Support setting preview window's size to achieve a specific items list size

[komar007]

This PR implements negative preview window sizes which result in adjusting the preview window's size such that the items list has a specific size.

I didn't find a way to achieve this specific behavior where I want a full-size window with a specific small size of the list and a preview that takes the rest of the space.

[junegunn]

Thanks. But I noticed this option doesn't work nicely with adaptive --height.

# Works as expected
seq 10 | go run main.go --preview 'echo {}' --preview-window up:10  --height ~100%

# Doesn't work as expected
seq 10 | go run main.go --preview 'echo {}' --preview-window up:-10  --height ~100%

# Crashes
seq 10 | go run main.go --preview 'echo {}' --preview-window up:-20  --height ~100%

Also, I wonder if have you tested it with the extra borders. Are these the results you expected?

# 10 items in the list section
seq 100 | go run main.go --preview 'echo {}' --preview-window up:-10
seq 100 | go run main.go --preview 'echo {}' --preview-window up:-10 --info=inline
seq 100 | go run main.go --preview 'echo {}' --preview-window up:-10 --no-input

# 8 items in the list
seq 100 | go run main.go --preview 'echo {}' --preview-window up:-10 --input-border
seq 100 | go run main.go --preview 'echo {}' --preview-window up:-10 --list-border

# 6 items
seq 100 | go run main.go --preview 'echo {}' --preview-window up:-10 --style full

# 3 items
seq 100 | go run main.go --preview 'echo {}' --preview-window up:-10 --style full --header hello

[komar007]

Thanks, @junegunn,

I didn't know about adaptive height, I'll look into this and the other extra borders problem. I just tested with variations of --border and --preview-window ...,border-none

Let me work some more on this.