sass_layer: Bundling Sass layers
In sass: Syntactically Awesome Style Sheets ('Sass')

Description Usage Arguments Functions Examples

Sass layers are a way to group a set of related Sass variable definitions, function/mixin declarations, and CSS rules into a single object. Use sass_layer() to create these objects, and sass_bundle() to combine two or more layers or bundles objects into a Sass bundle; this ability to be merged is the main benefit of using Sass layers versus lower-level forms of sass input. At a later time, Sass layers may be removed from Sass bundles by referencing the same name that was used when creating the Sass bundle.

sass_layer(
  defaults = NULL,
  declarations = NULL,
  rules = NULL,
  html_deps = NULL,
  file_attachments = character(0),
  tags = NULL
)

sass_bundle(...)

sass_bundle_remove(bundle, name)

is_sass_bundle(x)

`defaults`	A suitable `as_sass()` `input`. Intended for declaring variables with `!default`. When layers are combined, defaults are merged in reverse order; that is, `sass_bundle(layer1, layer2)` will include `layer2$defaults` before `layer1$defaults`.
`declarations`	A suitable `as_sass()` `input`. Intended for function and mixin declarations, and variable declarations without `!default`; not intended for actual CSS rules. These will be merged in forward order; that is, `sass_bundle(layer1, layer2)` will include `layer1$declarations` before `layer2$declarations`.
`rules`	A suitable `as_sass()` `input`. Intended for actual CSS rules. These will be merged in forward order; that is, `sass_bundle(layer1, layer2)` will include `layer1$rules` before `layer2$rules`.
`html_deps`	An HTML dependency (or a list of them).
`file_attachments`	A named character vector, representing file assets that are referenced (using relative paths) from the sass in this layer. The vector names should be a relative path, and the corresponding vector values should be absolute paths to files or directories that exist; at render time, each value will be copied to the relative path indicated by its name. (For directories, the contents of the source directory will be copied into the destination directory; the directory itself will not be copied.) You can also omit the name, in which case that file or directory will be copied directly into the output directory.
`tags`	Deprecated. Preserve meta information using a key in `sass_bundle(KEY = val)`. preserve simple metadata as layers are merged.
`...`	A collection of `sass_layer()`s and/or objects that `as_sass()` understands. Arguments should be provided in reverse priority order: defaults, declarations, and rules in later layers will take precedence over those of previous layers. Non-layer values will be converted to layers by calling `sass_layer(rules = ...)`.
`bundle`	Output value from `sass_layer()` or `sass_bundle()`
`name`	If a Sass layer name is contained in `name`, the matching Sass layer will be removed from the `bundle`
`x`	object to inspect

sass_layer: Compose the parts of a single Sass layer. Object returned is a sass_bundle() with a single Sass layer
sass_bundle: Collect sass_bundle() and/or sass_layer() objects. Unnamed Sass bundles will be concatenated together, preserving their internal name structures. Named Sass bundles will be condensed into a single Sass layer for easier removal from the returned Sass bundle.
sass_bundle_remove: Remove a whole sass_layer() from a sass_bundle() object.
is_sass_bundle: Check if x is a Sass bundle object

blue <- list(color = "blue !default")
red <- list(color = "red !default")
green <- list(color = "green !default")

# a sass_layer() by itself is not very useful, it just defines some
# SASS to place before (defaults) and after (declarations, rules)
core <- sass_layer(defaults = blue, rules = "body { color: $color; }")
core
sass(core)

# However, by stacking sass_layer()s, we have ability to place
# SASS both before and after some other sass (e.g., core)
# Here we place a red default _before_ the blue default and export the
# color SASS variable as a CSS variable _after_ the core
red_layer <- sass_layer(red, rules = ":root{ --color: #{$color}; }")
sass(sass_bundle(core, red_layer))
sass(sass_bundle(core, red_layer, sass_layer(green)))

# Example of merging layers and removing a layer
# Remember to name the layers that are removable
core_layers <- sass_bundle(core, red = red_layer, green = sass_layer(green))
core_layers # pretty printed for console
core_slim <- sass_bundle_remove(core_layers, "red")
sass(core_slim)


# File attachment example: Create a checkboard pattern .png, then
# use it from a sass layer

tmp_png <- tempfile(fileext = ".png")
grDevices::png(filename = tmp_png, width = 20, height = 20,
  bg = "transparent", antialias = "none")
par(mar = rep_len(0,4), xaxs = "i", yaxs = "i")
plot.new()
rect(c(0,0.5), c(0,0.5), c(0.5,1), c(0.5,1), col = "#00000044", border=NA)
dev.off()

layer <- sass_layer(
  rules = ".bg-check { background-image: url(images/demo_checkboard_bg.png) }",
  file_attachments = c("images/demo_checkboard_bg.png" = tmp_png)
)

output_path <- tempfile(fileext = ".css")
sass(layer, output = output_path, write_attachments = TRUE)