Under heavy development and very much a work in progress (unless I stop working on it and forget to update this readme...)

This is a viewer app for RUSTC_LOG, intended for development on rustc. The default format omits several extremely useful bits of information that you typically don't want to see, but sometimes you do, preferably without running rustc with different log flags. So, this is a GUI app that lets you dynamically view/hide/filter RUSTC_LOG information.

Developed as a personal project, not currently intended to be used by others, but published in case someone wants to either use it or take inspiration from it (MIT licensed). Please send me a message if you find this useful, I'd love to hear from you!

Export RUSTC_LOG_FORMAT_JSON=1 and set RUSTC_LOG_OUTPUT_TARGET to a file path. Pass that file path into this program, or leave RUSTC_LOG_OUTPUT_TARGET exported and run this program without args (it reads that var if there are no arguments).

Personally, I use this fish function, shoved into ~/.config/fish/functions/viewlog.fish:

function viewlog --wraps='rustc +stage1'
    if test -d $PWD/build/viewlog-output
        rm -r $PWD/build/viewlog-output
    end
    if test ! -p /tmp/viewlog
        mkfifo /tmp/viewlog
    end
    cargo run --release --manifest-path ~/me/khys-rustc-log-viewer/Cargo.toml -- /tmp/viewlog &
    set -fx RUSTC_LOG_FORMAT_JSON 1
    set -fx RUSTC_LOG_OUTPUT_TARGET /tmp/viewlog
    if ! set -q RUSTC_LOG
        set -fx RUSTC_LOG trace
    end
    rustc +stage1 --out-dir $PWD/build/viewlog-output $argv
end

• creates a named pipe, /tmp/viewlog, to not actually need to store the json on disk (it can be several gigabytes)
  • idk if a similar concept exists on windows - if you're using a regular file though (totally fine to do), you'll need to wait for rustc to finish running before opening this log viewer
• sets up the RUSTC_LOG_FORMAT_JSON and RUSTC_LOG_OUTPUT_TARGET vars
• allows you to specify a filter for RUSTC_LOG, defaulting to trace if not set (note that if the log viewer hasn't compiled yet, RUSTC_LOG will apply to the viewer...)
• presumes you've set up +stage1
• passes through $argv to rustc, presumably a path to a UI test

Once the app is running, uuuh, it's a bit of a WIP mess right now, there's vaguely less/vim-like keybindings I guess

I handrolled my own json parser for this (sorry...). That means that if you try to use this, it might be kinda brittle. The reason I did so is because the handrolled version is ~9x faster than facet_json, which is the difference between waiting 14 seconds and waiting 1.5 seconds to parse a 1.5GiB file (typical for RUSTC_LOG=trace on a basic ui test). The custom parser mostly assumes the input is well-formed, it doesn't do sanity checks like duplicate field detection. Hopefully, if the format changes, it's relatively easy to patch up the parser!