`lib.path.subpath.components`: init #242695

infinisil · 2023-07-10T19:21:03Z

Description of changes

Adds a new function:

lib.path.subpath.components: Split a subpath into its path component strings.
```
subpath.components "./foo//bar/./baz/"
-> [ "foo" "bar" "baz" ]
```

Partly motivated by feedback in #238013. This is also part of the path library effort.

This work is sponsored by Antithesis ✨

Things done

Documentation
Tests

infinisil · 2023-07-10T19:30:40Z

lib/path/default.nix

@@ -336,6 +336,34 @@ in /* No rec! Add dependencies on this file at the top. */ {
              ${subpathInvalidReason path}''
      ) 0 subpaths;

+  /* Split a subpath into its path component strings.
+  Throw an error if the subpath isn't valid, see `lib.path.subpath.isValid`.
+  Note that the returned path component strings are not valid subpaths themselves.


This is a bit unfortunate, because we decided to always prefix subpaths with ./: https://github.com/NixOS/nixpkgs/tree/master/lib/path#leading-dots-for-relative-paths

This is the only reason why subpaths are not valid as components.

Anyways, it's already too late now, and it's not like a big problem, just a bit unfortunate 🙃

I don't even think it's unfortunate. Those are clearly components, not subpaths. No ambiguity there, no inconsistency.

Oh this has a mistake in it. The resulting strings are valid subpaths, they're just not normalised.

Edit: Now reworded

roberth · 2023-07-19T15:49:50Z

lib/path/default.nix

@@ -336,6 +336,34 @@ in /* No rec! Add dependencies on this file at the top. */ {
              ${subpathInvalidReason path}''
      ) 0 subpaths;

+  /* Split a subpath into its path component strings.


Here subpath should also be a link to a definition, but I'll merge this so you can do it in the other PR where I said the same.

(for reference: #244358 (comment))

Let's conclude that thread first before merging here.

I now added a link to subpath.isValid, which after the above PR is merged will contain a definition for it. This PR is not dependent on that PR however.

roberth · 2023-07-19T15:50:55Z

@ofborg eval

Looks like it got stuck earlier.

infinisil · 2023-07-20T20:37:05Z

lib/path/README.md

+### Prefer returning subpaths over components
+[subpath-preference]: #prefer-returning-subpaths-over-components


Here's why this was added: #244358 (comment)

lib/path/README.md

lib/path/default.nix

roberth · 2023-07-21T10:05:14Z

lib/path/default.nix

+        subpath.join (subpath.components s) == subpath.normalise s
+
+  Type:
+    subpath.components :: String -> [ String ]


Suggested change

subpath.components :: String -> [ String ]

subpath.components :: String -> List String

I wish we didn't repeat Haskell's mistake. At your discretion.

All of lib.lists uses [ ] so let's stick with that for now. Am wondering what the problem with [ ] in Haskell is though (I only know Idris doesn't support [ ])

That's right, it's a problem with dependent types, which hints at the more general problem that the list type is not a list.
In Nix we can exemplify this by asking the question what is [ Attrs String ]?
a. A type for lists of any number of elements, each of which is an attrset with string values only,
b1. A type for two-element heterogeneous lists where the first is an attrset and the second is a string,
b2. A type for one-element lists where the element is an attrset with string values only.

That just looks like ambiguous notation to me, same as if you wrote List Attrs String. Needs parenthesis to make sense

I guess the b1/b2 distinction was a distraction. a/b2 is the one that's the problem: the list type is not a list, so it shouldn't use the notation of the list literal.

Ah I get it now, if both list values and types use the same syntax it's ambiguous and confusing. [ x ] could either be a single-value list with the element x, or if x is a type the type of a list of x's. In comparison [ x y ] can only be one.

So using List x for the type and [ ... ] for values disambiguates them better

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>

infinisil · 2023-07-26T21:30:25Z

I think this is ready to get merged

infinisil requested review from roberth and fricklerhandwerk July 10, 2023 19:21

infinisil requested a review from edolstra as a code owner July 10, 2023 19:21

github-actions bot added the 6.topic: lib The Nixpkgs function library label Jul 10, 2023

infinisil mentioned this pull request Jul 10, 2023

Path library functions #210426

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infinisil changed the title ~~lib.path.subpath.components: init~~ lib.path.subpath.components: init Jul 10, 2023

infinisil mentioned this pull request Jul 10, 2023

lib.path.removePrefix: init #238013

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infinisil commented Jul 10, 2023

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ofborg bot added 10.rebuild-darwin: 0 This PR does not cause any packages to rebuild on Darwin 10.rebuild-linux: 1-10 labels Jul 10, 2023

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infinisil force-pushed the lib.path.subpath.components branch from 82560f0 to 89cf3e1 Compare July 19, 2023 14:29

infinisil mentioned this pull request Jul 19, 2023

[WIP] File set combinators #222981

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roberth approved these changes Jul 19, 2023

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infinisil mentioned this pull request Jul 19, 2023

lib.path.splitRoot: init #244358

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infinisil force-pushed the lib.path.subpath.components branch 3 times, most recently from 713651f to 109502d Compare July 20, 2023 20:36

infinisil commented Jul 20, 2023

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infinisil and others added 2 commits July 26, 2023 23:29

lib.path.subpath.components: init

4e14f5f

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

lib/path/README.md: Justify returning subpaths

407db58

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>

infinisil force-pushed the lib.path.subpath.components branch from 9cfa604 to 407db58 Compare July 26, 2023 21:30

infinisil mentioned this pull request Jul 27, 2023

File set combinators base: lib.fileset.toSource #245623

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roberth merged commit 8fa1697 into NixOS:master Aug 4, 2023

infinisil deleted the lib.path.subpath.components branch August 4, 2023 15:01

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`lib.path.subpath.components`: init #242695

`lib.path.subpath.components`: init #242695

infinisil commented Jul 10, 2023

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infinisil commented Jul 26, 2023

		### Prefer returning subpaths over components
		[subpath-preference]: #prefer-returning-subpaths-over-components

	subpath.components :: String -> [ String ]
	subpath.components :: String -> List String

lib.path.subpath.components: init #242695

lib.path.subpath.components: init #242695

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infinisil commented Jul 10, 2023

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infinisil commented Jul 26, 2023

`lib.path.subpath.components`: init #242695

`lib.path.subpath.components`: init #242695

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