Errors in config options can cause renderer to crash without notice

[bennofs]

Describe the issue

If you have an error in a config option that is accessed in the renderer::renderer component constructor, the renderer not be constructed and no feedback is given to the user (and because the renderer won't be constructed, no bar is drawn).

Expected behavior:

There should be a clear error presented to the user about what is wrong and polybar should either exit or assume a reasonable default.

Actual behavior:

Polybar (the process) keeps running but no bar is visible.

Was it working before?
Haven't tested this (didn't experience it with my own configuration)

To Reproduce

A minimal but complete config with which the problem occurs:

[bar/example]
modules-left = title
fixed-center = ${vars.true}

[module/title]
type = internal/xwindow

Polybar Log

(The "EXCEPTION CAUGHT" and some other logs are printed by debug logging I patched into my polybar and is not actually there in master):

* Loading config: /tmp/c
- config: Current bar section: [bar/example]
warn: No monitor specified, using "eDP-1"
* Loaded monitor eDP-1 (1920x1080+0+0)
* Bar geometry: 1920x24+0+0
- bar: Attach X event sink
- bar: Attach signal receiver
- controller: Install signal handler
- controller: Setup user-defined modules
* Starting application
- controller: Main thread id = 1
* Starting module/title
* Entering event loop (thread-id=1)
- module/title: Thread id = 2
* Eventqueue worker (thread-id=3)
- bar: Create renderer
- renderer: Get TrueColor visual
- renderer: Allocate colormap
- renderer: Allocate output window
- renderer: Allocate window pixmaps
- renderer: Allocate graphic contexts
- renderer: Allocate alignment blocks
- renderer: Allocate cairo components
- renderer: Load fonts
* Configured DPI = 96x96
warn: No fonts specified, using fallback font "fixed"
- load font start
* Loaded font "fixed" (name=DejaVu Sans, offset=0, file=/usr/share/fonts/TTF/DejaVuSans.ttf)
- load font done
- all fonts done
- doing transparency stuff
- done transparency stuff
- 1
- 2
- 3
- 4
- 5
EXCEPTION CAUGHT: The reference ${vars.true} does not exist (no fallback set)

Environment:

• WM: i3
• Output of polybar -vvv:

polybar 3.0.5-338-gb728fea

Features: +alsa +curl +i3 +mpd +network(libnl) +pulseaudio +xkeyboard

X extensions: +randr (+monitors) -render -damage -sync +composite +xkb +xrm +xcursor

Build type: Debug
Compiler: /usr/bin/c++
Compiler flags:  -Wall -Wextra -Werror -Wno-noexcept-type -pedantic -pedantic-errors
Linker flags:

[bennofs]

The issue is this part of the code where the exception is ignored (catch (...) {}):

https://github.com/jaagr/polybar/blob/b728fea5be06733c040fc02b2f629863627bfa04/include/events/signal_emitter.hpp#L25-L37

Then, this line in renderer could throw an exception if the config option fails to evaluate:

https://github.com/jaagr/polybar/blob/b728fea5be06733c040fc02b2f629863627bfa04/src/components/renderer.cpp#L181

[patrick96]

I noticed the signal handler swallowing all exceptions (see #1451).

I have changed the code to log an error on every exception. But I noticed that exceptions get thrown in quite a few places and not caught until the signal emitter does (not really optimal), will see what I can do about that.

[patrick96]

Alright, wasn't that bad to fix.