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docs: fill out language/types.md#type-path

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Ryan Hendrickson 2024-07-08 00:41:19 -04:00
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18
doc/manual/src/language/syntax.md
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@ -190,18 +190,13 @@ This section covers syntax and semantics of the Nix language.
### Path {#path-literal}
*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.
*Paths* can be expressed by path literals such as `./builder.sh`.
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 are resolved relative to their [base directory](@docroot@/glossary.md#gloss-base-directory).
Path literals may also refer to absolute paths by starting with a slash.
> **Note**
@ -215,15 +210,6 @@ This section covers syntax and semantics of the Nix language.
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/<hash>-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. Use `:r` to reset the repl as needed.
[store path]: @docroot@/store/store-path.md
Path literals can also include [string interpolation], besides being [interpolated into other expressions].
[interpolated into other expressions]: ./string-interpolation.md#interpolated-expressions

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doc/manual/src/language/types.md
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@ -50,8 +50,37 @@ The function [`builtins.isString`](builtins.md#builtins-isString) can be used to
### Path {#type-path}
<!-- TODO(@rhendric, #10970): Incorporate content from syntax.md#path-literal -->
A _path_ in the Nix language is an immutable, finite-length sequence of bytes starting with `/`, representing a POSIX-style, canonical file system path.
Path values are distinct from string values, even if they contain the same sequence of bytes.
Operations that produce paths will simplify the result as the standard C function [`realpath`] would, except that there is no symbolic link resolution.
[`realpath`]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/realpath.html
Paths are suitable for referring to local files, and are often preferable over strings.
- Path values do not contain trailing or duplicate slashes, `.`, or `..`.
- Relative path literals are automatically resolved relative to their [base directory].
- Tooling can recognize path literals and provide additional features, such as autocompletion, refactoring automation and jump-to-file.
[base directory]: @docroot@/glossary.md#gloss-base-directory
A file is not required to exist at a given path in order for that path value to be valid, but a path that is converted to a string with [string interpolation] or [string-and-path concatenation] must resolve to a readable file or directory which will be copied into the Nix store.
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/<hash>-foo.txt"`.
Operations such as [`import`] can also expect a path to resolve to a readable file or directory.
[string interpolation]: string-interpolation.md#interpolated-expression
[string-and-path concatenation]: operators.md#string-and-path-concatenation
[`import`]: builtins.md#builtins-import
> **Note**
>
> 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.
> Use `:r` to reset the repl as needed.
[store path]: @docroot@/store/store-path.md
Path values can be expressed as [path literals](syntax.md#path-literal).
The function [`builtins.isPath`](builtins.md#builtins-isPath) can be used to determine if a value is a path.
### Null {#type-null}