diff options
Diffstat (limited to 'lib/fileset/README.md')
| -rw-r--r-- | lib/fileset/README.md | 29 |
1 files changed, 28 insertions, 1 deletions
diff --git a/lib/fileset/README.md b/lib/fileset/README.md index 6e57f1f8f2b..2ef7b81e885 100644 --- a/lib/fileset/README.md +++ b/lib/fileset/README.md @@ -41,9 +41,16 @@ An attribute set with these values: - `_type` (constant string `"fileset"`): Tag to indicate this value is a file set. -- `_internalVersion` (constant `2`, the current version): +- `_internalVersion` (constant `3`, the current version): Version of the representation. +- `_internalIsEmptyWithoutBase` (bool): + Whether this file set is the empty file set without a base path. + If `true`, `_internalBase*` and `_internalTree` are not set. + This is the only way to represent an empty file set without needing a base path. + + Such a value can be used as the identity element for `union` and the return value of `unions []` and co. + - `_internalBase` (path): Any files outside of this path cannot influence the set of files. This is always a directory. @@ -111,6 +118,26 @@ Arguments: - (+) This can be removed later, if we discover it's too restrictive - (-) It leads to errors when a sensible result could sometimes be returned, such as in the above example. +### Empty file set without a base + +There is a special representation for an empty file set without a base path. +This is used for return values that should be empty but when there's no base path that would makes sense. + +Arguments: +- Alternative: This could also be represented using `_internalBase = /.` and `_internalTree = null`. + - (+) Removes the need for a special representation. + - (-) Due to [influence tracking](#influence-tracking), + `union empty ./.` would have `/.` as the base path, + which would then prevent `toSource { root = ./.; fileset = union empty ./.; }` from working, + which is not as one would expect. + - (-) With the assumption that there can be multiple filesystem roots (as established with the [path library](../path/README.md)), + this would have to cause an error with `union empty pathWithAnotherFilesystemRoot`, + which is not as one would expect. +- Alternative: Do not have such a value and error when it would be needed as a return value + - (+) Removes the need for a special representation. + - (-) Leaves us with no identity element for `union` and no reasonable return value for `unions []`. + From a set theory perspective, which has a well-known notion of empty sets, this is unintuitive. + ### Empty directories File sets can only represent a _set_ of local files, directories on their own are not representable. |