Merge remote-tracking branch 'upstream/master' into 503-hover-doc-links

1623 files changed, 130529 insertions, 128337 deletions

diff --git a/.cargo/config b/.cargo/config
index 560ab3075..f6b0b66bf 100644
--- a/.cargo/config
+++ b/.cargo/config
@@ -3,3 +3,6 @@ xtask = "run --package xtask --bin xtask --"
 install-ra = "run --package xtask --bin xtask -- install" # for backwards compat
 tq = "test -- -q"
 qt = "tq"
+
+[target.x86_64-pc-windows-msvc]
+linker = "rust-lld"
diff --git a/.gitattributes b/.gitattributes
index 4cd50e481..7c2f752d6 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,5 +1,5 @@
 * text=auto eol=lf
-crates/ra_syntax/test_data/** -text eof=LF
+crates/syntax/test_data/** -text eof=LF
 # Older git versions try to fix line endings on images, this prevents it.
 *.png binary
 *.jpg binary
diff --git a/.github/FUNDING.yml b/.github/FUNDING.yml
index d78a14e2c..73892ddaa 100644
--- a/.github/FUNDING.yml
+++ b/.github/FUNDING.yml
@@ -1,12 +1,2 @@
-# These are supported funding model platforms
-
-github: # Replace with up to 4 GitHub Sponsors-enabled usernames e.g., [user1, user2]
-patreon: # Replace with a single Patreon username
+github: rust-analyzer
 open_collective: rust-analyzer
-ko_fi: # Replace with a single Ko-fi username
-tidelift: # Replace with a single Tidelift platform-name/package-name e.g., npm/babel
-community_bridge: # Replace with a single Community Bridge project-name e.g., cloud-foundry
-liberapay: # Replace with a single Liberapay username
-issuehunt: # Replace with a single IssueHunt username
-otechie: # Replace with a single Otechie username
-custom: # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']
diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 2acd44012..fb077e28d 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -16,20 +16,6 @@ env:
   RUSTUP_MAX_RETRIES: 10
 
 jobs:
-  # rust-audit:
-  #   name: Audit Rust vulnerabilities
-  #   runs-on: ubuntu-latest
-  #   steps:
-  #   - name: Checkout repository
-  #     uses: actions/checkout@v2
-
-  #   - uses: actions-rs/[email protected]
-  #     with:
-  #       crate: cargo-audit
-  #       use-tool-cache: true
-
-  #   - run: cargo audit
-
   rust:
     name: Rust
     runs-on: ${{ matrix.os }}
@@ -84,15 +70,14 @@ jobs:
     - name: Prepare cache
       run: cargo xtask pre-cache
 
-    - name: Prepare cache 2
-      if: matrix.os == 'windows-latest'
-      run: Remove-Item ./target/debug/xtask.exe, ./target/debug/deps/xtask.exe
-
-  # Weird target to catch non-portable code
-  rust-power:
-    name: Rust Power
+  # Weird targets to catch non-portable code
+  rust-cross:
+    name: Rust Cross
     runs-on: ubuntu-latest
 
+    env:
+      targets: "powerpc-unknown-linux-gnu x86_64-unknown-linux-musl"
+
     steps:
     - name: Checkout repository
       uses: actions/checkout@v2
@@ -103,7 +88,9 @@ jobs:
         toolchain: stable
         profile: minimal
         override: true
-        target: 'powerpc-unknown-linux-gnu'
+
+    - name: Install Rust targets
+      run: rustup target add ${{ env.targets }}
 
     - name: Cache cargo directories
       uses: actions/cache@v2
@@ -114,14 +101,17 @@ jobs:
         key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
 
     - name: Check
-      run: cargo check --target=powerpc-unknown-linux-gnu --all-targets
+      run: |
+        for target in ${{ env.targets }}; do
+          cargo check --target=$target --all-targets
+        done
 
   typescript:
     name: TypeScript
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, windows-latest, macos-latest]
+        os: [ubuntu-latest, windows-latest]
 
     runs-on: ${{ matrix.os }}
 
diff --git a/Cargo.lock b/Cargo.lock
index 08d122e77..1f8e7a29d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -16,15 +16,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ee2a4ec343196209d6594e19543ae87a39f96d5534d7174822a3ad825dd6ed7e"
 
 [[package]]
-name = "aho-corasick"
-version = "0.7.13"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "043164d8ba5c4c3035fec9bbee8647c0261d788f3474306f93bb65901cae0e86"
-dependencies = [
- "memchr",
-]
-
-[[package]]
 name = "ansi_term"
 version = "0.12.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -46,12 +37,33 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "33954243bd79057c2de7338850b85983a44588021f8a5fee574a8888c6de4344"
 
 [[package]]
+name = "arena"
+version = "0.0.0"
+
+[[package]]
 name = "arrayvec"
 version = "0.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cff77d8686867eceff3105329d4698d96c2391c176d5d03adc90c7389162b5b8"
 
 [[package]]
+name = "assists"
+version = "0.0.0"
+dependencies = [
+ "base_db",
+ "either",
+ "hir",
+ "ide_db",
+ "itertools",
+ "profile",
+ "rustc-hash",
+ "stdx",
+ "syntax",
+ "test_utils",
+ "text_edit",
+]
+
+[[package]]
 name = "atty"
 version = "0.2.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -64,9 +76,9 @@ dependencies = [
 
 [[package]]
 name = "autocfg"
-version = "1.0.0"
+version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f8aac770f1885fd7e387acedd76065302551364496e46b3dd00860b2f8359b9d"
+checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
 
 [[package]]
 name = "backtrace"
@@ -89,6 +101,21 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3441f0f7b02788e948e47f457ca01f1d7e6d92c693bc132c22b087d3141c03ff"
 
 [[package]]
+name = "base_db"
+version = "0.0.0"
+dependencies = [
+ "cfg",
+ "profile",
+ "rustc-hash",
+ "salsa",
+ "stdx",
+ "syntax",
+ "test_utils",
+ "tt",
+ "vfs",
+]
+
+[[package]]
 name = "bitflags"
 version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -113,9 +140,19 @@ dependencies = [
 
 [[package]]
 name = "cc"
-version = "1.0.58"
+version = "1.0.59"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f9a06fb2e53271d7c279ec1efea6ab691c35a2ae67ec0d91d7acec0caf13b518"
+checksum = "66120af515773fb005778dc07c261bd201ec8ce50bd6e7144c927753fe013381"
+
+[[package]]
+name = "cfg"
+version = "0.0.0"
+dependencies = [
+ "mbe",
+ "rustc-hash",
+ "syntax",
+ "tt",
+]
 
 [[package]]
 name = "cfg-if"
@@ -125,9 +162,9 @@ checksum = "4785bdd1c96b2a846b2bd7cc02e86b6b3dbf14e7e53446c4f54c92a361040822"
 
 [[package]]
 name = "chalk-derive"
-version = "0.19.0"
+version = "0.23.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "654c611946ba2629c5028cb7708687af975faf2c29d731824cb294c873df4697"
+checksum = "c3cb438e961fd7f1183dc5e0bdcfd09253bf9b90592cf665d1ce6787d8a4908f"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -137,9 +174,9 @@ dependencies = [
 
 [[package]]
 name = "chalk-ir"
-version = "0.19.0"
+version = "0.23.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0a5341fbc654ca886b73b804a36aebf0e621057ccc1a68e9815b5b39b3ac9ae8"
+checksum = "bb332abfcb015b148c6fbab39b1d13282745b0f7f312019dd8e138f5f3f0855d"
 dependencies = [
  "chalk-derive",
  "lazy_static",
@@ -147,9 +184,9 @@ dependencies = [
 
 [[package]]
 name = "chalk-recursive"
-version = "0.19.0"
+version = "0.23.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4484807b155b5a411e6135d330295f9ba5042e2920b8712c6574ca6ea91e9ee5"
+checksum = "e7c7673f10c5fa1acf7fa07d4f4c5917cbcf161ed3a952d14530c79950de32d2"
 dependencies = [
  "chalk-derive",
  "chalk-ir",
@@ -160,9 +197,9 @@ dependencies = [
 
 [[package]]
 name = "chalk-solve"
-version = "0.19.0"
+version = "0.23.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "281f82facd2538997fbe52132b1941ed213d266748215c31d15f62a8664429ad"
+checksum = "802de4eff72e5a5d2828e6c07224c74d66949dc6308aff025d0ae2871a11b4eb"
 dependencies = [
  "chalk-derive",
  "chalk-ir",
@@ -177,9 +214,9 @@ dependencies = [
 
 [[package]]
 name = "chrono"
-version = "0.4.13"
+version = "0.4.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c74d84029116787153e02106bf53e66828452a4b325cc8652b788b5967c0a0b6"
+checksum = "942f72db697d8767c22d46a598e01f2d3b475501ea43d0db4f16d90259182d0b"
 dependencies = [
  "num-integer",
  "num-traits",
@@ -279,15 +316,15 @@ checksum = "524cbf6897b527295dff137cec09ecf3a05f4fddffd7dfcd1585403449e74198"
 
 [[package]]
 name = "drop_bomb"
-version = "0.1.4"
+version = "0.1.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "69b26e475fd29098530e709294e94e661974c851aed42512793f120fed4e199f"
+checksum = "9bda8e21c04aca2ae33ffc2fd8c23134f3cac46db123ba97bd9d3f3b8a4a85e1"
 
 [[package]]
 name = "either"
-version = "1.5.3"
+version = "1.6.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bb1f6b1ce1c140482ea30ddd3335fc0024ac7ee112895426e0a629a6c20adfe3"
+checksum = "cd56b59865bce947ac5958779cfa508f6c3b9497cc762b7e24a12d11ccde2c4f"
 
 [[package]]
 name = "ena"
@@ -308,19 +345,20 @@ dependencies = [
 ]
 
 [[package]]
-name = "expect"
+name = "expect-test"
 version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a3e383741ea1982866572109d1a8c807bd36aad91fca701489fdca56ef92b3b8"
 dependencies = [
  "difference",
  "once_cell",
- "stdx",
 ]
 
 [[package]]
 name = "filetime"
-version = "0.2.11"
+version = "0.2.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e500da2fab70bdc43f8f0e0b350a227f31c72311c56aba48f01d5cd62bb0345b"
+checksum = "3ed85775dcc68644b5c950ac06a2b23768d3bc9390464151aaf27136998dcf9e"
 dependencies = [
  "cfg-if",
  "libc",
@@ -336,9 +374,9 @@ checksum = "37ab347416e802de484e4d03c7316c48f1ecb56574dfd4a46a80f173ce1de04d"
 
 [[package]]
 name = "flate2"
-version = "1.0.16"
+version = "1.0.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "68c90b0fc46cf89d227cc78b40e494ff81287a92dd07631e5af0d06fe3cf885e"
+checksum = "766d0e77a2c1502169d4a93ff3b8c15a71fd946cd0126309752104e5f3c46d94"
 dependencies = [
  "cfg-if",
  "crc32fast",
@@ -348,14 +386,14 @@ dependencies = [
 
 [[package]]
 name = "flycheck"
-version = "0.1.0"
+version = "0.0.0"
 dependencies = [
  "cargo_metadata",
  "crossbeam-channel",
  "jod-thread",
  "log",
- "ra_toolchain",
  "serde_json",
+ "toolchain",
 ]
 
 [[package]]
@@ -418,9 +456,9 @@ dependencies = [
 
 [[package]]
 name = "hashbrown"
-version = "0.8.1"
+version = "0.8.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "34f595585f103464d8d2f6e9864682d74c1601fed5e07d62b1c9058dba8246fb"
+checksum = "e91b62f79061a0bc2e046024cb7ba44b08419ed238ecbd9adbd787434b9e8c25"
 dependencies = [
  "autocfg",
 ]
@@ -444,6 +482,98 @@ dependencies = [
 ]
 
 [[package]]
+name = "hir"
+version = "0.0.0"
+dependencies = [
+ "arrayvec",
+ "base_db",
+ "either",
+ "hir_def",
+ "hir_expand",
+ "hir_ty",
+ "itertools",
+ "log",
+ "profile",
+ "rustc-hash",
+ "stdx",
+ "syntax",
+ "tt",
+ "url",
+]
+
+[[package]]
+name = "hir_def"
+version = "0.0.0"
+dependencies = [
+ "anymap",
+ "arena",
+ "base_db",
+ "cfg",
+ "drop_bomb",
+ "either",
+ "expect-test",
+ "fst",
+ "hir_expand",
+ "indexmap",
+ "itertools",
+ "log",
+ "mbe",
+ "once_cell",
+ "profile",
+ "rustc-hash",
+ "smallvec",
+ "stdx",
+ "syntax",
+ "test_utils",
+ "tt",
+]
+
+[[package]]
+name = "hir_expand"
+version = "0.0.0"
+dependencies = [
+ "arena",
+ "base_db",
+ "either",
+ "log",
+ "mbe",
+ "parser",
+ "profile",
+ "rustc-hash",
+ "syntax",
+ "test_utils",
+ "tt",
+]
+
+[[package]]
+name = "hir_ty"
+version = "0.0.0"
+dependencies = [
+ "arena",
+ "arrayvec",
+ "base_db",
+ "chalk-ir",
+ "chalk-recursive",
+ "chalk-solve",
+ "ena",
+ "expect-test",
+ "hir_def",
+ "hir_expand",
+ "itertools",
+ "log",
+ "profile",
+ "rustc-hash",
+ "scoped-tls",
+ "smallvec",
+ "stdx",
+ "syntax",
+ "test_utils",
+ "tracing",
+ "tracing-subscriber",
+ "tracing-tree",
+]
+
+[[package]]
 name = "home"
 version = "0.5.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -453,6 +583,51 @@ dependencies = [
 ]
 
 [[package]]
+name = "ide"
+version = "0.0.0"
+dependencies = [
+ "assists",
+ "base_db",
+ "cfg",
+ "either",
+ "expect-test",
+ "hir",
+ "ide_db",
+ "indexmap",
+ "itertools",
+ "log",
+ "oorandom",
+ "profile",
+ "pulldown-cmark",
+ "pulldown-cmark-to-cmark",
+ "rustc-hash",
+ "ssr",
+ "stdx",
+ "syntax",
+ "test_utils",
+ "text_edit",
+]
+
+[[package]]
+name = "ide_db"
+version = "0.0.0"
+dependencies = [
+ "base_db",
+ "either",
+ "fst",
+ "hir",
+ "log",
+ "once_cell",
+ "profile",
+ "rayon",
+ "rustc-hash",
+ "stdx",
+ "syntax",
+ "test_utils",
+ "text_edit",
+]
+
+[[package]]
 name = "idna"
 version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -465,9 +640,9 @@ dependencies = [
 
 [[package]]
 name = "indexmap"
-version = "1.5.0"
+version = "1.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5b88cd59ee5f71fea89a62248fc8f387d44400cefe05ef548466d61ced9029a7"
+checksum = "86b45e59b16c76b11bf9738fd5d38879d3bd28ad292d7b313608becb17ae2df9"
 dependencies = [
  "autocfg",
  "hashbrown",
@@ -547,15 +722,15 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "lazycell"
-version = "1.2.1"
+version = "1.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b294d6fa9ee409a054354afc4352b0b9ef7ca222c69b8812cbea9e7d2bf3783f"
+checksum = "830d08ce1d1d941e6b30645f1a0eb5643013d835ce3779a5fc208261dbe10f55"
 
 [[package]]
 name = "libc"
-version = "0.2.74"
+version = "0.2.76"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a2f02823cf78b754822df5f7f268fb59822e7296276d3e069d8e8cb26a14bd10"
+checksum = "755456fae044e6fa1ebbbd1b3e902ae19e73097ed4ed87bb79934a867c007bc3"
 
 [[package]]
 name = "libloading"
@@ -568,9 +743,9 @@ dependencies = [
 
 [[package]]
 name = "libmimalloc-sys"
-version = "0.1.15"
+version = "0.1.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a27252ec1d0c4e0dd6142cbc572da50b363ab56fc334f7aa8fadf295b2e24e74"
+checksum = "677c4be79b14bd72496b87789b702ba02cd1a9f16a59369fe847082fd03efd88"
 dependencies = [
  "cmake",
 ]
@@ -595,9 +770,9 @@ dependencies = [
 
 [[package]]
 name = "lsp-server"
-version = "0.3.3"
+version = "0.3.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "53b4ace8ebe5d2aff3687ce0ed507f6020d6a47a7de2b0d3d664ea237ffb0c62"
+checksum = "87fce8851309a325974ec76efe7c9d954d152c9ff4fded6520eb3c96d0aa3a96"
 dependencies = [
  "crossbeam-channel",
  "log",
@@ -641,6 +816,19 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "60302e4db3a61da70c0cb7991976248362f30319e88850c487b9b95bbf059e00"
 
 [[package]]
+name = "mbe"
+version = "0.0.0"
+dependencies = [
+ "log",
+ "parser",
+ "rustc-hash",
+ "smallvec",
+ "syntax",
+ "test_utils",
+ "tt",
+]
+
+[[package]]
 name = "memchr"
 version = "2.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -667,9 +855,9 @@ dependencies = [
 
 [[package]]
 name = "mimalloc"
-version = "0.1.19"
+version = "0.1.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6c52de2069999f01bd26436564dbe7de3a87898feeb7a0d0ff9eb20a05bb7ca0"
+checksum = "00759bcf69082fa629ae8823fcc72f7454a90c6476110297a1ae5fb3a559e474"
 dependencies = [
  "libmimalloc-sys",
 ]
@@ -794,9 +982,9 @@ checksum = "1ab52be62400ca80aa00285d25253d7f7c437b7375c4de678f5405d3afe82ca5"
 
 [[package]]
 name = "once_cell"
-version = "1.4.0"
+version = "1.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0b631f7e854af39a1739f401cf34a8a013dfe09eac4fa4dba91e9768bd28168d"
+checksum = "260e51e7efe62b592207e9e13a68e43692a7a279171d6ba57abd208bf23645ad"
 
 [[package]]
 name = "oorandom"
@@ -831,8 +1019,15 @@ dependencies = [
 ]
 
 [[package]]
+name = "parser"
+version = "0.0.0"
+dependencies = [
+ "drop_bomb",
+]
+
+[[package]]
 name = "paths"
-version = "0.1.0"
+version = "0.0.0"
 
 [[package]]
 name = "percent-encoding"
@@ -842,9 +1037,9 @@ checksum = "d4fd5641d01c8f18a23da7b6fe29298ff4b55afcccdf78973b24cf3175fee32e"
 
 [[package]]
 name = "perf-event"
-version = "0.4.4"
+version = "0.4.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "76c42ba5d85a2f4472b99f475fb60cf336d9b4c85b1ea8bb300fef2e3c7c8f89"
+checksum = "273069d0b956939ba75e8b5663328b9b7f0dc2e262b3306c6be66c4d87e2240a"
 dependencies = [
  "libc",
  "perf-event-open-sys",
@@ -852,9 +1047,9 @@ dependencies = [
 
 [[package]]
 name = "perf-event-open-sys"
-version = "0.3.1"
+version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "95db63e37862bc1b842135d2234ef9418f222cc660c6752f45e7cf9ddfb97f96"
+checksum = "66f37842e29d92d05872a3c0271ba6717842695ecb896cb2e147a825c804b207"
 dependencies = [
  "libc",
 ]
@@ -871,9 +1066,9 @@ dependencies = [
 
 [[package]]
 name = "pico-args"
-version = "0.3.3"
+version = "0.3.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1b1eee8b1f4966c8343d7ca0f5a8452cd35d5610a2e0efbe2a68cae44bef2046"
+checksum = "28b9b4df73455c861d7cbf8be42f01d3b373ed7f02e378d55fa84eafc6f638b1"
 
 [[package]]
 name = "plain"
@@ -891,362 +1086,97 @@ dependencies = [
 ]
 
 [[package]]
-name = "pulldown-cmark"
-version = "0.7.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ca36dea94d187597e104a5c8e4b07576a8a45aa5db48a65e12940d3eb7461f55"
-dependencies = [
- "bitflags",
- "memchr",
- "unicase",
-]
-
-[[package]]
-name = "pulldown-cmark-to-cmark"
-version = "5.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "32accf4473121d8c0b508ca5673363703762d6cc59cf25af1df48f653346f736"
-dependencies = [
- "pulldown-cmark",
-]
-
-[[package]]
-name = "quote"
-version = "1.0.7"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "aa563d17ecb180e500da1cfd2b028310ac758de548efdd203e18f283af693f37"
-dependencies = [
- "proc-macro2",
-]
-
-[[package]]
-name = "ra_arena"
-version = "0.1.0"
-
-[[package]]
-name = "ra_assists"
-version = "0.1.0"
-dependencies = [
- "either",
- "itertools",
- "ra_db",
- "ra_fmt",
- "ra_hir",
- "ra_ide_db",
- "ra_prof",
- "ra_syntax",
- "ra_text_edit",
- "rustc-hash",
- "stdx",
- "test_utils",
-]
-
-[[package]]
-name = "ra_cfg"
-version = "0.1.0"
-dependencies = [
- "ra_mbe",
- "ra_syntax",
- "ra_tt",
- "rustc-hash",
-]
-
-[[package]]
-name = "ra_db"
-version = "0.1.0"
-dependencies = [
- "ra_cfg",
- "ra_prof",
- "ra_syntax",
- "ra_tt",
- "rustc-hash",
- "salsa",
- "stdx",
- "test_utils",
- "vfs",
-]
-
-[[package]]
-name = "ra_fmt"
-version = "0.1.0"
-dependencies = [
- "itertools",
- "ra_syntax",
-]
-
-[[package]]
-name = "ra_hir"
-version = "0.1.0"
-dependencies = [
- "arrayvec",
- "either",
- "itertools",
- "log",
- "ra_db",
- "ra_hir_def",
- "ra_hir_expand",
- "ra_hir_ty",
- "ra_prof",
- "ra_syntax",
- "ra_tt",
- "rustc-hash",
- "stdx",
- "url",
-]
-
-[[package]]
-name = "ra_hir_def"
-version = "0.1.0"
-dependencies = [
- "anymap",
- "drop_bomb",
- "either",
- "expect",
- "fst",
- "indexmap",
- "itertools",
- "log",
- "once_cell",
- "ra_arena",
- "ra_cfg",
- "ra_db",
- "ra_hir_expand",
- "ra_mbe",
- "ra_prof",
- "ra_syntax",
- "ra_tt",
- "rustc-hash",
- "smallvec",
- "stdx",
- "test_utils",
-]
-
-[[package]]
-name = "ra_hir_expand"
-version = "0.1.0"
-dependencies = [
- "either",
- "log",
- "ra_arena",
- "ra_db",
- "ra_mbe",
- "ra_parser",
- "ra_prof",
- "ra_syntax",
- "ra_tt",
- "rustc-hash",
- "test_utils",
-]
-
-[[package]]
-name = "ra_hir_ty"
-version = "0.1.0"
-dependencies = [
- "arrayvec",
- "chalk-ir",
- "chalk-recursive",
- "chalk-solve",
- "ena",
- "expect",
- "itertools",
- "log",
- "ra_arena",
- "ra_db",
- "ra_hir_def",
- "ra_hir_expand",
- "ra_prof",
- "ra_syntax",
- "rustc-hash",
- "scoped-tls",
- "smallvec",
- "stdx",
- "test_utils",
- "tracing",
- "tracing-subscriber",
- "tracing-tree",
-]
-
-[[package]]
-name = "ra_ide"
-version = "0.1.0"
-dependencies = [
- "either",
- "expect",
- "indexmap",
- "itertools",
- "log",
- "oorandom",
- "pulldown-cmark",
- "pulldown-cmark-to-cmark",
- "ra_assists",
- "ra_cfg",
- "ra_db",
- "ra_fmt",
- "ra_hir",
- "ra_ide_db",
- "ra_prof",
- "ra_ssr",
- "ra_syntax",
- "ra_text_edit",
- "rustc-hash",
- "stdx",
- "test_utils",
-]
-
-[[package]]
-name = "ra_ide_db"
-version = "0.1.0"
-dependencies = [
- "either",
- "fst",
- "log",
- "once_cell",
- "ra_db",
- "ra_hir",
- "ra_prof",
- "ra_syntax",
- "ra_text_edit",
- "rayon",
- "rustc-hash",
- "stdx",
- "test_utils",
-]
-
-[[package]]
-name = "ra_mbe"
-version = "0.1.0"
-dependencies = [
- "log",
- "ra_parser",
- "ra_syntax",
- "ra_tt",
- "rustc-hash",
- "smallvec",
- "test_utils",
-]
-
-[[package]]
-name = "ra_parser"
-version = "0.1.0"
-dependencies = [
- "drop_bomb",
-]
-
-[[package]]
-name = "ra_proc_macro"
-version = "0.1.0"
+name = "proc_macro_api"
+version = "0.0.0"
 dependencies = [
  "crossbeam-channel",
  "jod-thread",
  "log",
- "ra_tt",
  "serde",
  "serde_json",
+ "tt",
 ]
 
 [[package]]
-name = "ra_proc_macro_srv"
-version = "0.1.0"
+name = "proc_macro_srv"
+version = "0.0.0"
 dependencies = [
  "cargo_metadata",
  "difference",
  "goblin",
  "libloading",
+ "mbe",
  "memmap",
- "ra_mbe",
- "ra_proc_macro",
- "ra_toolchain",
- "ra_tt",
+ "proc_macro_api",
+ "proc_macro_test",
  "serde_derive",
  "test_utils",
+ "toolchain",
+ "tt",
 ]
 
 [[package]]
-name = "ra_prof"
-version = "0.1.0"
+name = "proc_macro_test"
+version = "0.0.0"
+
+[[package]]
+name = "profile"
+version = "0.0.0"
 dependencies = [
+ "arena",
  "backtrace",
  "cfg-if",
  "libc",
  "once_cell",
  "perf-event",
- "ra_arena",
 ]
 
 [[package]]
-name = "ra_project_model"
-version = "0.1.0"
+name = "project_model"
+version = "0.0.0"
 dependencies = [
  "anyhow",
+ "arena",
+ "base_db",
  "cargo_metadata",
+ "cfg",
  "log",
  "paths",
- "ra_arena",
- "ra_cfg",
- "ra_db",
- "ra_proc_macro",
- "ra_toolchain",
+ "proc_macro_api",
  "rustc-hash",
  "serde",
  "serde_json",
  "stdx",
+ "toolchain",
 ]
 
 [[package]]
-name = "ra_ssr"
-version = "0.1.0"
-dependencies = [
- "expect",
- "ra_db",
- "ra_hir",
- "ra_ide_db",
- "ra_syntax",
- "ra_text_edit",
- "rustc-hash",
- "test_utils",
-]
-
-[[package]]
-name = "ra_syntax"
-version = "0.1.0"
-dependencies = [
- "arrayvec",
- "expect",
- "itertools",
- "once_cell",
- "ra_parser",
- "ra_text_edit",
- "rayon",
- "rowan",
- "rustc-ap-rustc_lexer",
- "rustc-hash",
- "serde",
- "smol_str",
- "stdx",
- "test_utils",
- "walkdir",
-]
-
-[[package]]
-name = "ra_text_edit"
-version = "0.1.0"
+name = "pulldown-cmark"
+version = "0.7.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ca36dea94d187597e104a5c8e4b07576a8a45aa5db48a65e12940d3eb7461f55"
 dependencies = [
- "text-size",
+ "bitflags",
+ "memchr",
+ "unicase",
 ]
 
 [[package]]
-name = "ra_toolchain"
-version = "0.1.0"
+name = "pulldown-cmark-to-cmark"
+version = "5.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32accf4473121d8c0b508ca5673363703762d6cc59cf25af1df48f653346f736"
 dependencies = [
- "home",
+ "pulldown-cmark",
 ]
 
 [[package]]
-name = "ra_tt"
-version = "0.1.0"
+name = "quote"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa563d17ecb180e500da1cfd2b028310ac758de548efdd203e18f283af693f37"
 dependencies = [
- "smol_str",
- "stdx",
+ "proc-macro2",
 ]
 
 [[package]]
@@ -1286,10 +1216,7 @@ version = "1.3.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9c3780fcf44b193bc4d09f36d2a3c87b251da4a046c87795a0d35f4f927ad8e6"
 dependencies = [
- "aho-corasick",
- "memchr",
  "regex-syntax",
- "thread_local",
 ]
 
 [[package]]
@@ -1322,45 +1249,45 @@ dependencies = [
 
 [[package]]
 name = "rust-analyzer"
-version = "0.1.0"
+version = "0.0.0"
 dependencies = [
  "anyhow",
+ "base_db",
+ "cfg",
  "crossbeam-channel",
  "env_logger",
- "expect",
+ "expect-test",
  "flycheck",
+ "hir",
+ "hir_def",
+ "hir_ty",
+ "ide",
+ "ide_db",
  "itertools",
  "jod-thread",
  "log",
  "lsp-server",
  "lsp-types",
+ "mbe",
  "mimalloc",
  "oorandom",
  "parking_lot",
  "pico-args",
- "ra_cfg",
- "ra_db",
- "ra_hir",
- "ra_hir_def",
- "ra_hir_ty",
- "ra_ide",
- "ra_ide_db",
- "ra_mbe",
- "ra_proc_macro_srv",
- "ra_prof",
- "ra_project_model",
- "ra_ssr",
- "ra_syntax",
- "ra_text_edit",
- "ra_toolchain",
- "ra_tt",
+ "proc_macro_srv",
+ "profile",
+ "project_model",
  "rayon",
  "rustc-hash",
  "serde",
  "serde_json",
+ "ssr",
  "stdx",
+ "syntax",
  "test_utils",
+ "text_edit",
  "threadpool",
+ "toolchain",
+ "tt",
  "vfs",
  "vfs-notify",
  "winapi 0.3.9",
@@ -1368,9 +1295,9 @@ dependencies = [
 
 [[package]]
 name = "rustc-ap-rustc_lexer"
-version = "671.0.0"
+version = "673.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "22e1221f3bfa2943c942cf8da319ab2346887f8757778c29c7f1822cd27b521f"
+checksum = "f6b71fa1285bdefe5fb61e59b63d6cc246abf337f4acafdd620d721bc488e671"
 dependencies = [
  "unicode-xid",
 ]
@@ -1395,9 +1322,9 @@ checksum = "71d301d4193d031abdd79ff7e3dd721168a9572ef3fe51a1517aba235bd8f86e"
 
 [[package]]
 name = "salsa"
-version = "0.15.1"
+version = "0.15.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d4cdc109fcc9e9450c7ef47fb7474e99bffd51799da03ed0a6c7f0e2cb3848a6"
+checksum = "9ab29056d4fb4048a5f0d169c9b6e5526160c9ec37aded5a6879c2c9c445a8e4"
 dependencies = [
  "crossbeam-utils",
  "indexmap",
@@ -1412,9 +1339,9 @@ dependencies = [
 
 [[package]]
 name = "salsa-macros"
-version = "0.15.0"
+version = "0.15.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2c280ac85b15ac214b86ac4b407626a48e6a1c4f90769a582fec74aa57942b9f"
+checksum = "a1c3aec007c63c4ed4cd7a018529fb0b5575c4562575fc6a40d6cd2ae0b792ef"
 dependencies = [
  "heck",
  "proc-macro2",
@@ -1481,18 +1408,18 @@ checksum = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
 
 [[package]]
 name = "serde"
-version = "1.0.114"
+version = "1.0.115"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5317f7588f0a5078ee60ef675ef96735a1442132dc645eb1d12c018620ed8cd3"
+checksum = "e54c9a88f2da7238af84b5101443f0c0d0a3bbdc455e34a5c9497b1903ed55d5"
 dependencies = [
  "serde_derive",
 ]
 
 [[package]]
 name = "serde_derive"
-version = "1.0.114"
+version = "1.0.115"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2a0be94b04690fbaed37cddffc5c134bf537c8e3329d53e982fe04c374978f8e"
+checksum = "609feed1d0a73cc36a0182a840a9b37b4a82f0b1150369f0536a9e3f2a31dc48"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1538,9 +1465,9 @@ checksum = "c111b5bd5695e56cffe5129854aa230b39c93a305372fdbb2668ca2394eea9f8"
 
 [[package]]
 name = "smallvec"
-version = "1.4.1"
+version = "1.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3757cb9d89161a2f24e1cf78efa0c1fcff485d18e3f55e0aa3480824ddaa0f3f"
+checksum = "fbee7696b84bbf3d89a1c2eccff0850e3047ed46bfcd2e92c29a2d074d57e252"
 
 [[package]]
 name = "smol_str"
@@ -1552,14 +1479,29 @@ dependencies = [
 ]
 
 [[package]]
+name = "ssr"
+version = "0.0.0"
+dependencies = [
+ "base_db",
+ "expect-test",
+ "hir",
+ "ide_db",
+ "itertools",
+ "rustc-hash",
+ "syntax",
+ "test_utils",
+ "text_edit",
+]
+
+[[package]]
 name = "stdx"
-version = "0.1.0"
+version = "0.0.0"
 
 [[package]]
 name = "syn"
-version = "1.0.36"
+version = "1.0.38"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4cdb98bcb1f9d81d07b536179c269ea15999b5d14ea958196413869445bb5250"
+checksum = "e69abc24912995b3038597a7a593be5053eb0fb44f3cc5beec0deb421790c1f4"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1579,6 +1521,27 @@ dependencies = [
 ]
 
 [[package]]
+name = "syntax"
+version = "0.0.0"
+dependencies = [
+ "arrayvec",
+ "expect-test",
+ "itertools",
+ "once_cell",
+ "parser",
+ "rayon",
+ "rowan",
+ "rustc-ap-rustc_lexer",
+ "rustc-hash",
+ "serde",
+ "smol_str",
+ "stdx",
+ "test_utils",
+ "text_edit",
+ "walkdir",
+]
+
+[[package]]
 name = "termcolor"
 version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1589,7 +1552,7 @@ dependencies = [
 
 [[package]]
 name = "test_utils"
-version = "0.1.0"
+version = "0.0.0"
 dependencies = [
  "difference",
  "rustc-hash",
@@ -1605,6 +1568,13 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f03e7efdedc3bc78cb2337f1e2785c39e45f5ef762d9e4ebb137fff7380a6d8a"
 
 [[package]]
+name = "text_edit"
+version = "0.0.0"
+dependencies = [
+ "text-size",
+]
+
+[[package]]
 name = "thin-dst"
 version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1640,15 +1610,22 @@ dependencies = [
 
 [[package]]
 name = "tinyvec"
-version = "0.3.3"
+version = "0.3.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "53953d2d3a5ad81d9f844a32f14ebb121f50b650cd59d0ee2a07cf13c617efed"
+checksum = "238ce071d267c5710f9d31451efec16c5ee22de34df17cc05e56cbc92e967117"
+
+[[package]]
+name = "toolchain"
+version = "0.0.0"
+dependencies = [
+ "home",
+]
 
 [[package]]
 name = "tracing"
-version = "0.1.17"
+version = "0.1.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "dbdf4ccd1652592b01286a5dbe1e2a77d78afaa34beadd9872a5f7396f92aaa9"
+checksum = "6d79ca061b032d6ce30c660fded31189ca0b9922bf483cd70759f13a2d86786c"
 dependencies = [
  "cfg-if",
  "tracing-attributes",
@@ -1657,9 +1634,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-attributes"
-version = "0.1.9"
+version = "0.1.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f0693bf8d6f2bf22c690fc61a9d21ac69efdbb894a17ed596b9af0f01e64b84b"
+checksum = "80e0ccfc3378da0cce270c946b676a376943f5cd16aeba64568e7939806f4ada"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1668,9 +1645,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-core"
-version = "0.1.11"
+version = "0.1.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "94ae75f0d28ae10786f3b1895c55fe72e79928fd5ccdebb5438c75e93fec178f"
+checksum = "db63662723c316b43ca36d833707cc93dff82a02ba3d7e354f342682cc8b3545"
 dependencies = [
  "lazy_static",
 ]
@@ -1698,9 +1675,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-subscriber"
-version = "0.2.9"
+version = "0.2.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e4f5dd7095c2481b7b3cbed71c8de53085fb3542bc3c2b4c73cba43e8f11c7ba"
+checksum = "abd165311cc4d7a555ad11cc77a37756df836182db0d81aac908c8184c584f40"
 dependencies = [
  "ansi_term",
  "chrono",
@@ -1711,6 +1688,7 @@ dependencies = [
  "serde_json",
  "sharded-slab",
  "smallvec",
+ "thread_local",
  "tracing-core",
  "tracing-log",
  "tracing-serde",
@@ -1718,9 +1696,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-tree"
-version = "0.1.4"
+version = "0.1.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "37ee7f0f53ed2093971a698db799ef56a2dfd89b32e3aeb5165f0e637a02be04"
+checksum = "e1a3dc4774db3a6b2d66a4f8d8de670e874ec3ed55615860c994927419b32c5f"
 dependencies = [
  "ansi_term",
  "atty",
@@ -1731,10 +1709,18 @@ dependencies = [
 ]
 
 [[package]]
+name = "tt"
+version = "0.0.0"
+dependencies = [
+ "smol_str",
+ "stdx",
+]
+
+[[package]]
 name = "ungrammar"
-version = "0.1.0"
+version = "1.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0ee12e4891ab3acc2d95d5023022ace22020247bb8a8d1ece875a443f7dab37d"
+checksum = "bab6142ac77be714b1ea78faca6efaed5478c50724786b0fe80d8528d10692b3"
 
 [[package]]
 name = "unicase"
@@ -1795,7 +1781,7 @@ checksum = "b5a972e5669d67ba988ce3dc826706fb0a8b01471c088cb0b6110b805cc36aed"
 
 [[package]]
 name = "vfs"
-version = "0.1.0"
+version = "0.0.0"
 dependencies = [
  "fst",
  "paths",
@@ -1804,7 +1790,7 @@ dependencies = [
 
 [[package]]
 name = "vfs-notify"
-version = "0.1.0"
+version = "0.0.0"
 dependencies = [
  "crossbeam-channel",
  "jod-thread",
@@ -1871,6 +1857,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
 
 [[package]]
+name = "write-json"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "06069a848f95fceae3e5e03c0ddc8cb78452b56654ee0c8e68f938cf790fb9e3"
+
+[[package]]
 name = "ws2_32-sys"
 version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1891,4 +1883,5 @@ dependencies = [
  "quote",
  "ungrammar",
  "walkdir",
+ "write-json",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index 612e6809f..218581d9d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,37 +2,34 @@
 members = [ "crates/*", "xtask/" ]
 
 [profile.dev]
-# disabling debug info speeds up builds a bunch,
+# Disabling debug info speeds up builds a bunch,
 # and we don't rely on it for debugging that much.
 debug = 0
 
+[profile.dev.package]
+# These speed up local tests.
+rowan.opt-level = 3
+rustc-hash.opt-level = 3
+smol_str.opt-level = 3
+text-size.opt-level = 3
+# This speeds up `cargo xtask dist`.
+miniz_oxide.opt-level = 3
+
 [profile.release]
 incremental = true
-debug = 0 # set this to 1 or 2 to get more useful backtraces in debugger
-
-# ideally, we would use `build-override` here, but some crates are also
-# needed at run-time and we end up compiling them twice
-[profile.release.package.proc-macro2]
-opt-level = 0
-[profile.release.package.quote]
-opt-level = 0
-[profile.release.package.syn]
-opt-level = 0
-[profile.release.package.serde_derive]
-opt-level = 0
-[profile.release.package.chalk-derive]
-opt-level = 0
-[profile.release.package.salsa-macros]
-opt-level = 0
-[profile.release.package.tracing-attributes]
-opt-level = 0
-[profile.release.package.xtask]
-opt-level = 0
+debug = 0 # Set this to 1 or 2 to get more useful backtraces in debugger.
 
-# Gzipping the artifacts is up to 10 times faster with optimizations (`cargo xtask dist`).
-# `miniz_oxide` is the direct dependency of `flate2` which does all the heavy lifting
-[profile.dev.package.miniz_oxide]
-opt-level = 3
+# Ideally, we would use `build-override` here, but some crates are also
+# needed at run-time and we end up compiling them twice.
+[profile.release.package]
+chalk-derive.opt-level = 0
+proc-macro2.opt-level = 0
+quote.opt-level = 0
+salsa-macros.opt-level = 0
+serde_derive.opt-level = 0
+syn.opt-level = 0
+tracing-attributes.opt-level = 0
+xtask.opt-level = 0
 
 [patch.'crates-io']
 # rowan = { path = "../rowan" }
diff --git a/README.md b/README.md
index 16c980400..264e4da70 100644
--- a/README.md
+++ b/README.md
@@ -39,7 +39,7 @@ https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Frls-2.2E0
 
 * Website: https://rust-analyzer.github.io/
 * Metrics: https://rust-analyzer.github.io/metrics/
-* API docs: https://rust-analyzer.github.io/rust-analyzer/ra_ide/
+* API docs: https://rust-analyzer.github.io/rust-analyzer/ide/
 
 ## License
 
diff --git a/bors.toml b/bors.toml
index 13ce236df..4c980a24d 100644
--- a/bors.toml
+++ b/bors.toml
@@ -1,9 +1,8 @@
 status = [
     "Rust (ubuntu-latest)",
     "Rust (windows-latest)",
-    "Rust (macos-latest)",
+    # "Rust (macos-latest)",
     "TypeScript (ubuntu-latest)",
     "TypeScript (windows-latest)",
-    "TypeScript (macos-latest)",
 ]
 delete_merged_branches = true
diff --git a/crates/arena/Cargo.toml b/crates/arena/Cargo.toml
new file mode 100644
index 000000000..f2bb5cc45
--- /dev/null
+++ b/crates/arena/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "arena"
+version = "0.0.0"
+license = "MIT OR Apache-2.0"
+authors = ["rust-analyzer developers"]
+edition = "2018"
+
+[lib]
+doctest = false
diff --git a/crates/ra_arena/src/lib.rs b/crates/arena/src/lib.rs
index 3169aa5b8..3169aa5b8 100644
--- a/crates/ra_arena/src/lib.rs
+++ b/crates/arena/src/lib.rs
diff --git a/crates/ra_arena/src/map.rs b/crates/arena/src/map.rs
index 0f33907c0..0f33907c0 100644
--- a/crates/ra_arena/src/map.rs
+++ b/crates/arena/src/map.rs
diff --git a/crates/assists/Cargo.toml b/crates/assists/Cargo.toml
new file mode 100644
index 000000000..a560a35c7
--- /dev/null
+++ b/crates/assists/Cargo.toml
@@ -0,0 +1,23 @@
+[package]
+name = "assists"
+version = "0.0.0"
+license = "MIT OR Apache-2.0"
+authors = ["rust-analyzer developers"]
+edition = "2018"
+
+[lib]
+doctest = false
+
+[dependencies]
+rustc-hash = "1.1.0"
+itertools = "0.9.0"
+either = "1.5.3"
+
+stdx = { path = "../stdx" }
+syntax = { path = "../syntax" }
+text_edit = { path = "../text_edit" }
+profile = { path = "../profile" }
+base_db = { path = "../base_db" }
+ide_db = { path = "../ide_db" }
+hir = { path = "../hir" }
+test_utils = { path = "../test_utils" }
diff --git a/crates/ra_assists/src/assist_config.rs b/crates/assists/src/assist_config.rs
index cda2abfb9..cda2abfb9 100644
--- a/crates/ra_assists/src/assist_config.rs
+++ b/crates/assists/src/assist_config.rs
diff --git a/crates/assists/src/assist_context.rs b/crates/assists/src/assist_context.rs
new file mode 100644
index 000000000..11c171fc2
--- /dev/null
+++ b/crates/assists/src/assist_context.rs
@@ -0,0 +1,293 @@
+//! See `AssistContext`
+
+use std::mem;
+
+use algo::find_covering_element;
+use base_db::{FileId, FileRange};
+use hir::Semantics;
+use ide_db::{
+    label::Label,
+    source_change::{SourceChange, SourceFileEdit},
+    RootDatabase,
+};
+use syntax::{
+    algo::{self, find_node_at_offset, SyntaxRewriter},
+    AstNode, SourceFile, SyntaxElement, SyntaxKind, SyntaxToken, TextRange, TextSize,
+    TokenAtOffset,
+};
+use text_edit::{TextEdit, TextEditBuilder};
+
+use crate::{
+    assist_config::{AssistConfig, SnippetCap},
+    Assist, AssistId, AssistKind, GroupLabel, ResolvedAssist,
+};
+
+/// `AssistContext` allows to apply an assist or check if it could be applied.
+///
+/// Assists use a somewhat over-engineered approach, given the current needs.
+/// The assists workflow consists of two phases. In the first phase, a user asks
+/// for the list of available assists. In the second phase, the user picks a
+/// particular assist and it gets applied.
+///
+/// There are two peculiarities here:
+///
+/// * first, we ideally avoid computing more things then necessary to answer "is
+///   assist applicable" in the first phase.
+/// * second, when we are applying assist, we don't have a guarantee that there
+///   weren't any changes between the point when user asked for assists and when
+///   they applied a particular assist. So, when applying assist, we need to do
+///   all the checks from scratch.
+///
+/// To avoid repeating the same code twice for both "check" and "apply"
+/// functions, we use an approach reminiscent of that of Django's function based
+/// views dealing with forms. Each assist receives a runtime parameter,
+/// `resolve`. It first check if an edit is applicable (potentially computing
+/// info required to compute the actual edit). If it is applicable, and
+/// `resolve` is `true`, it then computes the actual edit.
+///
+/// So, to implement the original assists workflow, we can first apply each edit
+/// with `resolve = false`, and then applying the selected edit again, with
+/// `resolve = true` this time.
+///
+/// Note, however, that we don't actually use such two-phase logic at the
+/// moment, because the LSP API is pretty awkward in this place, and it's much
+/// easier to just compute the edit eagerly :-)
+pub(crate) struct AssistContext<'a> {
+    pub(crate) config: &'a AssistConfig,
+    pub(crate) sema: Semantics<'a, RootDatabase>,
+    pub(crate) frange: FileRange,
+    source_file: SourceFile,
+}
+
+impl<'a> AssistContext<'a> {
+    pub(crate) fn new(
+        sema: Semantics<'a, RootDatabase>,
+        config: &'a AssistConfig,
+        frange: FileRange,
+    ) -> AssistContext<'a> {
+        let source_file = sema.parse(frange.file_id);
+        AssistContext { config, sema, frange, source_file }
+    }
+
+    pub(crate) fn db(&self) -> &RootDatabase {
+        self.sema.db
+    }
+
+    pub(crate) fn source_file(&self) -> &SourceFile {
+        &self.source_file
+    }
+
+    // NB, this ignores active selection.
+    pub(crate) fn offset(&self) -> TextSize {
+        self.frange.range.start()
+    }
+
+    pub(crate) fn token_at_offset(&self) -> TokenAtOffset<SyntaxToken> {
+        self.source_file.syntax().token_at_offset(self.offset())
+    }
+    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.offset())
+    }
+    pub(crate) fn find_node_at_offset_with_descend<N: AstNode>(&self) -> Option<N> {
+        self.sema.find_node_at_offset_with_descend(self.source_file.syntax(), self.offset())
+    }
+    pub(crate) fn covering_element(&self) -> SyntaxElement {
+        find_covering_element(self.source_file.syntax(), self.frange.range)
+    }
+    // FIXME: remove
+    pub(crate) fn covering_node_for_range(&self, range: TextRange) -> SyntaxElement {
+        find_covering_element(self.source_file.syntax(), range)
+    }
+}
+
+pub(crate) struct Assists {
+    resolve: bool,
+    file: FileId,
+    buf: Vec<(Assist, Option<SourceChange>)>,
+    allowed: Option<Vec<AssistKind>>,
+}
+
+impl Assists {
+    pub(crate) fn new_resolved(ctx: &AssistContext) -> Assists {
+        Assists {
+            resolve: true,
+            file: ctx.frange.file_id,
+            buf: Vec::new(),
+            allowed: ctx.config.allowed.clone(),
+        }
+    }
+
+    pub(crate) fn new_unresolved(ctx: &AssistContext) -> Assists {
+        Assists {
+            resolve: false,
+            file: ctx.frange.file_id,
+            buf: Vec::new(),
+            allowed: ctx.config.allowed.clone(),
+        }
+    }
+
+    pub(crate) fn finish_unresolved(self) -> Vec<Assist> {
+        assert!(!self.resolve);
+        self.finish()
+            .into_iter()
+            .map(|(label, edit)| {
+                assert!(edit.is_none());
+                label
+            })
+            .collect()
+    }
+
+    pub(crate) fn finish_resolved(self) -> Vec<ResolvedAssist> {
+        assert!(self.resolve);
+        self.finish()
+            .into_iter()
+            .map(|(label, edit)| ResolvedAssist { assist: label, source_change: edit.unwrap() })
+            .collect()
+    }
+
+    pub(crate) fn add(
+        &mut self,
+        id: AssistId,
+        label: impl Into<String>,
+        target: TextRange,
+        f: impl FnOnce(&mut AssistBuilder),
+    ) -> Option<()> {
+        if !self.is_allowed(&id) {
+            return None;
+        }
+        let label = Label::new(label.into());
+        let assist = Assist { id, label, group: None, target };
+        self.add_impl(assist, f)
+    }
+
+    pub(crate) fn add_group(
+        &mut self,
+        group: &GroupLabel,
+        id: AssistId,
+        label: impl Into<String>,
+        target: TextRange,
+        f: impl FnOnce(&mut AssistBuilder),
+    ) -> Option<()> {
+        if !self.is_allowed(&id) {
+            return None;
+        }
+        let label = Label::new(label.into());
+        let assist = Assist { id, label, group: Some(group.clone()), target };
+        self.add_impl(assist, f)
+    }
+
+    fn add_impl(&mut self, assist: Assist, f: impl FnOnce(&mut AssistBuilder)) -> Option<()> {
+        let source_change = if self.resolve {
+            let mut builder = AssistBuilder::new(self.file);
+            f(&mut builder);
+            Some(builder.finish())
+        } else {
+            None
+        };
+
+        self.buf.push((assist, source_change));
+        Some(())
+    }
+
+    fn finish(mut self) -> Vec<(Assist, Option<SourceChange>)> {
+        self.buf.sort_by_key(|(label, _edit)| label.target.len());
+        self.buf
+    }
+
+    fn is_allowed(&self, id: &AssistId) -> bool {
+        match &self.allowed {
+            Some(allowed) => allowed.iter().any(|kind| kind.contains(id.1)),
+            None => true,
+        }
+    }
+}
+
+pub(crate) struct AssistBuilder {
+    edit: TextEditBuilder,
+    file_id: FileId,
+    is_snippet: bool,
+    change: SourceChange,
+}
+
+impl AssistBuilder {
+    pub(crate) fn new(file_id: FileId) -> AssistBuilder {
+        AssistBuilder {
+            edit: TextEdit::builder(),
+            file_id,
+            is_snippet: false,
+            change: SourceChange::default(),
+        }
+    }
+
+    pub(crate) fn edit_file(&mut self, file_id: FileId) {
+        self.file_id = file_id;
+    }
+
+    fn commit(&mut self) {
+        let edit = mem::take(&mut self.edit).finish();
+        if !edit.is_empty() {
+            let new_edit = SourceFileEdit { file_id: self.file_id, edit };
+            assert!(!self.change.source_file_edits.iter().any(|it| it.file_id == new_edit.file_id));
+            self.change.source_file_edits.push(new_edit);
+        }
+    }
+
+    /// Remove specified `range` of text.
+    pub(crate) fn delete(&mut self, range: TextRange) {
+        self.edit.delete(range)
+    }
+    /// Append specified `text` at the given `offset`
+    pub(crate) fn insert(&mut self, offset: TextSize, text: impl Into<String>) {
+        self.edit.insert(offset, text.into())
+    }
+    /// Append specified `snippet` at the given `offset`
+    pub(crate) fn insert_snippet(
+        &mut self,
+        _cap: SnippetCap,
+        offset: TextSize,
+        snippet: impl Into<String>,
+    ) {
+        self.is_snippet = true;
+        self.insert(offset, snippet);
+    }
+    /// Replaces specified `range` of text with a given string.
+    pub(crate) fn replace(&mut self, range: TextRange, replace_with: impl Into<String>) {
+        self.edit.replace(range, replace_with.into())
+    }
+    /// Replaces specified `range` of text with a given `snippet`.
+    pub(crate) fn replace_snippet(
+        &mut self,
+        _cap: SnippetCap,
+        range: TextRange,
+        snippet: impl Into<String>,
+    ) {
+        self.is_snippet = true;
+        self.replace(range, snippet);
+    }
+    pub(crate) fn replace_ast<N: AstNode>(&mut self, old: N, new: N) {
+        algo::diff(old.syntax(), new.syntax()).into_text_edit(&mut self.edit)
+    }
+    pub(crate) fn rewrite(&mut self, rewriter: SyntaxRewriter) {
+        let node = rewriter.rewrite_root().unwrap();
+        let new = rewriter.rewrite(&node);
+        algo::diff(&node, &new).into_text_edit(&mut self.edit);
+    }
+
+    // FIXME: kill this API
+    /// Get access to the raw `TextEditBuilder`.
+    pub(crate) fn text_edit_builder(&mut self) -> &mut TextEditBuilder {
+        &mut self.edit
+    }
+
+    fn finish(mut self) -> SourceChange {
+        self.commit();
+        let mut change = mem::take(&mut self.change);
+        if self.is_snippet {
+            change.is_snippet = true;
+        }
+        change
+    }
+}
diff --git a/crates/assists/src/ast_transform.rs b/crates/assists/src/ast_transform.rs
new file mode 100644
index 000000000..5216862ba
--- /dev/null
+++ b/crates/assists/src/ast_transform.rs
@@ -0,0 +1,200 @@
+//! `AstTransformer`s are functions that replace nodes in an AST and can be easily combined.
+use rustc_hash::FxHashMap;
+
+use hir::{HirDisplay, PathResolution, SemanticsScope};
+use syntax::{
+    algo::SyntaxRewriter,
+    ast::{self, AstNode},
+};
+
+pub fn apply<'a, N: AstNode>(transformer: &dyn AstTransform<'a>, node: N) -> N {
+    SyntaxRewriter::from_fn(|element| match element {
+        syntax::SyntaxElement::Node(n) => {
+            let replacement = transformer.get_substitution(&n)?;
+            Some(replacement.into())
+        }
+        _ => None,
+    })
+    .rewrite_ast(&node)
+}
+
+pub trait AstTransform<'a> {
+    fn get_substitution(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode>;
+
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a>;
+    fn or<T: AstTransform<'a> + 'a>(self, other: T) -> Box<dyn AstTransform<'a> + 'a>
+    where
+        Self: Sized + 'a,
+    {
+        self.chain_before(Box::new(other))
+    }
+}
+
+struct NullTransformer;
+
+impl<'a> AstTransform<'a> for NullTransformer {
+    fn get_substitution(&self, _node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
+        None
+    }
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
+        other
+    }
+}
+
+pub struct SubstituteTypeParams<'a> {
+    source_scope: &'a SemanticsScope<'a>,
+    substs: FxHashMap<hir::TypeParam, ast::Type>,
+    previous: Box<dyn AstTransform<'a> + 'a>,
+}
+
+impl<'a> SubstituteTypeParams<'a> {
+    pub fn for_trait_impl(
+        source_scope: &'a SemanticsScope<'a>,
+        // FIXME: there's implicit invariant that `trait_` and  `source_scope` match...
+        trait_: hir::Trait,
+        impl_def: ast::Impl,
+    ) -> SubstituteTypeParams<'a> {
+        let substs = get_syntactic_substs(impl_def).unwrap_or_default();
+        let generic_def: hir::GenericDef = trait_.into();
+        let substs_by_param: FxHashMap<_, _> = generic_def
+            .params(source_scope.db)
+            .into_iter()
+            // this is a trait impl, so we need to skip the first type parameter -- this is a bit hacky
+            .skip(1)
+            // The actual list of trait type parameters may be longer than the one
+            // used in the `impl` block due to trailing default type parameters.
+            // For that case we extend the `substs` with an empty iterator so we
+            // can still hit those trailing values and check if they actually have
+            // a default type. If they do, go for that type from `hir` to `ast` so
+            // the resulting change can be applied correctly.
+            .zip(substs.into_iter().map(Some).chain(std::iter::repeat(None)))
+            .filter_map(|(k, v)| match v {
+                Some(v) => Some((k, v)),
+                None => {
+                    let default = k.default(source_scope.db)?;
+                    Some((
+                        k,
+                        ast::make::ty(
+                            &default
+                                .display_source_code(source_scope.db, source_scope.module()?.into())
+                                .ok()?,
+                        ),
+                    ))
+                }
+            })
+            .collect();
+        return SubstituteTypeParams {
+            source_scope,
+            substs: substs_by_param,
+            previous: Box::new(NullTransformer),
+        };
+
+        // FIXME: It would probably be nicer if we could get this via HIR (i.e. get the
+        // trait ref, and then go from the types in the substs back to the syntax).
+        fn get_syntactic_substs(impl_def: ast::Impl) -> Option<Vec<ast::Type>> {
+            let target_trait = impl_def.trait_()?;
+            let path_type = match target_trait {
+                ast::Type::PathType(path) => path,
+                _ => return None,
+            };
+            let generic_arg_list = path_type.path()?.segment()?.generic_arg_list()?;
+
+            let mut result = Vec::new();
+            for generic_arg in generic_arg_list.generic_args() {
+                match generic_arg {
+                    ast::GenericArg::TypeArg(type_arg) => result.push(type_arg.ty()?),
+                    ast::GenericArg::AssocTypeArg(_)
+                    | ast::GenericArg::LifetimeArg(_)
+                    | ast::GenericArg::ConstArg(_) => (),
+                }
+            }
+
+            Some(result)
+        }
+    }
+    fn get_substitution_inner(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
+        let type_ref = ast::Type::cast(node.clone())?;
+        let path = match &type_ref {
+            ast::Type::PathType(path_type) => path_type.path()?,
+            _ => return None,
+        };
+        let resolution = self.source_scope.speculative_resolve(&path)?;
+        match resolution {
+            hir::PathResolution::TypeParam(tp) => Some(self.substs.get(&tp)?.syntax().clone()),
+            _ => None,
+        }
+    }
+}
+
+impl<'a> AstTransform<'a> for SubstituteTypeParams<'a> {
+    fn get_substitution(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
+        self.get_substitution_inner(node).or_else(|| self.previous.get_substitution(node))
+    }
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
+        Box::new(SubstituteTypeParams { previous: other, ..self })
+    }
+}
+
+pub struct QualifyPaths<'a> {
+    target_scope: &'a SemanticsScope<'a>,
+    source_scope: &'a SemanticsScope<'a>,
+    previous: Box<dyn AstTransform<'a> + 'a>,
+}
+
+impl<'a> QualifyPaths<'a> {
+    pub fn new(target_scope: &'a SemanticsScope<'a>, source_scope: &'a SemanticsScope<'a>) -> Self {
+        Self { target_scope, source_scope, previous: Box::new(NullTransformer) }
+    }
+
+    fn get_substitution_inner(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
+        // FIXME handle value ns?
+        let from = self.target_scope.module()?;
+        let p = ast::Path::cast(node.clone())?;
+        if p.segment().and_then(|s| s.param_list()).is_some() {
+            // don't try to qualify `Fn(Foo) -> Bar` paths, they are in prelude anyway
+            return None;
+        }
+        let resolution = self.source_scope.speculative_resolve(&p)?;
+        match resolution {
+            PathResolution::Def(def) => {
+                let found_path = from.find_use_path(self.source_scope.db.upcast(), def)?;
+                let mut path = path_to_ast(found_path);
+
+                let type_args = p
+                    .segment()
+                    .and_then(|s| s.generic_arg_list())
+                    .map(|arg_list| apply(self, arg_list));
+                if let Some(type_args) = type_args {
+                    let last_segment = path.segment().unwrap();
+                    path = path.with_segment(last_segment.with_type_args(type_args))
+                }
+
+                Some(path.syntax().clone())
+            }
+            PathResolution::Local(_)
+            | PathResolution::TypeParam(_)
+            | PathResolution::SelfType(_) => None,
+            PathResolution::Macro(_) => None,
+            PathResolution::AssocItem(_) => None,
+        }
+    }
+}
+
+impl<'a> AstTransform<'a> for QualifyPaths<'a> {
+    fn get_substitution(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
+        self.get_substitution_inner(node).or_else(|| self.previous.get_substitution(node))
+    }
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
+        Box::new(QualifyPaths { previous: other, ..self })
+    }
+}
+
+pub(crate) fn path_to_ast(path: hir::ModPath) -> ast::Path {
+    let parse = ast::SourceFile::parse(&path.to_string());
+    parse
+        .tree()
+        .syntax()
+        .descendants()
+        .find_map(ast::Path::cast)
+        .unwrap_or_else(|| panic!("failed to parse path {:?}, `{}`", path, path))
+}
diff --git a/crates/assists/src/handlers/add_custom_impl.rs b/crates/assists/src/handlers/add_custom_impl.rs
new file mode 100644
index 000000000..8757fa33f
--- /dev/null
+++ b/crates/assists/src/handlers/add_custom_impl.rs
@@ -0,0 +1,208 @@
+use itertools::Itertools;
+use syntax::{
+    ast::{self, AstNode},
+    Direction, SmolStr,
+    SyntaxKind::{IDENT, WHITESPACE},
+    TextRange, TextSize,
+};
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    AssistId, AssistKind,
+};
+
+// Assist: add_custom_impl
+//
+// Adds impl block for derived trait.
+//
+// ```
+// #[derive(Deb<|>ug, Display)]
+// struct S;
+// ```
+// ->
+// ```
+// #[derive(Display)]
+// struct S;
+//
+// impl Debug for S {
+//     $0
+// }
+// ```
+pub(crate) fn add_custom_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let attr = ctx.find_node_at_offset::<ast::Attr>()?;
+    let input = attr.token_tree()?;
+
+    let attr_name = attr
+        .syntax()
+        .descendants_with_tokens()
+        .filter(|t| t.kind() == IDENT)
+        .find_map(|i| i.into_token())
+        .filter(|t| *t.text() == "derive")?
+        .text()
+        .clone();
+
+    let trait_token =
+        ctx.token_at_offset().find(|t| t.kind() == IDENT && *t.text() != attr_name)?;
+
+    let annotated = attr.syntax().siblings(Direction::Next).find_map(ast::Name::cast)?;
+    let annotated_name = annotated.syntax().text().to_string();
+    let start_offset = annotated.syntax().parent()?.text_range().end();
+
+    let label =
+        format!("Add custom impl `{}` for `{}`", trait_token.text().as_str(), annotated_name);
+
+    let target = attr.syntax().text_range();
+    acc.add(AssistId("add_custom_impl", AssistKind::Refactor), label, target, |builder| {
+        let new_attr_input = input
+            .syntax()
+            .descendants_with_tokens()
+            .filter(|t| t.kind() == IDENT)
+            .filter_map(|t| t.into_token().map(|t| t.text().clone()))
+            .filter(|t| t != trait_token.text())
+            .collect::<Vec<SmolStr>>();
+        let has_more_derives = !new_attr_input.is_empty();
+
+        if has_more_derives {
+            let new_attr_input = format!("({})", new_attr_input.iter().format(", "));
+            builder.replace(input.syntax().text_range(), new_attr_input);
+        } else {
+            let attr_range = attr.syntax().text_range();
+            builder.delete(attr_range);
+
+            let line_break_range = attr
+                .syntax()
+                .next_sibling_or_token()
+                .filter(|t| t.kind() == WHITESPACE)
+                .map(|t| t.text_range())
+                .unwrap_or_else(|| TextRange::new(TextSize::from(0), TextSize::from(0)));
+            builder.delete(line_break_range);
+        }
+
+        match ctx.config.snippet_cap {
+            Some(cap) => {
+                builder.insert_snippet(
+                    cap,
+                    start_offset,
+                    format!("\n\nimpl {} for {} {{\n    $0\n}}", trait_token, annotated_name),
+                );
+            }
+            None => {
+                builder.insert(
+                    start_offset,
+                    format!("\n\nimpl {} for {} {{\n\n}}", trait_token, annotated_name),
+                );
+            }
+        }
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn add_custom_impl_for_unique_input() {
+        check_assist(
+            add_custom_impl,
+            "
+#[derive(Debu<|>g)]
+struct Foo {
+    bar: String,
+}
+            ",
+            "
+struct Foo {
+    bar: String,
+}
+
+impl Debug for Foo {
+    $0
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn add_custom_impl_for_with_visibility_modifier() {
+        check_assist(
+            add_custom_impl,
+            "
+#[derive(Debug<|>)]
+pub struct Foo {
+    bar: String,
+}
+            ",
+            "
+pub struct Foo {
+    bar: String,
+}
+
+impl Debug for Foo {
+    $0
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn add_custom_impl_when_multiple_inputs() {
+        check_assist(
+            add_custom_impl,
+            "
+#[derive(Display, Debug<|>, Serialize)]
+struct Foo {}
+            ",
+            "
+#[derive(Display, Serialize)]
+struct Foo {}
+
+impl Debug for Foo {
+    $0
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn test_ignore_derive_macro_without_input() {
+        check_assist_not_applicable(
+            add_custom_impl,
+            "
+#[derive(<|>)]
+struct Foo {}
+            ",
+        )
+    }
+
+    #[test]
+    fn test_ignore_if_cursor_on_param() {
+        check_assist_not_applicable(
+            add_custom_impl,
+            "
+#[derive<|>(Debug)]
+struct Foo {}
+            ",
+        );
+
+        check_assist_not_applicable(
+            add_custom_impl,
+            "
+#[derive(Debug)<|>]
+struct Foo {}
+            ",
+        )
+    }
+
+    #[test]
+    fn test_ignore_if_not_derive() {
+        check_assist_not_applicable(
+            add_custom_impl,
+            "
+#[allow(non_camel_<|>case_types)]
+struct Foo {}
+            ",
+        )
+    }
+}
diff --git a/crates/assists/src/handlers/add_explicit_type.rs b/crates/assists/src/handlers/add_explicit_type.rs
new file mode 100644
index 000000000..563cbf505
--- /dev/null
+++ b/crates/assists/src/handlers/add_explicit_type.rs
@@ -0,0 +1,211 @@
+use hir::HirDisplay;
+use syntax::{
+    ast::{self, AstNode, LetStmt, NameOwner},
+    TextRange,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: add_explicit_type
+//
+// Specify type for a let binding.
+//
+// ```
+// fn main() {
+//     let x<|> = 92;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     let x: i32 = 92;
+// }
+// ```
+pub(crate) fn add_explicit_type(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let let_stmt = ctx.find_node_at_offset::<LetStmt>()?;
+    let module = ctx.sema.scope(let_stmt.syntax()).module()?;
+    let expr = let_stmt.initializer()?;
+    // Must be a binding
+    let pat = match let_stmt.pat()? {
+        ast::Pat::IdentPat(bind_pat) => bind_pat,
+        _ => return None,
+    };
+    let pat_range = pat.syntax().text_range();
+    // The binding must have a name
+    let name = pat.name()?;
+    let name_range = name.syntax().text_range();
+    let stmt_range = let_stmt.syntax().text_range();
+    let eq_range = let_stmt.eq_token()?.text_range();
+    // Assist should only be applicable if cursor is between 'let' and '='
+    let let_range = TextRange::new(stmt_range.start(), eq_range.start());
+    let cursor_in_range = let_range.contains_range(ctx.frange.range);
+    if !cursor_in_range {
+        return None;
+    }
+    // Assist not applicable if the type has already been specified
+    // and it has no placeholders
+    let ascribed_ty = let_stmt.ty();
+    if let Some(ty) = &ascribed_ty {
+        if ty.syntax().descendants().find_map(ast::InferType::cast).is_none() {
+            return None;
+        }
+    }
+    // Infer type
+    let ty = ctx.sema.type_of_expr(&expr)?;
+
+    if ty.contains_unknown() || ty.is_closure() {
+        return None;
+    }
+
+    let inferred_type = ty.display_source_code(ctx.db(), module.into()).ok()?;
+    acc.add(
+        AssistId("add_explicit_type", AssistKind::RefactorRewrite),
+        format!("Insert explicit type `{}`", inferred_type),
+        pat_range,
+        |builder| match ascribed_ty {
+            Some(ascribed_ty) => {
+                builder.replace(ascribed_ty.syntax().text_range(), inferred_type);
+            }
+            None => {
+                builder.insert(name_range.end(), format!(": {}", inferred_type));
+            }
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    #[test]
+    fn add_explicit_type_target() {
+        check_assist_target(add_explicit_type, "fn f() { let a<|> = 1; }", "a");
+    }
+
+    #[test]
+    fn add_explicit_type_works_for_simple_expr() {
+        check_assist(add_explicit_type, "fn f() { let a<|> = 1; }", "fn f() { let a: i32 = 1; }");
+    }
+
+    #[test]
+    fn add_explicit_type_works_for_underscore() {
+        check_assist(
+            add_explicit_type,
+            "fn f() { let a<|>: _ = 1; }",
+            "fn f() { let a: i32 = 1; }",
+        );
+    }
+
+    #[test]
+    fn add_explicit_type_works_for_nested_underscore() {
+        check_assist(
+            add_explicit_type,
+            r#"
+            enum Option<T> {
+                Some(T),
+                None
+            }
+
+            fn f() {
+                let a<|>: Option<_> = Option::Some(1);
+            }"#,
+            r#"
+            enum Option<T> {
+                Some(T),
+                None
+            }
+
+            fn f() {
+                let a: Option<i32> = Option::Some(1);
+            }"#,
+        );
+    }
+
+    #[test]
+    fn add_explicit_type_works_for_macro_call() {
+        check_assist(
+            add_explicit_type,
+            r"macro_rules! v { () => {0u64} } fn f() { let a<|> = v!(); }",
+            r"macro_rules! v { () => {0u64} } fn f() { let a: u64 = v!(); }",
+        );
+    }
+
+    #[test]
+    fn add_explicit_type_works_for_macro_call_recursive() {
+        check_assist(
+            add_explicit_type,
+            r#"macro_rules! u { () => {0u64} } macro_rules! v { () => {u!()} } fn f() { let a<|> = v!(); }"#,
+            r#"macro_rules! u { () => {0u64} } macro_rules! v { () => {u!()} } fn f() { let a: u64 = v!(); }"#,
+        );
+    }
+
+    #[test]
+    fn add_explicit_type_not_applicable_if_ty_not_inferred() {
+        check_assist_not_applicable(add_explicit_type, "fn f() { let a<|> = None; }");
+    }
+
+    #[test]
+    fn add_explicit_type_not_applicable_if_ty_already_specified() {
+        check_assist_not_applicable(add_explicit_type, "fn f() { let a<|>: i32 = 1; }");
+    }
+
+    #[test]
+    fn add_explicit_type_not_applicable_if_specified_ty_is_tuple() {
+        check_assist_not_applicable(add_explicit_type, "fn f() { let a<|>: (i32, i32) = (3, 4); }");
+    }
+
+    #[test]
+    fn add_explicit_type_not_applicable_if_cursor_after_equals() {
+        check_assist_not_applicable(
+            add_explicit_type,
+            "fn f() {let a =<|> match 1 {2 => 3, 3 => 5};}",
+        )
+    }
+
+    #[test]
+    fn add_explicit_type_not_applicable_if_cursor_before_let() {
+        check_assist_not_applicable(
+            add_explicit_type,
+            "fn f() <|>{let a = match 1 {2 => 3, 3 => 5};}",
+        )
+    }
+
+    #[test]
+    fn closure_parameters_are_not_added() {
+        check_assist_not_applicable(
+            add_explicit_type,
+            r#"
+fn main() {
+    let multiply_by_two<|> = |i| i * 3;
+    let six = multiply_by_two(2);
+}"#,
+        )
+    }
+
+    #[test]
+    fn default_generics_should_not_be_added() {
+        check_assist(
+            add_explicit_type,
+            r#"
+struct Test<K, T = u8> {
+    k: K,
+    t: T,
+}
+
+fn main() {
+    let test<|> = Test { t: 23u8, k: 33 };
+}"#,
+            r#"
+struct Test<K, T = u8> {
+    k: K,
+    t: T,
+}
+
+fn main() {
+    let test: Test<i32> = Test { t: 23u8, k: 33 };
+}"#,
+        );
+    }
+}
diff --git a/crates/assists/src/handlers/add_missing_impl_members.rs b/crates/assists/src/handlers/add_missing_impl_members.rs
new file mode 100644
index 000000000..83a2ada9a
--- /dev/null
+++ b/crates/assists/src/handlers/add_missing_impl_members.rs
@@ -0,0 +1,766 @@
+use hir::HasSource;
+use syntax::{
+    ast::{
+        self,
+        edit::{self, AstNodeEdit, IndentLevel},
+        make, AstNode, NameOwner,
+    },
+    SmolStr,
+};
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    ast_transform::{self, AstTransform, QualifyPaths, SubstituteTypeParams},
+    utils::{get_missing_assoc_items, render_snippet, resolve_target_trait, Cursor},
+    AssistId, AssistKind,
+};
+
+#[derive(PartialEq)]
+enum AddMissingImplMembersMode {
+    DefaultMethodsOnly,
+    NoDefaultMethods,
+}
+
+// Assist: add_impl_missing_members
+//
+// Adds scaffold for required impl members.
+//
+// ```
+// trait Trait<T> {
+//     Type X;
+//     fn foo(&self) -> T;
+//     fn bar(&self) {}
+// }
+//
+// impl Trait<u32> for () {<|>
+//
+// }
+// ```
+// ->
+// ```
+// trait Trait<T> {
+//     Type X;
+//     fn foo(&self) -> T;
+//     fn bar(&self) {}
+// }
+//
+// impl Trait<u32> for () {
+//     fn foo(&self) -> u32 {
+//         ${0:todo!()}
+//     }
+// }
+// ```
+pub(crate) fn add_missing_impl_members(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    add_missing_impl_members_inner(
+        acc,
+        ctx,
+        AddMissingImplMembersMode::NoDefaultMethods,
+        "add_impl_missing_members",
+        "Implement missing members",
+    )
+}
+
+// Assist: add_impl_default_members
+//
+// Adds scaffold for overriding default impl members.
+//
+// ```
+// trait Trait {
+//     Type X;
+//     fn foo(&self);
+//     fn bar(&self) {}
+// }
+//
+// impl Trait for () {
+//     Type X = ();
+//     fn foo(&self) {}<|>
+//
+// }
+// ```
+// ->
+// ```
+// trait Trait {
+//     Type X;
+//     fn foo(&self);
+//     fn bar(&self) {}
+// }
+//
+// impl Trait for () {
+//     Type X = ();
+//     fn foo(&self) {}
+//
+//     $0fn bar(&self) {}
+// }
+// ```
+pub(crate) fn add_missing_default_members(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    add_missing_impl_members_inner(
+        acc,
+        ctx,
+        AddMissingImplMembersMode::DefaultMethodsOnly,
+        "add_impl_default_members",
+        "Implement default members",
+    )
+}
+
+fn add_missing_impl_members_inner(
+    acc: &mut Assists,
+    ctx: &AssistContext,
+    mode: AddMissingImplMembersMode,
+    assist_id: &'static str,
+    label: &'static str,
+) -> Option<()> {
+    let _p = profile::span("add_missing_impl_members_inner");
+    let impl_def = ctx.find_node_at_offset::<ast::Impl>()?;
+    let impl_item_list = impl_def.assoc_item_list()?;
+
+    let trait_ = resolve_target_trait(&ctx.sema, &impl_def)?;
+
+    let def_name = |item: &ast::AssocItem| -> Option<SmolStr> {
+        match item {
+            ast::AssocItem::Fn(def) => def.name(),
+            ast::AssocItem::TypeAlias(def) => def.name(),
+            ast::AssocItem::Const(def) => def.name(),
+            ast::AssocItem::MacroCall(_) => None,
+        }
+        .map(|it| it.text().clone())
+    };
+
+    let missing_items = get_missing_assoc_items(&ctx.sema, &impl_def)
+        .iter()
+        .map(|i| match i {
+            hir::AssocItem::Function(i) => ast::AssocItem::Fn(i.source(ctx.db()).value),
+            hir::AssocItem::TypeAlias(i) => ast::AssocItem::TypeAlias(i.source(ctx.db()).value),
+            hir::AssocItem::Const(i) => ast::AssocItem::Const(i.source(ctx.db()).value),
+        })
+        .filter(|t| def_name(&t).is_some())
+        .filter(|t| match t {
+            ast::AssocItem::Fn(def) => match mode {
+                AddMissingImplMembersMode::DefaultMethodsOnly => def.body().is_some(),
+                AddMissingImplMembersMode::NoDefaultMethods => def.body().is_none(),
+            },
+            _ => mode == AddMissingImplMembersMode::NoDefaultMethods,
+        })
+        .collect::<Vec<_>>();
+
+    if missing_items.is_empty() {
+        return None;
+    }
+
+    let target = impl_def.syntax().text_range();
+    acc.add(AssistId(assist_id, AssistKind::QuickFix), label, target, |builder| {
+        let n_existing_items = impl_item_list.assoc_items().count();
+        let source_scope = ctx.sema.scope_for_def(trait_);
+        let target_scope = ctx.sema.scope(impl_item_list.syntax());
+        let ast_transform = QualifyPaths::new(&target_scope, &source_scope)
+            .or(SubstituteTypeParams::for_trait_impl(&source_scope, trait_, impl_def));
+        let items = missing_items
+            .into_iter()
+            .map(|it| ast_transform::apply(&*ast_transform, it))
+            .map(|it| match it {
+                ast::AssocItem::Fn(def) => ast::AssocItem::Fn(add_body(def)),
+                ast::AssocItem::TypeAlias(def) => ast::AssocItem::TypeAlias(def.remove_bounds()),
+                _ => it,
+            })
+            .map(|it| edit::remove_attrs_and_docs(&it));
+        let new_impl_item_list = impl_item_list.append_items(items);
+        let first_new_item = new_impl_item_list.assoc_items().nth(n_existing_items).unwrap();
+
+        let original_range = impl_item_list.syntax().text_range();
+        match ctx.config.snippet_cap {
+            None => builder.replace(original_range, new_impl_item_list.to_string()),
+            Some(cap) => {
+                let mut cursor = Cursor::Before(first_new_item.syntax());
+                let placeholder;
+                if let ast::AssocItem::Fn(func) = &first_new_item {
+                    if let Some(m) = func.syntax().descendants().find_map(ast::MacroCall::cast) {
+                        if m.syntax().text() == "todo!()" {
+                            placeholder = m;
+                            cursor = Cursor::Replace(placeholder.syntax());
+                        }
+                    }
+                }
+                builder.replace_snippet(
+                    cap,
+                    original_range,
+                    render_snippet(cap, new_impl_item_list.syntax(), cursor),
+                )
+            }
+        };
+    })
+}
+
+fn add_body(fn_def: ast::Fn) -> ast::Fn {