NixOS/nix

builtins.fetchTree behaves differently if uri or attrs are parsed

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#12,860 建立於 2025年4月1日

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描述

While implementing builtins.fetchTree for https://snix.dev/ I've noticed revCount is missing when it shouldn't:

nixpkgs on  master [$] took 3s 
❯ /nix/store/pkw2fif96sahwnnkfxsmdzs0dl1nr5ln-nix-2.26.3/bin/nix-instantiate -E "builtins.fetchTree git+https://github.com/cachix/devenv" --eval
{ lastModified = 1743521698; lastModifiedDate = "20250401153458"; narHash = "sha256-bvl7YmNZjGEZhyH86mGiJdhZGMaRot1TMM6cjwrwH6k="; outPath = "/nix/store/b9319a8ffx2h1vd1bv7ip2ris0sf2sq2-source"; rev = "4917f16d045f12d938d0a29fb1cbfb9e24ae6d0d"; revCount = 3463; shortRev = "4917f16"; submodules = false; }

nixpkgs on  master [$] 
❯ /nix/store/pkw2fif96sahwnnkfxsmdzs0dl1nr5ln-nix-2.26.3/bin/nix-instantiate -E "builtins.fetchTree (builtins.parseFlakeRef git+https://github.com/cachix/devenv)" --eval
{ lastModified = 1743521698; lastModifiedDate = "20250401153458"; narHash = "sha256-bvl7YmNZjGEZhyH86mGiJdhZGMaRot1TMM6cjwrwH6k="; outPath = "/nix/store/b9319a8ffx2h1vd1bv7ip2ris0sf2sq2-source"; rev = "4917f16d045f12d938d0a29fb1cbfb9e24ae6d0d"; shortRev = "4917f16"; submodules = false; }

Property builtins.fetchTree input == builtins.fetchTree (builtins.parseFlakeRef input) should hold.

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技術棧
cpp
領域
backend
議題類型
bug
難度面向新貢獻者的預計實作難度，1 表示很小改動，5 表示專家級工作。
3
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清晰度議題是否清楚說明預期改動、驗收標準和下一步。
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前置要求
Nix builtinsfetchTreeflake referencesC++
新手友善度1-100 的估計分數，表示該議題對首次貢獻者的友善程度。
40
研究方向
Investigate the discrepancy between fetchTree when called with a URI string directly vs. when called with the result of builtins.parseFlakeRef. Compare the code paths in the Nix source, likely in src/libexpr/primops/fetchTree.cc and related flake handling code. Look for differences in how revCount is computed or omitted in the attrs path.