Do it "more properly": use intrusive list linkage to manage three
indices:
* hash lookup
* recency
* frequency
eviction is frequency based, but in order to avoid things that were
super hot in the past and that are no longer hot clogging up the cache,
eviction will incrementally age out least recently used entries that
haven't been active in the span of some number of get/put operations.
Aging scales down the frequency value to reduce its strength, so an aged
item isn't necessarily immediately a candidate for removal, it just
makes it more likely to be picked up by the frequency based removal as
it goes unused for an extended period.
It's now possible to specify a validation function for config
items.
Use that to validate line_height:
```
; ./target/debug/wezterm --config line_height=-1
08:41:10.576 ERROR wezterm > Error converting lua value from overrides to Config struct: Error processing Config::line_height: Illegal value -1 for line_height; it must be positive and greater than zero!; terminating
```
refs: https://github.com/wez/wezterm/issues/2247
The issue here was that the from_dynamic impl derived for a struct
that was inlined in an enum didn't respect the the field properties
defined for the struct.
Refactor to reuse the same field_info helper used by the struct
code.
Update docs to clarify what the default value actually is.
refs: https://github.com/wez/wezterm/issues/2179
Invalid option names, or values that evaluate as nil (such as the `foo`
above: that's treated as a global variable reference, but `foo` isn't a
defined global and evaluates as `nil`) will now cause the program
startup to error out with an actionable error message.
Previously, the invalid config name would generate a warning, and the
invalid value would silently have no effect as it has the same effect as
omitting the named value and leaving it as its default value.
I think these cases should both immediately error out and stop
further processing, so that's what we're doing.
This commit also adds support for adding:
```
#[dynamic(deprecated = "use newer option instead")]
pub some_config_value: bool,
```
but not options currently use this.
