[MangelMaxime]

Fixes #5253.

[github-actions]

Python Type Checking Results (Pyright)

Metric	Value
Total errors	33
Files with errors	4
Excluded files	4
New errors	✅ No

Excluded files with errors (4 files)

These files have known type errors and are excluded from CI. Remove from pyrightconfig.ci.json as errors are fixed.

File	Errors	Status
temp/tests/Python/test_hash_set.py	18	Excluded
temp/tests/Python/test_applicative.py	11	Excluded
temp/tests/Python/test_nested_and_recursive_pattern.py	2	Excluded
temp/tests/Python/fable_modules/thoth_json_python/encode.py	2	Excluded

[Copilot]

🟡 Changes recommended

Caching the source before update expressions run can copy stale unchanged fields when a mutable struct is reassigned during an update, requiring deferred dereferencing and a regression test.

1 open issue

• Mutable struct updates copy stale fields after reassignment · New

What changed in this PR

This PR addresses #5253, where copy-and-update expressions on mutable struct records lose unchanged fields. It adjusts the shared F# transformation stage and adds regression tests across five targets.

Changes:

• Unwrap addresses for compiler-generated record-copy bindings and field reads on non-Rust targets.
• Test preservation of unchanged fields when copying mutable struct locals.
• Add mutable-field and module-level source coverage in selected target suites.

File	Description
tests/​Rust/​tests/​src/​RecordTests.fs	Adds mutable struct copy-and-update coverage.
tests/​Python/​TestRecordType.fs	Tests local, mutable-field, and module-level cases.
tests/​Js/​Main/​RecordTypeTests.fs	Tests local, mutable-field, and module-level cases.
tests/​Dart/​src/​RecordTests.fs	Tests mutable locals and records with mutable fields.
tests/​Beam/​RecordTests.fs	Tests mutable locals and records with mutable fields.
src/​Fable.Transforms/​FSharp2Fable.fs	Changes address handling for record-copy bindings and field reads.

_{Review effort: Balanced}