diff --git a/Cargo.lock b/Cargo.lock
index ad60376e65..5f7e5322ce 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3,6 +3,7 @@ name = "sccache"
 version = "0.2.1"
 dependencies = [
  "app_dirs 1.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "assert_cli 0.5.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "base64 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -36,7 +37,7 @@ dependencies = [
  "rust-crypto 0.2.36 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_json 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempdir 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempfile 2.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -88,6 +89,19 @@ dependencies = [
  "xdg 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "assert_cli"
+version = "0.5.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "colored 1.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "difference 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "environment 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "error-chain 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "skeptic 0.13.2 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "atty"
 version = "0.2.2"
@@ -98,6 +112,29 @@ dependencies = [
  "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "backtrace"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "backtrace-sys 0.1.16 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cfg-if 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "dbghelp-sys 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "kernel32-sys 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.23 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc-demangle 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "backtrace-sys"
+version = "0.1.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "cc 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.23 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "base64"
 version = "0.5.2"
@@ -140,6 +177,11 @@ name = "bitflags"
 version = "0.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "bytecount"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "byteorder"
 version = "1.0.0"
@@ -154,11 +196,28 @@ dependencies = [
  "iovec 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "cargo_metadata"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "error-chain 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "semver 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "case"
 version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "cc"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "cfg-if"
 version = "0.1.1"
@@ -197,6 +256,14 @@ dependencies = [
  "scopeguard 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "colored"
+version = "1.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "lazy_static 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "conv"
 version = "0.3.3"
@@ -244,6 +311,15 @@ dependencies = [
  "libc 0.2.23 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "dbghelp-sys"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi-build 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "derive-error"
 version = "0.0.3"
@@ -254,6 +330,11 @@ dependencies = [
  "syn 0.11.11 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "difference"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "dtoa"
 version = "0.4.1"
@@ -273,11 +354,24 @@ dependencies = [
  "regex 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "environment"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "error-chain"
 version = "0.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "error-chain"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "backtrace 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "fern"
 version = "0.3.5"
@@ -341,6 +435,11 @@ name = "getopts"
 version = "0.2.14"
 source = "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 = "httparse"
 version = "1.2.3"
@@ -425,7 +524,7 @@ dependencies = [
  "ring 0.9.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_json 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "untrusted 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -724,6 +823,14 @@ dependencies = [
  "getopts 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "pulldown-cmark"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "bitflags 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "quote"
 version = "0.3.15"
@@ -820,6 +927,11 @@ dependencies = [
  "time 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "rustc-demangle"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "rustc-serialize"
 version = "0.3.24"
@@ -905,6 +1017,20 @@ name = "semver"
 version = "0.1.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "semver"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "semver-parser"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "serde"
 version = "1.0.8"
@@ -931,7 +1057,7 @@ dependencies = [
 
 [[package]]
 name = "serde_json"
-version = "1.0.2"
+version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "dtoa 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -963,6 +1089,21 @@ dependencies = [
  "tempdir 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "skeptic"
+version = "0.13.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "bytecount 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cargo_metadata 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "error-chain 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "glob 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "pulldown-cmark 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tempdir 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "walkdir 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "slab"
 version = "0.3.0"
@@ -1344,31 +1485,42 @@ dependencies = [
 "checksum aho-corasick 0.6.3 (registry+https://github.com/rust-lang/crates.io-index)" = "500909c4f87a9e52355b26626d890833e9e1d53ac566db76c36faa984b889699"
 "checksum ansi_term 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "23ac7c30002a5accbf7e8987d0632fa6de155b7c3d39d0067317a391e00a2ef6"
 "checksum app_dirs 1.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "b7d1c0d48a81bbb13043847f957971f4d87c81542d80ece5e84ba3cba4058fd4"
+"checksum assert_cli 0.5.4 (registry+https://github.com/rust-lang/crates.io-index)" = "72342c21057a3cb5f7c2d849bf7999a83795434dd36d74fa8c24680581bd1930"
 "checksum atty 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "d912da0db7fa85514874458ca3651fe2cddace8d0b0505571dbdcd41ab490159"
+"checksum backtrace 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "99f2ce94e22b8e664d95c57fff45b98a966c2252b60691d0b7aeeccd88d70983"
+"checksum backtrace-sys 0.1.16 (registry+https://github.com/rust-lang/crates.io-index)" = "44585761d6161b0f57afc49482ab6bd067e4edef48c12a152c237eb0203f7661"
 "checksum base64 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)" = "30e93c03064e7590d0466209155251b90c22e37fab1daf2771582598b5827557"
 "checksum base64 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)" = "96434f987501f0ed4eb336a411e0631ecd1afa11574fe148587adc4ff96143c9"
 "checksum bincode 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e103c8b299b28a9c6990458b7013dc4a8356a9b854c51b9883241f5866fac36e"
 "checksum bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "aad18937a628ec6abcd26d1489012cc0e18c21798210f491af69ded9b881106d"
 "checksum bitflags 0.8.2 (registry+https://github.com/rust-lang/crates.io-index)" = "1370e9fc2a6ae53aea8b7a5110edbd08836ed87c88736dfabccade1c2b44bff4"
 "checksum bitflags 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)" = "4efd02e230a02e18f92fc2735f44597385ed02ad8f831e7c1c1156ee5e1ab3a5"
+"checksum bytecount 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "af27422163679dea46a1a7239dffff64d3dcdc3ba5fe9c49c789fbfe0eb949de"
 "checksum byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "c40977b0ee6b9885c9013cd41d9feffdd22deb3bb4dc3a71d901cc7a77de18c8"
 "checksum bytes 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)" = "8b24f16593f445422331a5eed46b72f7f171f910fead4f2ea8f17e727e9c5c14"
+"checksum cargo_metadata 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "b41aa83cb513b27e28882e97423e7cdef5554b3bd65ff48b32b66c20ce1c6afa"
 "checksum case 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e88b166b48e29667f5443df64df3c61dc07dc2b1a0b0d231800e07f09a33ecc1"
+"checksum cc 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "ef4019bdb99c0c1ddd56c12c2f507c174d729c6915eca6bd9d27c42f3d93b0f4"
 "checksum cfg-if 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "d0c47d456a36ebf0536a6705c83c1cbbcb9255fbc1d905a6ded104f479268a29"
 "checksum chrono 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)" = "d9123be86fd2a8f627836c235ecdf331fdd067ecf7ac05aa1a68fbcf2429f056"
 "checksum clap 2.24.2 (registry+https://github.com/rust-lang/crates.io-index)" = "6b8f69e518f967224e628896b54e41ff6acfb4dcfefc5076325c36525dac900f"
 "checksum coco 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "c06169f5beb7e31c7c67ebf5540b8b472d23e3eade3b2ec7d1f5b504a85f91bd"
+"checksum colored 1.5.3 (registry+https://github.com/rust-lang/crates.io-index)" = "c1d4a2a8e207306352a8b08263af6c83c0be745b21cd2eedfe03a5f49ec8cd93"
 "checksum conv 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "78ff10625fd0ac447827aa30ea8b861fead473bb60aeb73af6c1c58caf0d1299"
 "checksum core-foundation 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "25bfd746d203017f7d5cbd31ee5d8e17f94b6521c7af77ece6c9e4b2d4b16c67"
 "checksum core-foundation-sys 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "065a5d7ffdcbc8fa145d6f0746f3555025b9097a9e9cda59f7467abae670c78d"
 "checksum crypt32-sys 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e34988f7e069e0b2f3bfc064295161e489b2d4e04a2e4248fb94360cdf00b4ec"
 "checksum custom_derive 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)" = "ef8ae57c4978a2acd8b869ce6b9ca1dfe817bff704c220209fdef2c0b75a01b9"
 "checksum daemonize 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "0239832c1b4ca406d5ec73728cf4c7336d25cf85dd32db9e047e9e706ee0e935"
+"checksum dbghelp-sys 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "97590ba53bcb8ac28279161ca943a924d1fd4a8fb3fa63302591647c4fc5b850"
 "checksum derive-error 0.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "629f1bb3abce791912ca85a24676fff54464f7deb122906adabc90fb96e876d3"
+"checksum difference 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "b3304d19798a8e067e48d8e69b2c37f0b5e9b4e462504ad9e27e9f3fce02bba8"
 "checksum dtoa 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)" = "80c8b71fd71146990a9742fc06dcbbde19161a267e0ad4e572c35162f4578c90"
 "checksum either 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "18785c1ba806c258137c937e44ada9ee7e69a37e3c72077542cd2f069d78562a"
 "checksum env_logger 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3ddf21e73e016298f5cb37d6ef8e8da8e39f91f9ec8b0df44b7deb16a9f8cd5b"
+"checksum environment 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "1f4b14e20978669064c33b4c1e0fb4083412e40fe56cbea2eae80fd7591503ee"
 "checksum error-chain 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "d9435d864e017c3c6afeac1654189b06cdb491cf2ff73dbf0d73b0f292f42ff8"
+"checksum error-chain 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ff511d5dc435d703f4971bc399647c9bc38e20cb41452e3b9feb4765419ed3f3"
 "checksum fern 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)" = "4d2f58d053ad7791bfaad58a3f3541fe2d2aecc564dd82aee7f92fa402c054b2"
 "checksum filetime 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)" = "5363ab8e4139b8568a6237db5248646e5a8a2f89bd5ccb02092182b11fd3e922"
 "checksum flate2 0.2.19 (registry+https://github.com/rust-lang/crates.io-index)" = "36df0166e856739905cd3d7e0b210fe818592211a008862599845e012d8d304c"
@@ -1378,6 +1530,7 @@ dependencies = [
 "checksum gcc 0.3.51 (registry+https://github.com/rust-lang/crates.io-index)" = "120d07f202dcc3f72859422563522b66fe6463a4c513df062874daad05f85f0a"
 "checksum gdi32-sys 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "0912515a8ff24ba900422ecda800b52f4016a56251922d397c576bf92c690518"
 "checksum getopts 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)" = "d9047cfbd08a437050b363d35ef160452c5fe8ea5187ae0a624708c91581d685"
+"checksum glob 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)" = "8be18de09a56b60ed0edf84bc9df007e30040691af7acd1c41874faac5895bfb"
 "checksum httparse 1.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "af2f2dd97457e8fb1ae7c5a420db346af389926e36f43768b96f101546b04a07"
 "checksum hyper 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "b8590f308416a428dca05ca67020283105344e94059fd2f02cc72e9c913c30fb"
 "checksum hyper-tls 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e6829541bb9b1716568b3cf353bbcf0566578874b0ffa147922eadc67c7aa3a6"
@@ -1420,6 +1573,7 @@ dependencies = [
 "checksum pkg-config 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)" = "3a8b4c6b8165cd1a1cd4b9b120978131389f64bdaf456435caa41e630edba903"
 "checksum podio 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "e5422a1ee1bc57cc47ae717b0137314258138f38fd5f3cea083f43a9725383a0"
 "checksum pulldown-cmark 0.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "8361e81576d2e02643b04950e487ec172b687180da65c731c03cf336784e6c07"
+"checksum pulldown-cmark 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "a656fdb8b6848f896df5e478a0eb9083681663e37dcb77dd16981ff65329fe8b"
 "checksum quote 0.3.15 (registry+https://github.com/rust-lang/crates.io-index)" = "7a6e920b65c65f10b2ae65c831a81a073a89edd28c7cce89475bff467ab4167a"
 "checksum rand 0.3.15 (registry+https://github.com/rust-lang/crates.io-index)" = "022e0636ec2519ddae48154b028864bdce4eaf7d35226ab8e65c611be97b189d"
 "checksum rayon 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)" = "a77c51c07654ddd93f6cb543c7a849863b03abc7e82591afda6dc8ad4ac3ac4a"
@@ -1431,6 +1585,7 @@ dependencies = [
 "checksum retry 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "29460f6011a25fc70b22010e796bd98330baccaa0005cba6f90b858a510dec0d"
 "checksum ring 0.9.7 (registry+https://github.com/rust-lang/crates.io-index)" = "24293de46bac74c9b9c05b40ff8496bbc8b9ae242a9b89f754e1154a43bc7c4c"
 "checksum rust-crypto 0.2.36 (registry+https://github.com/rust-lang/crates.io-index)" = "f76d05d3993fd5f4af9434e8e436db163a12a9d40e1a58a726f27a01dfd12a2a"
+"checksum rustc-demangle 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "aee45432acc62f7b9a108cc054142dac51f979e69e71ddce7d6fc7adf29e817e"
 "checksum rustc-serialize 0.3.24 (registry+https://github.com/rust-lang/crates.io-index)" = "dcf128d1287d2ea9d80910b5f1120d0b8eede3fbf1abe91c40d39ea7d51e6fda"
 "checksum rustc_version 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)" = "c5f5376ea5e30ce23c03eb77cbe4962b988deead10910c372b226388b594c084"
 "checksum safemem 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e27a8b19b835f7aea908818e871f5cc3a5a186550c30773be987e155e8163d8f"
@@ -1442,12 +1597,15 @@ dependencies = [
 "checksum security-framework 0.1.14 (registry+https://github.com/rust-lang/crates.io-index)" = "42ddf098d78d0b64564b23ee6345d07573e7d10e52ad86875d89ddf5f8378a02"
 "checksum security-framework-sys 0.1.14 (registry+https://github.com/rust-lang/crates.io-index)" = "5bacdada57ea62022500c457c8571c17dfb5e6240b7c8eac5916ffa8c7138a55"
 "checksum semver 0.1.20 (registry+https://github.com/rust-lang/crates.io-index)" = "d4f410fedcf71af0345d7607d246e7ad15faaadd49d240ee3b24e5dc21a820ac"
+"checksum semver 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "bee2bc909ab2d8d60dab26e8cad85b25d795b14603a0dcb627b78b9d30b6454b"
+"checksum semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
 "checksum serde 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)" = "c2f530d36fb84ec48fb7146936881f026cdbf4892028835fd9398475f82c1bb4"
 "checksum serde_derive 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)" = "10552fad5500771f3902d0c5ba187c5881942b811b7ba0d8fbbfbf84d80806d3"
 "checksum serde_derive_internals 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)" = "37aee4e0da52d801acfbc0cc219eb1eda7142112339726e427926a6f6ee65d3a"
-"checksum serde_json 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "48b04779552e92037212c3615370f6bd57a40ebba7f20e554ff9f55e41a69a7b"
+"checksum serde_json 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)" = "ee28c1d94a7745259b767ca9e5b95d55bafbd3205ca3acb978cad84a6ed6bc62"
 "checksum sha1 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "cc30b1e1e8c40c121ca33b86c23308a090d19974ef001b4bf6e61fd1a0fb095c"
 "checksum shell32-sys 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "72f20b8f3c060374edb8046591ba28f62448c369ccbdc7b02075103fb3a9e38d"
+"checksum skeptic 0.13.2 (registry+https://github.com/rust-lang/crates.io-index)" = "c8431f8fca168e2db4be547bd8329eac70d095dff1444fee4b0fa0fabc7df75a"
 "checksum skeptic 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "24ebf8a06f5f8bae61ae5bbc7af7aac4ef6907ae975130faba1199e5fe82256a"
 "checksum slab 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "17b4fcaed89ab08ef143da37bc52adbcc04d4a69014f4c1208d6b51f0c47bc23"
 "checksum slab 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "fdeff4cd9ecff59ec7e3744cbca73dfe5ac35c2aedb2cfba8a1c715a18912e9d"
diff --git a/Cargo.toml b/Cargo.toml
index 2369b65d9d..f87dfd395b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -60,6 +60,7 @@ which = "1.0"
 zip = { version = "0.2", default-features = false }
 
 [dev-dependencies]
+assert_cli = "0.5"
 gcc = "0.3"
 itertools = "0.6"
 
@@ -85,3 +86,4 @@ unstable = []
 debug = true
 
 [workspace]
+exclude = ["tests/test-crate"]
diff --git a/src/compiler/rust.rs b/src/compiler/rust.rs
index baf33833d0..8e7fa8d91d 100644
--- a/src/compiler/rust.rs
+++ b/src/compiler/rust.rs
@@ -33,7 +33,7 @@ use std::process::{self, Stdio};
 use std::time::Instant;
 use tempdir::TempDir;
 use util::{fmt_duration_as_secs, run_input_output, Digest};
-use util::HashToDigest;
+use util::{HashToDigest, OsStrExt};
 
 use errors::*;
 
@@ -636,7 +636,8 @@ impl<T> CompilerHasher<T> for RustHasher
             let mut env_vars = env_vars.clone();
             env_vars.sort();
             for &(ref var, ref val) in env_vars.iter() {
-                if var.to_str().map(|s| s.starts_with("CARGO_")).unwrap_or(false) {
+                // CARGO_MAKEFLAGS will have jobserver info which is extremely non-cacheable.
+                if var.starts_with("CARGO_") && var != "CARGO_MAKEFLAGS" {
                     var.hash(&mut HashToDigest { digest: &mut m });
                     m.update(b"=");
                     val.hash(&mut HashToDigest { digest: &mut m });
diff --git a/tests/sccache_cargo.rs b/tests/sccache_cargo.rs
new file mode 100644
index 0000000000..a8193eddbe
--- /dev/null
+++ b/tests/sccache_cargo.rs
@@ -0,0 +1,104 @@
+//! System tests for compiling Rust code with cargo.
+//!
+//! Any copyright is dedicated to the Public Domain.
+//! http://creativecommons.org/publicdomain/zero/1.0/
+
+extern crate assert_cli;
+extern crate chrono;
+extern crate env_logger;
+#[macro_use]
+extern crate log;
+extern crate tempdir;
+
+use std::env;
+use std::fs;
+use std::path::{Path, PathBuf};
+use std::process::{Command, Stdio};
+
+use assert_cli::{Assert, Environment};
+use env_logger::LogBuilder;
+use chrono::Local;
+use tempdir::TempDir;
+
+fn find_sccache_binary() -> PathBuf {
+    // Older versions of cargo put the test binary next to the sccache binary.
+    // Newer versions put it in the deps/ subdirectory.
+    let exe = env::current_exe().unwrap();
+    let this_dir = exe.parent().unwrap();
+    let dirs = &[&this_dir, &this_dir.parent().unwrap()];
+    dirs
+        .iter()
+        .map(|d| d.join("sccache").with_extension(env::consts::EXE_EXTENSION))
+        .filter_map(|d| fs::metadata(&d).ok().map(|_| d))
+        .next()
+        .expect(&format!("Error: sccache binary not found, looked in `{:?}`. Do you need to run `cargo build`?", dirs))
+}
+
+fn stop(sccache: &Path) {
+    //TODO: should be able to use Assert::ignore_status when that is released.
+    let output = Command::new(&sccache)
+        .arg("--stop-server")
+        .stdout(Stdio::null())
+        .stderr(Stdio::null())
+        .output()
+        .unwrap();
+    trace!("stop-server returned {}", output.status);
+}
+
+/// Test that building a simple Rust crate with cargo using sccache results in a cache hit
+/// when built a second time.
+#[test]
+fn test_rust_cargo() {
+    drop(LogBuilder::new()
+         .format(|record| {
+             format!("{} [{}] - {}",
+                     Local::now().format("%Y-%m-%dT%H:%M:%S%.3f"),
+                     record.level(),
+                     record.args())
+         })
+        .parse(&env::var("RUST_LOG").unwrap_or_default())
+        .init());
+    let cargo = env!("CARGO");
+    debug!("cargo: {}", cargo);
+    let sccache = find_sccache_binary();
+    debug!("sccache: {:?}", sccache);
+    let crate_dir = Path::new(file!()).parent().unwrap().join("test-crate");
+    // Ensure there's no existing sccache server running.
+    trace!("sccache --stop-server");
+    stop(&sccache);
+    // Create a temp directory to use for the disk cache.
+    let tempdir = TempDir::new("sccache_test_rust_cargo").unwrap();
+    let env = Environment::inherit().insert("SCCACHE_DIR", tempdir.path());
+    // Start a new sccache server.
+    trace!("sccache --start-server");
+    Assert::command(&[&sccache.to_string_lossy()])
+        .with_args(&["--start-server"]).with_env(env).succeeds().unwrap();
+    // `cargo clean` first, just to be sure there's no leftover build objects.
+    let env = Environment::inherit().insert("RUSTC_WRAPPER", &sccache);
+    let a = Assert::command(&[&cargo])
+        .with_args(&["clean"]).with_env(&env).current_dir(&crate_dir).succeeds();
+    trace!("cargo clean: {:?}", a);
+    a.unwrap();
+    // Now build the crate with cargo.
+    let a = Assert::command(&[&cargo])
+        .with_args(&["build"]).with_env(&env).current_dir(&crate_dir).succeeds();
+    trace!("cargo build: {:?}", a);
+    a.unwrap();
+    // Clean it so we can build it again.
+    let a = Assert::command(&[&cargo])
+        .with_args(&["clean"]).with_env(&env).current_dir(&crate_dir).succeeds();
+    trace!("cargo clean: {:?}", a);
+    a.unwrap();
+    let a = Assert::command(&[&cargo])
+        .with_args(&["build"]).with_env(&env).current_dir(&crate_dir).succeeds();
+    trace!("cargo build: {:?}", a);
+    a.unwrap();
+    // Now get the stats and ensure that we had a cache hit for the second build.
+    trace!("sccache --show-stats");
+    Assert::command(&[&sccache.to_string_lossy()])
+        .with_args(&["--show-stats", "--stats-format=json"])
+        .stdout().contains(r#""cache_hits":1"#).succeeds().execute()
+        .expect("Should have had 1 cache hit");
+    trace!("sccache --stop-server");
+    stop(&sccache);
+}
diff --git a/tests/test-crate/Cargo.lock b/tests/test-crate/Cargo.lock
new file mode 100644
index 0000000000..d8c6ae9f3e
--- /dev/null
+++ b/tests/test-crate/Cargo.lock
@@ -0,0 +1,4 @@
+[root]
+name = "test-crate"
+version = "0.1.0"
+
diff --git a/tests/test-crate/Cargo.toml b/tests/test-crate/Cargo.toml
new file mode 100644
index 0000000000..ac454f0cb5
--- /dev/null
+++ b/tests/test-crate/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "test-crate"
+version = "0.1.0"
+authors = ["Ted Mielczarek <ted@mielczarek.org>"]
+
+[dependencies]
diff --git a/tests/test-crate/src/lib.rs b/tests/test-crate/src/lib.rs
new file mode 100644
index 0000000000..31e1bb209f
--- /dev/null
+++ b/tests/test-crate/src/lib.rs
@@ -0,0 +1,7 @@
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn it_works() {
+        assert_eq!(2 + 2, 4);
+    }
+}