Something is causing Cargo to rebuild every time

[Mark-Simulacrum]

Refiling rust-lang/rust#36483 per @sfackler's comment.

Each cargo build causes a rebuild of the crate. The log suggests that at least part of the problem may be related to Macros 1.1; though the mtime None != ... problems are also of unknown cause.

I have not yet worked on a minimal test case, but can do so upon request, for now this should reproduce this behavior.

Full log when building RUST_LOG=cargo::ops::cargo_rustc::fingerprint=info cargo test:

INFO:cargo::ops::cargo_rustc::fingerprint: stale: /home/mark/Edit/rustc-perf/backend/rustc-macro source code -- missing
INFO:cargo::ops::cargo_rustc::fingerprint: fingerprint error for rustc-perf v0.1.0 (file:///home/mark/Edit/rustc-perf/backend): mtime based components have changed: None != Some(FileTime { seconds: 1473893323, nanos: 644877469 }), paths are "/home/mark/Edit/rustc-perf/backend/target/debug/.fingerprint/rustc-perf-8d2c967c83377789/dep-test-lib-rustc-perf" and "/home/mark/Edit/rustc-perf/backend/target/debug/.fingerprint/rustc-perf-8d2c967c83377789/dep-test-lib-rustc-perf"
INFO:cargo::ops::cargo_rustc::fingerprint: stale: /home/mark/Edit/rustc-perf/backend/rustc-macro source code -- missing
INFO:cargo::ops::cargo_rustc::fingerprint: fingerprint error for rustc-perf v0.1.0 (file:///home/mark/Edit/rustc-perf/backend): new (rustc-perf v0.1.0 (file:///home/mark/Edit/rustc-perf/backend)) != old (rustc-perf v0.1.0 (file:///home/mark/Edit/rustc-perf/backend))
INFO:cargo::ops::cargo_rustc::fingerprint: fingerprint error for rustc-perf v0.1.0 (file:///home/mark/Edit/rustc-perf/backend): mtime based components have changed: None != Some(FileTime { seconds: 1473893323, nanos: 232877796 }), paths are "/home/mark/Edit/rustc-perf/backend/target/debug/.fingerprint/rustc-perf-8d2c967c83377789/dep-lib-rustc-perf" and "/home/mark/Edit/rustc-perf/backend/target/debug/.fingerprint/rustc-perf-8d2c967c83377789/dep-lib-rustc-perf"
INFO:cargo::ops::cargo_rustc::fingerprint: fingerprint error for rustc-perf v0.1.0 (file:///home/mark/Edit/rustc-perf/backend): new (rustc-perf v0.1.0 (file:///home/mark/Edit/rustc-perf/backend)) != old (rustc-perf v0.1.0 (file:///home/mark/Edit/rustc-perf/backend))
INFO:cargo::ops::cargo_rustc::fingerprint: fingerprint error for rustc-perf v0.1.0 (file:///home/mark/Edit/rustc-perf/backend): new (rustc-perf v0.1.0 (file:///home/mark/Edit/rustc-perf/backend)) != old (rustc-perf v0.1.0 (file:///home/mark/Edit/rustc-perf/backend))

Condensed (path and leading part of each line stripped):

stale: /root/rustc-macro source code -- missing
fingerprint error for rustc-perf v0.1.0 (file:///root): mtime based components have changed: None != Some(FileTime { seconds: 1473893323, nanos: 644877469 }), paths are "/root/target/debug/.fingerprint/rustc-perf-8d2c967c83377789/dep-test-lib-rustc-perf" and "/root/target/debug/.fingerprint/rustc-perf-8d2c967c83377789/dep-test-lib-rustc-perf"
stale: /root/rustc-macro source code -- missing
fingerprint error for rustc-perf v0.1.0 (file:///root): new (rustc-perf v0.1.0 (file:///root)) != old (rustc-perf v0.1.0 (file:///root))
fingerprint error for rustc-perf v0.1.0 (file:///root): mtime based components have changed: None != Some(FileTime { seconds: 1473893323, nanos: 232877796 }), paths are "/root/target/debug/.fingerprint/rustc-perf-8d2c967c83377789/dep-lib-rustc-perf" and "/root/target/debug/.fingerprint/rustc-perf-8d2c967c83377789/dep-lib-rustc-perf"
fingerprint error for rustc-perf v0.1.0 (file:///root): new (rustc-perf v0.1.0 (file:///root)) != old (rustc-perf v0.1.0 (file:///root))
fingerprint error for rustc-perf v0.1.0 (file:///root): new (rustc-perf v0.1.0 (file:///root)) != old (rustc-perf v0.1.0 (file:///root))

cc @tikue since this is happening to you as well.

[tikue]

In the crate affected by this, I'm using serde_derive as well as a plugin.

[arthurprs]

Sub, I'm getting hurt bigtime by this.

[Mark-Simulacrum]

Minimal reproduction here: https://github.com/Mark-Simulacrum/cargo-issues-3094

[arthurprs]

Maybe it's related to this #3095

[Thinkofname]

rustc seems to be putting rustc-macro\ source\ code into the dep-info it generates which is confusing cargo. Seems like a rustc bug

[alexcrichton]

Thanks for the report @Mark-Simulacrum! Sorry for the runaround, but I believe @Thinkofname hit the nail on the head with rust-lang/rust#36625. Those file names shouldn't show up at all, and I believe it's a compiler bug that they are.

I'm going to close this in favor of rust-lang/rust#36625.