From 0629b82536e9fdd9579584c0dd2bddf7ab105744 Mon Sep 17 00:00:00 2001
From: Trevin Chow <trevin@trevinchow.com>
Date: Sun, 19 Apr 2026 01:48:20 -0700
Subject: [PATCH] refactor(hir): audit #[allow(dead_code)] stubs per #2
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Three `#[allow(dead_code)]` items in cssl-hir reviewed against the
issue's "work pending vs landed" question:

1) compiler-rs/crates/cssl-hir/src/cap_check.rs:137 `fn emit(...)`
   T3.4-phase-2.5 (the body-walk slice this helper was reserved for)
   is still listed under "Deferred" in DECISIONS.md § T5-D3 and is
   not in the Session-1 STATUS line. The function stays; its tracking
   comment is upgraded from the bare "reserved for T3.4-phase-2.5
   expression walk" hint to an explicit reference to DECISIONS.md
   § T5-D3 (which is where "full linear-use tracking through every
   expression" + "handler-one-shot enforcement" are formally deferred).

2) compiler-rs/crates/cssl-hir/src/cap_check.rs:231 `fn matrix(...)`
   Same DECISIONS.md § T5-D3 dependency -- it's the AliasMatrix
   accessor the deferred body walk needs in order to call
   `AliasMatrix::can_pass_through` / `param_subtype_check` at call
   sites. Comment upgraded to the same T5-D3 tracker; `#[allow]`
   kept.

3) compiler-rs/crates/cssl-hir/src/lower.rs:1271 `const fn _span_referenced`
   The stub existed solely to keep the `Span` import from flagging as
   unused under cargo -D warnings. Searching lower.rs for other `Span`
   uses shows none outside the stub (3 matches: the import, the
   stub's comment, and the stub's signature). The stub is dead code
   that props up a dead import, so both the stub and the `Span` entry
   in `use cssl_ast::{...}` are removed. `SourceFile` remains since
   it IS used at lines 49/56/919.

`cargo build --workspace` is clean. `cargo test -p cssl-hir` passes
(195 tests).

Closes #2
---
 compiler-rs/crates/cssl-hir/src/cap_check.rs | 14 ++++++++++++--
 compiler-rs/crates/cssl-hir/src/lower.rs     |  5 +----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/compiler-rs/crates/cssl-hir/src/cap_check.rs b/compiler-rs/crates/cssl-hir/src/cap_check.rs
index 8ac0d412..43a2804b 100644
--- a/compiler-rs/crates/cssl-hir/src/cap_check.rs
+++ b/compiler-rs/crates/cssl-hir/src/cap_check.rs
@@ -134,7 +134,14 @@ impl CapCtx {
         }
     }
 
-    #[allow(dead_code)] // reserved for T3.4-phase-2.5 expression walk
+    // Reserved for the deferred T3.4-phase-2.5 body-walk slice of cap_check.
+    // The signature-level minimum-viable check landed in DECISIONS.md § T5-D3
+    // (Cap-check pass sig-level only for stage-0 ; full expr walk deferred),
+    // which explicitly defers "full linear-use tracking through every
+    // expression" + "handler-one-shot enforcement" to T3.4-phase-2.5. This
+    // helper will be wired in when that slice lands; until then, cargo
+    // -D warnings needs the allow.
+    #[allow(dead_code)] // T5-D3: wired in at T3.4-phase-2.5
     fn emit(&mut self, message: impl Into<String>, span: Span) {
         self.diagnostics
             .push(Diagnostic::error(message).with_span(span));
@@ -228,7 +235,10 @@ impl CapCtx {
         }
     }
 
-    #[allow(dead_code)] // reserved for T3.4-phase-2.5 expression walk
+    // See `emit` above for the DECISIONS.md § T5-D3 tracking note -- matrix() is
+    // the AliasMatrix accessor the deferred T3.4-phase-2.5 body-walk needs to
+    // run `AliasMatrix::can_pass_through`/`param_subtype_check` at call sites.
+    #[allow(dead_code)] // T5-D3: wired in at T3.4-phase-2.5
     fn matrix(&self) -> &AliasMatrix {
         &self.matrix
     }
diff --git a/compiler-rs/crates/cssl-hir/src/lower.rs b/compiler-rs/crates/cssl-hir/src/lower.rs
index 99dc906a..f224b286 100644
--- a/compiler-rs/crates/cssl-hir/src/lower.rs
+++ b/compiler-rs/crates/cssl-hir/src/lower.rs
@@ -18,7 +18,7 @@
 //!     `HirExprKind::Compound` with the operator-class preserved.
 
 use cssl_ast::cst;
-use cssl_ast::{DiagnosticBag, Ident, Module as CstModule, SourceFile, Span};
+use cssl_ast::{DiagnosticBag, Ident, Module as CstModule, SourceFile};
 
 use crate::arena::{DefId, HirArena, HirId};
 use crate::attr::{HirAttr, HirAttrArg, HirAttrKind};
@@ -1267,9 +1267,6 @@ fn resolve_struct_body(b: &mut HirStructBody, scope: &ScopeMap) {
     }
 }
 
-/// Hide the empty Span+SourceFile re-export so the `Span` import doesn't show as unused.
-#[allow(dead_code)]
-const fn _span_referenced(_: Span) {}
 
 #[cfg(test)]
 mod tests {