Specialize polymorphic values before binding to pattern

Closes #2811

compiler/mono/src/ir.rs

@@ -3053,7 +3053,7 @@ fn specialize_naked_symbol<'a>(
     let opt_fn_var = Some(variable);
 
     // if this is a function symbol, ensure that it's properly specialized!
-    reuse_function_symbol(
+    specialize_symbol(
         env,
         procs,
         layout_cache,
@@ -3558,7 +3558,7 @@ pub fn with_hole<'a>(
                         // this symbol is already defined; nothing to do
                     }
                     Field::Function(symbol, variable) => {
-                        stmt = reuse_function_symbol(
+                        stmt = specialize_symbol(
                             env,
                             procs,
                             layout_cache,
@@ -4114,7 +4114,7 @@ pub fn with_hole<'a>(
                                 Stmt::Let(*symbol, access_expr, *field_layout, arena.alloc(stmt));
 
                             if record_needs_specialization {
-                                stmt = reuse_function_symbol(
+                                stmt = specialize_symbol(
                                     env,
                                     procs,
                                     layout_cache,
@@ -4804,8 +4804,7 @@ fn construct_closure_data<'a>(
     // symbols to be inlined when specializing the closure body elsewhere.
     for &&(symbol, var) in symbols {
         if procs.partial_exprs.contains(symbol) {
-            result =
-                reuse_function_symbol(env, procs, layout_cache, Some(var), symbol, result, symbol);
+            result = specialize_symbol(env, procs, layout_cache, Some(var), symbol, result, symbol);
         }
     }
 
@@ -6318,6 +6317,20 @@ fn store_pattern_help<'a>(
 
     match can_pat {
         Identifier(symbol) => {
+            if let Some((_, var)) = procs.partial_exprs.get(outer_symbol) {
+                // It might be the case that symbol we're storing hasn't been reified to a value
+                // yet, if it's polymorphic. Do that now.
+                stmt = specialize_symbol(
+                    env,
+                    procs,
+                    layout_cache,
+                    Some(var),
+                    *symbol,
+                    stmt,
+                    outer_symbol,
+                );
+            }
+
             substitute_in_exprs(env.arena, &mut stmt, *symbol, outer_symbol);
         }
         Underscore => {
@@ -6771,7 +6784,7 @@ fn let_empty_struct<'a>(assigned: Symbol, hole: &'a Stmt<'a>) -> Stmt<'a> {
 
 /// If the symbol is a function, make sure it is properly specialized
 // TODO: rename this now that we handle polymorphic non-function expressions too
-fn reuse_function_symbol<'a>(
+fn specialize_symbol<'a>(
     env: &mut Env<'a, '_>,
     procs: &mut Procs<'a>,
     layout_cache: &mut LayoutCache<'a>,
@@ -6980,7 +6993,7 @@ fn assign_to_symbol<'a>(
     match can_reuse_symbol(env, procs, &loc_arg.value) {
         Imported(original) | LocalFunction(original) | UnspecializedExpr(original) => {
             // for functions we must make sure they are specialized correctly
-            reuse_function_symbol(
+            specialize_symbol(
                 env,
                 procs,
                 layout_cache,

compiler/test_gen/src/gen_str.rs

@@ -1587,3 +1587,19 @@ fn str_to_dec() {
         RocDec
     );
 }
+
+#[test]
+#[cfg(any(feature = "gen-llvm"))]
+fn issue_2811() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+            x = Command { tool: "bash" }
+            Command c = x
+            c.tool
+            "#
+        ),
+        RocStr::from("bash"),
+        RocStr
+    );
+}

compiler/test_mono/generated/issue_2811.txt

@@ -0,0 +1,3 @@
+procedure Test.0 ():
+    let Test.6 : Str = "bash";
+    ret Test.6;

compiler/test_mono/src/tests.rs

@@ -1282,6 +1282,17 @@ fn issue_2583_specialize_errors_behind_unified_branches() {
     )
 }
 
+#[mono_test]
+fn issue_2811() {
+    indoc!(
+        r#"
+        x = Command { tool: "bash" }
+        Command c = x
+        c.tool
+        "#
+    )
+}
+
 // #[ignore]
 // #[mono_test]
 // fn static_str_closure() {