Print recursion vars correctly

ast/src/constrain.rs

@@ -2051,7 +2051,7 @@ pub mod test_constrain {
                 let subs = solved.inner_mut();
 
                 // name type vars
-                name_all_type_vars(var, subs);
+                let named_result = name_all_type_vars(var, subs);
 
                 let content = subs.get_content_without_compacting(var);
 
@@ -2063,7 +2063,7 @@ pub mod test_constrain {
                     all_ident_ids: dep_idents,
                 };
 
-                let actual_str = content_to_string(content, subs, mod_id, &interns);
+                let actual_str = content_to_string(content, subs, mod_id, &interns, named_result);
 
                 assert_eq!(actual_str, expected_str);
             }

compiler/load_internal/tests/test_load.rs

@@ -237,10 +237,10 @@ mod test_load {
         expected_types: &mut HashMap<&str, &str>,
     ) {
         for (symbol, expr_var) in &def.pattern_vars {
-            name_all_type_vars(*expr_var, subs);
+            let named_result = name_all_type_vars(*expr_var, subs);
 
             let content = subs.get_content_without_compacting(*expr_var);
-            let actual_str = content_to_string(content, subs, home, interns);
+            let actual_str = content_to_string(content, subs, home, interns, named_result);
             let fully_qualified = symbol.fully_qualified(interns, home).to_string();
             let expected_type = expected_types
                 .remove(fully_qualified.as_str())

compiler/solve/tests/solve_expr.rs

@@ -172,18 +172,12 @@ mod solve_expr {
 
         let subs = solved.inner_mut();
 
-        // name type vars
-        for var in exposed_to_host.values() {
-            name_all_type_vars(*var, subs);
-        }
-
-        let content = {
         debug_assert!(exposed_to_host.len() == 1);
         let (_symbol, variable) = exposed_to_host.into_iter().next().unwrap();
-            subs.get_content_without_compacting(variable)
+        let named_result = name_all_type_vars(variable, subs);
-        };
+        let content = subs.get_content_without_compacting(variable);
 
-        let actual_str = content_to_string(content, subs, home, &interns);
+        let actual_str = content_to_string(content, subs, home, &interns, named_result);
 
         Ok((type_problems, can_problems, actual_str))
     }
@@ -282,9 +276,9 @@ mod solve_expr {
             let var = find_type_at(region, &decls)
                 .expect(&format!("No type for {} ({:?})!", &text, region));
 
-            name_all_type_vars(var, subs);
+            let named_result = name_all_type_vars(var, subs);
             let content = subs.get_content_without_compacting(var);
-            let actual_str = content_to_string(content, subs, home, &interns);
+            let actual_str = content_to_string(content, subs, home, &interns, named_result);
 
             solved_queries.push(format!("{} : {}", text, actual_str));
         }
@@ -5445,26 +5439,19 @@ mod solve_expr {
     }
 
     #[test]
-    fn copy_vars_referencing_copied_vars_specialized() {
+    fn generalize_and_specialize_recursion_var() {
         infer_eq_without_problem(
             indoc!(
                 r#"
-                Job a : [ Job [ Command ] (Job a) (List (Job a)) a ]
+                Job a : [ Job (List (Job a)) a ]
 
                 job : Job Str
 
                 when job is
-                    Job _ j lst _ ->
+                    Job lst s -> P lst s
-                        when j is
-                            Job _ _ _ s ->
-                                { j, lst, s }
                 "#
             ),
-            // TODO: this means that we're doing our job correctly, as now both `Job a`s have been
+            "[ P (List [ Job (List a) Str ] as a) Str ]*",
-            // specialized to the same type, and the second destructuring proves the reified type
-            // is `Job Str`. But we should just print the structure of the recursive type directly.
-            // See https://github.com/rtfeldman/roc/issues/2513
-            "{ j : a, lst : List a, s : Str }",
         )
     }
 

compiler/types/src/pretty_print.rs

@@ -233,7 +233,11 @@ fn find_names_needed(
     }
 }
 
-pub fn name_all_type_vars(variable: Variable, subs: &mut Subs) {
+pub struct NamedResult {
+    recursion_structs_to_expand: Vec<Variable>,
+}
+
+pub fn name_all_type_vars(variable: Variable, subs: &mut Subs) -> NamedResult {
     let mut roots = Vec::new();
     let mut letters_used = 0;
     let mut appearances = MutMap::default();
@@ -242,12 +246,29 @@ pub fn name_all_type_vars(variable: Variable, subs: &mut Subs) {
     // Populate names_needed
     find_names_needed(variable, subs, &mut roots, &mut appearances, &mut taken);
 
+    let mut recursion_structs_to_expand = vec![];
+
     for root in roots {
         // show the type variable number instead of `*`. useful for debugging
         // set_root_name(root, (format!("<{:?}>", root).into()), subs);
-        if let Some(Appearances::Multiple) = appearances.get(&root) {
+        match appearances.get(&root) {
+            Some(Appearances::Multiple) => {
                 letters_used = name_root(letters_used, root, subs, &mut taken);
             }
+            Some(Appearances::Single) => {
+                if let Content::RecursionVar { structure, .. } =
+                    subs.get_content_without_compacting(root)
+                {
+                    recursion_structs_to_expand.push(*structure);
+                    letters_used = name_root(letters_used, root, subs, &mut taken);
+                }
+            }
+            _ => {}
+        }
+    }
+
+    NamedResult {
+        recursion_structs_to_expand,
     }
 }
 
@@ -312,6 +333,7 @@ fn set_root_name(root: Variable, name: Lowercase, subs: &mut Subs) {
 #[derive(Default)]
 struct Context<'a> {
     able_variables: Vec<(&'a str, Symbol)>,
+    recursion_structs_to_expand: Vec<Variable>,
 }
 
 pub fn content_to_string(
@@ -319,10 +341,14 @@ pub fn content_to_string(
     subs: &Subs,
     home: ModuleId,
     interns: &Interns,
+    named_result: NamedResult,
 ) -> String {
     let mut buf = String::new();
     let env = Env { home, interns };
-    let mut ctx = Context::default();
+    let mut ctx = Context {
+        able_variables: vec![],
+        recursion_structs_to_expand: named_result.recursion_structs_to_expand,
+    };
 
     write_content(&env, &mut ctx, content, subs, &mut buf, Parens::Unnecessary);
 
@@ -381,12 +407,34 @@ fn write_content<'a>(
             ctx.able_variables.push((name, *ability));
             buf.push_str(name);
         }
-        RecursionVar { opt_name, .. } => match opt_name {
+        RecursionVar {
+            opt_name,
+            structure,
+        } => match opt_name {
             Some(name_index) => {
+                if let Some(idx) = ctx
+                    .recursion_structs_to_expand
+                    .iter()
+                    .position(|v| v == structure)
+                {
+                    ctx.recursion_structs_to_expand.swap_remove(idx);
+
+                    write_content(
+                        env,
+                        ctx,
+                        subs.get_content_without_compacting(*structure),
+                        subs,
+                        buf,
+                        parens,
+                    );
+                } else {
                     let name = &subs.field_names[name_index.index as usize];
                     buf.push_str(name.as_str())
                 }
-            None => buf.push_str(WILDCARD),
+            }
+            None => {
+                unreachable!("This should always be filled in!")
+            }
         },
         Structure(flat_type) => write_flat_type(env, ctx, flat_type, subs, buf, parens),
         Alias(symbol, args, _actual, _kind) => {

compiler/types/src/subs.rs

@@ -2172,23 +2172,6 @@ impl Content {
             Content::Structure(FlatType::Apply(Symbol::NUM_NUM, _))
         )
     }
-
-    #[cfg(debug_assertions)]
-    #[allow(dead_code)]
-    pub fn dbg(self, subs: &Subs) -> Self {
-        let home = roc_module::symbol::ModuleIds::default().get_or_insert(&"#Dbg".into());
-        let interns = roc_module::symbol::Interns {
-            all_ident_ids: roc_module::symbol::IdentIds::exposed_builtins(0),
-            ..Default::default()
-        };
-
-        eprintln!(
-            "{}",
-            crate::pretty_print::content_to_string(&self, subs, home, &interns)
-        );
-
-        self
-    }
 }
 
 #[derive(Clone, Copy, Debug)]

editor/src/editor/mvc/ed_update.rs

@@ -59,6 +59,7 @@ use roc_collections::all::MutMap;
 use roc_module::ident::Lowercase;
 use roc_module::symbol::Symbol;
 use roc_region::all::Region;
+use roc_types::pretty_print::name_all_type_vars;
 use roc_types::solved_types::Solved;
 use roc_types::subs::{Subs, Variable};
 use roc_types::{pretty_print::content_to_string, subs::VarStore};
@@ -462,6 +463,8 @@ impl<'a> EdModel<'a> {
 
         let subs = solved.inner_mut();
 
+        let named_result = name_all_type_vars(var, subs);
+
         let content = subs.get_content_without_compacting(var);
 
         PoolStr::new(
@@ -470,6 +473,7 @@ impl<'a> EdModel<'a> {
                 subs,
                 self.module.env.home,
                 &self.loaded_module.interns,
+                named_result,
             ),
             self.module.env.pool,
         )

repl_cli/src/lib.rs

@@ -227,9 +227,9 @@ fn gen_and_eval_llvm<'a>(
     let main_fn_var = *main_fn_var;
 
     // pretty-print the expr type string for later.
-    name_all_type_vars(main_fn_var, &mut subs);
+    let named_result = name_all_type_vars(main_fn_var, &mut subs);
     let content = subs.get_content_without_compacting(main_fn_var);
-    let expr_type_str = content_to_string(content, &subs, home, &interns);
+    let expr_type_str = content_to_string(content, &subs, home, &interns, named_result);
 
     let (_, main_fn_layout) = match procedures.keys().find(|(s, _)| *s == main_fn_symbol) {
         Some(layout) => *layout,

repl_wasm/src/repl.rs

@@ -184,9 +184,9 @@ pub async fn entrypoint_from_js(src: String) -> Result<String, String> {
     let main_fn_var = *main_fn_var;
 
     // pretty-print the expr type string for later.
-    name_all_type_vars(main_fn_var, &mut subs);
+    let named_result = name_all_type_vars(main_fn_var, &mut subs);
     let content = subs.get_content_without_compacting(main_fn_var);
-    let expr_type_str = content_to_string(content, &subs, module_id, &interns);
+    let expr_type_str = content_to_string(content, &subs, module_id, &interns, named_result);
 
     let (_, main_fn_layout) = match procedures.keys().find(|(s, _)| *s == main_fn_symbol) {
         Some(layout) => *layout,