Examples:
- you try to write file but disk is full
- you have two Teliva files being edited at the same time
Both are situations where it's impossible to avoid some data loss.
However, we should now at least have some valid state of the .tlv file
saved to disk where we'd previously end up with a zero-size file or
garbage.
Teliva emits timestamps in multi-line format end in a newline. As a
result, notes get rendered on the next line and are then immediately
overwritten by the contents of the definition.
This bug was masked by my hacky 'original' timestamps which don't use
multi-line format.
This reverts commit 7c1b9d0b91.
The 'big hammer' isn't good enough. The recent changes view seems to
need state on the stack across invocations of the editor.
Lua is often not very functional. Available primitives often mutate data
destructively rather than create new values. Perhaps I shouldn't be
trying to go against the grain. We'll see. The above changes are based
on using Teliva intensively for 2 weeks of Advent of Code 2021. But that
isn't quite the ideal use case for Teliva.
This is a complete mess. I want to abstract reading multiline strings
behind a function, but the lookahead requirements for that are quite
stringent. What's a reasonable abstraction here?
I really wanted to avoid getting into defining or parsing new file
formats. However, using the entire power of Lua is not ideal, as
described earlier in Konrad Hinsen's bug. In addition to everything
else, it's a vector for arbitrary code execution when someone loads an
untrusted image.
I could use JSON, but it requires ugly string escaping. Seems cleaner to
just use YAML. But YAML is complex and needs its own dependencies. If
I'm going to do my own, might as well make the multi-line string format
really clear.
I can't yet write the new format.
Steps to reproduce:
* Run teliva with some app.
* Press ctrl-e to edit the app.
* Select some function.
* Press ctrl-g and type in some Lua keyword like 'function' or 'while'
(Since the first word in a function is often 'function', it becomes
the default if you press ctrl-g immediately after entering the editor
for a function.)
* Type nothing. Run the app.
Desired behavior: app continues to run. The definition for the keyword
is silently ignored (in future we may want to provide an error message)
Behavior before this commit: app silently exited with non-zero status,
and refused to restart thereafter until the .tlv file was manually
edited to delete the definition for the Lua keyword.
Behavior after this commit: app throws an error message like these:
* For `function`:
```
src/teliva: x.tlv:99: '(' expected near '='
sorry, you'll need to edit the image directly. press any key to exit.
```
* For `while`:
```
src/teliva: x.tlv:99: unexpected symbol near 'while'
sorry, you'll need to edit the image directly. press any key to exit.
```
You still need to edit the .tlv file manually, but the steps for
recovery are a bit more discoverable.
To fix this properly I also need to fix a looming security hole I've
been thinking about for some time. The long-term goal of Teliva is to
put the human running apps in control of what they do, by sandboxing
accesses to the file system, network and so on. However, even after we
build gates on all of Lua's standard libraries, we're still parsing .tlv
files as Lua, with all of its power available.
Solution: load .tlv files as some sort of JSON-like subset of Lua. Maybe
I should just use JSON, and rely on code that's already in Teliva, even
if I'm introducing a new notation in the process.
Kartik K. Agaram