(1 + 2)<|> * 4;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     let var_name = (1 + 2);
+//     var_name * 4;
+// }
+// ```
+pub(crate) fn introduce_variable(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
    if ctx.frange.range.is_empty() {
        return None;
    }
@@ -29,7 +43,7 @@ pub(crate) fn introduce_variable(mut ctx: AssistCtx<impl HirDatabase>) -> Option
    if indent.kind() != WHITESPACE {
        return None;
    }
-    ctx.add_action(AssistId("introduce_variable"), "introduce variable", move |edit| {
+    ctx.add_assist(AssistId("introduce_variable"), "introduce variable", move |edit| {
        let mut buf = String::new();
        let cursor_offset = if wrap_in_block {
@@ -74,9 +88,7 @@ pub(crate) fn introduce_variable(mut ctx: AssistCtx<impl HirDatabase>) -> Option
            }
        }
        edit.set_cursor(anchor_stmt.text_range().start() + cursor_offset);
-    });
+    })
-    ctx.build()
 }
 /// Check whether the node is a valid expression which can be extracted to a variable.
diff --git a/crates/ra_assists/src/assists/merge_match_arms.rs b/crates/ra_assists/src/assists/merge_match_arms.rs
index 17baa98f9..e9f2cae91 100644
--- a/crates/ra_assists/src/assists/merge_match_arms.rs
+++ b/crates/ra_assists/src/assists/merge_match_arms.rs
@@ -1,11 +1,33 @@
-//! FIXME: write short doc here
 use crate::{Assist, AssistCtx, AssistId, TextRange, TextUnit};
 use hir::db::HirDatabase;
 use ra_syntax::ast::{AstNode, MatchArm};
-pub(crate) fn merge_match_arms(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: merge_match_arms
-    let current_arm = ctx.node_at_offset::<MatchArm>()?;
+//
+// Merges identical match arms.
+//
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         <|>Action::Move(..) => foo(),
+//         Action::Stop => foo(),
+//     }
+// }
+// ```
+// ->
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move(..) | Action::Stop => foo(),
+//     }
+// }
+// ```
+pub(crate) fn merge_match_arms(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let current_arm = ctx.find_node_at_offset::<MatchArm>()?;
    // We check if the following match arm matches this one. We could, but don't,
    // compare to the previous match arm as well.
@@ -30,7 +52,7 @@ pub(crate) fn merge_match_arms(mut ctx: AssistCtx<impl HirDatabase>) -> Option<A
    let cursor_to_end = current_arm.syntax().text_range().end() - ctx.frange.range.start();
-    ctx.add_action(AssistId("merge_match_arms"), "merge match arms", |edit| {
+    ctx.add_assist(AssistId("merge_match_arms"), "merge match arms", |edit| {
        fn contains_placeholder(a: &MatchArm) -> bool {
            a.pats().any(|x| match x {
                ra_syntax::ast::Pat::PlaceholderPat(..) => true,
@@ -58,9 +80,7 @@ pub(crate) fn merge_match_arms(mut ctx: AssistCtx<impl HirDatabase>) -> Option<A
        edit.target(current_arm.syntax().text_range());
        edit.replace(TextRange::from_to(start, end), arm);
        edit.set_cursor(start + offset);
-    });
+    })
-    ctx.build()
 }
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/move_bounds.rs b/crates/ra_assists/src/assists/move_bounds.rs
index d2444b6b9..3145d7625 100644
--- a/crates/ra_assists/src/assists/move_bounds.rs
+++ b/crates/ra_assists/src/assists/move_bounds.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
 use hir::db::HirDatabase;
 use ra_syntax::{
    ast::{self, edit, make, AstNode, NameOwner, TypeBoundsOwner},
@@ -9,8 +7,23 @@ use ra_syntax::{
 use crate::{Assist, AssistCtx, AssistId};
-pub(crate) fn move_bounds_to_where_clause(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: move_bounds_to_where_clause
-    let type_param_list = ctx.node_at_offset::<ast::TypeParamList>()?;
+//
+// Moves inline type bounds to a where clause.
+//
+// ```
+// fn apply<T, U, <|>F: FnOnce(T) -> U>(f: F, x: T) -> U {
+//     f(x)
+// }
+// ```
+// ->
+// ```
+// fn apply<T, U, F>(f: F, x: T) -> U where F: FnOnce(T) -> U {
+//     f(x)
+// }
+// ```
+pub(crate) fn move_bounds_to_where_clause(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let type_param_list = ctx.find_node_at_offset::<ast::TypeParamList>()?;
    let mut type_params = type_param_list.type_params();
    if type_params.all(|p| p.type_bound_list().is_none()) {
@@ -33,38 +46,30 @@ pub(crate) fn move_bounds_to_where_clause(mut ctx: AssistCtx<impl HirDatabase>)
        _ => return None,
    };
-    ctx.add_action(
+    ctx.add_assist(AssistId("move_bounds_to_where_clause"), "move_bounds_to_where_clause", |edit| {
-        AssistId("move_bounds_to_where_clause"),
+        let new_params = type_param_list
-        "move_bounds_to_where_clause",
+            .type_params()
-        |edit| {
+            .filter(|it| it.type_bound_list().is_some())
-            let new_params = type_param_list
+            .map(|type_param| {
-                .type_params()
+                let without_bounds = type_param.remove_bounds();
-                .filter(|it| it.type_bound_list().is_some())
+                (type_param, without_bounds)
-                .map(|type_param| {
+            });
-                    let without_bounds = type_param.remove_bounds();
-                    (type_param, without_bounds)
+        let new_type_param_list = edit::replace_descendants(&type_param_list, new_params);
-                });
+        edit.replace_ast(type_param_list.clone(), new_type_param_list);
-            let new_type_param_list = edit::replace_descendants(&type_param_list, new_params);
+        let where_clause = {
-            edit.replace_ast(type_param_list.clone(), new_type_param_list);
+            let predicates = type_param_list.type_params().filter_map(build_predicate);
+            make::where_clause(predicates)
-            let where_clause = {
+        };
-                let predicates = type_param_list.type_params().filter_map(build_predicate);
-                make::where_clause(predicates)
+        let to_insert = match anchor.prev_sibling_or_token() {
-            };
+            Some(ref elem) if elem.kind() == WHITESPACE => format!("{} ", where_clause.syntax()),
+            _ => format!(" {}", where_clause.syntax()),
-            let to_insert = match anchor.prev_sibling_or_token() {
+        };
-                Some(ref elem) if elem.kind() == WHITESPACE => {
+        edit.insert(anchor.text_range().start(), to_insert);
-                    format!("{} ", where_clause.syntax())
+        edit.target(type_param_list.syntax().text_range());
-                }
+    })
-                _ => format!(" {}", where_clause.syntax()),
-            };
-            edit.insert(anchor.text_range().start(), to_insert);
-            edit.target(type_param_list.syntax().text_range());
-        },
-    );
-    ctx.build()
 }
 fn build_predicate(param: ast::TypeParam) -> Option<ast::WherePred> {
diff --git a/crates/ra_assists/src/assists/move_guard.rs b/crates/ra_assists/src/assists/move_guard.rs
index 51aea6334..b49ec6172 100644
--- a/crates/ra_assists/src/assists/move_guard.rs
+++ b/crates/ra_assists/src/assists/move_guard.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
 use hir::db::HirDatabase;
 use ra_syntax::{
    ast,
@@ -9,8 +7,33 @@ use ra_syntax::{
 use crate::{Assist, AssistCtx, AssistId};
-pub(crate) fn move_guard_to_arm_body(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: move_guard_to_arm_body
-    let match_arm = ctx.node_at_offset::<MatchArm>()?;
+//
+// Moves match guard into match arm body.
+//
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } <|>if distance > 10 => foo(),
+//         _ => (),
+//     }
+// }
+// ```
+// ->
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } => if distance > 10 { foo() },
+//         _ => (),
+//     }
+// }
+// ```
+pub(crate) fn move_guard_to_arm_body(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let match_arm = ctx.find_node_at_offset::<MatchArm>()?;
    let guard = match_arm.guard()?;
    let space_before_guard = guard.syntax().prev_sibling_or_token();
@@ -18,7 +41,7 @@ pub(crate) fn move_guard_to_arm_body(mut ctx: AssistCtx<impl HirDatabase>) -> Op
    let arm_expr = match_arm.expr()?;
    let buf = format!("if {} {{ {} }}", guard_conditions.syntax().text(), arm_expr.syntax().text());
-    ctx.add_action(AssistId("move_guard_to_arm_body"), "move guard to arm body", |edit| {
+    ctx.add_assist(AssistId("move_guard_to_arm_body"), "move guard to arm body", |edit| {
        edit.target(guard.syntax().text_range());
        let offseting_amount = match space_before_guard.and_then(|it| it.into_token()) {
            Some(tok) => {
@@ -38,12 +61,36 @@ pub(crate) fn move_guard_to_arm_body(mut ctx: AssistCtx<impl HirDatabase>) -> Op
        edit.set_cursor(
            arm_expr.syntax().text_range().start() + TextUnit::from(3) - offseting_amount,
        );
-    });
+    })
-    ctx.build()
 }
-pub(crate) fn move_arm_cond_to_match_guard(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: move_arm_cond_to_match_guard
-    let match_arm: MatchArm = ctx.node_at_offset::<MatchArm>()?;
+//
+// Moves if expression from match arm body into a guard.
+//
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } => <|>if distance > 10 { foo() },
+//         _ => (),
+//     }
+// }
+// ```
+// ->
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } if distance > 10 => foo(),
+//         _ => (),
+//     }
+// }
+// ```
+pub(crate) fn move_arm_cond_to_match_guard(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let match_arm: MatchArm = ctx.find_node_at_offset::<MatchArm>()?;
    let last_match_pat = match_arm.pats().last()?;
    let arm_body = match_arm.expr()?;
@@ -62,7 +109,7 @@ pub(crate) fn move_arm_cond_to_match_guard(mut ctx: AssistCtx<impl HirDatabase>)
    let buf = format!(" if {}", cond.syntax().text());
-    ctx.add_action(
+    ctx.add_assist(
        AssistId("move_arm_cond_to_match_guard"),
        "move condition to match guard",
        |edit| {
@@ -79,8 +126,7 @@ pub(crate) fn move_arm_cond_to_match_guard(mut ctx: AssistCtx<impl HirDatabase>)
            edit.insert(last_match_pat.syntax().text_range().end(), buf);
            edit.set_cursor(last_match_pat.syntax().text_range().end() + TextUnit::from(1));
        },
-    );
+    )
-    ctx.build()
 }
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/raw_string.rs b/crates/ra_assists/src/assists/raw_string.rs
index 2d2e31e51..58f7157ae 100644
--- a/crates/ra_assists/src/assists/raw_string.rs
+++ b/crates/ra_assists/src/assists/raw_string.rs
@@ -1,17 +1,29 @@
-//! FIXME: write short doc here
 use hir::db::HirDatabase;
-use ra_syntax::{ast::AstNode, ast::Literal, TextRange, TextUnit};
+use ra_syntax::{
+    SyntaxKind::{RAW_STRING, STRING},
+    TextRange, TextUnit,
+};
 use rustc_lexer;
 use crate::{Assist, AssistCtx, AssistId};
-pub(crate) fn make_raw_string(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: make_raw_string
-    let literal = ctx.node_at_offset::<Literal>()?;
+//
-    if literal.token().kind() != ra_syntax::SyntaxKind::STRING {
+// Adds `r#` to a plain string literal.
-        return None;
+//
-    }
+// ```
-    let token = literal.token();
+// fn main() {
+//     "Hello,<|> World!";
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     r#"Hello, World!"#;
+// }
+// ```
+pub(crate) fn make_raw_string(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let token = ctx.find_token_at_offset(STRING)?;
    let text = token.text().as_str();
    let usual_string_range = find_usual_string_range(text)?;
    let start_of_inside = usual_string_range.start().to_usize() + 1;
@@ -29,97 +41,131 @@ pub(crate) fn make_raw_string(mut ctx: AssistCtx<impl HirDatabase>) -> Option<As
    if error.is_err() {
        return None;
    }
-    ctx.add_action(AssistId("make_raw_string"), "make raw string", |edit| {
+    ctx.add_assist(AssistId("make_raw_string"), "make raw string", |edit| {
-        edit.target(literal.syntax().text_range());
+        edit.target(token.text_range());
        let max_hash_streak = count_hashes(&unescaped);
        let mut hashes = String::with_capacity(max_hash_streak + 1);
        for _ in 0..hashes.capacity() {
            hashes.push('#');
        }
-        edit.replace(
+        edit.replace(token.text_range(), format!("r{}\"{}\"{}", hashes, unescaped, hashes));
-            literal.syntax().text_range(),
+    })
-            format!("r{}\"{}\"{}", hashes, unescaped, hashes),
-        );
-    });
-    ctx.build()
-}
-fn count_hashes(s: &str) -> usize {
-    let mut max_hash_streak = 0usize;
-    for idx in s.match_indices("\"#").map(|(i, _)| i) {
-        let (_, sub) = s.split_at(idx + 1);
-        let nb_hash = sub.chars().take_while(|c| *c == '#').count();
-        if nb_hash > max_hash_streak {
-            max_hash_streak = nb_hash;
-        }
-    }
-    max_hash_streak
-}
-fn find_usual_string_range(s: &str) -> Option<TextRange> {
-    Some(TextRange::from_to(
-        TextUnit::from(s.find('"')? as u32),
-        TextUnit::from(s.rfind('"')? as u32),
-    ))
 }
-pub(crate) fn make_usual_string(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: make_usual_string
-    let literal = ctx.node_at_offset::<Literal>()?;
+//
-    if literal.token().kind() != ra_syntax::SyntaxKind::RAW_STRING {
+// Turns a raw string into a plain string.
-        return None;
+//
-    }
+// ```
-    let token = literal.token();
+// fn main() {
+//     r#"Hello,<|> "World!""#;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     "Hello, \"World!\"";
+// }
+// ```
+pub(crate) fn make_usual_string(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let token = ctx.find_token_at_offset(RAW_STRING)?;
    let text = token.text().as_str();
    let usual_string_range = find_usual_string_range(text)?;
-    ctx.add_action(AssistId("make_usual_string"), "make usual string", |edit| {
+    ctx.add_assist(AssistId("make_usual_string"), "make usual string", |edit| {
-        edit.target(literal.syntax().text_range());
+        edit.target(token.text_range());
        // parse inside string to escape `"`
        let start_of_inside = usual_string_range.start().to_usize() + 1;
        let end_of_inside = usual_string_range.end().to_usize();
        let inside_str = &text[start_of_inside..end_of_inside];
        let escaped = inside_str.escape_default().to_string();
-        edit.replace(literal.syntax().text_range(), format!("\"{}\"", escaped));
+        edit.replace(token.text_range(), format!("\"{}\"", escaped));
-    });
+    })
-    ctx.build()
 }
-pub(crate) fn add_hash(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: add_hash
-    let literal = ctx.node_at_offset::<Literal>()?;
+//
-    if literal.token().kind() != ra_syntax::SyntaxKind::RAW_STRING {
+// Adds a hash to a raw string literal.
-        return None;
+//
-    }
+// ```
-    ctx.add_action(AssistId("add_hash"), "add hash to raw string", |edit| {
+// fn main() {
-        edit.target(literal.syntax().text_range());
+//     r#"Hello,<|> World!"#;
-        edit.insert(literal.syntax().text_range().start() + TextUnit::of_char('r'), "#");
+// }
-        edit.insert(literal.syntax().text_range().end(), "#");
+// ```
-    });
+// ->
-    ctx.build()
+// ```
+// fn main() {
+//     r##"Hello, World!"##;
+// }
+// ```
+pub(crate) fn add_hash(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let token = ctx.find_token_at_offset(RAW_STRING)?;
+    ctx.add_assist(AssistId("add_hash"), "add hash to raw string", |edit| {
+        edit.target(token.text_range());
+        edit.insert(token.text_range().start() + TextUnit::of_char('r'), "#");
+        edit.insert(token.text_range().end(), "#");
+    })
 }
-pub(crate) fn remove_hash(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: remove_hash
-    let literal = ctx.node_at_offset::<Literal>()?;
+//
-    if literal.token().kind() != ra_syntax::SyntaxKind::RAW_STRING {
+// Removes a hash from a raw string literal.
-        return None;
+//
-    }
+// ```
-    let token = literal.token();
+// fn main() {
+//     r#"Hello,<|> World!"#;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     r"Hello, World!";
+// }
+// ```
+pub(crate) fn remove_hash(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let token = ctx.find_token_at_offset(RAW_STRING)?;
    let text = token.text().as_str();
    if text.starts_with("r\"") {
        // no hash to remove
        return None;
    }
-    ctx.add_action(AssistId("remove_hash"), "remove hash from raw string", |edit| {
+    ctx.add_assist(AssistId("remove_hash"), "remove hash from raw string", |edit| {
-        edit.target(literal.syntax().text_range());
+        edit.target(token.text_range());
        let result = &text[2..text.len() - 1];
-        let result = if result.starts_with("\"") {
+        let result = if result.starts_with('\"') {
            // no more hash, escape
            let internal_str = &result[1..result.len() - 1];
            format!("\"{}\"", internal_str.escape_default().to_string())
        } else {
            result.to_owned()
        };
-        edit.replace(literal.syntax().text_range(), format!("r{}", result));
+        edit.replace(token.text_range(), format!("r{}", result));
-    });
+    })
-    ctx.build()
+}
+fn count_hashes(s: &str) -> usize {
+    let mut max_hash_streak = 0usize;
+    for idx in s.match_indices("\"#").map(|(i, _)| i) {
+        let (_, sub) = s.split_at(idx + 1);
+        let nb_hash = sub.chars().take_while(|c| *c == '#').count();
+        if nb_hash > max_hash_streak {
+            max_hash_streak = nb_hash;
+        }
+    }
+    max_hash_streak
+}
+fn find_usual_string_range(s: &str) -> Option<TextRange> {
+    let left_quote = s.find('"')?;
+    let right_quote = s.rfind('"')?;
+    if left_quote == right_quote {
+        // `s` only contains one quote
+        None
+    } else {
+        Some(TextRange::from_to(
+            TextUnit::from(left_quote as u32),
+            TextUnit::from(right_quote as u32),
+        ))
+    }
 }
 #[cfg(test)]
@@ -159,6 +205,23 @@ string"#;
    }
    #[test]
+    fn make_raw_string_works_inside_macros() {
+        check_assist(
+            make_raw_string,
+            r#"
+            fn f() {
+                format!(<|>"x = {}", 92)
+            }
+            "#,
+            r##"
+            fn f() {
+                format!(<|>r#"x = {}"#, 92)
+            }
+            "##,
+        )
+    }
+    #[test]
    fn make_raw_string_hashes_inside_works() {
        check_assist(
            make_raw_string,
@@ -212,6 +275,30 @@ string"###;
    }
    #[test]
+    fn make_raw_string_not_works_on_partial_string() {
+        check_assist_not_applicable(
+            make_raw_string,
+            r#"
+            fn f() {
+                let s = "foo<|>
+            }
+            "#,
+        )
+    }
+    #[test]
+    fn make_usual_string_not_works_on_partial_string() {
+        check_assist_not_applicable(
+            make_usual_string,
+            r#"
+            fn main() {
+                let s = r#"bar<|>
+            }
+            "#,
+        )
+    }
+    #[test]
    fn add_hash_target() {
        check_assist_target(
            add_hash,
diff --git a/crates/ra_assists/src/assists/remove_dbg.rs b/crates/ra_assists/src/assists/remove_dbg.rs
index 1a7e2b305..aedf8747f 100644
--- a/crates/ra_assists/src/assists/remove_dbg.rs
+++ b/crates/ra_assists/src/assists/remove_dbg.rs
@@ -1,14 +1,28 @@
-//! FIXME: write short doc here
-use crate::{Assist, AssistCtx, AssistId};
 use hir::db::HirDatabase;
 use ra_syntax::{
    ast::{self, AstNode},
    TextUnit, T,
 };
-pub(crate) fn remove_dbg(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+use crate::{Assist, AssistCtx, AssistId};
-    let macro_call = ctx.node_at_offset::<ast::MacroCall>()?;
+// Assist: remove_dbg
+//
+// Removes `dbg!()` macro call.
+//
+// ```
+// fn main() {
+//     <|>dbg!(92);
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     92;
+// }
+// ```
+pub(crate) fn remove_dbg(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let macro_call = ctx.find_node_at_offset::<ast::MacroCall>()?;
    if !is_valid_macrocall(&macro_call, "dbg")? {
        return None;
@@ -44,13 +58,11 @@ pub(crate) fn remove_dbg(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist>
        text.slice(without_parens).to_string()
    };
-    ctx.add_action(AssistId("remove_dbg"), "remove dbg!()", |edit| {
+    ctx.add_assist(AssistId("remove_dbg"), "remove dbg!()", |edit| {
        edit.target(macro_call.syntax().text_range());
        edit.replace(macro_range, macro_content);
        edit.set_cursor(cursor_pos);
-    });
+    })
-    ctx.build()
 }
 /// Verifies that the given macro_call actually matches the given name
diff --git a/crates/ra_assists/src/assists/replace_if_let_with_match.rs b/crates/ra_assists/src/assists/replace_if_let_with_match.rs
index 749ff338a..dff84d865 100644
--- a/crates/ra_assists/src/assists/replace_if_let_with_match.rs
+++ b/crates/ra_assists/src/assists/replace_if_let_with_match.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
 use format_buf::format;
 use hir::db::HirDatabase;
 use ra_fmt::extract_trivial_expression;
@@ -7,8 +5,34 @@ use ra_syntax::{ast, AstNode};
 use crate::{Assist, AssistCtx, AssistId};
-pub(crate) fn replace_if_let_with_match(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: replace_if_let_with_match
-    let if_expr: ast::IfExpr = ctx.node_at_offset()?;
+//
+// Replaces `if let` with an else branch with a `match` expression.
+//
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     <|>if let Action::Move { distance } = action {
+//         foo(distance)
+//     } else {
+//         bar()
+//     }
+// }
+// ```
+// ->
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } => foo(distance),
+//         _ => bar(),
+//     }
+// }
+// ```
+pub(crate) fn replace_if_let_with_match(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let if_expr: ast::IfExpr = ctx.find_node_at_offset()?;
    let cond = if_expr.condition()?;
    let pat = cond.pat()?;
    let expr = cond.expr()?;
@@ -18,14 +42,12 @@ pub(crate) fn replace_if_let_with_match(mut ctx: AssistCtx<impl HirDatabase>) ->
        ast::ElseBranch::IfExpr(_) => return None,
    };
-    ctx.add_action(AssistId("replace_if_let_with_match"), "replace with match", |edit| {
+    ctx.add_assist(AssistId("replace_if_let_with_match"), "replace with match", |edit| {
        let match_expr = build_match_expr(expr, pat, then_block, else_block);
        edit.target(if_expr.syntax().text_range());
        edit.replace_node_and_indent(if_expr.syntax(), match_expr);
        edit.set_cursor(if_expr.syntax().text_range().start())
-    });
+    })
-    ctx.build()
 }
 fn build_match_expr(
diff --git a/crates/ra_assists/src/assists/split_import.rs b/crates/ra_assists/src/assists/split_import.rs
index fe3e64af5..5f8d6b0be 100644
--- a/crates/ra_assists/src/assists/split_import.rs
+++ b/crates/ra_assists/src/assists/split_import.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
 use std::iter::successors;
 use hir::db::HirDatabase;
@@ -7,8 +5,19 @@ use ra_syntax::{ast, AstNode, TextUnit, T};
 use crate::{Assist, AssistCtx, AssistId};
-pub(crate) fn split_import(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+// Assist: split_import
-    let colon_colon = ctx.token_at_offset().find(|leaf| leaf.kind() == T![::])?;
+//
+// Wraps the tail of import into braces.
+//
+// ```
+// use std::<|>collections::HashMap;
+// ```
+// ->
+// ```
+// use std::{collections::HashMap};
+// ```
+pub(crate) fn split_import(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let colon_colon = ctx.find_token_at_offset(T![::])?;
    let path = ast::Path::cast(colon_colon.parent())?;
    let top_path = successors(Some(path), |it| it.parent_path()).last()?;
@@ -23,14 +32,12 @@ pub(crate) fn split_import(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assis
        None => top_path.syntax().text_range().end(),
    };
-    ctx.add_action(AssistId("split_import"), "split import", |edit| {
+    ctx.add_assist(AssistId("split_import"), "split import", |edit| {
        edit.target(colon_colon.text_range());
        edit.insert(l_curly, "{");
        edit.insert(r_curly, "}");
        edit.set_cursor(l_curly + TextUnit::of_str("{"));
-    });
+    })
-    ctx.build()
 }
 #[cfg(test)]
diff --git a/crates/ra_assists/src/doc_tests.rs b/crates/ra_assists/src/doc_tests.rs
new file mode 100644
index 000000000..6e1e3de84
--- /dev/null
+++ b/crates/ra_assists/src/doc_tests.rs
@@ -0,0 +1,34 @@
+//! Each assist definition has a special comment, which specifies docs and
+//! example.
+//!
+//! We collect all the example and write the as tests in this module.
+mod generated;
+use hir::mock::MockDatabase;
+use ra_db::FileRange;
+use test_utils::{assert_eq_text, extract_range_or_offset};
+fn check(assist_id: &str, before: &str, after: &str) {
+    let (selection, before) = extract_range_or_offset(before);
+    let (db, _source_root, file_id) = MockDatabase::with_single_file(&before);
+    let frange = FileRange { file_id, range: selection.into() };
+    let (_assist_id, action) = crate::assists(&db, frange)
+        .into_iter()
+        .find(|(id, _)| id.id.0 == assist_id)
+        .unwrap_or_else(|| {
+            panic!(
+                "\n\nAssist is not applicable: {}\nAvailable assists: {}",
+                assist_id,
+                crate::assists(&db, frange)
+                    .into_iter()
+                    .map(|(id, _)| id.id.0)
+                    .collect::<Vec<_>>()
+                    .join(", ")
+            )
+        });
+    let actual = action.edit.apply(&before);
+    assert_eq_text!(after, &actual);
+}
diff --git a/crates/ra_assists/src/doc_tests/generated.rs b/crates/ra_assists/src/doc_tests/generated.rs
new file mode 100644
index 000000000..1bee76f59
--- /dev/null
+++ b/crates/ra_assists/src/doc_tests/generated.rs
@@ -0,0 +1,526 @@
+//! Generated file, do not edit by hand, see `crate/ra_tools/src/codegen`
+use super::check;
+#[test]
+fn doctest_add_derive() {
+    check(
+        "add_derive",
+        r#####"
+struct Point {
+    x: u32,
+    y: u32,<|>
+}
+"#####,
+        r#####"
+#[derive()]
+struct Point {
+    x: u32,
+    y: u32,
+}
+"#####,
+    )
+}
+#[test]
+fn doctest_add_explicit_type() {
+    check(
+        "add_explicit_type",
+        r#####"
+fn main() {
+    let x<|> = 92;
+}
+"#####,
+        r#####"
+fn main() {
+    let x: i32 = 92;
+}
+"#####,
+    )
+}
+#[test]
+fn doctest_add_hash() {
+    check(
+        "add_hash",
+        r#####"
+fn main() {
+    r#"Hello,<|> World!"#;
+}
+"#####,
+        r#####"
+fn main() {
+    r##"Hello, World!"##;
+}
+"#####,
+    )
+}
+#[test]
+fn doctest_add_impl() {
+    check(
+        "add_impl",
+        r#####"
+struct Ctx<T: Clone> {
+     data: T,<|>
+}
+"#####,
+        r#####"
+struct Ctx<T: Clone> {
+     data: T,
+}
+impl<T: Clone> Ctx<T> {
+}
+"#####,
+    )
+}
+#[test]
+fn doctest_add_impl_default_members() {
+    check(
+        "add_impl_default_members",
+        r#####"
+trait T {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+impl T for () {
+    Type X = ();
+    fn foo(&self) {}<|>
+}
+"#####,
+        r#####"
+trait T {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+impl T for () {
+    Type X = ();
+    fn foo(&self) {}
+    fn bar(&self) {}
+}
+"#####,
+    )
+}
+#[test]
+fn doctest_add_impl_missing_members() {
+    check(
+        "add_impl_missing_members",
+        r#####"
+trait T {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+impl T for () {<|>
+}
+"#####,
+        r#####"
+trait T {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+impl T for () {
+    fn foo(&self) { unimplemented!() }
+}
+"#####,
+    )
+}
+#[test]
+fn doctest_add_import() {
+    check(
+        "add_import",
+        r#####"
+fn process(map: std::collections::<|>HashMap<String, String>) {}
+"#####,
+        r#####"
+use std::collections::HashMap;
+fn process(map: HashMap<String, String>) {}
+"#####,
+    )
+}
+#[test]
+fn doctest_apply_demorgan() {
+    check(
+        "apply_demorgan",
+        r#####"
+fn main() {
+    if x != 4 ||<|> !y {}
+}
+"#####,
+        r#####"
+fn main() {
+    if !(x == 4 && y) {}
+}
+"#####,
+    )
+}
+#[test]
+fn doctest_change_visibility() {
+    check(
+        "change_visibility",
+        r#####"
+<|>fn frobnicate() {}
+"#####,
+        r#####"
+pub(crate) fn frobnicate() {}
+"#####,
+    )
+}
+#[test]
+fn doctest_convert_to_guarded_return() {
+    check(
+        "convert_to_guarded_return",
+        r#####"
+fn main() {
+    <|>if cond {
+        foo();
+        bar();
+    }
+}
+"#####,
+        r#####"
+fn main() {
+    if !cond {
+        return;
+    }
+    foo();
+    bar();
+}
+"#####,
+    )
+}
+#[test]
+fn doctest_fill_match_arms() {
+    check(
+        "fill_match_arms",
+        r#####"
+enum Action { Move { distance: u32 }, Stop }
+fn handle(action: Action) {
+    match action {
+        <|>
+    }
+}
+"#####,
+        r#####"
+enum Action { Move { distance: u32 }, Stop }
+fn handle(action: Action) {
+    match action {
+        Action::Move { distance } => (),
+        Action::Stop => (),
+    }
+}
+"#####,
+    )
+}
+#[test]
+fn doctest_flip_binexpr() {
+    check(
+        "flip_binexpr",
+        r#####"
+fn main() {
+    let _ = 90 +<|> 2;
+}
+"#####,
+        r#####"
+fn main() {
+    let _ = 2 + 90;
+}
+"#####,
+    )
+}
+#[test]
+fn doctest_flip_comma() {
+    check(
+        "flip_comma",
+        r#####"
+fn main() {
+    ((1, 2),<|> (3, 4));
+}
+"#####,
+        r#####"
+fn main() {
+    ((3, 4), (1, 2));
+}
+"#####,
+    )
+}
+#[test]
+fn doctest_flip_trait_bound() {
+    check(