Repository: dtolnay/cargo-expand (language: rust)

Issue:
Support non-nightly rustfmt
When someone runs `cargo +stable expand`, it calls `cargo +nightly expand` which calls `rustfmt`. Apparently that only finds rustfmt if the system has a nightly rustfmt. If they have nightly cargo-expand but stable rustfmt, then rustfmt does not get found.

Let's update the logic for invoking rustfmt so that it any rustfmt will work.


Discussion / hints:

Fix patch:
diff --git a/Cargo.lock b/Cargo.lock
index 44cf2a2..1fece0e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -27,6 +27,23 @@ dependencies = [
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "argon2rs"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "blake2-rfc 0.2.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "scoped_threadpool 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "arrayvec"
+version = "0.4.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "nodrop 0.1.13 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "atty"
 version = "0.2.11"
@@ -87,6 +104,15 @@ name = "bitflags"
 version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "blake2-rfc"
+version = "0.2.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "arrayvec 0.4.10 (registry+https://github.com/rust-lang/crates.io-index)",
+ "constant_time_eq 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "build_const"
 version = "0.2.1"
@@ -108,6 +134,7 @@ dependencies = [
  "structopt 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
  "syn 0.15.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempfile 3.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "toolchain_find 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -169,6 +196,11 @@ dependencies = [
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "constant_time_eq"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "content_inspector"
 version = "0.2.4"
@@ -270,6 +302,16 @@ dependencies = [
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "dirs"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "libc 0.2.47 (registry+https://github.com/rust-lang/crates.io-index)",
+ "redox_users 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "encoding"
 version = "0.2.33"
@@ -335,6 +377,26 @@ dependencies = [
  "backtrace 0.3.13 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "failure"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "backtrace 0.3.13 (registry+https://github.com/rust-lang/crates.io-index)",
+ "failure_derive 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "failure_derive"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "proc-macro2 0.4.26 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.6.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.15.26 (registry+https://github.com/rust-lang/crates.io-index)",
+ "synstructure 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "flate2"
 version = "1.0.6"
@@ -546,6 +608,11 @@ dependencies = [
  "miniz_oxide 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "nodrop"
+version = "0.1.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "onig"
 version = "4.3.1"
@@ -675,6 +742,18 @@ dependencies = [
  "proc-macro2 0.4.26 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "rand"
+version = "0.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "fuchsia-zircon 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.47 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand_core 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rdrand 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "rand"
 version = "0.6.4"
@@ -773,6 +852,17 @@ dependencies = [
  "redox_syscall 0.1.51 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "redox_users"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "argon2rs 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "failure 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "redox_syscall 0.1.51 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "regex"
 version = "1.1.0"
@@ -832,6 +922,11 @@ dependencies = [
  "winapi-util 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "scoped_threadpool"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "scopeguard"
 version = "0.3.3"
@@ -928,6 +1023,17 @@ dependencies = [
  "unicode-xid 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "synstructure"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "proc-macro2 0.4.26 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.6.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.15.26 (registry+https://github.com/rust-lang/crates.io-index)",
+ "unicode-xid 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "syntect"
 version = "3.0.2"
@@ -996,6 +1102,16 @@ dependencies = [
  "lazy_static 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "toolchain_find"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "dirs 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "walkdir 2.2.7 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "ucd-util"
 version = "0.1.3"
@@ -1138,6 +1254,8 @@ dependencies = [
 "checksum aho-corasick 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)" = "1e9a933f4e58658d7b12defcf96dc5c720f20832deebe3e0a19efd3b6aaeeb9e"
 "checksum ansi_colours 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "1d0f302a81afc6a7f4350c04f0ba7cfab529cc009bca3324b3fb5764e6add8b6"
 "checksum ansi_term 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ee49baf6cb617b853aa8d93bf420db2383fab46d314482ca2803b40d5fde979b"
+"checksum argon2rs 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)" = "3f67b0b6a86dae6e67ff4ca2b6201396074996379fba2b92ff649126f37cb392"
+"checksum arrayvec 0.4.10 (registry+https://github.com/rust-lang/crates.io-index)" = "92c7fb76bc8826a8b33b4ee5bb07a247a81e76764ab4d55e8f73e3a4d8808c71"
 "checksum atty 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)" = "9a7d5b8723950951411ee34d271d99dddcc2035a16ab25310ea2c8cfd4369652"
 "checksum autocfg 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "a6d640bee2da49f60a4068a7fae53acde8982514ab7bae8b8cea9e88cbcfd799"
 "checksum backtrace 0.3.13 (registry+https://github.com/rust-lang/crates.io-index)" = "b5b493b66e03090ebc4343eb02f94ff944e0cbc9ac6571491d170ba026741eb5"
@@ -1145,6 +1263,7 @@ dependencies = [
 "checksum base64 0.9.3 (registry+https://github.com/rust-lang/crates.io-index)" = "489d6c0ed21b11d038c31b6ceccca973e65d73ba3bd8ecb9a2babf5546164643"
 "checksum bincode 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "9f2fb9e29e72fd6bc12071533d5dc7664cb01480c59406f656d7ac25c7bd8ff7"
 "checksum bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)" = "228047a76f468627ca71776ecdebd732a3423081fcf5125585bcd7c49886ce12"
+"checksum blake2-rfc 0.2.18 (registry+https://github.com/rust-lang/crates.io-index)" = "5d6d530bdd2d52966a6d03b7a964add7ae1a288d25214066fd4b600f0f796400"
 "checksum build_const 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "39092a32794787acd8525ee150305ff051b0aa6cc2abaf193924f5ab05425f39"
 "checksum byteorder 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "60f0b0d4c0a382d2734228fd12b5a6b5dac185c60e938026fd31b265b94f9bd2"
 "checksum cc 1.0.28 (registry+https://github.com/rust-lang/crates.io-index)" = "bb4a8b715cb4597106ea87c7c84b2f1d452c7492033765df7f32651e66fcf749"
@@ -1153,6 +1272,7 @@ dependencies = [
 "checksum clicolors-control 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1f84dec9bc083ce2503908cd305af98bd363da6f54bf8d4bf0ac14ee749ad5d1"
 "checksum cloudabi 0.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "ddfc5b9aa5d4507acaf872de71051dfd0e309860e88966e1051e462a077aac4f"
 "checksum console 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)" = "ecd48adf136733979b49e15bc3b4c43cc0d3c85ece7bd08e6daa414c6fcb13e6"
+"checksum constant_time_eq 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "8ff012e225ce166d4422e0e78419d901719760f62ae2b7969ca6b564d1b54a9e"
 "checksum content_inspector 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)" = "b7bda66e858c683005a53a9a60c69a4aca7eeaa45d124526e389f7aec8e62f38"
 "checksum crc 1.8.1 (registry+https://github.com/rust-lang/crates.io-index)" = "d663548de7f5cca343f1e0a48d14dcfb0e9eb4e079ec58883b7251539fa10aeb"
 "checksum crc32fast 1.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "e91d5240c6975ef33aeb5f148f35275c25eda8e8a5f95abe421978b05b8bf192"
@@ -1163,6 +1283,7 @@ dependencies = [
 "checksum derive_builder 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "15d9e4f0be540b522e95c1de6200be0b12946fdd8408c093a1948de638e16f55"
 "checksum derive_builder_core 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e1cffc940f53a89045824e676302b840a5a60d447560704d352316e2039125a2"
 "checksum directories 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "72d337a64190607d4fcca2cb78982c5dd57f4916e19696b48a575fa746b6cb0f"
+"checksum dirs 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)" = "88972de891f6118092b643d85a0b28e0678e0f948d7f879aa32f2d5aafe97d2a"
 "checksum encoding 0.2.33 (registry+https://github.com/rust-lang/crates.io-index)" = "6b0d943856b990d12d3b55b359144ff341533e516d94098b1d3fc1ac666d36ec"
 "checksum encoding-index-japanese 1.20141219.5 (registry+https://github.com/rust-lang/crates.io-index)" = "04e8b2ff42e9a05335dbf8b5c6f7567e5591d0d916ccef4e0b1710d32a0d0c91"
 "checksum encoding-index-korean 1.20141219.5 (registry+https://github.com/rust-lang/crates.io-index)" = "4dc33fb8e6bcba213fe2f14275f0963fd16f0a02c878e3095ecfdf5bee529d81"
@@ -1171,6 +1292,8 @@ dependencies = [
 "checksum encoding-index-tradchinese 1.20141219.5 (registry+https://github.com/rust-lang/crates.io-index)" = "fd0e20d5688ce3cab59eb3ef3a2083a5c77bf496cb798dc6fcdb75f323890c18"
 "checksum encoding_index_tests 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "a246d82be1c9d791c5dfde9a2bd045fc3cbba3fa2b11ad558f27d01712f00569"
 "checksum error-chain 0.12.0 (registry+https://github.com/rust-lang/crates.io-index)" = "07e791d3be96241c77c43846b665ef1384606da2cd2a48730abe606a12906e02"
+"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 flate2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)" = "2291c165c8e703ee54ef3055ad6188e3d51108e2ded18e9f2476e774fc5ad3d4"
 "checksum fnv 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)" = "2fad85553e09a6f881f739c29f0b00b0f01357c743266d478b68951ce23285f3"
 "checksum fuchsia-zircon 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "2e9763c69ebaae630ba35f74888db465e49e259ba1bc0eda7d06f4a067615d82"
@@ -1197,6 +1320,7 @@ dependencies = [
 "checksum miniz-sys 0.1.11 (registry+https://github.com/rust-lang/crates.io-index)" = "0300eafb20369952951699b68243ab4334f4b10a88f411c221d444b36c40e649"
 "checksum miniz_oxide 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5ad30a47319c16cde58d0314f5d98202a80c9083b5f61178457403dfb14e509c"
 "checksum miniz_oxide_c_api 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "28edaef377517fd9fe3e085c37d892ce7acd1fbeab9239c5a36eec352d8a8b7e"
+"checksum nodrop 0.1.13 (registry+https://github.com/rust-lang/crates.io-index)" = "2f9667ddcc6cc8a43afc9b7917599d7216aa09c463919ea32c59ed6cac8bc945"
 "checksum onig 4.3.1 (registry+https://github.com/rust-lang/crates.io-index)" = "2e69a05d35a8f30d626a1df53c8636fe1b689407d744c0c7623aa825c0a3356e"
 "checksum onig_sys 69.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "388410bf5fa341f10e58e6db3975f4bea1ac30247dd79d37a9e5ced3cb4cc3b0"
 "checksum openssl-probe 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "77af24da69f9d9341038eba93a073b1fdaaa1b788221b00a69bce9e762cb32de"
@@ -1211,6 +1335,7 @@ dependencies = [
 "checksum proc-macro2 0.4.26 (registry+https://github.com/rust-lang/crates.io-index)" = "38fddd23d98b2144d197c0eca5705632d4fe2667d14a6be5df8934f8d74f1978"
 "checksum quick-error 1.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "9274b940887ce9addde99c4eee6b5c44cc494b182b97e73dc8ffdcb3397fd3f0"
 "checksum quote 0.6.11 (registry+https://github.com/rust-lang/crates.io-index)" = "cdd8e04bd9c52e0342b406469d494fcb033be4bdbe5c606016defbb1681411e1"
+"checksum rand 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)" = "dee497e66d8d76bf08ce20c8d36e16f93749ab0bf89975b4f8ae5cee660c2da2"
 "checksum rand 0.6.4 (registry+https://github.com/rust-lang/crates.io-index)" = "3906503e80ac6cbcacb2c2973fa8e473f24d7e2747c8c92bb230c2441cad96b5"
 "checksum rand_chacha 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "556d3a1ca6600bfcbab7c7c91ccb085ac7fbbcd70e008a98742e7847f4f7bcef"
 "checksum rand_core 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "0905b6b7079ec73b314d4c748701f6931eb79fd97c668caa3f1899b22b32c6db"
@@ -1222,6 +1347,7 @@ dependencies = [
 "checksum rdrand 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "678054eb77286b51581ba43620cc911abf02758c91f93f479767aed0f90458b2"
 "checksum redox_syscall 0.1.51 (registry+https://github.com/rust-lang/crates.io-index)" = "423e376fffca3dfa06c9e9790a9ccd282fafb3cc6e6397d01dbf64f9bacc6b85"
 "checksum redox_termios 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "7e891cfe48e9100a70a3b6eb652fef28920c117d366339687bd5576160db0f76"
+"checksum redox_users 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "214a97e49be64fd2c86f568dd0cb2c757d2cc53de95b273b6ad0a1c908482f26"
 "checksum regex 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "37e7cbbd370869ce2e8dff25c7018702d10b21a20ef7135316f8daecd6c25b7f"
 "checksum regex-syntax 0.6.4 (registry+https://github.com/rust-lang/crates.io-index)" = "4e47a2ed29da7a9e1960e1639e7a982e6edc6d49be308a3b02daf511504a16d1"
 "checksum remove_dir_all 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "3488ba1b9a2084d38645c4c08276a1752dcbf2c7130d74f1569681ad5d2799c5"
@@ -1230,6 +1356,7 @@ dependencies = [
 "checksum ryu 0.2.7 (registry+https://github.com/rust-lang/crates.io-index)" = "eb9e9b8cde282a9fe6a42dd4681319bfb63f121b8a8ee9439c6f4107e58a46f7"
 "checksum safemem 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "8dca453248a96cb0749e36ccdfe2b0b4e54a61bfef89fb97ec621eb8e0a93dd9"
 "checksum same-file 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)" = "8f20c4be53a8a1ff4c1f1b2bd14570d2f634628709752f0702ecdd2b3f9a5267"
+"checksum scoped_threadpool 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)" = "1d51f5df5af43ab3f1360b429fa5e0152ac5ce8c0bd6485cae490332e96846a8"
 "checksum scopeguard 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "94258f53601af11e6a49f722422f6e3425c52b06245a5cf9bc09908b174f5e27"
 "checksum semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
 "checksum semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
@@ -1243,12 +1370,14 @@ dependencies = [
 "checksum structopt 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)" = "670ad348dc73012fcf78c71f06f9d942232cdd4c859d4b6975e27836c3efc0c3"
 "checksum structopt-derive 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)" = "ef98172b1a00b0bec738508d3726540edcbd186d50dfd326f2b1febbb3559f04"
 "checksum syn 0.15.26 (registry+https://github.com/rust-lang/crates.io-index)" = "f92e629aa1d9c827b2bb8297046c1ccffc57c99b947a680d3ccff1f136a3bee9"
+"checksum synstructure 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)" = "73687139bf99285483c96ac0add482c3776528beac1d97d444f6e91f203a2015"
 "checksum syntect 3.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "e02dd9df97a68a2d005ace28ff24c610abfc3ce17afcfdb22a077645dabb599a"
 "checksum tempfile 3.0.5 (registry+https://github.com/rust-lang/crates.io-index)" = "7e91405c14320e5c79b3d148e1c86f40749a36e490642202a31689cb1a3452b2"
 "checksum termion 1.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "689a3bdfaab439fd92bc87df5c4c78417d3cbe537487274e9b0b2dce76e92096"
 "checksum termios 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)" = "72b620c5ea021d75a735c943269bb07d30c9b77d6ac6b236bc8b5c496ef05625"
 "checksum textwrap 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "307686869c93e71f94da64286f9a9524c0f308a9e1c87a583de8e9c9039ad3f6"
 "checksum thread_local 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)" = "c6b53e329000edc2b34dbe8545fd20e55a333362d0a321909685a19bd28c3f1b"
+"checksum toolchain_find 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "55703a3dde9a404783aeef3d21be00bd47d66b97c4bafa89c301900861d75b97"
 "checksum ucd-util 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "535c204ee4d8434478593480b8f86ab45ec9aae0e83c568ca81abf0fd0e88f86"
 "checksum unicode-bidi 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)" = "49f2bd0c6468a8230e1db229cff8029217cf623c767ea5d60bfbd42729ea54d5"
 "checksum unicode-normalization 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)" = "141339a08b982d942be2ca06ff8b076563cbe223d1befd5450716790d44e2426"
diff --git a/Cargo.toml b/Cargo.toml
index 1da285e..5a2d572 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -18,6 +18,7 @@ proc-macro2 = "0.4"
 quote = { version = "0.6", default-features = false }
 structopt = "0.2"
 tempfile = "3.0"
+toolchain_find = "0.1"
 
 [dependencies.syn]
 version = "0.15"
diff --git a/src/main.rs b/src/main.rs
index ffeea76..d2e5425 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -96,7 +96,7 @@ fn cargo_expand() -> Result<i32> {
             return Ok(1);
         }
         (Some(item), false) => {
-            which_rustfmt = which("rustfmt");
+            which_rustfmt = toolchain_find::find_installed_component("rustfmt");
             if which_rustfmt.is_none() {
                 eprintln!(
                     "ERROR: cannot expand single item ({}) without rustfmt.",
@@ -107,7 +107,7 @@ fn cargo_expand() -> Result<i32> {
             }
         }
         (None, true) => which_rustfmt = None,
-        (None, false) => which_rustfmt = which("rustfmt"),
+        (None, false) => which_rustfmt = toolchain_find::find_installed_component("rustfmt"),
     }
 
     let mut builder = tempfile::Builder::new();
@@ -288,41 +288,6 @@ fn apply_args(cmd: &mut Command, args: &Args, outfile: &Path) {
     cmd.arg("--pretty=expanded");
 }
 
-fn which(cmd: &str) -> Option<OsString> {
-    if env::args_os().any(|arg| arg == *"--help") {
-        return None;
-    }
-
-    if let Some(which) = env::var_os(&cmd.to_uppercase()) {
-        return if which.is_empty() { None } else { Some(which) };
-    }
-
-    let spawn = Command::new(cmd)
-        .stdin(Stdio::null())
-        .stdout(Stdio::null())
-        .stderr(Stdio::null())
-        .spawn();
-    let mut child = match spawn {
-        Ok(child) => child,
-        Err(_) => {
-            return None;
-        }
-    };
-
-    let exit = match child.wait() {
-        Ok(exit) => exit,
-        Err(_) => {
-            return None;
-        }
-    };
-
-    if exit.success() {
-        Some(cmd.into())
-    } else {
-        None
-    }
-}
-
 fn filter_err(cmd: &mut Command, ignore: fn(&str) -> bool) -> io::Result<i32> {
     let mut child = cmd.stderr(Stdio::piped()).spawn()?;
     let mut stderr = io::BufReader::new(child.stderr.take().unwrap());


Test patch: