Three findings from one morning, all of them things that were invisible
rather than wrong. docs/RUST.md's two new sections have the full account.
**`cargo test --workspace` was taking half an hour, and it was debug
info.** rustc's default `debug = true`, times eight test binaries each
statically linking the whole wgpu + naga + winit + parley graph, means
every one of them gets a private copy of that graph's DWARF written into
it: the linkers for one run had written ~54 GB between them and were
still going at thirty minutes -- the worst single one 16.9 GB for one
test binary -- leaving an 88 GB target/. It was not CPU: the machine was
87% idle, and rust-lld's threads were in D state in btrfs
`handle_reserve_ticket`, blocked on space reservation at 83% full. So
`debug = "line-tables-only"` on both `profile.dev` and `profile.test` --
both, because `cargo test` builds dependencies under one and the test
targets under the other. Cold, with all 19 suites run: 69 s and a 3.7 GB
target. Backtraces keep file and line; `RUSTFLAGS="-C debuginfo=2"` per
run buys back variable inspection when a debugger actually needs it.
**The desktop had no logger at all**, so every `log::` call on that side
went to `log`'s no-op default -- including the GLES fallback warning
added hours earlier. `DefaultApp::run` installs a stderr logger
(`src/default/logging.rs`, no new dependency: a level and a line is a
page of code against env_logger plus its filter dialect), and the
renderer now says which adapter won at `info`. That line is the point:
with a silent fallback, a layer-2 screenshot rendered by llvmpipe and one
rendered by the host's GPU are the same PNG, and which one it was is
exactly what the screenshot is being taken to judge.
**`tests/mask_sdf.rs` is a render pass now, not a compute pass.** It
asked for `adapter.limits()` because `iris_core::device_limits()`
deliberately zeroes the six `max_compute_*` fields -- a decision on
record since 2026-09-05, which this quietly worked around instead of
following. It now asks for what iris asks for and calls the function from
the fragment stage, where the renderer calls it. The compute pass was
*not* why it crashed, and the record should not say it was: the rewrite
crashes identically. What the crash is: dropping a wgpu device on this
VM's Venus adapter segfaults, after the test has produced its answer
(worst CPU/shader disagreement 5.8e-6). Narrowed -- plain Vulkan creating
and destroying five VkDevices on the same adapter is clean, and the same
binary with Vulkan hidden falls back to GL and exits clean. Worked around
at `Gpu::leak`, with the reason and the delete-me condition written
there.
`rigs/virtgpu-probe` is the new rig behind the Venus half: which capsets
the host offers (0x16 -- VIRGL, VIRGL2, VENUS; no capset 6, so no DRM
native context without host-side work), whether the device has compute
(it does: 1024 invocations/workgroup -- the "no compute" finding on
record is about the Android emulator's SwiftShader, a different machine),
and whether plain Vulkan teardown is clean.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
