`rust_analyzer:gen_rust_project` fails silently when aquery generates an error

[rdelfin]

I recently hit an issue generating the rust project file for rust analyzer. It was difficult to debug because the error was hidden by the parsing logic in gen_rust_project. In this instance, the failure looked as follows:

$ bazel run @rules_rust//tools/rust_analyzer:gen_rust_project
INFO: Analyzed target @@rules_rust+//tools/rust_analyzer:gen_rust_project (208 packages loaded, 7813 targets configured).
INFO: Found 1 target...
Target @@rules_rust+//tools/rust_analyzer:gen_rust_project up-to-date:
  bazel-bin/external/rules_rust+/tools/rust_analyzer/gen_rust_project
INFO: Elapsed time: 0.399s, Critical Path: 0.03s
INFO: 1 process: 378 action cache hit, 1 internal.
INFO: Build completed successfully, 1 total action
INFO: Running command line: bazel-bin/external/rules_rust+/tools/rust_analyzer/gen_rust_project
Error: Failed to parse aquery output as JSON

After setting RUST_LOG=trace I was able to rerun the exact same aquery command and find the actual error:

$ bazel --output_base=$output_dir aquery --include_aspects --include_artifacts --aspects=@@rules_rust+//rust:defs.bzl%rust_analyzer_aspect --output_groups=rust_analyzer_crate_spec "outputs(\".*\\.rust_analyzer_crate_spec\\.json\",deps(@//...))" --output=jsonproto
Starting local Bazel server (8.3.1) and connecting to it...
INFO: Analyzed 75 targets (389 packages loaded, 41655 targets configured).
INFO: Found 75 targets...
ERROR: Queries based on analysis results are not allowed if incrementality state is not being kept
INFO: Elapsed time: 14.385s, Critical Path: 0.00s
INFO: 0 processes.
ERROR: Build did NOT complete successfully

While I'm still not sure what the cause is here, I think as a first thing it would be good to:

• Document the fact that env_logger is used by this binary and that RUST_LOG can be set to debug issues
• Surface stdout and stderr from aquery when the command fails
• Proactively check error codes when calling aquery

I'll try to find time to open some of these fixes, but let me know what you all think. Thanks!