[css-grid] Allow 0 as first argument to repeat()

[vrugtehagel]

This proposal is rather simple; I'd like to allow 0 as a first argument to repeat(). The spec defines the argument to be <integer [1,∞]>. Can we loosen it to <integer [0,∞]>? The primary use-case for this is when using custom properties for the amount of rows or columns in a grid. For example:

.grid {
    --column-amount: 3;
    --first-column-width: 200px;
    --default-column-width: 1fr;
    display: grid;
    grid-template: auto
        / var(--first-column-width) repeat(calc(var(--column-amount) - 1), var(--default-column-width));
}

This example breaks when setting --column-amount: 1, but it doesn't have to.

Although the use-case is admittedly relatively niche (yet I believe not insignificant), it seems to be very low-cost to allow this.

Semi-formally, repeat(0, ...) just ends up being ignored in the declaration. So, auto repeat(0, 1fr) 200px would be equivalent to auto 200px.

[Loirooriol]

Note it's not just being ignored, e.g. repeat(0, auto) would need to be treated as none I guess? And what about [a] repeat(0, auto) [b], the line names should probably merge like [a b], but that alone is not valid, and can't be combined with none.

Could be done, but need to be careful with a few things, I'm not convinced it's worth it.

I think grid-auto-columns: var(--default-column-width) would be a better way to define the default column size.

[vrugtehagel]

I suppose this may be naive, but I simply thought of it as just serializing as nothing. So grid-template-columns: repeat(0, auto) is equivalent to grid-template-columns: ; and [a] repeat(0, auto) [b] is equivalent to writing [a] [b]. I suppose in some cases it is not pretty that an expression can turn invalid depending on its arguments, but presumably that's up to the author.

[Loirooriol]

No, serialization should round-trip. Can't serialize a valid value as something invalid.

[vrugtehagel]

I see. I suppose this is more complex to implement properly than I initially imagined. Closing this because of that - it just doesn't seem worth the complexity.