Tracing

rust-gpu has a lot of debug! (or trace!) calls, which print out logging information at many points. These are very useful to at least narrow down the location of a bug if not to find it entirely, or just to orient yourself as to why the compiler backend is doing a particular thing.

To see the logs, you need to set the RUSTGPU_LOG environment variable to your log filter (note the "GPU" in the name). The full syntax of the log filters can be found in the rustdoc of tracing-subscriber.

Use RUSTGPU_LOG_FORMAT to control log output format ("tree", "flat", or "json") and RUSTGPU_LOG_COLOR to manage color output ("always", "never", or "auto").

To trace non-rust-gpu parts of the compiler, set the standard RUSTC_LOG environment variable.

Replacements for old codegen arguments

Before rust-gpu supported tracing, there were special codegen arguments to aid observability. As of PR#196 the they have been removed and replaced with the following:

• --specializer-debug → RUSTGPU_LOG=rustc_codegen_spirv::specializer=debug