[INFO] updating cached repository Michael-F-Bryan/mdbook-test
[INFO] running `"git" "fetch" "--all"`
[INFO] [stdout] Fetching origin
[INFO] [stderr] From git://github.com/Michael-F-Bryan/mdbook-test
[INFO] [stderr]  * branch            HEAD       -> FETCH_HEAD
[INFO] running `"git" "clone" "work/cache/sources/gh/Michael-F-Bryan/mdbook-test" "work/ex/pr-57967/sources/master#c1c3c4e95b69dfeaca5c5db6c622d7f90ad30a54/gh/Michael-F-Bryan/mdbook-test"`
[INFO] [stderr] Cloning into 'work/ex/pr-57967/sources/master#c1c3c4e95b69dfeaca5c5db6c622d7f90ad30a54/gh/Michael-F-Bryan/mdbook-test'...
[INFO] [stderr] done.
[INFO] running `"git" "clone" "work/cache/sources/gh/Michael-F-Bryan/mdbook-test" "work/ex/pr-57967/sources/try#7fea0229842e79db1159ea58ad9a653b288efee9/gh/Michael-F-Bryan/mdbook-test"`
[INFO] [stderr] Cloning into 'work/ex/pr-57967/sources/try#7fea0229842e79db1159ea58ad9a653b288efee9/gh/Michael-F-Bryan/mdbook-test'...
[INFO] [stderr] done.
[INFO] running `"git" "rev-parse" "HEAD"`
[INFO] [stdout] c0d94abccc187754d6dca27df1ecfdcc50fb2095
[INFO] sha for GitHub repo Michael-F-Bryan/mdbook-test: c0d94abccc187754d6dca27df1ecfdcc50fb2095
[INFO] validating manifest of Michael-F-Bryan/mdbook-test on toolchain master#c1c3c4e95b69dfeaca5c5db6c622d7f90ad30a54
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+c1c3c4e95b69dfeaca5c5db6c622d7f90ad30a54-alt" "read-manifest" "--manifest-path" "Cargo.toml"`
[INFO] validating manifest of Michael-F-Bryan/mdbook-test on toolchain try#7fea0229842e79db1159ea58ad9a653b288efee9
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+7fea0229842e79db1159ea58ad9a653b288efee9-alt" "read-manifest" "--manifest-path" "Cargo.toml"`
[INFO] started frobbing Michael-F-Bryan/mdbook-test
[INFO] finished frobbing Michael-F-Bryan/mdbook-test
[INFO] frobbed toml for Michael-F-Bryan/mdbook-test written to work/ex/pr-57967/sources/master#c1c3c4e95b69dfeaca5c5db6c622d7f90ad30a54/gh/Michael-F-Bryan/mdbook-test/Cargo.toml
[INFO] started frobbing Michael-F-Bryan/mdbook-test
[INFO] finished frobbing Michael-F-Bryan/mdbook-test
[INFO] frobbed toml for Michael-F-Bryan/mdbook-test written to work/ex/pr-57967/sources/try#7fea0229842e79db1159ea58ad9a653b288efee9/gh/Michael-F-Bryan/mdbook-test/Cargo.toml
[INFO] crate Michael-F-Bryan/mdbook-test has a lockfile. skipping
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+c1c3c4e95b69dfeaca5c5db6c622d7f90ad30a54-alt" "fetch" "--locked" "--manifest-path" "Cargo.toml"`
[INFO] [stderr]     Updating git repository `https://github.com/Michael-F-Bryan/mdbook`
[INFO] [stderr] error: failed to load source for a dependency on `mdbook`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   Unable to update https://github.com/Michael-F-Bryan/mdbook?branch=alternate_backends#186d6344
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   revspec '186d6344e1d57e05723da70e4e038e63b46ae29c' not found; class=Reference (4); code=NotFound (-3)
[ERROR] this task or one of its parent failed!
[ERROR] command `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+c1c3c4e95b69dfeaca5c5db6c622d7f90ad30a54-alt" "fetch" "--locked" "--manifest-path" "Cargo.toml"` failed