This PR improves how the `text-{size}` utilities interact with the
`leading-*`, `tracking-*`, and `font-{weight}` utilities, ensuring that
if the user explicitly uses any of those utilities that those values are
not squashed by any defaults baked into the `text-{size}` utilities.
Prior to this PR, if you wrote something like this:
```html
<div class="text-lg leading-none md:text-2xl">
```
…the `leading-none` class would be overridden by the default line-height
value baked into the `text-2xl` utility at the `md` breakpoint. This has
been a point of confusion and frustration for people [in the
past](https://github.com/tailwindlabs/tailwindcss/issues/6504) who are
annoyed they have to keep repeating their custom `leading-*` value like
this:
```html
<div class="text-lg leading-none md:text-2xl md:leading-none lg:text-4xl lg:leading-none">
```
This PR lets you write this HTML instead but get the same behavior as
above:
```html
<div class="text-lg leading-none md:text-2xl lg:text-4xl">
```
It's important to note that this change _only_ applies to line-height
values set explicitly with a `leading-*` utility, and does not apply to
the line-height modifier.
In this example, the line-height set by `text-sm/6` does _not_ override
the default line-height included in the `md:text-lg` utility:
```html
<div class="text-sm/6 md:text-lg">
```
That means these two code snippets behave differently:
```html
<div class="text-sm/6 md:text-lg">…</div>
<div class="text-sm leading-6 md:text-lg">…</div>
```
In the top one, the line-height `md:text-lg` overrides the line-height
set by `text-sm/6`, but in the bottom one, the explicit `leading-6`
utility takes precedence.
This PR applies the same improvements to `tracking-*` and
`font-{weight}` as well, since all font size utilities can also
optionally specify default `letter-spacing` and `font-weight` values.
We achieve this using new semi-private CSS variables like we do for
things like transforms, shadows, etc., which are set by the `leading-*`,
`tracking-*`, and `font-{weight}` utilities respectively. The
`text-{size}` utilities always use these values first if they are
defined, and the default values become fallbacks for those variables if
they aren't present.
We use `@property` to make sure these variables are reset to `initial`
on a per element basis so that they are never inherited, like with every
other variable we define.
This PR does slightly increase the amount of CSS generated, because now
utilities like `leading-5` look like this:
```diff
.leading-5 {
+ --tw-leading: 1.25rem;
line-height: 1.25rem;
}
```
…and utilites like `text-sm` include a `var(…)` lookup that they didn't
include before:
```diff
.text-sm {
font-size: 0.875rem;
- line-height: var(--font-size-sm--line-height, 1.25rem);
+ line-height: var(--tw-leading, var(--font-size-sm--line-height, 1.25rem));
}
```
If this extra CSS doesn't feel worth it for the small improvement in
behavior, we may consider just closing this PR and keeping things as
they are.
This PR is also a breaking change for anyone who was depending on the
old behavior, and expected the line-height baked into the `md:text-lg`
class to take precedence over the explicit `leading-6` class:
```html
<div class="text-sm leading-6 md:text-lg">…</div>
```
Personally I am comfortable with this because of the fact that you can
still get the old behavior by preferring a line-height modifier:
```html
<div class="text-sm/6 md:text-lg">…</div>
```
---------
Co-authored-by: Adam Wathan <4323180+adamwathan@users.noreply.github.com>
Co-authored-by: Jordan Pittman <jordan@cryptica.me>
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