Register temp roots in a few places

[edolstra]

Motivation

Includes upstream NixOS#15720, plus a less ambitious version of NixOS#15719.

Context

Summary by CodeRabbit

• Bug Fixes
  • Enhanced stability of store path operations during closure fetching and path copying processes to prevent data loss scenarios.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 71c4bfed-2ae0-434e-834d-e5fa9ff6936e

📥 Commits

Reviewing files that changed from the base of the PR and between d5cb6d4 and 734a205.

📒 Files selected for processing (2)

• src/libexpr/primops/fetchClosure.cc
• src/libstore/store-api.cc

---

📝 Walkthrough

Walkthrough

Adds temporary GC root registrations to prevent garbage collection of store paths. Three closure-fetch helper functions in fetchClosure.cc now root their paths before validation; copyPaths in store-api.cc roots destination paths before the validity check loop.

Changes

GC Root Registration

Layer / File(s)	Summary
Fetch closure GC root registrations src/libexpr/primops/fetchClosure.cc	runFetchClosureWithRewrite registers toPathMaybe as a temporary root; runFetchClosureWithContentAddressedPath and runFetchClosureWithInputAddressedPath both register fromPath as a temporary root before validation and closure-copy operations.
Copy paths GC root registration src/libstore/store-api.cc	copyPaths registers each destination path in the storePaths set as a temporary root via a new loop before validity checking and substitution logic.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~4 minutes

🐰 A rabbit hops with glee,
"Roots protect paths, wild and free!"
Garbage can't sweep away with care,
These stored bunny treasures fair. 🥕

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Register temp roots in a few places' accurately and concisely describes the main change across both modified files—adding temporary GC root registration in fetchClosure and copyPaths functions.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch temp-roots

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 Infer (1.2.0)

src/libexpr/primops/fetchClosure.cc

src/libexpr/primops/fetchClosure.cc:1:10: fatal error: 'nix/expr/primops.hh' file not found
1 | #include "nix/expr/primops.hh"
| ^~~~~~~~~~~~~~~~~~~~~
1 error generated.
src/libexpr/primops/fetchClosure.cc:26:1-72:1: ERROR translating statement 'CompoundStmt'
Aborting translation of method 'nix::runFetchClosureWithRewrite' in file 'src/libexpr/primops/fetchClosure.cc': "Assert_failure src/clang/cAst_utils.ml:249:53"
Uncaught Internal Error: "Assert_failure src/clang/cAst_utils.ml:249:53"
Error backtrace:
Raised at ClangFrontend__CAst_utils.get_decl_from_typ_ptr in file "src/clang/cAst_utils.ml", line 249, characters 53-65
Called from ClangFrontend__CTrans.CTrans_funct.get_destructor_decl_ref in file "src/clang/cTrans.ml", line 658, characters 12-59
Called from ClangFrontend__CTrans.CTrans_funct.destructor_calls.(fun) in file "src/clang/cTrans.ml", line 2048, characters 12-69
Called from Base__List.rev_filter_map.loop in file "src/list.ml", line 944, characters 13-17

... [truncated 2200 characters] ...

in file "src/clang/cFrontend_decl.ml" (inlined), line 54, characters 4-52
Called from ClangFrontend__CFrontend_decl.CFrontend_decl_funct.function_decl in file "src/clang/cFrontend_decl.ml", line 90, characters 12-151
Called from ClangFrontend__CFrontend_decl.CFrontend_decl_funct.translate_one_declaration in file "src/clang/cFrontend_decl.ml", line 453, characters 10-56
Called from ClangFrontend__CFrontend_decl.CFrontend_decl_funct.translate_one_declaration.translate in file "src/clang/cFrontend_decl.ml" (inlined), line 448, characters 24-96
Called from Stdlib__List.iter in file "list.ml" (inlined), line 110, characters 12-15
Called from Stdlib__List.iter in file "list.ml" (inlined), line 108, characters 13-64
Called from Base__List0.iter in file "src/list0.ml" (inlined), line 25, characte

src/libstore/store-api.cc

src/libstore/store-api.cc:1:10: fatal error: 'nix/util/logging.hh' file not found
1 | #include "nix/util/logging.hh"
| ^~~~~~~~~~~~~~~~~~~~~
1 error generated.
src/libstore/store-api.cc:995:5-12: ERROR translating statement 'ReturnStmt'
Aborting translation of method 'nix::copyStorePath' in file 'src/libstore/store-api.cc': "Assert_failure src/clang/cAst_utils.ml:249:53"
Uncaught Internal Error: "Assert_failure src/clang/cAst_utils.ml:249:53"
Error backtrace:
Raised at ClangFrontend__CAst_utils.get_decl_from_typ_ptr in file "src/clang/cAst_utils.ml", line 249, characters 53-65
Called from ClangFrontend__CTrans.CTrans_funct.get_destructor_decl_ref in file "src/clang/cTrans.ml", line 658, characters 12-59
Called from ClangFrontend__CTrans.CTrans_funct.destructor_calls.(fun) in file "src/clang/cTrans.ml", line 2048, characters 12-69
Called from Base__List.rev_filter_map.loop in file "src/list.ml", line 944, characters 13-17
Called from Base__List.filter_map in file "src

... [truncated 2200 characters] ...

ine 4784, characters 10-1023
Called from ClangFrontend__CTrans.CTrans_funct.instruction in file "src/clang/cTrans.ml" (inlined), line 4765, characters 38-71
Called from ClangFrontend__CTrans.CTrans_funct.exec_with_node_creation in file "src/clang/cTrans.ml" (inlined), line 104, characters 20-38
Called from ClangFrontend__CTrans.CTrans_funct.get_clang_stmt_trans in file "src/clang/cTrans.ml" (inlined), line 5395, characters 4-69
Called from ClangFrontend__CTrans.CTrans_funct.get_custom_stmt_trans in file "src/clang/cTrans.ml", line 5401, characters 8-55
Called from ClangFrontend__CTrans.CTrans_funct.exec_trans_instrs.exec_trans_instrs_rev in file "src/clang/cTrans.ml" (inlined), line 5365, characters 28-54
Called from ClangFrontend__CTrans.CTrans_funct.exec_trans_instrs in file "src/clang/c

---

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