fix(rust-lsp): keep proc-macro expansion on in Reduced Memory mode (#2598)

[sinelaw]

Fixes #2598.

Problem

Switching rust-analyzer to Reduced Memory mode ("Rust LSP: Configure Mode" → Reduced Memory) silently killed hover (Alt+K) and Go to Definition (F12) for:

• the macro name itself (println!), and
• any symbol inside a macro invocation's arguments — e.g. a plain function called inside println!(...), or a method call inside format!(...).

F12 worked on a bare call but returned No definition found on the identical call one line up that happened to sit inside a println!, so the feature looked randomly broken. Positions inside println!/format!/assert! args are among the most common cursor positions in real Rust code.

Root cause

Reduced Memory mode restarted rust-analyzer with procMacro.enable: false. rust-analyzer resolves identifiers inside a macro invocation's arguments (and the macro name itself) through macro expansion, so disabling proc-macro expansion takes navigation there down with it — including the built-in println!/format!/assert! macros, whose name doesn't obviously imply a proc-macro dependency. The mode's own status even claimed it only disabled checkOnSave, procMacro, cachePriming, none of which explains losing built-in-macro navigation to a user.

I isolated this by driving rust-analyzer directly over LSP against a minimal crate and toggling one option at a time. procMacro.enable: false is the sole cause; everything else in the reduced-mode options is fine.

Fix

Keep procMacro enabled in Reduced Memory mode. Its expansion cost is small next to checkOnSave/cachePriming, and the 50% RAM / 90% CPU process limits still apply, so the mode keeps its memory character while navigation stays intact.

Changes:

• crates/fresh-editor/plugins/rust-lsp.ts: procMacro.enable: true in REDUCED_MEMORY_INIT_OPTIONS; comment explains why it must stay on; status message updated (no longer claims procMacro is disabled).
• crates/fresh-editor/config.example.json: mirror the same change in the sample reduced-memory config.
• docs/features/lsp.md: fix the palette command name (the doc said "Switch Rust Analyzer Mode"; the real command is Rust LSP: Configure Mode — a discrepancy also noted in the issue) and describe what Reduced Memory mode disables.
• CHANGELOG.md: bug-fix entry.

Validation

Drove rust-analyzer 1.95.0 over LSP against a minimal crate:

fn main() {
    println!("{}", describe());   // in-macro arg
    let s = describe();           // bare call
}
fn describe() -> String { "x".to_string() }

Reduced-mode config	def inside println! arg	def on println name	def on bare call
shipped (procMacro on)	✅ resolves	✅ resolves	✅ resolves
pre-fix (procMacro off)	❌ empty	❌ empty	✅ resolves

The pre-fix column reproduces exactly the bug from the report; the shipped column shows it fixed. Plugin type-check (check-types.sh) passes.

Notes / out of scope

The issue's secondary observation — a ~30–60 s window after a Reduced-mode restart where all requests return empty while the status reads ready — stems from cachePriming.enable: false (no background priming) and is an inherent, documented trade-off of the mode, not part of this navigation bug. Left as-is.

🤖 Generated with Claude Code

https://claude.ai/code/session_014bSc9dVgYMs4C1cbm1p3bx

---

Generated by Claude Code