Store specialized variable for use in dbg as fake symbol in lowlevel call

crates/compiler/alias_analysis/src/lib.rs

@@ -1287,6 +1287,14 @@ fn lowlevel_spec<'a>(
 
             builder.add_make_tuple(block, &[byte_index, string, is_ok, problem_code])
         }
+        Dbg => {
+            let arguments = [env.symbols[&arguments[0]]];
+
+            let result_type =
+                layout_spec(env, builder, interner, layout, &WhenRecursive::Unreachable)?;
+
+            builder.add_unknown_with(block, &arguments, result_type)
+        }
         _other => {
             // println!("missing {:?}", _other);
             // TODO overly pessimstic

crates/compiler/gen_llvm/src/llvm/lowlevel.rs

@@ -11,7 +11,7 @@ use roc_builtins::bitcode::{self, FloatWidth, IntWidth};
 use roc_error_macros::internal_error;
 use roc_module::{low_level::LowLevel, symbol::Symbol};
 use roc_mono::{
-    ir::HigherOrderLowLevel,
+    ir::{HigherOrderLowLevel, LookupType},
     layout::{Builtin, LambdaSet, Layout, LayoutIds},
 };
 use roc_target::PtrWidth;
@@ -1120,14 +1120,19 @@ pub(crate) fn run_low_level<'a, 'ctx, 'env>(
             }
         },
         Dbg => {
-            // now what
-            arguments!(condition);
+            assert_eq!(args.len(), 2);
+            let condition = load_symbol(scope, &args[0]);
+            let dbg_spec_var_symbol = args[1];
 
             if env.mode.runs_expects() {
                 let region = unsafe { std::mem::transmute::<_, roc_region::all::Region>(args[0]) };
 
                 let shared_memory = crate::llvm::expect::SharedMemoryPointer::get(env);
 
+                // HACK(dbg-spec-var): the specialized type variable is passed along as a fake symbol
+                let specialized_var =
+                    unsafe { LookupType::from_index(dbg_spec_var_symbol.ident_id().index() as _) };
+
                 crate::llvm::expect::clone_to_shared_memory(
                     env,
                     scope,
@@ -1136,7 +1141,7 @@ pub(crate) fn run_low_level<'a, 'ctx, 'env>(
                     args[0],
                     region,
                     &[args[0]],
-                    &[roc_mono::ir::LookupType::NULL], // TODO
+                    &[specialized_var],
                 );
 
                 crate::llvm::expect::notify_parent_dbg(env, &shared_memory);

crates/compiler/module/src/symbol.rs

@@ -594,6 +594,13 @@ impl IdentId {
     pub const fn index(self) -> usize {
         self.0 as usize
     }
+
+    /// # Safety
+    ///
+    /// The index is not guaranteed to know to exist.
+    pub unsafe fn from_index(index: u32) -> Self {
+        Self(index)
+    }
 }
 
 /// Stores a mapping between Ident and IdentId.

crates/compiler/mono/src/borrow.rs

@@ -948,7 +948,7 @@ pub fn lowlevel_borrow_signature(arena: &Bump, op: LowLevel) -> &[bool] {
 
         ListIsUnique => arena.alloc_slice_copy(&[borrowed]),
 
-        Dbg => arena.alloc_slice_copy(&[borrowed]),
+        Dbg => arena.alloc_slice_copy(&[borrowed, /* dbg-spec-var */ irrelevant]),
 
         BoxExpr | UnboxExpr => {
             unreachable!("These lowlevel operations are turned into mono Expr's")

crates/compiler/mono/src/inc_dec.rs

@@ -555,7 +555,13 @@ impl<'a, 'i> Context<'a, 'i> {
         match &call_type {
             LowLevel { op, .. } => {
                 let ps = crate::borrow::lowlevel_borrow_signature(self.arena, *op);
-                let b = self.add_dec_after_lowlevel(arguments, ps, b, b_live_vars);
+                let b = match op {
+                    roc_module::low_level::LowLevel::Dbg => {
+                        // NB(dbg-spec-var) second var is the Variable
+                        self.add_dec_after_lowlevel(&arguments[..1], ps, b, b_live_vars)
+                    }
+                    _ => self.add_dec_after_lowlevel(arguments, ps, b, b_live_vars),
+                };
 
                 let v = Expr::Call(crate::ir::Call {
                     call_type,

crates/compiler/mono/src/ir.rs

@@ -27,7 +27,7 @@ use roc_late_solve::storage::{ExternalModuleStorage, ExternalModuleStorageSnapsh
 use roc_late_solve::{resolve_ability_specialization, AbilitiesView, Resolved, UnificationFailed};
 use roc_module::ident::{ForeignSymbol, Lowercase, TagName};
 use roc_module::low_level::LowLevel;
-use roc_module::symbol::{IdentIds, ModuleId, Symbol};
+use roc_module::symbol::{IdentId, IdentIds, ModuleId, Symbol};
 use roc_problem::can::{RuntimeError, ShadowKind};
 use roc_region::all::{Loc, Region};
 use roc_std::RocDec;
@@ -6711,13 +6711,23 @@ pub fn from_can<'a>(
         } => {
             let rest = from_can(env, variable, loc_continuation.value, procs, layout_cache);
 
+            let spec_var = env
+                .expectation_subs
+                .as_mut()
+                .unwrap()
+                .fresh_unnamed_flex_var();
+            // HACK(dbg-spec-var): pass the specialized type variable along injected into a fake symbol
+            let dbg_spec_var_symbol = Symbol::new(ModuleId::ATTR, unsafe {
+                IdentId::from_index(spec_var.index())
+            });
+
             // TODO: need to store the specialized variable of this dbg in the expectation_subs
             let call = crate::ir::Call {
                 call_type: CallType::LowLevel {
                     op: LowLevel::Dbg,
                     update_mode: env.next_update_mode_id(),
                 },
-                arguments: env.arena.alloc([dbg_symbol]),
+                arguments: env.arena.alloc([dbg_symbol, dbg_spec_var_symbol]),
             };
 
             let dbg_layout = layout_cache
@@ -6745,6 +6755,10 @@ pub fn from_can<'a>(
                 );
             }
 
+            // Now that the dbg value has been specialized, export its specialized type into the
+            // expectations subs.
+            store_specialized_expectation_lookups(env, [variable], &[spec_var]);
+
             stmt
         }