Lazy paths by roberth · Pull Request #11367 · NixOS/nix

roberth · 2024-08-25T08:27:27Z

(This is #10252, but as an upstream branch for easier collaboration)

Motivation

Improve performance, and make the fetchTree interface more capable while keeping it clean.

Fixes Source roots result in /nix/store/<hash>-<hash>-source #10627 (the use case, not the overly broad framing of the issue)

Description

This makes fetchTree return lazy InputAccessor-based SourcePaths instead of "cowardly" fetching them to the store and returning absolute "system" paths.
It stays close to existing path semantics, including support for readFile "${toString p}/..", which some expressions rely on.
It does not go as far as lazy-trees, but judging from the amount of change I could reuse, and how little of my own I had to add, lazy-trees will be a natural extension of this PR.

Done:

Packages and NixOS evaluate as usual
- no hash changes, based on my limited testing
Flake is not added to store unless e.g.
- "${flake.outPath}"
- uses module system (needs clever lazy source strings, or a change to the module system)
Note that the above is already an improvement over the status quo - always fetching to the store
iirc 0.1s reduction on nixpkgs#hello, and 1s reduction on nixosTests.simple

Conclusion so far:
Viable

TODO:

Check the TODO and FIXMEs
Update the test suite
- probably some intended behavior change, such as removal of narHash in some observable places
  - do we want to do that now? not sure
- possibly finds a bug
Check performance again
Cherry-pick the toString path behavior to lazy-trees
Run flake-regressions in full to assess the breakage of changing (fetchTree x).outPath
Run flake-regressions in full to assess the breakage of changing flake.outPath

Context

Priorities and Process

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Co-authored-by: Eelco Dolstra <edolstra@gmail.com> Co-authored-by: Robert Hensing <robert@roberthensing.nl>

This fixes the double copy problem and improves performance for expressions that don't force the whole source to be added to the store. Rules for fast expressions: - Use path literals where possible - import ./foo.nix - Use + operator with slash in string - src = fetchTree foo + "/src"; - Use source filtering, lib.fileset - AVOID toString - If possible, AVOID interpolations ("${./.}") - If possible, move slashes into the interpolation to add less to the store - "${./src}/foo" -> "${./src/foo}" toString may be improved later as part of lazy-trees, so these recommendations are a snapshot. Path values are quite nice though.

This allows clever editors/IDEs to discern the path more easily for Ctrl+Click navigate to functionality, e.g. when building .?ref=HEAD

This showPath is getting a little too ad hoc, but it works for now.

#10252 (comment)

A string is only allowed to create one path component; containing no slashes.

tomberek · 2024-08-26T04:45:39Z

PosixAccessor calls assertNoSymlinks too often?

[ RUN      ] PrimOpTest.unsafeGetAttrPos
unknown file: Failure
C++ exception with description "error:
       … while calling the 'unsafeGetAttrPos' builtin
         at «string»:1:1:
            1| builtins.unsafeGetAttrPos "y" (import <nix/foo.nix>)
             | ^

       … while calling the 'import' builtin
         at «string»:1:32:
            1| builtins.unsafeGetAttrPos "y" (import <nix/foo.nix>)
             |                                ^

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: path '/home/tom/.nix-defexpr/channels' is a symlink" thrown in the test body.

[  FAILED  ] PrimOpTest.unsafeGetAttrPos (0 ms)

findFile prefix/suffix separator is ":" or "/"

+(lang.sh:61) bash lang/eval-fail-derivation-name.postprocess lang/eval-fail-derivation-name
--- lang/eval-fail-derivation-name.err.exp      2024-08-25 17:27:55.317195410 -0400
+++ lang/eval-fail-derivation-name.err  2024-08-26 00:34:52.148460570 -0400
@@ -1,20 +1,20 @@
 error:
        … while evaluating the attribute 'outPath'
-         at <nix/derivation-internal.nix>:<number>:<number>:
+         at <nix:derivation-internal.nix>:<number>:<number>:
      <number>|       value = commonAttrs // {
      <number>|         outPath = builtins.getAttr outputName strict;
              |         ^
      <number>|         drvPath = strict.drvPath;

        … while calling the 'getAttr' builtin
-         at <nix/derivation-internal.nix>:<number>:<number>:
+         at <nix:derivation-internal.nix>:<number>:<number>:
      <number>|       value = commonAttrs // {
      <number>|         outPath = builtins.getAttr outputName strict;
              |                   ^
      <number>|         drvPath = strict.drvPath;

        … while calling the 'derivationStrict' builtin
-         at <nix/derivation-internal.nix>:<number>:<number>:
+         at <nix:derivation-internal.nix>:<number>:<number>:
      <number>|
      <number>|   strict = derivationStrict drvAttrs;
              |            ^

SourceAccessor is relative to root not to absolute path

++(toString-path.sh:8) nix eval --raw --impure --expr 'builtins.readFile (builtins.toString (builtins.fetchTree { type = "path"; path = "/tmp/nix-shell.yXAp0S/nix-test/toString-path/foo"; } + "/bar"))'
error:
       … while calling the 'readFile' builtin
         at «string»:1:1:
            1| builtins.readFile (builtins.toString (builtins.fetchTree { type = "path"; path = "/tmp/nix-shell.yXAp0S/nix-test/toString-path/foo"; } + "/bar"))
             | ^

       error: opening file '/bar': No such file or directory
+(toString-path.sh:8) [[ '' = bla ]]
++(toString-path.sh:8) onError
++(/home/tom/nix/lazy-paths/build/src/nix-functional-tests/common/functions.sh:237) set +x
toString-path.sh: test failed at:
  main in toString-path.sh:8
――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――

117/183 nix-functional-tests:main / read-only-store

Absolute path is used relative to root

++(toString-path.sh:8) nix eval --raw --impure --expr 'builtins.readFile (builtins.toString (builtins.fetchTree { type = "path"; path = "/tmp/nix-shell.yXAp0S/nix-test/toString-path/foo"; } + "/bar"))'
error:
       … while calling the 'readFile' builtin
         at «string»:1:1:
            1| builtins.readFile (builtins.toString (builtins.fetchTree { type = "path"; path = "/tmp/nix-shell.yXAp0S/nix-test/toString-path/foo"; } + "/bar"))
             | ^

       error: opening file '/bar': No such file or directory
+(toString-path.sh:8) [[ '' = bla ]]
++(toString-path.sh:8) onError
++(/home/tom/nix/lazy-paths/build/src/nix-functional-tests/common/functions.sh:237) set +x
toString-path.sh: test failed at:
  main in toString-path.sh:8
――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――

117/183 nix-functional-tests:main / read-only-store

tomberek · 2024-08-26T05:22:34Z

Unable to find input at specified path

+(follow-paths.sh:80) nix flake metadata /tmp/nix-shell.yXAp0S/nix-test/flakes/follow-paths/follows/flakeA
warning: Git tree '/tmp/nix-shell.yXAp0S/nix-test/flakes/follow-paths/follows/flakeA' is dirty
error:
       … while updating the lock file of flake 'git+file:///tmp/nix-shell.yXAp0S/nix-test/flakes/follow-paths/follows/flakeA'

       … while updating the flake input 'B'

       … while fetching the input 'path:./flakeB'

       error: path 'flakeB' does not exist
++(follow-paths.sh:80) onError
++(/home/tom/nix/lazy-paths/build/src/nix-functional-tests/common/functions.sh:237) set +x
follow-paths.sh: test failed at:
  main in follow-paths.sh:80

roberth · 2024-08-26T08:41:06Z

PosixAccessor calls assertNoSymlinks too often?

error: path '/home/tom/.nix-defexpr/channels' is a symlink" thrown in the test body.

This is probably the right behavior for a SourceAccessor, but we shouldn't use a SourceAccessor directly, or not its low level methods or not for this purpose.

nixos-discourse · 2024-08-28T19:04:57Z

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2024-08-26-nix-team-meeting-minutes-172/51300/1

nixos-discourse · 2024-09-25T11:15:10Z

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/how-are-flake-dependencies-fetched/52638/8

tomberek · 2024-10-07T13:59:06Z

Next steps:

rebase
resolve remaining test failures
flake regression suite
long-term testing, rc? Or at beginning of release cycle.
announce in Discourse to get testers and review.

nixos-discourse · 2024-10-07T14:40:35Z

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2024-10-07-nix-team-meeting-minutes-184/54046/1

nixos-discourse · 2024-10-28T23:09:11Z

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/nix-team-member-suggests-removing-flakes-data-suggest-it-isnt-a-good-idea-please-remove-the-experimental-flag-instead/54959/113

tomberek and others added 8 commits August 23, 2024 23:52

fetchTree: Return a path instead of a store path

50b00b0

Co-authored-by: Eelco Dolstra <edolstra@gmail.com> Co-authored-by: Robert Hensing <robert@roberthensing.nl>

fixup: remove FlakeCache

b79c918

SourceAccessor: insert colon after prefix

5def18e

This allows clever editors/IDEs to discern the path more easily for Ctrl+Click navigate to functionality, e.g. when building .?ref=HEAD

Fix evalState::rootFS paths' to_string()

f3d2a16

This showPath is getting a little too ad hoc, but it works for now.

Fix nix flake init eval for path value

f13dc79

WIP fix baseNameOf (needs test maybe)

52c0ef2

#10252 (comment)

fix findFile assertion failure

1008847

A string is only allowed to create one path component; containing no slashes.

github-actions bot added new-cli Relating to the "nix" command with-tests Issues related to testing. PRs with tests have some priority fetching Networking with the outside (non-Nix) world, input locking labels Aug 25, 2024

This was referenced Aug 25, 2024

Lazy fetchTree outPath path values #10252

Closed

libgit2, GitRepo: Write (thin) packfiles #11330

Merged

tests: nix:derivation-internal.nix renders with a scheme now

68a5cfd

fixup: Re-enable import .drv code

359d124

roberth mentioned this pull request Sep 7, 2024

Fetch Git submodules lazily #11425

Draft

roberth mentioned this pull request Jan 20, 2025

Overhaul flake ignore system #12291

Open

2 tasks

roberth mentioned this pull request Feb 4, 2025

builtins.storeDir should return a path, and not a string #12158

Open

roberth mentioned this pull request Feb 25, 2025

Make rootFS's showPath() render the paths from the original accessors #12532

Closed

thislooksfun mentioned this pull request Mar 20, 2025

Don't ignore unstaged files in local flakes #6858

Open

This was referenced Apr 5, 2025

Source path error improvements #12915

Closed

Source roots result in /nix/store/<hash>-<hash>-source #10627

Open

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Lazy paths#11367

Lazy paths#11367
roberth wants to merge 10 commits intomasterfrom
lazy-paths

roberth commented Aug 25, 2024 •

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roberth commented Aug 25, 2024 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Motivation

Description

Context

Priorities and Process

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tomberek commented Aug 26, 2024

PosixAccessor calls assertNoSymlinks too often?

findFile prefix/suffix separator is ":" or "/"

SourceAccessor is relative to root not to absolute path

Absolute path is used relative to root

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tomberek commented Aug 26, 2024

Unable to find input at specified path

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roberth commented Aug 26, 2024

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nixos-discourse commented Aug 28, 2024

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roberth commented Aug 25, 2024 •

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