cache_make_key: Make a key for 'R.cache'

In r-lib/styler: Non-Invasive Pretty Printing of R Code

Make a key for R.cache

Description

This is used to determine if caching already corresponds to a style guide.

Usage

cache_make_key(text, transformers, more_specs)

Arguments

text	Code to create a cache for. This should be styled text, as the approach used by styler does not cache input, but styled code.
transformers	A list of transformer functions, because we can only know if text is already correct if we know which transformer function it should be styled with.
more_specs	A named vector coercible to character that determines the styling but are style guide independent, such as include_roxygen_examples or base_indention.

Details

We need to compare:

• text to style. Will be passed to hash function as is.

• styler version. Not an issue because for every version of styler, we build a new cache.

• transformers. Cannot easily hash them because two environments won't be identical even if they contain the same objects (see 'Experiments'). Simple as.character(transformers) will not consider infinitely recursive code dependencies. To fix this, transformers must have names and version number as described in create_style_guide(). Now, the only way to fool the cache invalidation is to replace a transformer with the same function body (but changing the function definition of the functions called in that body) interactively without changing version number of name at the same time. Remaining problem: purrr::partial() calls will render generic code, e.g. see as.character(list(purrr::partial(sum, x = 4))). For that reason, all arguments passed to a purrr::partial() call must be put in the style guide under more_specs_style_guide.

Experiments

There is unexplainable behavior in conjunction with hashing and environments:

• Functions created with purrr::partial() are not identical when compared with identical() (StackOverflow)

• except when they have the exact same parent environment, which must be an object created and then passed to purrr::partial(.env = ...), not created in-place.

• purrr::partial() seems to ignore .env after version 0.2.5, so until this is fixed, we'd have to work with version 0.2.5.

• Our caching backend package, R.cache, uses R.cache:::getChecksum.default (which uses digest::digest()) to hash the input. The latter does not seem to care if the environments are exactly equal (see 'Examples').

• However, under some circumstances, it does: Commit 9c94c022 (if not overwritten / rebased by now) contains a reprex. Otherwise, search for 43219ixmypi in commit messages and restore this commit to reproduce the behavior.

Examples

add <- function(x, y) {
  x + y
}
add1 <- purrr::partial(add, x = 1)
add2 <- purrr::partial(add, x = 1)
identical(add1, add2)
identical(digest::digest(add1), digest::digest(add2))
identical(digest::digest(styler::tidyverse_style()), digest::digest(styler::tidyverse_style()))

r-lib/styler documentation built on Dec. 13, 2024, 5:42 p.m.