diff --git a/doc/manual/src/language/values.md b/doc/manual/src/language/values.md index d4338e91e89..2dd52b379f6 100644 --- a/doc/manual/src/language/values.md +++ b/doc/manual/src/language/values.md @@ -92,39 +92,50 @@ - Path - *Paths*, e.g., `/bin/sh` or `./builder.sh`. A path must contain at - least one slash to be recognised as such. For instance, `builder.sh` - is not a path: it's parsed as an expression that selects the - attribute `sh` from the variable `builder`. If the file name is - relative, i.e., if it does not begin with a slash, it is made - absolute at parse time relative to the [base directory](@docroot@/glossary.md#gloss-base-directory). - For instance, if a Nix expression in - `/foo/bar/bla.nix` refers to `../xyzzy/fnord.nix`, the absolute path - is `/foo/xyzzy/fnord.nix`. - - If the first component of a path is a `~`, it is interpreted as if - the rest of the path were relative to the user's home directory. - e.g. `~/foo` would be equivalent to `/home/edolstra/foo` for a user - whose home directory is `/home/edolstra`. - - For instance, evaluating `"${./foo.txt}"` will cause `foo.txt` in the base directory to be copied into the Nix store and result in the string `"/nix/store/-foo.txt"`. - - Note that the Nix language assumes that all input files will remain _unchanged_ while evaluating a Nix expression. + *Paths* are distinct from strings and can be expressed by path literals such as `./builder.sh`. + + Paths are suitable for referring to local files, and are often preferable over strings. + - Path values do not contain trailing slashes, `.` and `..`, as they are resolved when evaluating a path literal. + - Path literals are automatically resolved relative to their [base directory](@docroot@/glossary.md#gloss-base-directory). + - The files referred to by path values are automatically copied into the Nix store when used in a string interpolation or concatenation. + - Tooling can recognize path literals and provide additional features, such as autocompletion, refactoring automation and jump-to-file. + + A path literal must contain at least one slash to be recognised as such. + For instance, `builder.sh` is not a path: + it's parsed as an expression that selects the attribute `sh` from the variable `builder`. + + Path literals may also refer to absolute paths by starting with a slash. + + > **Note** + > + > Absolute paths make expressions less portable. + > In the case where a function translates a path literal into an absolute path string for a configuration file, it is recommended to write a string literal instead. + > This avoids some confusion about whether files at that location will be used during evaluation. + > It also avoids unintentional situations where some function might try to copy everything at the location into the store. + + If the first component of a path is a `~`, it is interpreted such that the rest of the path were relative to the user's home directory. + For example, `~/foo` would be equivalent to `/home/edolstra/foo` for a user whose home directory is `/home/edolstra`. + Path literals that start with `~` are not allowed in [pure](@docroot@/command-ref/conf-file.md#conf-pure-eval) evaluation. + + Paths can be used in [string interpolation] and string concatenation. + For instance, evaluating `"${./foo.txt}"` will cause `foo.txt` from the same directory to be copied into the Nix store and result in the string `"/nix/store/-foo.txt"`. + + Note that the Nix language assumes that all input files will remain _unchanged_ while evaluating a Nix expression. For example, assume you used a file path in an interpolated string during a `nix repl` session. - Later in the same session, after having changed the file contents, evaluating the interpolated string with the file path again might not return a new [store path], since Nix might not re-read the file contents. + Later in the same session, after having changed the file contents, evaluating the interpolated string with the file path again might not return a new [store path], since Nix might not re-read the file contents. Use `:r` to reset the repl as needed. [store path]: @docroot@/glossary.md#gloss-store-path - Paths can include [string interpolation] and can themselves be [interpolated in other expressions]. + Path literals can also include [string interpolation], besides being [interpolated into other expressions]. - [interpolated in other expressions]: ./string-interpolation.md#interpolated-expressions + [interpolated into other expressions]: ./string-interpolation.md#interpolated-expressions At least one slash (`/`) must appear *before* any interpolated expression for the result to be recognized as a path. - `a.${foo}/b.${bar}` is a syntactically valid division operation. + `a.${foo}/b.${bar}` is a syntactically valid number division operation. `./a.${foo}/b.${bar}` is a path. - [Lookup paths](./constructs/lookup-path.md) such as `` resolve to path values. + [Lookup path](./constructs/lookup-path.md) literals such as `` also resolve to path values. - Boolean