Commits on Oct 9, 2015

1. Fix spurious rebuilds of the script crate …

   The script crate currently has a build script, and Cargo will consider all files
   in the script crate as inputs to the build script as it otherwise doesn't know
   [what the input files are][cargo-1162]. This means that if any file in the
   source tree of the script crate changes (or is created) then Cargo will think it
   needs to re-run the build script and rebuild the crate.
   
   [cargo-1162]: rust-lang/cargo#1162
   
   The build script of the script crate is invoking python, and consequently Python
   is generating some bytecode files in the source tree. On the second build of
   Servo, Cargo will see these new files, think that something has changed, and
   will re-run the build script of the script crate.
   
   This change passes the `-B` flag to python to avoid generating these bytecode
   files, which should avoid tampering with the source tree and appease Cargo by
   ensuring that it doesn't get rebuilt.
   
   ---
   
   As a helpful tip to if this comes up again, this was discovered by using the
   changes in rust-lang/cargo@c447e9d plus the change in rust-lang/cargo#2044. Once
   `RUST_LOG` was set to `cargo::ops::cargo_rustc::fingerprint=info`, the second
   run of `./mach build` printed out:
   
   ```
   precalculated components have changed:
     1444364448.000000000s (/build/servo/components/script/dom/bindings/codegen/parser/WebIDL.pyc) !=
     1444364235.000000000s (/build/servo/components/script/document_loader.rs)
   ```
   
   Which should help easily diagnose these kinds of problems in the future!

   

   alexcrichton committed Oct 9, 2015

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