Clippy `large_stack_arrays` false positive with `vec![]` macro

[josecelano]

Problem

Clippy reports a false positive large_stack_arrays lint when using the vec![] macro to create vectors of ServiceTopology items in tests.

Error Message

error: allocating a local array larger than 16384 bytes
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.93.0/index.html#large_stack_arrays
  = note: `-D clippy::large-stack-arrays` implied by `-D clippy::pedantic`
  = help: to override `-D clippy::pedantic` add `#[allow(clippy::large_stack_arrays)]`

Root Cause

This is a known clippy bug where the vec![] macro is incorrectly flagged for creating a large stack array. The vec![] macro creates a Vec<T> which allocates on the heap, not the stack. The lint is a false positive.

Upstream Issue: rust-lang/rust-clippy#12586

Affected Code

Tests in src/domain/topology/aggregate.rs that create vectors of ServiceTopology:

let topology = DockerComposeTopology::new(vec![
    ServiceTopology::with_networks(Service::Tracker, vec![Network::Database]),
    ServiceTopology::with_networks(Service::MySQL, vec![Network::Database]),
])
.unwrap();

Current Workaround

Crate-level #![allow(clippy::large_stack_arrays)] in src/lib.rs.

Local suppression methods (module-level, function-level) don't work because the lint fires during macro expansion before the allow attributes are processed.

Potential Regression

The upstream fix (PR #12624) was merged April 27, 2024 and should be in Rust 1.80.0+. However, we're still seeing this error on Rust 1.93.0 (January 2026). This suggests either:

1. Regression: The bug may have regressed in a later clippy version
2. Different code pattern: Our vec![] with ServiceTopology (large struct with EnumSet fields) might trigger a variant not covered by the original fix
3. CI environment: Some discrepancy in the clippy version used in CI

Acceptance Criteria

• Investigate if this is a regression in clippy
• Report upstream if confirmed as regression
• Remove crate-level allow once upstream fix is available

References

• Upstream clippy issue: clippy::large_stack_arrays reports vec! literals and provides a useless suggestion rust-lang/rust-clippy#12586
• Fix PR: fix [large_stack_arrays] linting in vec macro rust-lang/rust-clippy#12624
• Local documentation: docs/issues/302-clippy-large-stack-arrays-false-positive.md
• Related PR: refactor(infrastructure): [#301] Phase 4 - Extract ServiceTopology shared type #303 (Phase 4 Service Topology DDD Alignment)