diff --git a/Cargo.lock b/Cargo.lock
index 05d340e5f6..4ef0134d7d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -352,11 +352,6 @@ dependencies = [
  "syn 0.15.44 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
-[[package]]
-name = "deunicode"
-version = "0.4.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-
 [[package]]
 name = "difference"
 version = "2.0.0"
@@ -406,15 +401,6 @@ name = "encode_unicode"
 version = "0.3.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
-[[package]]
-name = "error-chain"
-version = "0.12.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "backtrace 0.3.34 (registry+https://github.com/rust-lang/crates.io-index)",
- "version_check 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
 [[package]]
 name = "failure"
 version = "0.1.5"
@@ -556,11 +542,6 @@ dependencies = [
  "wasi 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
-[[package]]
-name = "glob"
-version = "0.2.11"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-
 [[package]]
 name = "glob"
 version = "0.3.0"
@@ -586,21 +567,6 @@ dependencies = [
  "unicode-segmentation 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
-[[package]]
-name = "humansize"
-version = "1.1.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-
-[[package]]
-name = "idna"
-version = "0.1.5"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "matches 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "unicode-bidi 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)",
- "unicode-normalization 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
 [[package]]
 name = "idna"
 version = "0.2.0"
@@ -1007,11 +973,6 @@ dependencies = [
  "syn 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
-[[package]]
-name = "percent-encoding"
-version = "1.0.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-
 [[package]]
 name = "percent-encoding"
 version = "2.1.0"
@@ -1368,7 +1329,6 @@ dependencies = [
  "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 1.0.99 (registry+https://github.com/rust-lang/crates.io-index)",
- "teraron 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "walkdir 2.2.9 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1783,14 +1743,6 @@ name = "slab"
 version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
-[[package]]
-name = "slug"
-version = "0.1.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "deunicode 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
 [[package]]
 name = "smallvec"
 version = "0.6.10"
@@ -1869,36 +1821,6 @@ dependencies = [
  "winapi 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
-[[package]]
-name = "tera"
-version = "0.11.20"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "chrono 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "error-chain 0.12.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "glob 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
- "humansize 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "lazy_static 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "pest 2.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "pest_derive 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "regex 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.99 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_json 1.0.40 (registry+https://github.com/rust-lang/crates.io-index)",
- "slug 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
- "unic-segment 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "url 1.7.2 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
-[[package]]
-name = "teraron"
-version = "0.1.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "heck 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "ron 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "tera 0.11.20 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
 [[package]]
 name = "termios"
 version = "0.3.1"
@@ -1973,50 +1895,6 @@ name = "ucd-trie"
 version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
-[[package]]
-name = "unic-char-property"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "unic-char-range 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
-[[package]]
-name = "unic-char-range"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-
-[[package]]
-name = "unic-common"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-
-[[package]]
-name = "unic-segment"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "unic-ucd-segment 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
-[[package]]
-name = "unic-ucd-segment"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "unic-char-property 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "unic-char-range 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "unic-ucd-version 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
-[[package]]
-name = "unic-ucd-version"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "unic-common 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
 [[package]]
 name = "unicase"
 version = "2.4.0"
@@ -2061,16 +1939,6 @@ name = "unicode-xid"
 version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
-[[package]]
-name = "url"
-version = "1.7.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "idna 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
- "matches 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "percent-encoding 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
 [[package]]
 name = "url"
 version = "2.1.0"
@@ -2215,7 +2083,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum crossbeam-queue 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "7c979cd6cfe72335896575c6b5688da489e420d36a27a0b9eb0c73db574b4a4b"
 "checksum crossbeam-utils 0.6.6 (registry+https://github.com/rust-lang/crates.io-index)" = "04973fa96e96579258a5091af6003abde64af786b860f18622b82e026cca60e6"
 "checksum derive-new 0.5.7 (registry+https://github.com/rust-lang/crates.io-index)" = "c3fd04571b29c91cfbe1e7c9a228e069ac8635f180ffb4ccd6a6907617ee8bb0"
-"checksum deunicode 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)" = "850878694b7933ca4c9569d30a34b55031b9b139ee1fc7b94a527c4ef960d690"
 "checksum difference 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "524cbf6897b527295dff137cec09ecf3a05f4fddffd7dfcd1585403449e74198"
 "checksum digest 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)" = "f3d0c8c8752312f9713efd397ff63acb9f85585afbf179282e720e7704954dd5"
 "checksum drop_bomb 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "69b26e475fd29098530e709294e94e661974c851aed42512793f120fed4e199f"
@@ -2224,7 +2091,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum ena 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)" = "25b4e5febb25f08c49f1b07dc33a182729a6b21edfb562b5aef95f78e0dbe5bb"
 "checksum ena 0.13.0 (registry+https://github.com/rust-lang/crates.io-index)" = "3dc01d68e08ca384955a3aeba9217102ca1aa85b6e168639bf27739f1d749d87"
 "checksum encode_unicode 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)" = "90b2c9496c001e8cb61827acdefad780795c42264c137744cae6f7d9e3450abd"
-"checksum error-chain 0.12.1 (registry+https://github.com/rust-lang/crates.io-index)" = "3ab49e9dcb602294bc42f9a7dfc9bc6e936fca4418ea300dbfb84fe16de0b7d9"
 "checksum failure 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "795bd83d3abeb9220f257e597aa0080a508b27533824adf336529648f6abf7e2"
 "checksum failure_derive 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "ea1063915fd7ef4309e222a5a07cf9c319fb9c7836b1f89b85458672dbb127e1"
 "checksum fake-simd 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "e88a8acf291dafb59c2d96e8f59828f3838bb1a70398823ade51a84de6a6deed"
@@ -2242,12 +2108,9 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum fuchsia-zircon-sys 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3dcaa9ae7725d12cdb85b3ad99a434db70b468c09ded17e012d86b5c1010f7a7"
 "checksum generic-array 0.12.3 (registry+https://github.com/rust-lang/crates.io-index)" = "c68f0274ae0e023facc3c97b2e00f076be70e254bc851d972503b328db79b2ec"
 "checksum getrandom 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)" = "2512b3191f22e2763a5db387f1c9409379772e2050841722eb4a8c4f497bf096"
-"checksum glob 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)" = "8be18de09a56b60ed0edf84bc9df007e30040691af7acd1c41874faac5895bfb"
 "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"
-"checksum humansize 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "b6cab2627acfc432780848602f3f558f7e9dd427352224b0d9324025796d2a5e"
-"checksum idna 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "38f09e0f0b1fb55fdee1f17470ad800da77af5186a1a76c026b679358b7e844e"
 "checksum idna 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "02e2673c30ee86b5b96a9cb52ad15718aa1f966f5ab9ad54a8b95d5ca33120a9"
 "checksum indexmap 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "7e81a7c05f79578dbc15793d8b619db9ba32b4577003ef3af1a91c416798c58d"
 "checksum indicatif 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "2c60da1c9abea75996b70a931bba6c750730399005b61ccd853cee50ef3d0d0c"
@@ -2294,7 +2157,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum parking_lot_core 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)" = "b876b1b9e7ac6e1a74a6da34d25c42e17e8862aa409cbbbdcfc8d86c6f3bc62b"
 "checksum paste 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "423a519e1c6e828f1e73b720f9d9ed2fa643dce8a7737fb43235ce0b41eeaa49"
 "checksum paste-impl 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "4214c9e912ef61bf42b81ba9a47e8aad1b2ffaf739ab162bf96d1e011f54e6c5"
-"checksum percent-encoding 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "31010dd2e1ac33d5b46a5b413495239882813e0369f8ed8a5e266f173602f831"
 "checksum percent-encoding 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "d4fd5641d01c8f18a23da7b6fe29298ff4b55afcccdf78973b24cf3175fee32e"
 "checksum pest 2.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "933085deae3f32071f135d799d75667b63c8dc1f4537159756e3d4ceab41868c"
 "checksum pest_derive 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "833d1ae558dc601e9a60366421196a8d94bc0ac980476d0b67e1d0988d72b2d0"
@@ -2354,7 +2216,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum serde_yaml 0.8.9 (registry+https://github.com/rust-lang/crates.io-index)" = "38b08a9a90e5260fe01c6480ec7c811606df6d3a660415808c3c3fa8ed95b582"
 "checksum sha-1 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)" = "23962131a91661d643c98940b20fcaffe62d776a823247be80a48fcb8b6fce68"
 "checksum slab 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)" = "c111b5bd5695e56cffe5129854aa230b39c93a305372fdbb2668ca2394eea9f8"
-"checksum slug 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "b3bc762e6a4b6c6fcaade73e77f9ebc6991b676f88bb2358bddb56560f073373"
 "checksum smallvec 0.6.10 (registry+https://github.com/rust-lang/crates.io-index)" = "ab606a9c5e214920bb66c458cd7be8ef094f813f20fe77a54cc7dbfff220d4b7"
 "checksum smol_str 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)" = "590700be3630457c56f8c73c0ea39881476ad7076cd84057d44f4f38f79914fb"
 "checksum stacker 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "fb79482f57cf598af52094ec4cc3b3c42499d3ce5bd426f2ac41515b7e57404b"
@@ -2364,8 +2225,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum syn 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "2ae5cd13590144ea968ba5d5520da7a4c08415861014399b5b349f74591c375f"
 "checksum synstructure 0.10.2 (registry+https://github.com/rust-lang/crates.io-index)" = "02353edf96d6e4dc81aea2d8490a7e9db177bf8acb0e951c24940bf866cb313f"
 "checksum tempfile 3.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "7a6e24d9338a0a5be79593e2fa15a648add6138caa803e2d5bc782c371732ca9"
-"checksum tera 0.11.20 (registry+https://github.com/rust-lang/crates.io-index)" = "4b505279e19d8f7d24b1a9dc58327c9c36174b1a2c7ebdeac70792d017cb64f3"
-"checksum teraron 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "9a447d012fef5c222f4b11a98fcef2a7e347a57f28be9957c5c390ac9a0e41e0"
 "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"
 "checksum textwrap 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "d326610f408c7a4eb6f51c37c330e496b08506c9457c9d34287ecc38809fb060"
@@ -2374,12 +2233,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum time 0.1.42 (registry+https://github.com/rust-lang/crates.io-index)" = "db8dcfca086c1143c9270ac42a2bbd8a7ee477b78ac8e45b19abfb0cbede4b6f"
 "checksum typenum 1.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "612d636f949607bdf9b123b4a6f6d966dedf3ff669f7f045890d3a4a73948169"
 "checksum ucd-trie 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "8f00ed7be0c1ff1e24f46c3d2af4859f7e863672ba3a6e92e7cff702bf9f06c2"
-"checksum unic-char-property 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ce36d3f7ce754afdbccccf8ff0dd0134e50fb44aaae579f96218856e9e5dbd1e"
-"checksum unic-char-range 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "d9ab85fab42ad1b26cafc03bf891f69cb4d6e15f491030e89a0122197baa8ae8"
-"checksum unic-common 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ff8d4a7ade929ef7d971e16ced21a8cd56a63869aa6032dfb8cb083cf7d077bf"
-"checksum unic-segment 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "c9ca47cbb09fb5fcd066b5867d11dc528302fa465277882797d6a836e1ee6f9e"
-"checksum unic-ucd-segment 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "48f1a08ce0409a9e391b88d1930118eec48af12742fc538bcec55f775865776e"
-"checksum unic-ucd-version 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "cf1f5e6c6c53c2d0ece4a5964bc55fcff8602153063cb4fab20958ff32998ff6"
 "checksum unicase 2.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "a84e5511b2a947f3ae965dcb29b13b7b1691b6e7332cf5dbc1744138d5acb7f6"
 "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"
@@ -2387,7 +2240,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum unicode-width 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "882386231c45df4700b275c7ff55b6f3698780a650026380e72dabe76fa46526"
 "checksum unicode-xid 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "fc72304796d0818e357ead4e000d19c9c174ab23dc11093ac919054d20a6a7fc"
 "checksum unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "826e7639553986605ec5979c7dd957c7895e93eabed50ab2ffa7f6128a75097c"
-"checksum url 1.7.2 (registry+https://github.com/rust-lang/crates.io-index)" = "dd4e7c0d531266369519a4aa4f399d748bd37043b00bde1e4ff1f60a120b355a"
 "checksum url 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "75b414f6c464c879d7f9babf951f23bc3743fb7313c081b2e6ca719067ea9d61"
 "checksum uuid 0.7.4 (registry+https://github.com/rust-lang/crates.io-index)" = "90dbc611eb48397705a6b0f6e917da23ae517e4d127123d2cf7674206627d32a"
 "checksum vec_map 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)" = "05c78687fb1a80548ae3250346c3db86a80a7cdd77bda190189f2d0a0987c81a"
diff --git a/crates/ra_tools/Cargo.toml b/crates/ra_tools/Cargo.toml
index a40a452aaa..4c9aa1cc3f 100644
--- a/crates/ra_tools/Cargo.toml
+++ b/crates/ra_tools/Cargo.toml
@@ -6,7 +6,6 @@ authors = ["rust-analyzer developers"]
 publish = false
 
 [dependencies]
-teraron = "0.1.0"
 walkdir = "2.1.3"
 itertools = "0.8.0"
 clap = "2.32.0"
diff --git a/crates/ra_tools/src/lib.rs b/crates/ra_tools/src/lib.rs
index de8c472d15..c02dee9534 100644
--- a/crates/ra_tools/src/lib.rs
+++ b/crates/ra_tools/src/lib.rs
@@ -11,8 +11,6 @@ use std::{
 
 use itertools::Itertools;
 
-pub use teraron::{Mode, Overwrite, Verify};
-
 pub use self::codegen::generate;
 
 pub type Result<T> = std::result::Result<T, Box<dyn Error>>;
@@ -26,6 +24,13 @@ pub const SYNTAX_KINDS: &str = "crates/ra_parser/src/syntax_kind/generated.rs.te
 pub const AST: &str = "crates/ra_syntax/src/ast/generated.rs";
 const TOOLCHAIN: &str = "stable";
 
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum Mode {
+    Overwrite,
+    Verify,
+}
+pub use Mode::*;
+
 #[derive(Debug)]
 pub struct Test {
     pub name: String,
@@ -222,7 +227,7 @@ pub fn gen_tests(mode: Mode) -> Result<()> {
                     tests_dir.join(file_name)
                 }
             };
-            teraron::update(&path, &test.text, mode)?;
+            update(&path, &test.text, mode)?;
         }
         Ok(())
     }
@@ -306,3 +311,20 @@ fn existing_tests(dir: &Path, ok: bool) -> Result<HashMap<String, (PathBuf, Test
     }
     Ok(res)
 }
+
+/// A helper to update file on disk if it has changed.
+/// With verify = false,
+pub fn update(path: &Path, contents: &str, mode: Mode) -> Result<()> {
+    match fs::read_to_string(path) {
+        Ok(ref old_contents) if old_contents == contents => {
+            return Ok(());
+        }
+        _ => (),
+    }
+    if mode == Verify {
+        Err(format!("`{}` is not up-to-date", path.display()))?;
+    }
+    eprintln!("updating {}", path.display());
+    fs::write(path, contents)?;
+    Ok(())
+}