Unify variables directly when possible

instead of going through a solved type

compiler/mono/src/ir.rs

@@ -694,10 +694,8 @@ impl<'a> Procs<'a> {
         layout: ProcLayout<'a>,
         layout_cache: &mut LayoutCache<'a>,
     ) {
-        let tuple = (name, layout);
-
         // If we've already specialized this one, no further work is needed.
-        if self.specialized.contains_key(&tuple) {
+        if self.specialized.contains_key(&(name, layout)) {
             return;
         }
 
@@ -707,15 +705,12 @@ impl<'a> Procs<'a> {
             return;
         }
 
-        // We're done with that tuple, so move layout back out to avoid cloning it.
-        let (name, layout) = tuple;
-
-        let pending = PendingSpecialization::from_var(env.arena, env.subs, fn_var);
-
         // This should only be called when pending_specializations is Some.
         // Otherwise, it's being called in the wrong pass!
         match &mut self.pending_specializations {
             Some(pending_specializations) => {
+                let pending = PendingSpecialization::from_var(env.arena, env.subs, fn_var);
+
                 // register the pending specialization, so this gets code genned later
                 if self.module_thunks.contains(&name) {
                     debug_assert!(layout.arguments.is_empty());
@@ -736,7 +731,26 @@ impl<'a> Procs<'a> {
                 // (We had a bug around this before this system existed!)
                 self.specialized.insert((symbol, layout), InProgress);
 
-                match specialize(env, self, symbol, layout_cache, pending, partial_proc) {
+                // See https://github.com/rtfeldman/roc/issues/1600
+                //
+                // The annotation variable is the generic/lifted/top-level annotation.
+                // It is connected to the variables of the function's body
+                //
+                // fn_var is the variable representing the type that we actually need for the
+                // function right here.
+                //
+                // For some reason, it matters that we unify with the original variable. Extracting
+                // that variable into a SolvedType and then introducing it again severs some
+                // connection that turns out to be important
+                match specialize_variable(
+                    env,
+                    self,
+                    symbol,
+                    layout_cache,
+                    fn_var,
+                    Default::default(),
+                    partial_proc,
+                ) {
                     Ok((proc, _ignore_layout)) => {
                         // the `layout` is a function pointer, while `_ignore_layout` can be a
                         // closure. We only specialize functions, storing this value with a closure
@@ -2448,13 +2462,57 @@ fn specialize_solved_type<'a>(
     host_exposed_aliases: BumpMap<Symbol, SolvedType>,
     partial_proc: PartialProc<'a>,
 ) -> Result<SpecializeSuccess<'a>, SpecializeFailure<'a>> {
+    specialize_variable_help(
+        env,
+        procs,
+        proc_name,
+        layout_cache,
+        |env| introduce_solved_type_to_subs(env, &solved_type),
+        host_exposed_aliases,
+        partial_proc,
+    )
+}
+
+fn specialize_variable<'a>(
+    env: &mut Env<'a, '_>,
+    procs: &mut Procs<'a>,
+    proc_name: Symbol,
+    layout_cache: &mut LayoutCache<'a>,
+    fn_var: Variable,
+    host_exposed_aliases: BumpMap<Symbol, SolvedType>,
+    partial_proc: PartialProc<'a>,
+) -> Result<SpecializeSuccess<'a>, SpecializeFailure<'a>> {
+    specialize_variable_help(
+        env,
+        procs,
+        proc_name,
+        layout_cache,
+        |_| fn_var,
+        host_exposed_aliases,
+        partial_proc,
+    )
+}
+
+fn specialize_variable_help<'a, F>(
+    env: &mut Env<'a, '_>,
+    procs: &mut Procs<'a>,
+    proc_name: Symbol,
+    layout_cache: &mut LayoutCache<'a>,
+    fn_var_thunk: F,
+    host_exposed_aliases: BumpMap<Symbol, SolvedType>,
+    partial_proc: PartialProc<'a>,
+) -> Result<SpecializeSuccess<'a>, SpecializeFailure<'a>>
+where
+    F: FnOnce(&mut Env<'a, '_>) -> Variable,
+{
     // add the specializations that other modules require of us
     use roc_solve::solve::instantiate_rigids;
 
     let snapshot = env.subs.snapshot();
     let cache_snapshot = layout_cache.snapshot();
 
-    let fn_var = introduce_solved_type_to_subs(env, &solved_type);
+    // important: evaluate after the snapshot has been created!
+    let fn_var = fn_var_thunk(env);
 
     // for debugging only
     let raw = layout_cache
@@ -2723,7 +2781,10 @@ pub fn with_hole<'a>(
             hole,
         ),
 
-        Num(var, num) => match num_argument_to_int_or_float(env.subs, env.ptr_bytes, var, false) {
+        Num(var, num) => {
+            // first figure out what kind of number this is
+
+            match num_argument_to_int_or_float(env.subs, env.ptr_bytes, var, false) {
                 IntOrFloat::SignedIntType(precision) => Stmt::Let(
                     assigned,
                     Expr::Literal(Literal::Int(num.into())),
@@ -2748,7 +2809,8 @@ pub fn with_hole<'a>(
                     Layout::Builtin(Builtin::Decimal),
                     hole,
                 ),
-        },
+            }
+        }
         LetNonRec(def, cont, _) => {
             if let roc_can::pattern::Pattern::Identifier(symbol) = &def.loc_pattern.value {
                 if let Closure {
@@ -7865,6 +7927,12 @@ fn union_lambda_set_to_switch<'a>(
     assigned: Symbol,
     hole: &'a Stmt<'a>,
 ) -> Stmt<'a> {
+    // NOTE this can happen if there is a type error somewhere. Since the lambda set is empty,
+    // there is really nothing we can do here, so we just proceed with the hole itself and
+    // hope that the type error is communicated in a clear way elsewhere.
+    if lambda_set.is_empty() {
+        return hole.clone();
+    }
     debug_assert!(!lambda_set.is_empty());
 
     let join_point_id = JoinPointId(env.unique_symbol());

compiler/mono/src/layout.rs

@@ -554,10 +554,10 @@ impl<'a> LambdaSet<'a> {
             }
 
             Ok(()) | Err((_, Content::FlexVar(_))) => {
-                // TODO hack for builting functions.
+                // this can happen when there is a type error somewhere
                 Ok(LambdaSet {
                     set: &[],
-                    representation: arena.alloc(Layout::Struct(&[])),
+                    representation: arena.alloc(Layout::Union(UnionLayout::NonRecursive(&[]))),
                 })
             }
             _ => panic!("called LambdaSet.from_var on invalid input"),

compiler/test_gen/src/gen_primitives.rs

@@ -2683,26 +2683,50 @@ fn list_walk_until() {
 }
 
 #[test]
-#[ignore]
+fn int_literal_not_specialized_with_annotation() {
-fn int_literal_not_specialized() {
     // see https://github.com/rtfeldman/roc/issues/1600
     assert_evals_to!(
         indoc!(
             r#"
             app "test" provides [ main ] to "./platform"
 
-
+            main =
-            satisfy : (U8 -> Bool) -> Str
+                satisfy : (U8 -> Str) -> Str
                 satisfy = \_ -> "foo"
 
+                myEq : a, a -> Str
+                myEq = \_, _ -> "bar"
+
+                p1 : Num * -> Str
+                p1 = (\u -> myEq u 64)
+
+                when satisfy p1 is
+                    _ -> 32
+            "#
+        ),
+        32,
+        i64
+    );
+}
+
+#[test]
+fn int_literal_not_specialized_no_annotation() {
+    // see https://github.com/rtfeldman/roc/issues/1600
+    assert_evals_to!(
+        indoc!(
+            r#"
+            app "test" provides [ main ] to "./platform"
 
-            main : I64
             main =
-                p1 = (\u -> u == 97)
+                satisfy : (U8 -> Str) -> Str
+                satisfy = \_ -> "foo"
 
-                satisfyA = satisfy p1
+                myEq : a, a -> Str
+                myEq = \_, _ -> "bar"
 
-                when satisfyA is
+                p1 = (\u -> myEq u 64)
+
+                when satisfy p1 is
                     _ -> 32
             "#
         ),